penwithick final report v1.3 - cornwall council · 2014-09-09 · 4.3 comparing energy in use with...

Penwithick Green Deal Pilot project: Final report

Prepared for: Cornwall Council & The BRE Trust

Date: 25th February 2014

Report Number: 278 621 Version: 1

BRE Wales & South West Ethos Kings Road Swansea Waterfront SA1 8AS Customer Services 0333 321 8811 T + 44 (0) 1792 630100 F + 44 (0) 1792 630101 E [email protected] www.bre.co.uk

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of 63 Penwithick Green Deal Pilot project: Final report Report Number: 278 621

Commercial in confidence © Building Research Establishment Ltd 2014

25 February 2014 Version: 1

Prepared by

Name Caroline Weeks

Position Principal Consultant, BRE Wales & SW

Date 25th February 2014

Signature

Authorised by

Name Colin King

Position Associate Director, Wales

Date 25th February 2014

Signature




Executive Summary

As Technical Advisors to Cornwall Council on the Eco Communities development, BRE have provided guidance on the Green Deal retrofit pilot project for the village of Penwithick. The village was selected as being typical of Cornish villages with a mix of property construction types. It is also not served by mains gas. Previous reports document the selection of properties and measures for the pilot, the potential impact of occupancy patterns as measured by different modelling tools and the factors affecting the viability of the more costly measures (i.e. Air Source Heat Pumps and External wall insulation) under the Green Deal. This report provides both headline statistics and information on the retrofit project as a whole, as well as a detailed analysis of the performance of each technology and system, following a year-long in-use monitoring programme.

77 dwellings received measures under the pilot project, including a mix of Air Source Heat Pumps, External Wall Insulation, top up loft insulation, oil boiler replacements, Photovoltaic (PV) systems, single room heat recovery ventilation units and draught proofing measures. Initial energy savings were forecast using SAP to give an indication of the likely viability of measures under the Green Deal. These estimates have subsequently been compared with in-use data.

Overall, most measures have performed better than anticipated in SAP (i.e. resulted in lower energy use). The project is expected to save £32,725 per year and 166.65 tonnes CO2 per year – 20.0% and 17.5% higher respectively than forecast by SAP. EWI to solid wall dwellings has not performed as well as anticipated by SAP, likely due to elevated moisture content in the walls increasing their effective U value. Savings should increase over time in these situations as walls dry out, but ventilation is critical to facilitate this. It therefore follows that ventilation should be an integral consideration to any solid wall retrofit package, even if it is not considered a Green Deal measure in itself.

While various dynamic modelling tools are able to propose energy use specific to various occupancy patterns (as demonstrated earlier in this pilot using Design Builder software), such trends were not witnessed in practice. While occupancy and behavioural patterns will inevitably influence heating demand, behaviours appear to be too erratic to generalise and categorise for modelling purposes. It follows that although SAP may underestimate potential energy savings (according to this study), a cautious estimate will be more reassuring to householders considering the Green Deal.

There are various factors that will influence the savings made by households, including:

• Household heating preferences (temperature and duration of heating) compared to assumptions made by SAP

• Comfort taking by households after retrofit measures – warming the house more fully and/ or to higher temperatures than before making the situation incomparable, but providing a warmer internal environment

• Energy bill increases over the study period masking potential savings

• Regional climate conditions varying from year to year, which will result in varying heating requirements

Households considering the Green Deal should be made aware of the potential impact of these factors on loan payback.

Consistent positive feedback was received for Air Source Heat Pumps, likely because they provided a whole house centrally controlled heating system where there was previously none. While they have been




well received under this pilot scheme, it is also the measure most susceptible to comfort taking if installed in previously under-heated homes. However, overall they have still performed largely in line with, or better than forecast by SAP.

87% of households with insulation and/ or new heating systems installed felt it was easier to heat their home over winter, suggesting more affordable levels of comfort. 81% of all households in the pilot would recommend the measures they received to others. Interestingly, a notable area of disappointment was with PV systems; some households did not feel they benefitted from the PV especially, with periods of generation largely unsynchronised with household demand (and certainly heating demand). As such, of all the measures investigated under the pilot, PV is least likely to make a significant contribution to reducing the risk of fuel poverty amongst households.




Contents

Executive Summary 3 Glossary of frequently used acronyms 7 1. Introduction to this report 8 2. Overview of scheme benefits and key findings 9

2.1 Introduction and background 9 2.2 Results 10 2.3 Recommendations by construction type 14 2.4 Accuracy of various calculation tools 16 2.5 Household perceptions and feedback 16 2.6 Impact on fuel poverty 19 2.7 Wider implications for the Green Deal 20

3. Air Source Heat Pump performance in detail 22 3.1 Introduction and background 22 3.2 Results 22 3.3 Comparing real ASHP energy use with SAP forecasts 22 3.4 Comparing actual energy costs with ASHP with previous energy bills 24 3.5 Solid wall dwellings with ASHPs 26 3.6 Cornish Type II with cavity wall refurbishment with ASHPs 27 3.7 Feedback from occupants 27 3.8 Summary conclusions for ASHPs 28

4. External wall insulation to solid wall dwellings in detail 30 4.1 Introduction and background 30 4.2 Results 31 4.3 Comparing energy in use with SAP forecasts 31 4.4 Comparing actual energy costs following EWI installation with previous household energy bills 35 4.5 Feedback from occupants 37 4.6 Summary conclusions for EWI to solid wall dwellings 37

5. External wall insulation to the front & rear of timber hybrid dwellings in detail 39 5.1 Introduction and background 39 5.2 Results 39 5.3 Comparing energy in-use with SAP forecasts 39 5.4 Comparing actual energy costs following EWI installation with previous household energy bills 41 5.5 Feedback from occupants 43 5.6 Summary conclusions for EWI to timber hybrid dwellings 44 5.7 Potential for overheating in timber hybrid dwellings with EWI 44

6. Comparison of Timber hybrid properties receiving ASHPs versus EWI front and back 47 7. Oil boiler upgrades in detail 48

7.1 Introduction and background 48 7.2 Results 48 7.3 Comparing oil consumption with SAP forecasts 48 7.4 Comparing actual energy costs with new oil boiler upgrade with previous energy bills 49 7.5 Feedback from occupants 51 7.6 Summary conclusions for oil boiler upgrades 51




8. Loft/ roof insulation in detail 52 8.1 Introduction and background 52 8.2 Results 52 8.3 Flat roof insulation 53

9. Photovoltaic (PV) systems in detail 54 9.1 Introduction and background 54 9.2 Results 54 9.3 Feedback from occupants 57 9.4 Potential impact on fuel poverty 58 9.5 Summary conclusions for PV 59

10. Heat Recovery ventilation units in detail 60 10.1 Introduction and background 60 10.2 Results 60 10.3 Discussion 62 10.4 Summary conclusions for heat recovery fans 63

References 64




Glossary of frequently used acronyms

ASHP = Air Source Heat Pump

CO2 = Carbon Dioxide

CoP = Coefficient of Performance

DECC = Department for the Energy & Climate Change

ECO = Energy Company Obligation

EWI = External Wall Insulation

FIT = Feed in Tariff

HR fans = Heat Recovery fans

IWI = Internal Wall Insulation

LPG = Liquid Petroleum Gas

PV = Photovoltaic

RdSAP = Reduced Data Standard Assessment Procedure

RH = Relative Humidity

SAP = Standard Assessment Procedure




1. Introduction to this report

This report is the culmination of 2 years of research following Cornwall Council’s Green Deal Pilot project in the Cornish village of Penwithick, near St Austell. BRE’s activities have ranged from initial feasibility assessments and potential retrofit measures prioritisation for the various dwelling construction types in the village, through the selection of measures for participating households, to in-use surveying alongside the installation of data monitoring equipment.

The aim here is to provide both headline statistics and information on the performance of the retrofit project as a whole, as well as a detailed analysis of the performance of each technology and system. As such, section 2 provides an overview of the outcomes of the programme and presents key findings from the detailed research. The sections that follow are then dedicated to each individual technology; each section has been written so as to be relatively standalone in case readers are only concerned with parts of the research (i.e. specific technologies). There is also a set of conclusions relevant to each technology at the end of each sub section in lieu of a main set of conclusions.




2. Overview of scheme benefits and key findings

2.1 Introduction and background

The key aims of the retrofit pilot project were to:

• Establish which retrofit measures were suitable for typical property construction types in Cornwall and the associated cost and CO2 emissions savings

• Examine whether any particular modelling tools were more accurate for the forecasting of potential energy savings

• Determine whether measures were likely to be viable under the Green Deal and what factors were likely to be most influential (e.g. interest rates, etc.)

• Explore to what extent occupancy and behavioural factors influence the savings made

The village of Penwithick was selected as being typical of Cornish villages with a mix of property construction types that is not served by mains gas. Previous reports document the selection of properties and measures for the pilot1, the potential impact of occupancy patterns as measured by different modelling tools2 and the factors affecting the viability of the more costly measures (i.e. Air Source Heat Pumps and External wall insulation) under the Green Deal3.

All participating households were surveyed periodically over a year, with a selection additionally having monitoring equipment installed to gain a more detailed insight into the performance of key measures. This report gives quantitative and qualitative feedback on the retrofit project in order to reflect on the overall success of the various measures installed.

77 dwellings received a mix of measures under the pilot, including:

• 20 Air Source Heat Pumps (ASHPs)

• 13 External Wall insulation (EWI) to solid wall properties

• 2 External Wall insulation (EWI) to ground floor of Cornish Type II properties

• 9 External Wall insulation (EWI) to the front and rear facades of timber hybrid properties

• 24 Loft insulation (+ 1 insulated flat roof)

• 6 Oil boiler upgrades

• 22 Photovoltaic (PV) electricity generating systems

• 42 properties receiving single room heat recovery ventilation units to bathroom and/ or kitchen

• 9 Draught proofing measures (only done with other measures)

• 3 Window or door upgrades (to facilitate the installation of radiators for ASHPs in rooms that would otherwise experience excessive heat loss with the previous windows/doors)

These measures were applied selectively to a range of construction types, including traditional solid wall and cavity wall dwellings, Cornish Type II system-build and timber hybrid properties (timber frame dwellings with a blockwork gable wall). Measures were selected to aim to bring household heating and hot water costs (i.e. excluding unregulated energy loads) as close to £800 per year as possible/ feasible.

This study did not assess window upgrades as part of the retrofit pilot as they were not deemed a viable Green Deal measure in their own right. However, they were considered a supplementary measure in a limited number of cases in this study to facilitate the installation of a new heating system (i.e. an ASHP).




Although not directly associated with delivering energy savings, heat recovery ventilation units were also installed where properties were deemed to have inadequate ventilation. The aim was to help reduce the effects of high humidity and damp in houses and to improve or maintain reasonable ventilation rates in properties where improvement measures may block uncontrolled air leakage pathways that may have actually been providing useful ventilation (albeit with associated heat loss). For this reason, units with heat recovery were installed in preference to more typical ‘extraction’-type units so as to reduce the potential for heat losses via the ventilation. Additionally, air with a lower moisture content will require proportionally less energy to heat.

2.2 Results

Detailed analysis of the relative performance of each measure is given in the sections that follow. A summary of the key findings and an overview of the impacts of the scheme are detailed here.

For the Green Deal, RdSAP (Reduced data Standard Assessment Procedure) is used to forecast the potential savings made by measures. Earlier studies under the pilot2 determined that the full version of SAP was likely to be more accurate due to the ability to better represent dwellings in both their baseline and improved scenarios, although the overall savings forecast by both versions of the tool were often similar. For this analysis, the full version of SAP was used on the basis of the better perceived accuracy.

All dwellings were modelled in their baseline case (before the retrofit) in full SAP then compared with the actual energy use following the improvement measures established from the study. Where specific in-use data was available from surveying and monitoring, this data has been used. Where specific household data was not available for any reason (discussed elsewhere in this report) estimates have been made based on the improved full SAP model for each household, considering any broad trends seen for the types of retrofit measure applieda.

For PV, cost and CO2 savings are based on the reported annual electricity generation from household PV generation meters. (This does not imply whether households used this electricity or whether it was exported back to the grid. Either way, the impact would be a net CO2 saving for the region.)

Table 1 shows the sum of the forecast annual cost and CO2 savings assumed by SAP for all dwellings in the pilot, while Table 2 shows the sum of the savings derived from the in-use measurements from the pilot project compared with the same baselineb. It is evident that the in-use measurements have exceeded what was expected overall by around 20% (by cost). The largest savings have been realised from the solid wall/ Cornish Type II dwellings.

Figure 1 and Figure 2 show the sum of the relative cost and CO2 savings brought about by each measure (the few properties with both EWI and an ASHP have been reported separately as it is not possible to accurately apportion the savings to each measure). ASHPs bring about the largest overall single savings, even more-so for CO2 emissions as the ASHPs were often replacing more carbon intensive fuels or were using electricity in a more efficient way (thanks to the positive coefficient of performance (CoP) of heat pumps). EWI also brings about significant savings. a For ASHPs it was found that on average actual energy use was 83% of what was forecast by SAP (in non-Cornish II properties), hence a factor of 83% has been applied to SAP data for ASHPs where actual data is not available. For EWI to timber hybrid properties, the trend in actual energy use was 65% of what was forecast by SAP (excluding homes evidently under-heated). Savings from dwellings where loft insulation was carried out with no other significant retrofit measures (4 dwellings) remain as forecast by SAP since survey data was not deemed sufficiently accurate to warrant adjustment b All fuel costs and CO2 emissions have been standardised to those assumed in SAP from 2012 onwards for consistency and alignment with assumptions for Green Deal assessments




Table 1: Sum of annual cost and CO2 savings for all measures, as forecast by full SAP

Previously forecast from SAP

Annual cost savings

(all dwellings)

CO2 saved, tonnes/year

(all dwellings)

Lifetime (20 years)

cost savings (all dwellings)

Lifetime (20 years)

CO2 saved, tonnes

(all dwellings)

Solid/ Cornish dwellings £13,119 66.91 £262,380 1,338

Cavity £9,969 43.31 £199,380 866

Timber hybrid £4,175 31.65 £83,500 633

Total £27,263 141.87 £545,260 2,837

Table 2: Sum of annual cost and CO2 savings for all measures, based on in-use measurements

In use measurements compared to SAP

Annual cost savings

(all dwellings)

CO2 saved, tonnes/year

(all dwellings)

Lifetime (20 years)

cost savings (all dwellings)

Lifetime (20 years)

CO2 saved, tonnes

(all dwellings)

Solid/ Cornish dwellings £14,321 72.81 £286,420 1,456

Cavity £10,588 45.34 £211,760 907

Timber hybrid £7,817 48.50 £156,340 970

Total £32,726 166.65 £654,520 3,333

Figure 1: Chart of overall pilot project cost savings, attributed to each retrofit measure




Figure 2: Chart of overall pilot CO2 savings, attributed to each retrofit measure

In reality, each Green Deal scenario would be bespoke to the dwelling to which it applies. Although a little artificial, the overall savings have been used in Table 3 to determine average payback periods for each improvement, as a measure of their relative value for money delivered for the project.

Table 3: Average cost and CO2 savings per measure with indicative ‘value’ assessmentsc

Primary retrofit measure

Num

ber o

f in

stal

latio

ns

Average annual saving

Average CO2

saving, tonnes/year

Average lifetime

(20 years) saving

Average lifetime

(20 years) CO2

saving, tonnes

Total cost of

measures

Average payback (as an indicator of value for

money), years

Average cost for every

tonne of CO2 saved over

20 year period

ASHP 17 £625 3.56 £12,500 71.2 £186,174 17.5 £154

EWI & ASHP 3 £1,567 6.32 £31,340 126.4 £76,413 16.3 £202

EWI 12 £384 2.43 £7,680 48.6 £145,168 31.5 £249

EWI to timber hybrid 9 £394 1.99 £7,880 39.8 £74,981 21.1 £209

PV 22 £312 1.34 £6,240 26.8 £137,742 20.0 £246

Oil boiler 6 £339 1.69 £6,780 33.8 £38,227 18.8 £189

Lofts/ roofs 5 £66 0.32 £1,320 6.4 £5,142 15.7 £132

c Dwellings receiving only ventilation and draught proofing have been excluded from the table




Although the average payback may be higher than anticipated, loft/ roof insulation is the most cost effective measure. The only measure that does not in itself fall within a simple payback of 20 years is EWI. This is not surprising, as EWI is widely accepted as being unlikely to meet the Green Deal ‘golden rule’d in most circumstances, prompting the introduction of Energy Company Obligation (ECO) funding to subsidise such measures in hard to treat properties. In reality, all of these paybacks would be increased due to VAT and the effect of interest rates applied to Green Deal loans. What is perhaps most surprising is that ASHPs appear to show reasonable value for money, despite their relatively high unit cost. The data also shows that the ‘whole house approach’ of improving both the insulation and heating system together gives a higher overall benefit than each of the measures when taking an individual elemental approach.

Table 3 also provides an indicator of the cost of delivering relative CO2 savings via each measure. A period of 20 years has been assumed to coincide with the anticipated period of a Green Deal loan. However, it should be noted that measures other than insulation (i.e. ASHPs, PV and oil boilers) would be likely to attract additional maintenance costs over this period, which would increase their relative cost per tonne of CO2 saved. ASHPs again appear to offer good value with regard to CO2 savings, brought about by their positive CoP and the fact they were often replacing very CO2-intensive fuels such as coal. EWI is again seen to be a relatively expensive measure for the benefit it brings, though it is noteworthy that PV is shown to be a costly way of reducing CO2 emissions, which will be increased still further if inevitable inverter replacement costs were included in the calculations.

As is elaborated in the sections that follow, most retrofit measures show somewhat improved performance compared to SAP (also shown in Figure 3):

• ASHPs perform on average 22% better than forecast

• EWI to timber hybrid properties perform on average 57% better than forecast

• PV systems perform on average 16% better than forecast by SAP and 2% better than forecast by the proprietary PVSol software used in this study to forecast PV system performancee

• Oil boilers perform on average 14% better than forecast

• Few dwellings received only loft insulation and there is an insufficient sample to identify alternative trends to SAP forecasts

In theory, energy use lower than forecast from SAP would enable a Green Deal-type loan to be paid back more quickly than anticipated. The results above have also not taken account of potential ‘in use’ factors that are typically applied to payback calculations for retrofit measures, which would usually assume payback periods should be longer.

EWI to solid wall dwellings, although still offering savings overall, was the only measure that was not generally in line with SAPs forecast, showing energy use on average 18% higher than forecast by SAP in dwellings that had not also received an ASHP. (It is difficult to identify trends in Cornish Type II dwellings since there were only 2 included in the sample, one of which appeared to be under-heated and the other over-heated compared to SAP’s assumptions.) It is suggested that this discrepancy is likely to be a result of moisture being present in the walls, which will affect the ‘real’ U values and potentially lead to elevated RH readings as the buildings ‘dry out’. Adequate ventilation is therefore critical in these dwellings to aid the drying out process. In the longer term, as the dwellings dry out the energy performance would be expected to improve and consequently the relative savings to increase.

d The ‘Golden Rule’ assumes the cost of the measures will be paid back by the savings they bring within a reasonable timeframe (typically 20 years) e PVSol Pro 4.5 software by Valentin software: www.valentin-software.com/en

http://www.valentin-software.com/en




Figure 3: Difference in energy use resulting from each retrofit measure compared to SAP

The potential moisture content of solid walls is an issue that is almost certainly not currently considered during Green Deal Assessments. Methods are needed to:

• identify the likely moisture content of walls

• determine the impact this will have on the wall U values

• apply this to energy calculations for the Green Deal

Green Deal Assessors should include such considerations during their initial surveys. However, there does not appear to be good guidance available on how to address the above issues at this time or to accurately interpret the impact this may have on potential savings. A current project funded by DECC is investigating the heat loss from external walls4, which will look to address these issues and how they relate to the Green Deal assessment process.

2.3 Recommendations by construction type

For the four key construction types considered under the pilot project (cavity, solid wall, Cornish Type II and timber hybrid), the findings essentially support the recommendations made per for each property type

Key findings: • Most measures have performed better than anticipated in SAP (i.e. result in lower energy

use). Overall the project is expected to save £32,725 per year and 166.65 tonnes CO2 per year – 20.0% and 17.5% higher respectively than forecast by SAP

• The order of ‘value for money’ per measure, based on cost savings is: Loft insulation > ASHP > Oil boiler > PV > EWI timber hybrid > EWI solid

• The order of cost effectiveness of CO2 emissions savings is: Loft insulation > ASHP > Oil boiler > EWI timber hybrid > PV > EWI solid

• EWI to solid wall dwellings has not performed as well as anticipated by SAP, likely due to elevated moisture content in the walls increasing the effective U value. Savings are likely to increase over time as walls dry out. Ventilation is critical to facilitate this




in the initial measures selection report1. A preferred ‘hierarchy’ of improvement measures is given in Table 4.

In most cases, key insulation measures should be carried out first to reduce the overall energy demand of a dwelling, then consideration given to the suitability and efficiency of the heating system. (If done the opposite way around, the heating system specified may be larger than subsequently necessary following insulation.) For dwellings not served by mains gas, boiler upgrades should be viable for those with older boilers (>15 years). Those with an inefficient LPG system, particularly those relying on bottled LPG (rather than bulk), which tends to be relatively expensive, or those with no central heating system (i.e. relying on coal fires or portable electric heaters) may consider switching to a heat pump central heating system. It is generally not economically viable to switch from Economy 7 to other fuels due to the low rate tariff received for storage heaters.

Table 4: Recommended hierarchy of retrofit measures by construction type

* Typically it will be necessary to improve the thermal performance of the walls before a heat pump system would become viable. If needed, boiler upgrades may be viable without this step.

The payback indications previously given in Table 3 suggest ASHPs to offer better ‘value for money’ in timber hybrid dwellings than those that received EWI to the front and rear facades, hence these steps have been switched compared to other property types in Table 4. Feedback from occupants (reported in section 6) is not so clear cut and households believed both measures to be beneficial. If external works were likely to be required anyway for ongoing maintenance reasons, there would certainly be value in considering additional insulation to coincide with such improvements. The potential visual benefit to the dwelling may also encourage householders to prioritise EWI over heating system upgrades. Feedback from the study indicate either measure should ultimately bring similar benefits overall.

Cavity wall dwellings Solid wall dwellings Cornish Type II dwellings

Timber hybrid dwellings

Loft Loft Loft Loft

Cavity insulation External (or internal)

wall insulation (if feasible)

External insulation to ground floor walls*

Boiler upgrade (oil, bulk

LPG)

Heat pump (solid fuel, portable electric heaters, bottled LPG)


LPG)



LPG)



LPG)


EWI to front and rear façade

PV PV Internal insulation to first floor walls

EWI to gable wall

PV PV




It may not always be feasible to carry out all measures in the sequence indicated, particularly when considering EWI or internal insulation where practical features may inhibit measures. For instance, solid wall dwellings will be subject to the issues raised in this study regarding the moisture content of walls; some dwellings may be considered too damp to insulate. The benefits of providing additional EWI to the ground floors of original Cornish II dwellings has not been strongly demonstrated in this pilot since the sample of houses was unfortunately too small. However, feedback from households indicates that their houses are notably warmer since receiving insulation.

In such cases, skipping the insulation step and looking to install a new heating system may still be viable, though a larger-sized system specification would likely be required to compensate for the poorer thermal performance of the walls. As demonstrated with ASHPs in two small dwellings in this pilot, this may still bring benefits overall to householders.

In all cases, PV is indicated as the recommendation of last resort, since the benefit will be very dependent on household electricity usage patterns. Installation would not necessarily be linked to other measures.

2.4 Accuracy of various calculation tools

While this study has suggested that full SAP may underestimate potential energy savings to an extent, comparison with Design Builder modelling data from earlier in this pilot project suggests that Design Builder’s calculations are far too optimistic. In particular, anticipated variations in modelled energy use resulting from different applied occupancy patterns were not identifiable in reality. The use of SAP therefore appears to offer a more cautious approach, which is likely to be of reassurance to householders.

Use of the add-on ‘Green Deal Occupancy Assessment’ tool to calibrate SAP assessments against real energy bills for individual households should provide an indication of the extent of error that may be inherent to SAP. However, the reasons for this error may not be obvious for households and it will be important for Green Deal Assessors to understand household behavioural patterns and interpret how this many influence potential savings.

Analysis of PV electricity generation data suggests that using alternative proprietary assessment tools such as PVSol to forecast generation should be more accurate than relying on the estimates from SAP. However, neither tool offers an indication of the likely in-house usage versus exported electricity, which would influence the true benefit experienced by householders.

2.5 Household perceptions and feedback

While comparison of in-use data with SAP shows often significant savings should have been made, data and feedback from householders was often not so decisive. There are numerous reasons why households may not realise the savings forecast:

- If living patterns were notably different to the pre-retrofit assumptions made

Key findings: • While various dynamic modelling tools are able to propose energy use specific to various

occupancy patterns, such trends were not witnessed in practice. It follows that although SAP may underestimate potential energy savings (according to this study), a cautious estimate will be more reassuring to householders considering the Green Deal

• SAP is not particularly accurate at estimating PV usage because it does not take into account variations in regional solar irradiation. Use of proprietary tools, such as PVSol, present more accurate estimates for PV generation




- If energy price increases effectively mask savings being made

- Regional climate conditions could vary in reality compared to assumptions made (though in this study it may have been anticipated that the energy demand would be higher than assumed in SAP when comparing the degree days from the project’s weather station with those used for SAP calculations)

Even if households did not heat their home to the same extent assumed in SAP, there is still potential for savings if the behaviours before and after the retrofit measures are essentially equivalent (i.e. similar living temperatures and heating the same number of rooms, etc.). However, there is evidence that in many cases households have taken additional comfort from the new measures installed, rather than living as they did before. This is one of the most significant factors that will influence Green Deal loan payback, though some householders acknowledged that the additional comfort was worth the additional cost. This impact may be relatively short lived, as it is likely occupants would revert back to lower heating patterns as energy costs inevitably increase.

What has been somewhat unexpected is the lack of trends witnessed between households of different occupancy profiles, i.e. single occupants right through to families. The study has shown that while behavioural impacts inevitably have a notable influence, such as comfort taking and heating preferences, it is difficult to assign generic occupancy patterns to account for these variables. This is a significant factor that could very much influence the payback of Green Deal loans. It is therefore important that households are made aware of the impacts various behaviours may have on their loan payback.

There is a high chance that many considering a Green Deal loan to improve their home will expect both increased comfort and energy savings. It may be difficult for some households to accept that their energy bills will continue to increase in line with market energy price rises until their loan is paid off. In this pilot study there were numerous cases where households did not appear to be making actual savings to their energy bills compared to previous years without retrofit measures, even without loan repayments to consider. They may therefore not have been able to pay back a Green Deal loan within an acceptable timeframe.

While PV is not a measure that would be influenced by domestic heating preferences, its potential benefit is nonetheless affected by household behaviours. Once the Feed in Tariff is essentially removed from consideration (since the Generation Tariff would be used to payback a Green Deal loan), most benefit would be realised by offsetting incoming grid electricity. The pilot found that there was a lack of understanding in some households on how to get the most from their PV system and that although overall generation figures may have been as expected (or better), periods of generation were largely unsynchronised with the majority of household demand.

Overall, the strongest positive feedback was from households receiving ASHPs as it provided a comfortable, whole house central heating system where typically there previously was not one. The lack of need for deliveries and storage with ASHPs (compared to coal, oil or LPG) was often cited as an additional benefit. Certainly the additional levels of comfort reported will likely have a knock on beneficial effect on occupant health through the avoidance of stark changes in temperature in different zones of the house that may have been experienced with previous systems. The findings of the study would certainly seem to support the incorporation of ASHPs as an accepted Green Deal solution.

The measure with the most divided feedback was somewhat surprisingly PV systems. There was apparent variation in the extent to which householders felt they were benefitting from the system, which will be linked to their ability to optimise their energy use. There were also a small number of instances of unusual ‘fixed price’ energy tariffs being in place that negated the benefits seen by households. Potential




variables such as these should be better explained to households considering the adoption of PV to help manage their expectations of the system.

During the surveys, households were asked if they felt it was easier to heat their home following installation of the retrofit measures and whether they would recommend the measures they had received to others. Statistics for these questions are presented in Figure 4. 87% of households receiving relevant heating-related measures (i.e. insulation or heating systems) felt that it was easier to heat their home over winter with the new measures. 4% of households were not sure if it had helped. Of the remaining 9% where the measures had not made a notable difference, most had received only loft insulation, while 2 households had received EWI to timber hybrid properties. When all measures were considered, 81% of households would recommend the measures they received to others, while a further 8% were not sure. Of the remaining 11%, it is interesting to note that most of the households (i.e. 8%) had received PV systems.

Figure 4: Feedback from key household survey questions regarding comfort and overall satisfaction

Key findings: • Various household behavioural impacts will influence the savings that are achieved by

retrofit measures, including: § heating preferences compared to assumptions made by SAP § comfort taking by households after retrofit measures

• In addition, energy bill increases and regional climate conditions could further influence energy savings. Households should be made aware of the impact of these factors on potential Green Deal loan payback

• Some households did not feel they benefitted from PV, with periods of generation largely unsynchronised with household demand

• Consistent positive feedback was received for ASHPs, likely because they provided a whole house centrally controlled heating system where there was previously none

• 87% of households with insulation and/ or new heating systems felt it was easier to heat their home over winter. 81% of all households in the pilot would recommend their measures to others




2.6 Impact on fuel poverty

While energy and CO2 emissions reductions are a key driver for refurbishment measures under the Green Deal, another major objective is to help protect households from the risk of fuel poverty. Households are considered to be in fuel poverty if they are required to spend more than 10% of their income to adequately heat their home. Prior to the retrofit project, data provided from householders suggested that several may have been in that situation.

All retrofit measures that essentially reduce the energy demand of a home should help reduce the risk of fuel poverty. Improvements to the fabric of the building are generally seen to be most preferable and reliable, since they are ‘passive’ measures that will save money irrespective of the heating fuel type used by lowering the heating demand. Upgrading heating systems to more efficient ones that use less energy will also help reduce fuel bills, though periodic maintenance requirements and ultimately replacement of systems at their end of life mean that some additional ongoing costs will be inevitable.

In lieu of mains gas being available, the use of electrically-run heating systems that do not require periodic top up/ deliveries may be seen to be more beneficial to vulnerable households as they will not run the risk of potentially running out of fuel, plus it would allow them to more readily control their spending in a single bill without the need for high one-off payments for bulk deliveries. Of course, such systems may still be susceptible to power cuts, but this is often also true for fuels such as oil and LPG, where modern boilers tend to rely on electronic ignition and circulation pumps.

While PV systems may be viewed as having potential to protect households against electricity price rises by offering ‘free’ electricity, in reality PV is unlikely to help mitigate fuel poverty as periods of peak generation are fundamentally at odds with when energy is required for heating and lighting, as demonstrated in the Figures below.

Figure 5a shows the typical distribution of heating and DHW loading from one of the dwellings in Penwithick using an ASHP, while Figure 5b shows the typical annual generation profile for a 2.88kWp PV system. During the pilot, several households with PV commented that they did not feel they were benefiting from it, presumably because they were not optimising the offsetting of grid electricity. Without the incorporation of energy storage technologies, which of course would carry additional capital cost and the industry for which is in its relative infancy, PV will make a limited contribution to reducing fuel poverty, even if on a macro level it will offset grid electricity and contribute to national CO2 reductions.

Key findings: • Insulation measures will help protect households against the risk of fuel poverty by reducing

their overall energy consumption irrespective of the type of heating

• Efficient heating systems will also reduce energy demand, though they will inevitably require ongoing maintenance and renewal over time

• PV cannot be considered to protect against fuel poverty since periods of generation are unsynchronised with heating demand patterns




Figure 5a: Typical distribution of heating energy demand with ASHP

Figure 5b: Typical profile of electricity generation from PV

2.7 Wider implications for the Green Deal

The retrofit pilot has suggested that forecast energy savings for EWI on solid wall dwellings may be unreliable due to a lack of information being available about the state of moisture in such constructions. That is not to say that EWI may not be effective; it has been shown to provide increased levels of comfort and energy savings. However, even with the availability of ECO funding towards EWI, if savings predictions to aid households considering loans are not accurate, most are unlikely to want to risk installing EWI at this time. It is unfortunate that this is the case, as EWI has the potential to deliver significant cost and CO2 savings across Cornwall and the rest of the UK.

Ventilation measures are not currently considered under the Green Deal, though if there is a risk of potential moisture build-up in properties receiving impermeable insulation, ventilation solutions should be considered a fundamental component of the overall retrofit to mitigate against potential unintended consequences, such as mould growth in humid environments.

ASHPs have been generally very well received across the pilot, with seemingly improved performance compared to SAP forecasts. However, it may also be the measure most susceptible to ‘comfort taking’ as it will inevitably be substituting heating systems that typically lead to under-heating of homes (e.g. coal fires, portable electric heaters, etc; it would typically not be financially viable to switch from mains gas, oil




or economy 7 heating systems). Potential under-heating should be identified during the initial Green Deal Occupancy Assessment and the implications of comfort taking should be fully explained to households when considering measures under the Green Deal.

Some households may be happy to spread the cost of retrofit measures by paying via their electricity bills, even if it will cost them more as comfort is their key priority. However, there is not particularly any precedent for the implications of loans being associated with a property when it is sold. It seems inevitable that house values would be reduced if there was an outstanding Green Deal loan on the property and some prospective buyers may be put off due to the risk of their bills being higher than otherwise expected, yet beyond their control to a large extent.

In the short term, measures that have historically been trustworthy retrofit options, such as loft insulation, cavity wall insulation and boiler upgrades should be viable under the Green Deal, as capital costs will be relatively low and payback periods will likely be quite short. However, if householders are likely to require supplementary measures to facilitate a boiler upgrade for instance (e.g. new distribution system, new storage tanks for oil, etc.), these additional costs could hinder the viability of the upgrade, since they will add cost yet not contribute any further to the savings made.

Key findings: • If savings from EWI cannot be accurately forecast due to a lack of knowledge of the

condition and moisture content of solid walls it will inevitably put households off the Green Deal as a finance mechanism

• Ventilation should be considered an integral part of any EWI installation under the Green Deal to mitigate against potential unintended consequences such as mould growth in humid environments

• While ASHPs have been well received under this pilot scheme, it is also the measure most susceptible to comfort taking if installed in previously under-heated homes. Householders should be made aware of the potential consequences if under-heating is identified during initial Green Deal assessments

• The presence of a Green Deal loan linked to a property is likely to affect its potential sale price and/ or put householders off purchase in case their behaviours do not align with the usage assumed




3. Air Source Heat Pump performance in detail


Since the village is off gas, there were many houses relying on solid fuel fires (sometimes with back boilers), gas boilers using bottled LPG, or electric (peak rate) heaters (not storage heaters). These fuels are either intrinsically very expensive heating options and/ or have inadequate controls, particularly open fires where loading fuel can be a physically demanding task.

Under the retrofit pilot project, ASHPs were offered to a number of such dwellings in the village to provide a modern, controllable central heating system. ASHPs were one of the more expensive potential retrofit measures that typically would not appear viable under the timespans of the Green Deal. However, a key aim of this work was to investigate whether in reality they may be more viable for users when real usage data was considered, particularly in certain types of property or with certain occupancy patterns.

20 dwellings received ASHPs, covering a range of construction types including cavity walls (and cavity bungalows), Cornish Type II (refurbished with cavity walls), uninsulated and insulated solid walls plus timber hybrid dwellings. A range of occupancy profiles were also captured by these dwellings, including employed singles and couples, retired couples and families.

3.2 Results

Although all 20 dwellings in receipt of ASHPs had electricity sub-circuit monitoring equipment installed to log the energy consumption of the units, unfortunately not all have been able to provide complete datasets for the study. Although it was hoped that the loggers would not be disturbed during the monitoring period, it seems some may have lost power periodically resulting in gaps in the data provided. In instances where a full year of data is not available it is not possible to accurately compare with annual energy forecasts. However, qualitative analysis of the available data suggests usage in keeping with other properties in the sample, i.e. similar usage patterns over equivalent months. It is also noted that one property reported heating their house to higher temperatures as well as heating over the summer for health reasons. This is corroborated with data from temperature sensors in the dwelling. Since this usage is beyond ‘normal’ patterns (apparently even for the household in question) the data from that property has not been incorporated into the following analysis.

Two main comparisons are made here:

• Actual ASHP use against SAP forecasts à This comparison confirms whether the ASHP systems have performed in line with the modelled expectations

• Actual energy costs with ASHP against previous household energy bills à This comparison shows whether savings have been realised from the retrofit, as an indication of Green Deal viability

Some cases relating to particular types of construction are also explored in more detail.

3.3 Comparing real ASHP energy use with SAP forecasts

Earlier reports1-3 have indicated the likely payback periods and viability of the Green Deal for ASHPs. The purpose of this study is now to compare whether the real measured energy for ASHPs is in line with SAP’s forecasts, to confirm whether the anticipated savings would have been achieved or not. This of course assumes that the baseline condition for the houses pre-retrofit was also realistic and cannot account for under-heating of properties and other factors as discussed in the earlier ‘Comparison of energy tools’ report2.




3.3.1 Validity of the data in relation to assumed usage patterns Reviewing the energy use profiles of the properties with ASHPs, it can be seen that on the whole the usage patterns experienced with the Penwithick occupants was in keeping with the assumptions used in SAP. For instance, SAP assumes that the whole house would be heated, while virtually all householders stated that the whole house was indeed heated or, at worst, a single room in the dwelling was not heated to the same level. Hence the data should not particularly be skewed by ‘under heating’ of the properties. SAP assumes that the heating system will be used during the morning and the evening aiming for temperatures of 21°C in the main living area and 18°C in the remainder of the property with temperature ‘set backs’ in between. Analysis of the temperature patterns in the dwellings over the period from January to May indicate that the occupants appear to aim for similar conditions, with thermostats evidently being set to approximately 20°C and many properties experiencing set back periods that drop the overall average temperature somewhat. (Average temperatures are shown in Table 5). However, again it is anticipated that this should be in keeping with SAP’s modelled assumptions taking into account the building fabric properties.

Table 5: Energy use and comfort data for dwellings receiving ASHPs

Dwelling number

Dwelling floor area,

m2

Number of heated

rooms

Actual ASHP

energy, kWh

SAP ASHP energy

forecast, kWh

% actual versus SAP

Living room average

temperature (Jan-May), °C

Landing average

temperature (Jan-May), °C

93 65.1 5/5 3408 4127 0.83 20.1 19.4

37*# 74.0 5/6 2904 4171 0.67 19.4 17.7

39 74.8 6/6 3461 4411 0.78 19.8 21.9

58 75.1 6/6 3364 3558 0.95 20.1 15.3

90 75.6 7/7 2451 5696 0.43 19.0 16.6

6 77.0 5/5 2831 5695 0.50 18.7 15.7

68 78.3 5/7 3744 4072 0.92 16.4 18.4

5# 80.3 7/7 3951 5364 0.74 18.2 19.1

79* 82.5 8/8 2960 3973 0.74 18.5 18.7

91 82.8 7/8 3697 3785 0.98 19.5 15.2

85* 100.6 6/6 4523 5199 0.87 19.1 20.2

15# 108.2 8/8 6764 8470 0.80 17.4 14.3

* = Dwelling received additional EWI # = Dwelling received additional loft insulation

When considering the performance of heat pumps for the Green Deal, an ‘in use’ factor is applied to the forecast savings as previous test studies have suggested that refurbishment measures often do not realise the extent of the savings forecast by SAP. This could be for various reasons, but particularly for




ASHPs it is assumed that the Coefficient of Performance (CoP) quoted by manufacturers and used in energy modelling is not delivered in practice, resulting in higher energy usage. The in use factor of ASHPs is 0.25, i.e. a 25% reduction in the savings forecast by SAP and the Green Deal tool is applied, suggesting actual energy usage is generally anticipated to be higher than forecast in SAP.

All dwellings with fully quantifiable data (i.e. no anomalies) actually returned energy use for ASHPs lower than forecast by SAP. Most lie within around 10% of the SAP forecast and this covers a range of occupancy profiles, suggesting there are no specific trends experienced by low occupancy (e.g. single employed people), compared to families (i.e. at the two anticipated extremes). One timber hybrid dwelling and one insulated solid wall dwelling returned energy use from their ASHPs at 69% and 67% of the SAP forecasts respectively. The two pre-refurbished Cornish Type II dwellings actually returned energy use from their ASHPs at 50% or lower, suggesting a significant additional saving. These cases are discussed further in section 3.6. This being the case, households would actually save more than was initially forecast and may therefore make higher contributions to a Green Deal loan. This could potentially make a measure such as an ASHP more viable under such a finance mechanism.

There are various additional factors that will influence these findings. While SAP essentially makes generalised climate assumptions for central England for Regulatory comparative purposes, Penwithick being towards the very south of the UK it would be anticipated to have a milder climate and hence require less energy overall than SAP may forecast. Analysis of the likely impact of this variation was investigated with Design Builder software2 and suggested the energy savings experienced for ASHPs in the far south of the UK compared to SAP may be approximately 24% lower.

However, examination of data from the weather station that was set up in the village to correspond to the data collection period suggests a relatively significant increase in overall ‘degree days’ (i.e. the measure of the relative heating period for the year) for 2013 compared to SAP’s assumptions; 2225 compared with 1650 (at a base temperature of 15.5°C). Hence, it may be anticipated that the heating energy demand for the Penwithick households would have been approximately 33% higher than SAP forecast.

Considering these factors, it may still be expected that the ASHP energy demand should have been higher than SAP overall, whereas in fact the results have been lower. When modelling was previously carried out using Design Builder to assess the impact of various occupancy profiles, virtually all scenarios forecast lower energy use (from heating and hot water) than SAP. However, data collected for the pilot study suggests the Design Builder forecasts were in fact lower than has been observed across the village, indicating it to be too optimistic. When considering a potential Green Deal loan, a conservative estimate of forecast energy use would be ‘safer’ from the perspective of being likely to pay back the loan than an optimistic estimate, which could leave people with higher repayments than expected.

3.4 Comparing actual energy costs with ASHP with previous energy bills

Prior to the study, householders were asked how much they were paying for their energy. By examining ‘degree day’ data from nearby weather station locations around Cornwall, it is apparent that 2013 was a colder year than 2012 as shown by an approximately 5% increase in annual degree days in 2013. Therefore, in order to make a fairer comparison between the Penwithick household data, the fuel costs for 2012 reported from initial surveys have been increased by 5%.

Table 6 and Figure 6 show a comparison of these overall costs per household compared to the prices calculated from meter data collected during the study. (Standing charge of £80 per year for electricity has been added to cases where it was not explicitly known. This is an approximate average of the standard charges that were reported from bills across the village.)




Table 6: Annual household energy costs before and after ASHP installation

Dwelling number Dwelling description Cost with

ASHP, £

Cost before

ASHP, £

Savings, £

Number of rooms heated before

Number of rooms heated after

15 Cavity, Electric, Family# 1698 1764 66 3/8 8/8

39 Cavity, Solid Fuel, Family 883 1260 377 2/6 6/6

91 Cavity, Solid Fuel, Family 1380 1218 -162 3/7 7/8

5 Timber, Electric, Emp1# 628 756 128 2/7 7/7

2 Timber, Electric, Emp2 1009 945 -64 1/7 7/7

4 Timber, Electric, Family 1321 1260 -61 2/8 8/8

40 Timber, Electric, Family# 1117 1588 471 1/7 ?/7

57 Timber, Electric, Family 829 1298 469 2/6 6/6

6 Cornish, Electric, Family 852 1512 660 3/5 5/5

90 Cornish, Solid Fuel, Family 891 1189 298 5/7 7/7

79 Solid, Electric, Emp1* 977 1575 598 1/8 8/8

93 Solid, Solid Fuel, Emp2 724 693 -31 1/5 5/5

94 Solid, Electric, Rtd2# 805 1134 329 4/8 ?/8

85 Solid, Solid Fuel, Family* 1820 2247 427 1/6 6/6

* = Dwelling received additional EWI # = Dwelling received additional loft insulation ? = Data not reported

While the previous section indicated that ASHPs in Penwithick generally performed in line with or better than SAP forecast, Figure 6 shows that there are several instances where household energy bill prices are around the same as before or higher. This may be due to a number of factors, with the most likely being a result of increased energy prices over the period of study masking potential savings, inaccurate initial reporting of previous energy costs, or due to households heating the house more fully and/ or to a more comfortable level now compared with before they received the ASHP. Table 6 shows the latter to be a common factor (by the change in the number of rooms heated before and after measures) though most still experienced cost savings. It is possible that although households state they were not heating certain rooms, they may have used standalone heaters in those rooms periodically that would have driven their energy bills up prior to the installation of the retrofit measures. Hence they are now seeing savings, even though they are heating the house more fully. Those that received additional measures as part of their retrofit package (e.g. loft insulation or external wall insulation) all make a saving overall, though the extent of this saving is variable.




Figure 6: Graph of annual household energy costs before and after ASHP installation

It is difficult to establish trends linked to the dwelling construction type, occupancy, or the type of previous heating system being switched from, although overall more households seem to have made savings than have not. This indicates that although generalisations are made in modelling tools for equivalent constructions or occupancy patterns, individual behavioural characteristics can have a significant impact on whether savings would be realised and hence whether a Green Deal loan would be viable.

3.5 Solid wall dwellings with ASHPs

Anecdotally, concern is sometimes expressed as to whether solid walled properties would ‘cope’ with a relatively low temperature heating system such as an ASHP due to the relatively low thermal performance of solid walls (i.e. relatively high U values by comparison with other constructions, such as cavity walls). Two similar solid wall dwellings (both less than 80m2 floor area) in the pilot were of decorative stone construction and for this reason alone in one and combined with concerns over existing damp problems in the other they remained uninsulated. However, due to the lack of a working central heating system in both cases, they were recommended to receive an ASHP. Initial SAP forecasts indicated that each property should experience running cost savings by switching to an ASHP (assuming the house was essentially fully heated prior to the pilot). In actual fact, both report that they were not able to fully heat their homes previously, relying on electric heaters or fireplaces.

Key: Elec = Electric heating Emp1 = Single employed occupant * = Additional EWI installed SF = Solid Fuel Emp2 = Employed couple # = Additional loft insulation installed

Rtd2 = Retired couple




Energy bills for one of the houses were approximately the same or a little higher now than they were before the ASHP installation. However, the household acknowledge that they are now heating the house more fully and to more comfortable temperatures than before, so they were extremely happy with the new system. The energy use from the ASHP is in fact below the SAP forecast, suggesting they would have made savings if they had heated their home to the same extent before. The other household has saved approximately 25% on their fuel bills compared to what they reported they were paying before the retrofit yet they also commented that the house is now much more comfortable.

Overall, both households were very satisfied with their ASHPs, suggesting that they work as intended in small solid walled dwellings.

3.6 Cornish Type II with cavity wall refurbishment with ASHPs

Since the actual energy use in the Cornish test dwellings is so much less than forecast by SAP, the baseline conditions have been re-examined. It seems that the overall cost estimates for both RdSAP and full SAP from the ‘Comparison of Tools’ analysis report2 were largely in line with what householders were paying prior to the retrofit measures. However, the SAP estimates do not take into consideration unregulated energy loads (i.e. cooking, household appliances) that on average contribute approximately an additional 3000 kWh energy per year. Hence, the initial baseline SAP estimates were clearly an over-estimate of the baseline usage in these properties. It is likely that this is a result of the uncertainties associated with the actual U values achieved in practice by such non-traditional constructions. Both of these dwellings have in fact been previously refurbished with the traditional concrete panelised ground floor walls replaced by an insulated cavity. However, it is very difficult to estimate the thermal performance of the first floor mansard roof, particularly due to variations in thickness experienced across the roof/ wall profile. It can only be assumed that the thermal performance of these dwellings was in fact better than originally modelled as the ‘baseline’ scenario in SAP.

Despite this, the actual savings experienced by these households receiving ASHPs (assuming energy prices remained the same as prior to the study) are relatively close to the savings that were forecast by SAP. Unfortunately the sample of these type of dwellings and measures is not large enough to determine whether this is a reliable trend or somewhat of a coincidence. One of these households reported making significant savings on their energy bills. However, the other has apparently experienced fuel price increases from their energy supplier, which, comparing their unit prices before and after this increase, will have masked any savings made by the new heating system. This is a common factor that has arisen across this study that unfortunately influences households’ perception of whether measures have been of benefit (i.e. made them savings).

3.7 Feedback from occupants

Many very positive comments were received from occupants regarding the ASHPs, including that the system is much more convenient and easy to control than the heating system being replaced.

It is evident from Table 6 earlier that houses are now fully heated where they were not necessarily before and/ or occupants are now enjoying warmer temperatures delivered by the ASHP system than was possible with their previous heating system. Each of these factors are evidence of ‘comfort taking’, resulting in different behavioural conditions before and after measures were installed. This will inevitably impact on the savings that may be relied upon to pay back a Green Deal loan, although this was not a concern for the households in the pilot scheme. While it follows that those participating in the Green Deal may be more conscientious about the savings they need to make to repay their loan, it seems highly likely that under similar circumstances (i.e. of under-heating) virtually all households would seek improved comfort from such retrofit measures.




Although fan powered radiators were specified in some dwellings to deliver adequate heat to a space while using a smaller radiator, several occupants mentioned that they found these noisy and would rather have had standard radiators, even if they were larger. Hence, if this was likely to be an option for potential households, the implications of the fan radiator versus a larger radiator should be highlighted so they can make an informed choice.

Discussions with occupants revealed that in some cases householders were not sure if they were saving money because they had switched from using fuels with sporadic billing (i.e. coal, wood, LPG) to a single electricity bill. This will inevitably influence occupant perception of whether savings are being made.

18 out of 20 households state they would recommend ASHPs to others, with one saying they would maybe recommend it and another saying no. This latter instance was the household with unusually high energy usage over the study period and who had experienced some problems with their system installation and operation. Hence it is perhaps understandable that they would not have the confidence to recommend the system to others. Further to this, 17 households reported that if they had not been part of the pilot project and they could afford to pay for such measures they would look to do so, with most saying they would consider a Green Deal loan (17) or using their own money or savings (11) rather than taking out a personal loan (4).

Despite comfort taking, 9 out of the 20 think they are saving money compared to before, 5 could not tell and 6 thought they were not making savings, though some specifically acknowledged that their energy tariff’s had increased since installation. (One household in a timber hybrid house could see that they were using less units of electric compared to before from their bills, yet were paying about the same for their energy. However, they were very happy with this, since the house was now fully heated to a comfortable level, which had not been the case before.)

3.8 Summary conclusions for ASHPs

Overall, the study has found that ASHPs installed in a range of different property construction types have generally performed in line with or better than forecast by SAP. On the face of it, this would be an extremely positive finding, suggesting that ASHPs may be more viable under the Green Deal than initially anticipated and may forego the need to apply a cautionary ‘in use’ correction factor to the financial forecasts.

However, when comparing the overall energy costs with those reported by households prior to the installation of the retrofit measures, the benefits are not so clear cut. Retrofit measures would not have been installed unless there was an apparent saving to be made according to the initial SAP forecasts. But it is evident that additional factors have been influential and not all households have made financial savings. Key reasons include:

• Energy prices increasing for some households over the study period, thus masking anticipated savings

• Base case SAP forecasts being inaccurate due to households not fully heating their home prior to measures (i.e. not heating all rooms, not heating to the same temperature as assumed)

In these cases, householders may not have made sufficient savings to pay back a theoretical Green Deal loan covering the cost of the measures.

It seems that while households would inevitably desire both increased levels of comfort and decreased costs, the majority recognise that the new systems offer additional benefits compared to the heating systems they are replacing and are prepared to pay the same or a little more towards their energy bills for these ‘comforts’.




Those of note are:

• Not having to deal with solid fuel deliveries or the physically demanding nature of solid fuel burners/ fires (where applicable)

• Ability to heat all rooms from a single system (no need for additional secondary heating)

• Controllability of the new system, with flexibility to control timings and temperatures as desired

90% of those receiving ASHPs would recommend them to others, which is a testament to their physical performance. However, households looking to Green Deal loan arrangements would need to be realistic with their expectations, i.e. not necessarily expecting substantially increased comfort levels and cost savings if they were not fully heating their home prior to the installation. While higher than expected savings may have been made by some households, in nearly all cases this would still not be sufficient to pay back the cost of the ASHP within a period of 20 years without the upfront cost reducing or being subsidised.




4. External wall insulation to solid wall dwellings in detail


Many properties in the pilot village of Penwithick are of traditional solid wall construction (brickwork or stone walls). Such properties generally have the poorest thermal performance compared to other more modern types of construction, (e.g. cavity wall or modern timber frame) and yet are also the most difficult and costly to improve. Many occupants of such dwellings are likely to look to the Green Deal as a potential funding mechanism to enable internal wall insulation (IWI) or, more commonly, external wall insulation (EWI) to be installed. However, the price of such measures is currently prohibitive, leading to the introduction of the Energy Company Obligation (ECO) to provide subsidy funding towards the cost.

In order to demonstrate the potential benefits of such insulation to households, 13 traditional solid wall properties were insulated under the pilot project. These used various fuel types; most commonly oil, but some with LPG (1 x bulk LPG, 1 bottled LPG), some using Economy 7 storage heaters (2), a single instance of solid fuel use and one household effectively with no permanent heating system that was reliant on portable electric heaters. For households with no fixed heating system, on solid fuels or using bottled LPG (typically a very costly source of fuel), there was concern that persistent under-heating of the dwellings by these methods would undermine their contribution to the pilot study. These households had also indicated a desire for a new heating system. Hence these 3 dwellings were recommended to receive bot EWI and an ASHP under the retrofit pilot.

The selected dwellings captured a range of household occupancy types, including individual employed and retired people, employed and retired couples and families. Properties ranged from relatively small bungalows right through to very large detached dwellings. This variation led to inevitable cost differences for the measures from dwelling to dwelling – more so than with any other measure – since those with a larger surface area of walls cost proportionally more to retrofit with EWI. This would be an important factor for households considering a Green Deal loan, though it is expected that those with a larger external wall surface area would benefit proportionally more from the improvement.

In addition to the traditional solid wall dwellings, two Cornish Type II dwellings (that had not previously been refurbished with cavity walls at ground floor level as many in the village previously had) volunteered to take part in the pilot programme. These dwellings are constructed of pre-cast concrete panels at ground floor level, with a mansard roof to the first floor. The mansard is generally deemed very difficult to refurbish. One of the most commonly considered options is to apply internal wall insulation to the first floor, while external insulation can be applied to the ground floor. For the pilot project, the disruption, physical issues of thermal bridging at the intermediate floor level and additional cost brought about by internally insulating was deemed impractical. However, since Cornish Type II constructions are so prevalent across Cornwall (hence the name) the project team felt that it was important to at least pilot insulating the ground floor level as a ‘partial’ retrofit, to see if this could deliver meaningful benefits at a more nominal cost and with very little practical limitation and disruption. Hence two Cornish Type II dwellings, both using oil as heating fuel, received EWI to the ground floor concrete structure as part of the pilot project.

It is worth noting that due to adverse weather conditions the EWI caused significant disruption to the overall installation programme for the delivery contractor. The external render chosen could not be installed when the weather was wet and since the programme extended into the Autumn this became problematic. Some dwellings did not have their installation completed by the time of the first survey in




December 2013; the insulation had been fixed so would have been largely effective, but the render finish had not been applied. This is a practical issue that could either limit the suitable installation period for EWI or simply lead to householders suffering delayed installation through no particular fault of the contractor. Such issues may be avoided to some extent depending on the external finish chosen for the EWI system – some finishes may not be so weather dependent. However, it is imagined that the render finish chosen in Penwithick by most householders would be a popular choice and hence pose practical hurdles to the rollout of EWI measures.

4.2 Results

It is difficult to determine accurate data for the use of oil and LPG for heating since it was not directly metered. An approximation of the liquid fuel usage was gathered from delivery information during periodic household surveys. However, since it is often difficult to know exactly how much of each delivery has been consumed at the time of the survey, there is an unavoidable degree of error in the data obtained. (Estimates could be out by up to a month or two, which over the heating season could be between 12-25%.) Unfortunately not all property data could be adequately analysed and hence 4 have been excluded from the SAP comparison that follows. Reasons for these exclusions are:

• Lack of reliable information about fuel deliveries due to lead householder being absent at time of survey

• Household moving out part-way through survey period with new occupants adopting a very different heating regime

• Significant dwelling modifications being made since first technical survey meaning that data will not be comparable before and after measures


• Actual energy use against SAP forecasts à This comparison confirms whether the EWI has performed in line with the modelled expectations

• Actual energy costs with EWI against previous household energy bills à This comparison shows whether savings have been realised from the retrofit, as an indication of Green Deal viability

4.3 Comparing energy in use with SAP forecasts

Earlier studies1-3 have indicated the likely payback periods and viability of the Green Deal for EWI. The purpose of this study is now to compare whether the real measured energy for properties with EWI installation is in line with SAP’s forecasts, to confirm whether the anticipated savings would have been achieved or not. This of course assumes that the baseline condition for the houses pre-retrofit was also realistic and cannot account for under-heating of properties and other factors as discussed in the earlier ‘Comparison of energy tools’ report2.

4.3.1 Validity of the data in relation to assumed usage patterns Reviewing the energy use profiles of the properties with EWI, most are in keeping with the assumptions used in SAP, although there are a few notable exceptions. SAP assumes that the whole house would be heated and nearly all householders stated that the whole house was indeed heated or, at worst, a single room in the dwelling was not heated to the same level. However, dwelling number 33 is a very large property and half the house is not generally heated over the winter. It would therefore be expected that this property would show a lower energy use than forecast by SAP.

SAP also assumes that the heating system will be used during the morning and the evening aiming for temperatures of 21°C in the main living area and 18°C in the remainder of the property with temperature ‘set backs’ in between. Analysis of the temperature patterns in the dwellings over the period from January




to May indicate that the occupants appear to aim for similar conditions, with thermostats evidently being set to approximately 20-22°C and many properties experiencing set back periods that drop the overall average temperature somewhat. (Average temperatures are shown in Table 7). Two dwellings (7 and 71) appear to be heated to lower overall temperatures and/ or are only heated in the evening, hence resulting in lower average temperatures overall, which may be anticipated to result in lower energy usage than forecast by SAP. One of the Cornish dwellings (89) was apparently also heated over the summer period for health reasons. Hence the actual energy use would be anticipated to be higher than forecast by SAP.

Table 7: Energy use and comfort data for solid wall dwellings receiving EWI

Dwelling number

Heating fuel after retrofit

Dwelling floor

area, m2

Exposed solid wall surface area (for EWI), m2

Number of

rooms heated

Actual heating

and DHW

energy, kWh

SAP heating & DHW forecast,

kWh

% actual versus SAP

Living room average

temperature (Jan-May),

°C

Landing/ circulation average


°C

7 < Heating oil 78.49 32.7 7/7 11740 14318 0.82 14.4 -

89 > Heating oil 73.70 40.7 7/7 23480 11871 1.98 21.6 22.9

19 Heating oil 69.14 64.6 7/7 15262 12218 1.25 22.2 21.9

71 # < Bulk LPG 87.97 68.0 8/8 18637 12159 1.53 15.8 16.0

87 Heating oil 85.46 69.2 8/8 14652 11852 1.24 22.3 22.1

26 Heating oil 102.19 69.7 7/7 17610 13420 1.31 20.3 15.3

79 ASHP 82.48 84.1 8/8 2960 3973 0.74 18.5 18.7

35 Heating oil 132.64 87.6 10/10 26932 22951 1.17 17.0 19.0

85 ASHP 100.60 108.6 6/6 4523 5199 0.87 19.1 20.2

33 < Heating oil 151.84 114.4 8/15 24889 41957 0.59 18.9 17.8

37 # ASHP 73.96 122.5 5/6 2904 4171 0.67 19.4 17.7

Dwellings in italics are of Cornish Type II construction # = Dwelling received additional loft insulation < = Information provided by temperature sensors suggests these households are not fully heating their homes to the extent assumed in SAP. Hence, it would be anticipated that these dwellings would show a lower energy use than forecast > = Occupants continued to heat the dwelling over summer due to illness, so would anticipate this dwelling to show a higher energy use than forecast ? = Data not reported

The majority of the dwellings actually appear to use more energy for heating and hot water than forecast by SAP. The main exceptions are those that also received an ASHP as part of their retrofit package (it was noted in Section 3.2 that all ASHPs performed better than forecast by SAP), or those that are noted as being under-heated to an extent.

Examination of data from the weather station that was set up in the village to correspond to the data collection period suggests a relatively significant increase in overall ‘degree days’ (i.e. the measure of the




relative heating period for the year) for 2013 compared to SAP’s assumptions; 2225 compared with 1650 (at a base temperature of 15.5°C). Hence, it may be anticipated that the heating energy demand for the Penwithick households would have been approximately 33% higher than SAP forecast.

However, while SAP essentially makes generalised climate assumptions for central England for Regulatory comparative purposes, Penwithick being towards the very south of the UK it would be anticipated to have a milder climate and hence require less energy overall than SAP may forecast. If overall it is assumed that the harsher winter demonstrated via the weather station in the village would lead to an increase in energy use compared to SAP, it follows that other measures considered under this study (e.g. ASHPs or EWI to the front and rear of the timber hybrid properties) would have performed even better than implied in sections 3 and 5 respectively, which is unlikely.

In light of the SAP comparisons made for other measures in this report, the outcome here for EWI where actual energy usage is higher than SAP forecast is a little unexpected. It implies that there is a feature specific to the solid wall dwellings that is not experienced in others (particularly the timber hybrid properties, for which a number received EWI to the front and rear façades). It seems that the most likely influencing factor would be the moisture content of the walls.

Of the 15 properties put forward for EWI, all except 2 dwellings reported their homes to be damp to some extent prior to the installation of the retrofit measures. (Note that any households volunteering for the pilot programme where serious concerns about damp were identified at the initial survey stage were not put forward for EWI.) Data gathered from the weather station in the village indicated that the relative humidity in the area was in excess of 95% for over 56% of the year. This compares with between 5-20% of the year at key locations across the UK from averaged 20 year weather data. It is well known that the conductivity of materials is dependent on their moisture content, with dry materials being less conductive and wet materials being more conductive. It follows that the calculated U values of walls could be influenced by the moisture content.

Previous studies carried out by Glasgow Caledonian University for Historic Scotland5 and by Natural Building Technologies Ltd for Trinity College Cambridge6, have reported that in situ measurement of U values in a selection of solid wall buildings prove to be better in practice than the estimates assumed in SAP. They acknowledge that the moisture content of the wall will have an influence on the U values obtained, with the ‘improved’ cases seen being a result of very dry walls. A study by English Heritage investigated the influence of moisture in bricks on the potential U values of solid brick walls7. The study found that U values from dry bricks corresponded well with real in situ measurements and were lower than typical ‘default’ brick conductivity values that may be used in U value calculation software, while wet products produced significantly higher U values.

The average relative humidity of the solid wall homes previously reporting damp prior to receiving EWI was quite high over the year’s measuring period. (Note that while the RH of a room does not necessarily imply the level of moisture in the walls, high RH could result from wet walls drying out.) The pattern witnessed in all dwellings was similar to the example shown in Figure 7, which reflects typical wetting and drying cycles of buildings.

The overall RH remains relatively steady (taking into account the peaks and troughs relating to heating cycles) over the initial heating period from January to May. It then increases over the summer, which will be a result of natural drying out of the building following typically wetter winters during which the building fabric will inevitably have absorbed some moisture from the environment. Since in the summer the temperature may be warmer outdoors than indoors and the sun will directly heat the external walls, moisture in the structure may actually be driven into the building rather than out of it. During the winter when the internal temperatures are higher than the external temperatures, the opposite will be true, with moisture generally being driven from inside to out. It is expected that this moisture occurring inside will




ultimately be driven from the dwelling by ventilation systems and/ or opening windows during the summer and some may be driven back into the walls during winter. The RH then decreases from around the end of October towards December as the heating period begins again and the trend in moisture movement once more reverts to being driven out of the building. Overall this creates a net cycle that will form a dynamic equilibrium over time.

Figure 7: Temperature and relative humidity profile for a solid wall dwelling with EWI

However, by insulating the property externally, the dynamic of moisture being driven outwards from the building may be changed as in this case the insulation is impermeable. The only route for moisture will therefore be into the dwelling, to subsequently be driven out of the property by ventilation routes. It is likely to take more than a single heating season for a new equilibrium of moisture transfer in the building to be established and for any damp present in the walls to ‘dry out’.

Whether the moisture was present in the wall previously (hence influencing heat loss via the thermal conductivity of the wet wall) or whether the moisture is instead present in the air (thus increasing the thermal capacity of the air, which will increase the heating energy demand) it would follow that both the real-world uninsulated and insulated wall scenarios would likely result in a higher energy demand than determined by SAP in the corresponding case, as SAP will not account for moisture in the walls or high RH in the air. So while the dwellings with EWI may have given higher energy use than forecast by SAP here, it is likely that the same would have been true in the uninsulated base case, since the U values may have been underestimated by not taking into account the potential dampness of the wall. Households would still have potential to make savings when comparing walls in a relatively damp condition before and after retrofit measures, though the savings will increase (relatively, taking into account unit energy price rises) as the solid walls ‘dry out’ over time and the wall U values improve.

Since the phenomenon described above resulting from the application of EWI may increase the moisture in the dwelling in the short term as the walls dry out, it is very important that the properties have appropriate ventilation to facilitate this.

Other types of construction, such as cavity walls or timber hybrid, would not be anticipated to be influenced in this way, since cavities and air gaps in these constructions would isolate moisture

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec




conduction from the inner and outer surfaces of the property and stop damp from being able to build up in the first place. This would account for why a similar increase in energy demand compared to SAP was not witnessed with the timber hybrid dwellings; they were unlikely to have been particularly ‘wet’ in their uninsulated case since they are a relatively lightweight construction that could transfer moisture relatively easily.

4.4 Comparing actual energy costs following EWI installation with previous household energy bills


Table 8 and Figure 8 show a comparison of these overall costs per household against the prices calculated from meter data collected during the study. (A standing charge of £80 per year for electricity has been added to cases where the charge was not explicitly known. This is an approximate average of the standard charges that were reported from bills across the village.)

Table 8: Annual household energy costs before and after EWI installation

Dwelling number Dwelling description

Exposed wall surface

area (for EWI), m2

Cost with

EWI, £

Cost before EWI, £

Saving, £



7 Cornish, Oil, Empl2 < 32.7 1167 1134 -33 1/7 7/7

89 Cornish, Oil, Retd1 > 40.7 2015 2016 1 6/7 7/7

19 Solid, Oil, Empl2 64.6 1529 1159 -370 7/7 7/7

71 Solid, LPG, Retd2 # < 68.0 2495 1701 -794 6/8 8/8

87 Solid, Oil, Empl2 69.2 1793 1575 -218 5/8 8/8

26 Solid, Oil, Family 69.7 1623 1991 368 7/7 7/7

79 Solid, ASHP, Empl1 84.1 977 1575 598 1/8 8/8

35 Solid, Oil, Family 87.6 1993 2092 98 9/10 10/10

85 Solid, ASHP, Family 108.6 1820 2247 427 1/6 6/6

33 Solid, Oil, Family < 114.4 1849 3125 1276 7/15 8/15 # = Dwelling received additional loft insulation < = Evidence of under-heating of the dwelling > = Evidence of dwelling being heated over summer




Figure 8: Graph of annual household energy costs before and after EWI installation

Generally, the dwellings that indicated energy use higher than forecast in SAP in the previous section have similar or higher energy costs compared to before the retrofit. There are various reasons why this may be the case, with the most likely being inaccurate initial reporting of previous energy costs, or due to households heating the house more fully and/ or to a more comfortable level now compared with before the insulation retrofit. Table 8 shows the latter to be a relatively common factor (by the change in the number of rooms heated before and after measures). Although there was evidence of under-heating in 3 of the properties, one of these still actually shows a saving over what was paid the previous year, suggesting the EWI may have improved the ability to heat the home, even if only partially heating.

It is noteworthy that dwellings with larger areas of exposed wall receiving EWI are the properties that have made savings. The higher the area of external wall surfaces the more relative potential there is to achieve energy savings through improved insulation, which seems to hold true here.

It can be seen that dwellings occupied by families seem to have realised savings when compared to those of lower occupancy (one or two occupants) households. Though the pattern is not perfect (dwelling number 79 has only 1 occupant but has made savings) and the sample size is a little small to confirm the trend with confidence.

It should be noted that two of the dwellings in Figure 8 received a new ASHP along with the EWI as part of their retrofit package. The relative ratio of the anticipated savings according to SAP was examined and is shown in Table 9, indicating that the ASHP may be expected to contribute between 37-58%. It therefore follows that the savings experienced in these dwellings will not be a result of the EWI alone.

Key: Empl1 = Single employed occupant Empl2 = Employed couple Retd1 = Single retired occupant Retd2 = Retired couple

# = Additional loft insulation installed < = Dwelling under-heated > = Dwelling over-heated




Table 9: Forecast relative contribution of ASHP and EWI to overall savings in example dwellings

Dwelling number

Previous dwelling fuel

Total saving forecast by

SAP

Approximate attribution of

saving to ASHP

Approximate attribution of

saving to EWI

79 Portable electric 9820 kWh 37% 63%

85 Portable electric 8976 kWh 58% 42%

For the Cornish properties, it is apparent that the occupants have taken additional comfort from the new measures, heating more rooms and/ or heating to a higher average temperature. Feedback from the occupants was generally positive and they would recommend the measure to others, though one stated that they if it were not done via the retrofit project they thought it was too costly a measure to consider paying for themselves.

For the three solid wall dwellings whose bills increased after receiving EWI, this is likely to be a result of price increases masking potential savings to some extent and comfort-taking, with households heating more rooms and/ or heating to a higher average temperature. For those that have made savings, in most cases these would likely not be sufficient to pay back the cost of the EWI within a period of 20 years without the upfront cost reducing or being subsidised.


Some occupants commented that the dwelling felt much warmer and more comfortable overall than before the EWI was installed and that it stayed warmer for longer after the heating had switched off. Others remarked that they have filled up with oil later than they would have expected or have not had to refill with so much fuel at a similar time of year (i.e. not used so much).

13 out of 15 households state they would recommend EWI to others, with one saying they would maybe recommend it. (The final household had just moved into the property recently so did not answer this question. They also indicated that the EWI and the new render finish to the property did not particularly influence their decision to buy the house.) Further to this, 12 households reported that if they had not been part of the pilot project and they could afford to pay for such measures they would look to do so, with most saying they would consider looking at a Green Deal loan (11) rather than using their own money or savings (5) or taking out a personal loan (4).

4.6 Summary conclusions for EWI to solid wall dwellings

The study has indicated that solid wall properties receiving EWI (with no change in the main heating system, i.e. no ASHPs) have used more energy for heating and hot water than was forecast by SAP. It is postulated that the reason for this is that the walls of the dwellings are likely to be relatively damp due to the exposure and climate of the village, which would make the U values both before and after the insulation measures higher than assumed in SAP. In the short term, dwellings may indeed have a higher energy demand than expected while the properties ‘dry out’. Dryer walls will have improved thermal properties compared to wetter walls, hence additional benefit should be achieved in the longer term, assuming adequate ventilation is maintained in the insulated homes to remove the moisture present. This phenomenon is also likely to occur in the dwellings that additionally received ASHPs, though the effect has been masked by the extra savings brought about by the heat pump.

It follows that if there is uncertainty about the condition of the walls, particularly regarding the state of dampness, any potential energy calculations and payback rates for retrofit insulation measures will need




to be treated with caution. Previous studies have suggested that savings from EWI may be reduced if walls are very dry, since the baseline thermal performance is likely to be better than default assumptions. Conversely, if walls are damp, savings may still be possible but it may be more difficult to forecast the overall energy savings achievable and potential short term savings may be negated while buildings ‘dry out’. A simple method of testing to establish the likely moisture content of solid walls is required and this is a point of investigation in ongoing research studies commissioned by DECC.

When comparing the overall energy costs with those reported by households prior to the installation of retrofit measures, it is evident that some have made notable savings, while some appear to be spending more on their energy. Retrofit measures would not have been installed unless there was an apparent saving to be made according to the initial SAP forecasts, but there are additional factors that will have influenced whether savings have been realised by households. Key reasons include:

• Many properties with EWI are now heated more fully than before the retrofit measures and to a more comfortable level than before (i.e. to higher temperatures)

• Energy prices may have increased for some households over the study period, thus masking potential savings. In particular, the unit price of heating oil can be quite variable depending on when deliveries are made

• Inaccurate reporting of energy costs – particularly for liquid fuels, as deliveries may be irregular and actual usage has not been metered. These costs therefore unfortunately carry a relatively high level of error

Despite these inaccuracies, when considering households that have saved money, the savings are not likely to be sufficient to pay back a theoretical Green Deal loan covering the cost of the measures. There is some evidence to suggest that families may be more likely to make savings than other occupancy patterns, but the sample is a little small to declare this with confidence.

Nearly all those receiving EWI to their solid wall dwellings would recommend it to others, though households looking to Green Deal loan arrangements would need to be realistic with their expectations, i.e. not necessarily expecting substantially increased comfort levels and cost savings if they were not fully heating their home prior to the installation. Considering the high current expense of EWI as a measure, it is inevitable that installation prices would need to reduce substantially and/ or receive subsidising grants to become a viable option for households, particularly to account for uncertainties apparently witnessed at present with energy calculations.




5. External wall insulation to the front & rear of timber hybrid dwellings in detail


During initial surveys of householders volunteering to take part in the pilot project, many in the ‘timber hybrid’ dwellings made comments about their homes being very difficult to heat in the winter, being very draughty and that they would often overheat in the summer. This behaviour can be common in lightweight structures such as timber frame dwellings across the UK.

The timber hybrid dwellings are a little more unusual than ‘typical’ timber frame in that the gable wall is actually finished with an external blockwork skin, while the front and rear walls are made up of timber infill panels finished with PVC weatherboards, which are often attributed as the cause of draughts in these dwellings (i.e. poor airtightness). U value calculations derived for the construction indicated that the gable wall was likely to be of slightly improved thermal performance than the front and rear walls, with neither generally being poor enough to bring about significant cost savings through the installation of EWI. However, with the airtightness of the dwellings potentially being an additional issue, the decision was made to spend a lower amount of money to install external wall insulation (EWI) only to the poorer performing front and rear walls to see whether this would in fact offer more benefit than implied by SAP modelling.

9 timber hybrid dwellings were therefore selected to receive insulation measures. 7 of these had electrical heating while 2 had modern LPG boilers. They also covered a range of occupancy patterns, including an employed individual, employed couples, a retired couple and families. It should be noted that 5 properties were also identified to receive top-up loft insulation as part of their retrofit package.

5.2 Results

While nearly all of these properties received monitoring equipment (for two the consumer units were deemed too primitive to be able to provide useful information), it is difficult to determine accurate data for the use of LPG for heating since it was not directly metered. An approximation of the LPG usage was gathered from delivery information during periodic household surveys. As in other cases, interruption of the power supply prevents two further properties from presenting a full year of data, hence these have been excluded in the SAP comparison that follows.


• Actual energy use following EWI installation to the front and rear of the properties against SAP forecasts à This comparison confirms whether the insulation measures have performed in line with the modelled expectations

• Actual energy costs following EWI installation against previous household energy bills à This comparison shows whether savings have been realised from the retrofit, as an indication of Green Deal viability

5.3 Comparing energy in-use with SAP forecasts

Earlier studies1-3 have indicated the likely payback periods and viability of the Green Deal for EWI. The purpose of this study is now to compare whether the real measured energy for properties with EWI installation to the front and rear is in line with SAP’s forecasts, to confirm whether the anticipated savings would have been achieved or not. This of course assumes that the baseline condition for the houses pre-




retrofit was also realistic and cannot account for under-heating of properties and other factors as discussed in the earlier ‘Comparison of energy tools’ report2.

5.3.1 Validity of the data in relation to assumed usage patterns Reviewing the energy use profiles of the timber hybrid properties with EWI installed to the front and rear, there are some apparent differences to the heating patterns assumed in SAP. Since many of the properties have Economy 7 storage heaters, the heating profile would be anticipated to be quite regular, since heaters would usually be charged up overnight. However, some household patterns seem to be quite erratic, suggesting that they are instead using heaters during the day as needed rather than the storage heaters. This ad hoc use has resulted in relatively low average temperatures over the winter and spring months of January to May in some dwellings, plus there is additional evidence of under-heating, as some households have reported not heating all of the rooms. For households not using Economy 7 heating, heating patterns appear to be more in-line with SAP.

In all cases where data is available, the forecast energy use from the heating system after the EWI had been installed is lower than was forecast by SAP, as shown in Table 10. However, as mentioned above, there is also evidence that some of these homes may not have been heated to the same extent as assumed by SAP, hence it may be expected that the energy use for heating would not be as high. This is expected to be the case with property numbers 52 and 53.

Table 10: Energy use and comfort data for timber frame dwellings receiving EWI

Dwelling number

Heating fuel

Dwelling floor

area, m2

Number of heated

rooms

Actual heating & DHW fuel,

kWh

SAP heating & DHW forecast,

kWh

% actual versus SAP

Living room average


°C

Landing average


°C

48 # Economy 7 72.0 ?/6 5713 9094 0.63 19.8 21.0

43 Peak electric 77.8 4/6 5940 8517 0.70 20.8 20.2

47 # LPG 80.3 7/7 7628 9716 0.79 18.0 20.2

53 # < Economy 7 80.3 5/6 3661 10788 0.34 17.2 16.2

52 # < LPG 90.5 2/7 3855 8440 0.46 - -

44 Economy 7 96.2 4/7 7473 12064 0.62 21.1 22.2

49 Peak electric 100.7 9/9 5493 10526 0.52 20.9 19.2

Actual LPG usage information gathered from periodic surveys # = These properties also received top up loft insulation, which will have contributed to the energy savings made (this will also have been captured in the SAP energy forecast) < = Information provided by temperature sensors and/ or on heated rooms suggests these households are not fully heating their homes to the extent assumed in SAP. Hence, it would be anticipated that these dwellings would show a lower energy use than forecast ? = Data not reported




Also, although the sub-circuit electrical monitoring was intended to isolate the energy used for heating or hot water, if electrical heaters were used on a standard ring main or socket circuit in addition to those on the dedicated heating circuits (i.e. additional standalone portable heating) they could be very difficult to detect and account for. It is suspected that this may be the case for property numbers 48 and 49 in Table 10. However, total meter readings in these cases are in line with or lower than the annual SAP forecast (despite SAP not considering unregulated loads, which would obviously be included in household total meter readings) suggesting that the overall impression of energy use being lower than SAP is genuine, albeit not necessarily by the percentage indicated in the table.

Focussing on the homes that have average temperatures in line with those in SAP (aiming for 21°C in living areas and 18°C in other areas), the dwellings seem to have performed better than expected. While this occurrence could suggest that savings could be greater than expected and hence a Green Deal loan being more viable for such measures, the accuracy of the respective base case scenario models would also need to be taken into consideration.

When considering the performance of solid wall insulation for the Green Deal, an ‘in use’ factor is applied to the forecast savings as previous test studies have suggested that refurbishment measures often do not realise the extent of the savings forecast by SAP. This could be for various reasons, but particularly for EWI it is assumed that the U values of the walls prior to insulation may not be as poorly performing as assumed by SAP (particularly RdSAP, for which more generalised assumptions about the type of construction are usually made due to a lack of available information for existing buildings). Reduced savings may also be a result of ‘comfort taking’ by occupants following the improved insulation of their property (i.e. warming the house more fully and/ or to higher temperatures than before). EWI to timber frame dwellings has not had a formal in-use factor applied, since it is not anticipated to be a common measure, though wall insulation in-use factors are typically between 25-35% suggesting actual energy usage is generally anticipated to be higher than forecast in SAP.

This is opposed to the data in Table 10, suggesting in-use factors for EWI may potentially be too conservative. There are various additional factors that will influence these findings. While SAP essentially makes generalised climate assumptions for central England for Regulatory comparative purposes, Penwithick being towards the very south of the UK it would be anticipated to have a milder climate and hence require less energy overall than SAP may forecast. Analysis of the likely impact of this variation was investigated with Design Builder software2 which suggested the energy savings experienced for EWI in the far south of the UK compared to SAP may be approximately 31% lower.

However, examination of data from the weather station that was set up in the village to correspond to the data collection period suggests a relatively significant increase in overall ‘degree days’ (i.e. the measure of the relative heating period for the year) for 2013 compared to SAP’s assumptions; 2225 compared with 1650 (at a base temperature of 15.5°C). Hence, it may be anticipated that the heating energy demand for the Penwithick households would have been approximately 33% higher than SAP forecast.

Considering these factors, it may still be expected that the energy demand for the insulated dwellings should have been approximately the same as SAP overall, whereas in fact the results have been lower. When considering a potential Green Deal loan, a conservative estimate of forecast energy use would be ‘safer’ from the perspective of being likely to pay back the loan than an optimistic estimate, which could leave people with higher repayments than expected.

5.4 Comparing actual energy costs following EWI installation with previous household energy bills

Prior to the study, householders were asked how much they were paying for their energy. By examining ‘degree day’ data from nearby weather station locations around Cornwall, it is apparent that 2013 was a




colder year than 2012 as shown by an approximately 5% increase in annual degree days in 2013. Therefore, in order to make a fairer comparison between the Penwithick household data, the fuel costs for 2012 reported from initial surveys have been increased by 5%.

Table 11 and Figure 9 show a comparison of these overall costs per household against the prices calculated from meter data collected during the study. (A standing charge of £80 per year has been added to cases where the charge was not explicitly known. This is an approximate average of the standard charges that were reported from bills across the village.)

Despite the actual heating energy use appearing to be lower than forecast by SAP in all cases, the calculated heating cost for 5 of the 9 dwellings is similar or higher than before the retrofit. There are various reasons why this may be the case, with the most likely being a result of increased energy prices over the period of study masking potential savings, inaccurate initial reporting of previous energy costs, or due to households heating the house more fully and/ or to a more comfortable level now compared with before the insulation retrofit. Table 11 shows the latter to be a relatively common factor (by the change in the number of rooms heated before and after measures). In the remaining 4 dwellings, there is evidence of under-heating in 3 of the properties. However, these still actually show a saving over what was paid in previous years, suggesting the EWI may have improved the ability to heat the home, even if only partially heating.

Table 11: Annual household energy costs before and after EWI installation to front and rear of property

Dwelling number Dwelling description Cost with

EWI, £

Cost before EWI, £

Savings, £



43 Peak electric, Empl2 1158 1058 -100 1/6 4/6

49 Peak electric, Family 1639 1411 -227 7/9 9/9

47 LPG, Empl2 # 1063 1134 71 5/7 7/7

52 LPG, Family # < 1422 1806 384 2/7 2/7

53 Econ7, Empl1 # < 1011 1764 753 2/6 5/6

45 Econ7, Empl2 # < 401 1260 859 1/6 3/6

46 Econ7, Empl2 1486 1302 -184 1/6 2/6

48 Econ7, Retd2 # 973 1302 329 2/6 ?/6

44 Econ7, Family 1543 1512 -31 ?/7 4/7 # = Dwelling received additional loft insulation < = Evidence of under-heating of the dwelling

There do not appear to be any particular trends linked to occupancy or the type of heating system in the property. However, it is noteworthy that all of the properties that have made a saving also received loft insulation in their retrofit package. The attribution of the anticipated savings in SAP between the loft insulation and the EWI was examined for two dwellings – one with LPG heating the other with Economy 7. The relative ratio of these savings is shown in Table 12, indicating that loft insulation may contribute to




between and third and nearly half of the anticipated savings. It therefore follows that properties also receiving loft insulation would experience somewhat higher savings than those with EWI alone and certainly to an extent that is not so readily masked by compensating factors (e.g. energy price increases, comfort take back).

Figure 9: Graph of annual household energy costs before and after EWI installation

Table 12: Forecast relative contribution of loft insulation and EWI to overall savings in example dwellings

Dwelling number

Dwelling fuel

Total saving forecast by

SAP

Approximate attribution of saving

to loft insulation

Approximate attribution of saving

to EWI

47 LPG 1473 kWh 35% 65%

48 Economy 7 1817 kWh 44% 56%


Some occupants specifically commented that their property was noticeably warmer following the EWI installation to the front and rear façade. Others noted that the new external finish made the dwellings look more modern and appealing. One family acknowledged that they may be paying around the same as they were before but the house was more comfortable now.

Key: Empl1 = Single employed occupant Empl2 = Employed couple Retd2 = Retired couple

# = Additional loft insulation installed < = Dwelling under-heated




8 out of 9 occupants said that they would recommend the EWI to others. Further to this, 6 said that if they had not been part of the pilot project and they could afford to pay for such measures they would look to do so, with most saying they would consider using their own money or savings (5) or looking at a Green Deal loan (4) rather than taking out a personal loan (3).

Despite the mixed results when comparing cost savings with the previous year, 4 households felt they had saved money compared to previous winters, while 3 were not sure. Some specifically acknowledged that their energy prices had increased since the previous year.

5.6 Summary conclusions for EWI to timber hybrid dwellings

Considering all of these factors, it is difficult to determine the extent to which EWI applied to the front and rear of the timber hybrid properties has been of benefit. Comparison directly with SAP indicates that energy use following the insulation was lower than anticipated, while comparison with household energy costs before and after the retrofit suggests that approximately half are making savings while half are paying more, though the half making savings also received additional loft insulation, which will contribute to the savings experienced. The sample is a little small to identify whether there are any trends resulting from the type of fuel being used or from occupancy patterns.

Retrofit measures would not have been installed unless there was an apparent saving to be made according to the initial SAP forecasts. But it is evident that additional factors have been influential and not all households have made these savings. Key reasons include:

• Energy prices increasing for some households over the study period, thus masking anticipated savings

• Base case SAP forecasts being inaccurate due to households not fully heating their home prior to measures (i.e. not heating all rooms, not heating to the same temperature as assumed)

In these cases, the majority of householders are unlikely to have made sufficient savings to pay back a theoretical Green Deal loan covering the cost of the EWI insulation.

While most households were reportedly pleased with the measures, feedback was often somewhat less exuberant compared to households receiving other measures. While this is purely a qualitative observation, it does seem to reflect the magnitude of the benefits experienced (i.e. savings, increased comfort) compared to other retrofit measures discussed in this report.

5.7 Potential for overheating in timber hybrid dwellings with EWI

The lack of thermal mass in timber frame properties (i.e. exposed masonry elements that may buffer heating and cooling effects in dwellings) often makes them susceptible to swings in temperature. It was intended that the new insulation would help protect against heat losses during the heating season, but there was concern that they may subsequently be prone to overheating in the summer.

Temperature readings were logged in the main living room and on the first floor landing area of a number of timber hybrid dwellings as part of the study (14 out of 20 dwellings, half receiving ASHPs and half receiving EWI). Window sensors were also installed to a main window in the living room and kitchen on the ground floor and to the main bedroom and bathroom on the first floor. (Sensors were installed on windows householders said they were most likely to open.) Findings are reported in Table 13.

Data from the window sensors indicate that most properties did not open their windows during the study. While it cannot be ruled out that occupants may have instead opened a window without a sensor, this seems unlikely since they were aware of the sensors and had been asked to use those windows if need be. This could have implications for ventilation, though as part of the study any property that did not have




adequate mechanical ventilation in the kitchen and bathroom were offered heat recovery ventilation units. It therefore seems likely that most households did not feel the need to open the windows for additional ventilation, which would be beneficial for retaining heat during winter.

Although the key purpose of the window sensors was to detect overheating, it is apparent that some households opened the windows during the heating season (i.e. from January to May and October to December). The windows often appeared to remain open for extended periods of time (i.e. days in some cases), so were not simply used for short periods to boost ventilation during cooking or showering for example. Some occupants simply prefer fresh air from open windows. Under such circumstances it must be realised that over winter months this could result in increased heat loss and subsequently higher energy use for heating to compensate for this. However, for the dwellings to which this applies, the average temperatures reported from the living room and landing sensors were neither notably lower or higher compared to other similar dwellings and their energy demand does not appear to have been adversely affected during the analyses elsewhere in this report.

Table 13: Window opening hours and household temperatures for timber hybrid dwellings

Dwelling number

Measure received

Living room winter

temperature, °C

Landing winter

temperature, °C

Heating season (Jan-

May, Oct-Dec) window open,

hours

Living room summer

temperature, °C

Landing summer

temperature, °C

Summer (Jun-Sep) windows

open, hours Av Max Av Max Av Max Av Max

2 ASHP 19.8 25.0 19.4 21.5 0 22.4 29.0 21.6 27.5 0

4 ASHP 21.4 25.5 19.0 21.5 137 22.8 29.0 21.0 27.0 0

5 ASHP 18.0 23.5 19.1 21.0 352 22.2 31.0 23.0 31.0 274

40 ASHP 21.4 26.0 21.5 25.5 0 23.0 30.0 23.6 30.0 0

41 ASHP 21.1 24.0 20.7 23.0 0 22.2 28.5 21.8 28.5 93

42 ASHP 21.0 25.5 20.3 24.5 0 23.0 28.5 22.1 28.5 0

57 ASHP 19.8 27.0 18.0 22.5 6 21.8 29.5 21.0 28.0 0

43 EWI 20.8 25.5 20.2 23.5 33 21.8 27.5 21.4 28.5 128

44 EWI 20.8 24.5 22.0 26.0 0 22.1 26.5 23.3 29.0 0

45 EWI 18.0 26.5 18.0 25.0 - 19.6 26.5 20.0 27.0 -

47 EWI 18.0 23.0 20.2 25.5 0 21.4 31.5 21.4 31.5 0

48 EWI 19.3 25.5 20.6 25.0 592 23.8 31.5 24.6 29.5 682

49 EWI 20.8 24.0 19.2 22.0 0 24.3 32.5 24.3 32.5 0

53 EWI 16.7 22.0 15.1 18.5 - 21.0 27.5 21.4 28.5 -




When considering the summer situation, again few dwellings appeared to open their windows. Average and maximum indoor temperatures are somewhat higher during the summer compared with the heating season. While some maximum temperatures may appear particularly high, these will only have occurred for a limited period of time. When examining those that reached or exceeded 30°C, most appeared to exceed 25°C briefly over 10-17% of the days of the year, with one at ~25% of the days of the year. Despite this, none of these households reported that they felt the house overheated during the summer, suggesting they did not find these warm peaks especially uncomfortable. An interesting observation is that the average and maximum temperatures do not seem to differ particularly between the dwellings that did and did not open their windows or between those that had or had not received additional wall insulation. This indicates that the EWI does not appear to have led to an increased risk of overheating in these dwellings.




6. Comparison of Timber hybrid properties receiving ASHPs versus EWI front and back

Some households that received ASHPs or EWI are now paying more for their energy bills than they were prior to the retrofit measures, while some have made significant savings. Most of those making savings received additional measures (i.e. loft insulation) that will also have contributed to the reduced energy usage.

ASHPs were installed in timber hybrid properties where essentially no full central heating system was otherwise in place. While these dwellings will have had high forecast energy use in SAP (assuming the home was fully heated), in reality it is far more likely that these houses will previously have been under-heated. There would therefore be a high chance of additional comfort taking by households, which has been realised and acknowledged by many occupants. Considering the feedback received, the installation of a fully controllable ASHP central heating system has made a recognisably beneficial impact on people’s lives and behaviours, allowing them to heat their home more satisfactorily.

By comparison, all households receiving external insulation to the front and rear walls already had a ‘working’ heating system that they were content with; either Economy 7 storage heaters, an LPG central heating system, or programmable thermostat controlled electric room heaters (not Economy 7). It followed that some households could not readily tell whether they were receiving a benefit from the newly installed insulation, though some noted that the house seemed to heat up more quickly and a number commented on the visual improvement it made to the property.

When the data is compared for both measures, neither measure particularly presents itself as a clear winner from an energy saving perspective; both indicated lower energy usage compared to SAP forecasts across all sample dwellings, though neither consistently delivered meaningful cost savings. While it is unlikely that either measure would be universally viable under the Green Deal loan mechanism without the capital cost reducing quite significantly, it seems a higher proportion of householders may be more prepared to invest in a new ASHP heating system themselves than in the EWI. While this is opposed to the established ‘fabric first’ approach, it is understandable that households would fundamentally want to prioritise being able to effectively provide heat in every part of their home.




7. Oil boiler upgrades in detail


Since the village of Penwithick is off the mains gas network, many properties already used oil as their main fuel for heating and hot water. Initial feasibility modelling and analysis demonstrated that it was not logical to switch households from oil to any other fuel1. However, the initial research did suggest that if existing oil boilers were particularly old and inefficient there would be benefit in upgrading them to modern boilers.

As such, 6 properties received new oil boilers under the pilot project; 3 of these were of timber hybrid construction, 2 were of solid wall construction and 1 was of cavity wall construction. These encompassed a range of occupancy profiles, including employed and retired individuals, an employed couple and families.

7.2 Results

It is difficult to determine accurate data for the use of oil for heating since it was not directly metered. An approximation of the oil usage was gathered from delivery information during periodic household surveys. However, since it is often difficult to know exactly how much of each delivery has been consumed at the time of the survey, there is an unavoidable degree of error in the data obtained. (Estimates could be out by up to a month or two, which over the heating season could be between 12-25%.)


• Oil consumption against SAP forecasts à This comparison confirms whether the new oil boilers have performed in line with the modelled expectations

• Actual energy costs with new oil boiler against previous household energy bills à This comparison shows whether savings have been realised from the retrofit, as an indication of Green Deal viability

7.3 Comparing oil consumption with SAP forecasts

Earlier studies1-3 have indicated the likely payback periods and viability of the Green Deal for new oil boiler upgrades. The purpose of this study is now to compare whether the actual energy usage is in line with SAP’s forecasts, to confirm whether the anticipated savings would have been achieved or not. This of course assumes that the baseline condition for the houses pre-retrofit was also realistic and cannot account for under-heating of properties and other factors as discussed in the earlier ‘Comparison of energy tools’ report2.

7.3.1 Validity of the data in relation to assumed usage patterns SAP assumes that the whole house would be heated and that the heating system will be used during the morning and the evening aiming for temperatures of 21°C in the main living area and 18°C in the remainder of the property with temperature ‘set backs’ in between. Table 14 indicates that while some householders receiving boiler upgrades stated that the whole house was indeed heated, a few may be slightly under-heated compared to SAP, particularly when considering the typical thermostat temperatures reported by occupants.

Most dwellings indicate energy usage broadly in line with that forecast by SAP. Dwellings that are evidently under-heated unsurprisingly demonstrate the furthest discrepancy, which is to be expected since they are not heating to the same extent assumed by SAP.




Table 14: Energy use and comfort data for dwellings receiving oil boiler upgrades

Dwelling number

Dwelling floor area,

m2

Number of heated rooms

Typical thermostat

temperature setting, °C

Actual heating & DHW fuel,

kWh

SAP heating & DHW fuel,

kWh

% actual versus SAP

20# 78.1 6/6 18 10801 11111 0.97

24 80.3 4/6 18 9134 11480 0.80

55 80.3 6/6 20 11740 11764 1.00

72# 72.2 7/7 21 14018 11933 1.17

78 96.9 7/7 22 15297 15287 1.00

80 103.2 6/8 15 8218 13869 0.59

# = Dwelling received additional loft insulation

While SAP essentially makes generalised climate assumptions for central England for Regulatory comparative purposes, Penwithick being towards the very south of the UK it would be anticipated to have a milder climate and hence require less energy overall than SAP may forecast. However, examination of data from the weather station that was set up in the village to correspond to the data collection period suggests a relatively significant increase in overall ‘degree days’ (i.e. the measure of the relative heating period for the year) for 2013 compared to SAP’s assumptions; 2225 compared with 1650 (at a base temperature of 15.5°C). Hence, it may be anticipated that the heating energy demand for the Penwithick households would have been approximately 33% higher than SAP forecast. Considering these factors, it may still be expected that the energy demand for heating and hot water should have been higher than SAP overall, whereas in fact the results are generally in line with SAP.

7.4 Comparing actual energy costs with new oil boiler upgrade with previous energy bills


Table 15 and Figure 10 show a comparison of these overall costs per household compared to the prices calculated from meter readings and information collected during the study. (Standing charge of £80 per year for electricity has been added to cases where it was not explicitly known. This is an approximate average of the standard charges that were reported from bills across the village.)

While the previous section indicated that the new oil boilers in Penwithick generally performed better than forecast by SAP, it can be seen here that there are a few instances where household energy prices are higher than before. This may be due to a number of factors, including inaccuracies in reported energy bills skewing the data or increases in energy prices over the study period. For those that have made savings, the percentage saving has not been as high as was forecast by SAP for the timber hybrid dwellings (~11% compared to ~17%) but is in line with the savings forecast for solid wall dwellings (~16%).




Table 15: Annual household energy costs before and after oil boiler upgrades

Dwelling number Dwelling description

Floor area, m2

Cost with new

boiler, £

Cost before new

boiler, £

Saving, £

Number of

rooms heated before

Number of

rooms heated after

Typical thermostat

temperature setting, °C

20 Timber, Family# 78.1 1126 1260 134 6/6 6/6 18

24 Timber, Family 80.3 1180 1323 143 ?/6 4/6 18

55 Timber, Empl2 80.3 1153 1071 -82 6/6 6/6 20

72 Cavity bungalow, Retd1# 72.2 1083 981 -103 7/7 7/7 21

78 Solid, Family 96.9 1483 1764 281 6/7 7/7 22

80 Solid, Empl1 103.2 891 1071 180 2/8 6/8 15 # = Dwelling received additional loft insulation ? = Data not reported

Figure 10: Graph of annual household energy costs before and after oil boiler upgrades

Key: Empl1 = Single employed occupant Empl2 = Employed couple Retd1 = Single retired occupant # = Additional loft insulation installed




Although most households have made savings, it should be noted that the potential payback rates and hence the viability of the new oil boiler installation under a Green Deal loan would be very dependent on the extent of the upgrade required. For instance, if only a new boiler was required and the existing oil storage tank and distribution system were adequate, the new boiler would likely cost between £2000-3000, which in most cases would pay back within the anticipated 20 year timeframe. However, if a new radiator system and/ or bunded tank were required to comply with current Regulations, this would bring additional costs – where this was necessary in the pilot project, costs rose to approximately £5500 for the new system. In such instances, it is unlikely that the savings forecast from the upgrade would be viable under the Green Deal, hence householders would have to accept that they would need to additionally pay towards these supporting measures.


Most occupants stated after the initial winter period with the new boilers that they thought they were saving money compared to the old system, though sometimes it was difficult to tell depending on when they had received oil deliveries. Some comments were made about the ease of use of the new modern systems, with half of the households stating that they thought they were straightforward, but the other half commenting that user manuals were complicated and they were not confident changing things like the times the heating came on and went off. All householders would recommend the measures to others, with 4 of the 6 reporting that if they had not been part of the pilot project they would consider paying for it themselves via a Green Deal loan (4) rather than from their own money or savings (2) or a personal loan (2).

7.6 Summary conclusions for oil boiler upgrades

The study has found that new oil boilers installed in a range of different property construction types have generally performed better than forecast by SAP. On the face of it, this would suggest that such a measure may be more viable under the Green Deal than initially anticipated. However, when comparing the overall energy costs with those reported by households prior to the new installations, the savings are not always as high as anticipated and/ or costs have actually increased. This may be due to inaccuracies in the reported energy bills before and/ or after the installation or due to fuel price rises over the study period. In these cases, householders may not have made sufficient savings to pay back a theoretical Green Deal loan covering the cost of the measures. In particular, in instances where additional supporting works were required for the installation of the new boiler, such as a new oil tank, these costs would not be so readily recoverable via the Green Deal.

All household receiving new boilers would recommend the systems to others, suggesting that they have seen a notable benefit from the new system in the form of cost savings or in the practicality of usage and quality of heating provided.




8. Loft/ roof insulation in detail


Loft insulation is widely accepted as being a very cost effective way of bringing energy savings to dwellings. Top-up insulation will have proportionally less benefit, though as a relatively cheap measure it is expected that it would be readily viable under the Green Deal and/ or via other finance mechanisms.

Initial surveys suggested that many properties in the village may not have had their lofts insulated in line with current recommendations. Properties were therefore put forward for additional top-up loft insulation to 300mm if their current level was 150mm or less of mineral wool insulation (or equivalent).

24 properties were selected to receive loft insulation. This was most commonly done as part of a package of other retrofit measures, hence the benefits will be cumulative with the other associated measures and difficult to disaggregate. Only 4 dwellings surveyed received loft insulation without any other primary measures (3 of these also received ventilation units and/ draught proofing measures).

One dwelling in the village was identified as having a poorly insulated flat roof over a large portion of the house (over half the total roof area, including over bedrooms). This dwelling was put forward for a new, insulated flat roof to investigate the benefits this may bring, as it is likely to be a relatively common issue across the country, though more expensive than simply installing insulation within a loft.

8.2 Results

3 of the 4 dwellings receiving top up loft insulation used liquid fuels (LPG or oil) for their main heating system. It is difficult to determine accurate data for the use of such fuels since they were not directly metered. An approximation of the liquid fuel usage was gathered from delivery information during periodic household surveys. However, since it is often difficult to know exactly how much of each delivery has been consumed at the time of the survey, there is an unavoidable degree of error in the data obtained. (Estimates could be out by up to a month or two, which over the heating season could be between 12-25%.) Energy usage is compared with SAP in Table 16.

Table 16: Energy use and comfort data for dwellings receiving top up loft insulation

Dwelling number Heating fuel

Actual energy usage for heating &

DHW, kWh

SAP forecast energy usage for heating & DHW, kWh

% actual versus SAP

Did occupants find house

easier to heat?

Did occupants feel they were

saving money?

16 LPG 16132 13794 1.17 N N

36 Oil 16178 22914 0.71 N N

65 Economy 7 5971# 7755 0.77 Y Y

95 Oil 11740 19022 0.62 N N

# This dwelling was not sub-metered so an estimate of 2000kWh ‘unregulated’ energy usage has been made that has been subtracted from the metered energy use for the year of 7971kWh




3 of the 4 households do appear to have used less energy than forecast by SAP. However, only one household reported that they have felt a benefit from the loft insulation and believe they are saving money. Some discrepancy in the data reported may be a result of the fuels not being accurately metered, hence over or underestimating to an extent. Other reasons may be that the dwellings were not heated to the same extent (number of rooms and to equivalent temperatures) as assumed by SAP, which would obviously influence the energy use reported. It is also possible that households may in fact be making savings, but it is being masked by increases in energy prices. It may be particularly difficult to establish savings when deliveries of liquid fuels are sporadic and of varying quantity.

Dwelling number 65, which did evidently see benefit from the installation of loft insulation was a bungalow, which will have a high ratio of heat loss surfaces (walls, roof and floor) relative to its habitable floor area. This may be a contributing factor to why this household noticed more benefit from the loft insulation than the other households, since improving the loft will make a proportionally higher improvement to the building fabric overall compared with a two storey dwelling. The actual savings compared to previously reported energy bills are broadly in line with the cost savings forecast by SAP.

Findings presented in other sections of this report indicate that properties receiving loft insulation as part of a suite of retrofit measures generally experience improved savings compared to the corresponding measures in isolation, indicating that overall the loft insulation has made a positive contribution to the benefits experienced, even if its effects cannot be readily disaggregated.

Unfortunately the number and nature of dwellings in this particular sample of ‘loft insulation-only’ houses makes it difficult to demonstrate the benefit of top-up loft insulation. However, potential inaccuracies in the data reported for these households equally means that they cannot imply loft insulation to be unbeneficial. Overall, when considering the compound benefits witnessed from multiple measures during this study, loft insulation does seem to carry a notable benefit towards energy saving in homes.

8.3 Flat roof insulation

The dwelling that received flat roof insulation used oil as its heating fuel. Due to the timings of the reported deliveries, it is very difficult to determine how much oil is likely to have been actually used within the year’s monitoring period. Therefore, only the qualitative information provided by the household is considered here. The occupant commented that it was now possible to heat the upstairs rooms adequately. This is supported by data from temperature loggers that confirmed the temperature in the upstairs of the house (measured on the landing) was between 16°C and 22°C from January to May, with an average of 18.1°C, which is in line with the assumptions in SAP. After the initial winter monitoring period (up to May) the occupant also commented that they would have expected to have to purchase more oil by that time, so believed they were also making cost savings on their fuel. Due to the lack of reliable quantitative data available, it is difficult to determine the cost effectiveness of the improvement, though it is apparent that occupant comfort has been substantially increased.

It seems likely that homes in a similar circumstance (with uninsulated flat roofs) will be under-heating the spaces below the roof as it will be difficult to maintain an adequate level of heat, irrespective of whether it was affordable or not to do so. Savings estimated by energy models may therefore be unrealistic, since the house will likely not have been heated to the extent assumed in the model. However, households may be prepared to pay for improved comfort in such a situation, (i.e. accept they may not make such high savings) though this is not the principle of the Green Deal.




9. Photovoltaic (PV) systems in detail


In terms of practical feasibility, PV is not limited to, or dependent on any particular type of construction; the main influencing parameters are the orientation in relation to the sun (due south being preferable), space availability and potential overshading risk. A number of properties within the village of Penwithick had roofs facing within south east to south west and initial feasibility assessment of the potential electricity generation from PV in the area indicated that it could potentially offer significant benefits to householders. PV was therefore offered to households where the offset electricity generation would bring about greater savings than any other potential refurbishment measure. In reality, this covered dwellings where there were no, or limited potential retrofit options otherwise available (i.e. where existing heating systems were too efficient to warrant an upgrade, where wall insulation was not feasible or not desired). 22 properties received PV systems, ranging from 1.92kWp to 3.6kWp.

Since the PV systems were provided under a grant from the Council, households were not eligible for the Feed in Tariff (FIT). Initially this created some issues and disappointment, since some households had expected to receive the tariff despite receiving the PV for free. It also seems that since the launch of the FIT programme it is very unusual for households to receive a grant (since no ‘formal’ government grant programmes for PV otherwise exist) and hence energy companies do not know how to deal with households not captured by the FIT scheme. In theory, if not covered by the FIT, individuals can make arrangements with their energy supplier to ‘sell’ any excess electricity produced back to the grid, but it is apparent that most utility companies do not have obvious procedures in place to facilitate this (or certainly not as obvious as the procedures in place to apply for FIT). Hence households not utilising all of the electricity generated by their PV panels may not be receiving any form of export payments at present.

Despite this, the circumstances of the retrofit pilot project are in fact a very valid test for the analysis of PV systems under the Green Deal. Although the FIT rates appear generous since they are intended to cover the cost of purchasing and installing a system with a certain level of return on investment, it should be remembered that if households were looking to install PV using part payment via a Green Deal loan, it will be necessary to pay back the rate of the loan, including any interest over time. Hence, in the short-to-medium term (at least while the system costs are being repaid), the main benefit that a household may physically experience will be from using the electricity while it is being generated by the PV system to offset their grid electricity use. This will bring about savings in energy bills higher than any export tariff received from the FIT (since grid electricity is typically >15p/kWh and the current FIT export tariff is 4.5p/kWh). If it is assumed that FIT payments would be used to repay any capital and a Green Deal loan, the circumstances of the retrofit pilot project give an indication of the real-life benefits that may be experienced by PV users.

9.2 Results

Figure 11 shows the electricity generation recorded from the PV systems in the village. The arrows to the left of the chart show the approximate generation ranges achieved by various PV system sizes, though the absolute generation figure will depend on the system specification and orientation. This chart represents cumulative generation over the assessment period, indicating that generation increased dramatically after the initial winter as expected.

Table 17 gives a more detailed breakdown of the overall energy generation for each system alongside the forecasts that were made with SAP and proprietary PVSol software. While most systems perform in line




with or in excess of the modelling tools, it can be seen that the actual generation is somewhat lower than expected for 4 of the dwellings. Reasons for these irregularities are indicated in the footnotes.

Figure 11: Cumulative electricity generation for PV systems installed in Penwithick

SAP generally forecasts lower than the actual generation (on average by ~16%) (with the exception of instances where there appears to be a specific issue, i.e. generation notably lower than forecast.) PVSol forecasts vary around ±6%, though a few outliers outperformed the PVSol estimate by closer to 20%. SAP therefore offers a more conservative estimate for this region of the UK, while PVSol generally predicts the generation within closer tolerances (albeit still with an error of ± ~6% in this study).

It is interesting to see how even seemingly identical systems of the same size and orientation (even in the same street) showed variation in generation performance. This is likely to be due to slight differences in when initial readings were taken (depending on when surveys were returned – potentially a 2 week window) or subtle differences in the performance of panels.

For the cases where systems have not performed as expected, this is known (or assumed in some cases) to be due to the inverters. This highlights the importance of the accuracy of initial surveying for PV (with regard to orientation, roof pitch, potential shading, etc.) to ensure that an appropriate inverter is specified to optimise the output from the PV panels. The inverter is responsible for the conversion of solar energy from the panels into AC electricity for use in buildings. They operate within a defined voltage tolerance, known as the Maximum Power Point (MPP) voltage range. If the voltage received from the PV panels is higher or lower than the inverter’s set range, it will effectively not deliver power. If the inverter’s MPP range is too high, the system will not be effective in the winter when generation voltages are low. If the MPP range is too low, the inverter will self-limit to avoid overloading, meaning it will not be effective in the summer when generation voltages are high. Inverters should be selected so as to optimise the balance of both winter and summer generation as much as possible.

Systems up to 1.92kWp






Table 17: Electricity generation forecasts versus actual generation from PV systems

Dwelling number

Installed kWp Orientation

SAP forecast, kWh/yr

PVSol forecast, kWh/yr

Actual kWh/yr

% actual versus SAP

% actual versus PVSol

88f 1.44 SE 1183 1281 808 0.68 0.63

27 1.92 SW 1577 1778 1993 1.26 1.12

96 1.92 SE 1577 1786 1690 1.07 0.95

97 1.92 SE 1577 1786 1765 1.12 0.99

98 1.92 SE 1577 1786 2170 1.38 1.21

99 1.92 SE 1577 1786 1683 1.07 0.94

100 1.92 SE 1577 1786 1841 1.17 1.03

3 2.40 SSE 2060 2316 2458 1.19 1.06

14 2.40 SW 1972 2262 2300 1.17 1.02

38 2.40 SE 1972 2262 2217 1.12 0.98

81 2.40 SSW 2060 2342 2187 1.06 0.93

25 2.88 SSE 2472 2876 2768 1.12 0.96

28 2.88 S 2472 2828 2836 1.15 1.00

60 2.88 SE 2366 2730 2790 1.18 1.02

18 3.36 SW 2761 3128 3059 1.11 0.98

63 3.36 SW 2761 3128 3317 1.20 1.06

64 3.36 SW 2761 3128 3239 1.17 1.04

69 3.36 S 2884 3302 3370 1.17 1.02

84g 3.36 S 2884 3310 1054 0.37 0.32

12 3.60 S 3090 3526 4203 1.36 1.19

102h 3.60 S 3090 3526 1989 0.64 0.56

22h 3.60 SW 2958 3298 2637 0.89 0.80

f Initial inverter was incorrect and has subsequently been replaced, hence reading is known to be lower than forecast g Low readings have signified a problem with the setup of the inverter. This is now being investigated h These readings appear low relative to the equivalent system in dwelling no. 12. It is postulated that the inverter may not be operating as intended in these dwellings




The fuel costs in SAP from 2012 onwards for Green Deal assessments assumes a standard electricity rate of 13p/kWh. If all of the electricity reportedly generated by the PV systems in Penwithick was used to offset grid electricity it would total 52,375 kWh per year at a value of £6809, while offsetting 27 tonnes of CO2 per year (@0.517kg/kWh). Over the 20 year economic lifespan considered under FIT, this would amount to CO2 savings of 540 tonnes. The average price of standard rate electricity reported in the village is closer to 16p/kWh, which would increase the total saved to £8380. The average generation for each size system is given in Table 18. (3.60 kWhp systems have been excluded from the average due to the noted performance discrepancies.)

Table 18: Average annual electricity generation by PV system size

PV system size Average annual electricity generation

1.92 kWp 1857

2.40 kWp 2291

2.88 kWp 2798

3.36 kWp 3246

Whether householders will have been able to reap maximum benefit from this overall generation depends on people’s behavioural and energy use patterns. It is quite likely that on some high generation days the electricity produced will have exceeded what was being used within the dwelling and hence would have been exported back to the electrical grid. Unfortunately, since export meters were not installed under the project it is very difficult to tell whether household energy use has been reduced overall.

There are various ways of overcoming this issue:

• Match energy consuming activities to obvious periods of generation (e.g. use washing machines, dish washers, vacuum, etc. during sunny periods)

• Install batteries to store energy for use at another time. Unfortunately, this sort of technology at a domestic scale is relatively undeveloped and would carry additional cost

• Install diverter systems that make use of excess electricity by, for example, using it to charge storage heaters or heat domestic hot water immersion heaters

• While not an active solution, some older analogue energy meters actually ‘run backwards’ when electricity is exported to the grid. This will obviously be of direct benefit to householders for which this occurs but it is not something that is actively promoted by utility companies – if anything they would prefer households to be on modern smart meters. Although it is difficult to be sure, there is some evidence that households with PV systems have had meters running backwards under the pilot.


While exported electricity would be rewarded under the FIT mechanism, unfortunately the households participating in this scheme will not by default benefit from any exported electricity; not unless a one-to-one export rate agreement has been made with a utility company. Since grant-funded PV systems are essentially a rarity now, this is a quirk of the Penwithick pilot project. As such, it is apparent that householders’ perception of the benefit they may have received from their PV system is influenced by




how proactive they have been in using energy while it is generated and/ or how much electricity they naturally use during the day.

Of the 22 PV systems installed under the pilot, 14 said they would recommend the system to others, while 2 were not sure. Interestingly, only 9 of those that would recommend PV would consider investing in it themselves if they had not received it for free under the retrofit pilot project, with many others stating that they simply couldn’t afford it and would not want the liability of taking on a loan. Meanwhile, other householders in the village have evidently invested in PV systems themselves, as there are many more PV systems in Penwithick than were installed under the pilot project. Some householders mentioned anecdotally during survey visits that PV was something they were actively considering.

5 households reported that they did not feel they had benefited particularly from receiving a PV system, despite data demonstrating for all systems that not insignificant amounts of electricity had been generated during the pilot programme. It is worth noting that many households reported that their utility company had increased their energy bills during the period of the pilot, which could be masking financial savings that would otherwise be made. Other households stated that their bills were definitely reduced as a result of the PV system.

In particular, it was found that there are some ‘special’ tariffs in operation that fix energy rates (for a period of a year) and in these cases households would certainly not see any short term benefit from offset electricity usage. These situations were uncommon, but nonetheless would need to be a consideration. Such tariffs are generally reviewed annually and updated based on the preceding year’s usage, at which time any offset energy usage should be taken into account when calculating the new fixed rate.

It was apparent that the baseline level of understanding varied significantly amongst households as to what the PV system would offer, how it would work and how to get the best from the system. In particular, it was noted that some householders assumed that utility companies would automatically pay for any electricity fed back to the grid, hence did not worry about trying to optimise their offset usage. Others assumed that the systems would store electricity for use at a later time. These examples and others could obviously all contribute to unrealistic expectations of the system and hence disappointment with the overall performance.

It may be assumed that if an owner was actively considering paying for such measures themselves (rather than them being offered for free under a research project) they would carry out further due diligence before deciding whether it would benefit them. Consequently, it may be expected that they would seek to optimise their use of the system more and hence would be likely to have a higher level of satisfaction with the outcome.

9.4 Potential impact on fuel poverty

While the incentive of ‘free’ electricity from PV may seem like an inevitable benefit to help protect against fuel poverty, there are many considerations that will influence whether PV would truly help households. Heating and hot water demand is generally the main contributor to household energy bills and PV is not generally seen to helpfully contribute towards heating, since ultimately peak generation periods will be at odds with when homes will need to be heated (i.e. peak generation in summer during the day, peak heating demand in winter, particularly outside daylight hours).

Winter energy bills may still remain high, which could be problematic for households that cannot spread their annual billing out evenly across 12 months. PV can help deliver an overall reduction in energy bills over a year. However, this will still be dependent on whether occupants optimise the use of the ‘free’ electricity while it is being generated (assuming any FIT would go towards repayment of any capital or a Green Deal or other loan). The pilot study has indicated that many households, encompassing a full




range of occupancy patterns (including families, employed couples and retired individuals and couples) do not feel they particularly benefited from having a PV system.

However, for those that are likely to be able to take benefit from using free electricity while it is being generated, PV will offset inevitable increasing energy prices into the future. Though to truly make an impact on fuel poverty risk, it is likely that additional complementary technology would need to be employed, such as energy storage (e.g. batteries) or diverters that may otherwise optimise energy use and storage via heating systems. This will inevitably carry additional capital cost that would need to be taken into consideration.

9.5 Summary conclusions for PV

PV has the advantage of being flexible regarding the construction type to which it is applied, limited instead by orientation and the availability of space. The study found that electricity generation from the installed systems was higher than forecast by SAP (by approximately 16%) and more in line with forecasts made by PVSol proprietary software (±6%), offsetting around 27 tonnes of CO2 per year. PV may therefore initially be considered more beneficial than anticipated. However, it is also seen that households have not necessarily been able to make the most of these savings for the following reasons:

• Household energy use patterns do not coincide with peak generation periods, resulting in the majority of the electricity being exported to the grid with no remuneration

• Electricity prices have increased over the period of the study, masking savings to an extent

• In rare cases, fixed energy tariffs were in place that would have negated potential benefit from offset electricity (at least until the tariff was reviewed, usually annually)

A few occurrences highlight the importance of initial survey accuracy to ensure the optimised specification of inverters; the choice of inverter can make a significant impact on the overall energy obtained from PV panels.

While most households would recommend PV systems to others, it is interesting to note that less than half would have considered investing in such a system themselves if they were not part of the retrofit project. Since energy production via PV is generally out of sync with household heating demands, it is not likely to substantially reduce the risk of fuel poverty without the incorporation of storage technologies.

Awareness of how PV systems work and how to get the most out of them was varied across households in the study, though those considering purchasing PV themselves may be more informed and subsequently may more consciously optimise their energy utilisation to offset grid electricity use.




10. Heat Recovery ventilation units in detail


Inadequate ventilation is a common problem in dwellings that can lead to moisture build up and the risk of condensation and mould growth. In addition, properties may suffer from rising or penetrating damp. Building regulations8 recommend that ventilation/ extraction is provided in wet rooms to mitigate moisture build up.

Many occupants do not like the idea of using extractor fans as they remove heat from the dwelling while also removing moisture. To try to combat this on the project, single room Heat Recovery ventilation units (referred to here as HR fans) were specified for kitchens and bathrooms as necessary. The intention was that the fans could run constantly in a low energy trickle mode alternating with a higher rate ‘boost’ mode, as controlled by a humidistat (humidity sensor) depending on the relative humidity in the wet rooms. However the fan includes heat recovery at a rate of approximately 75-80% to minimise the loss of heat energy from the room.

Fans were installed in properties that reported damp/ condensation problems and/or those that did not have adequate ventilation at least in the kitchen and bathroom. Particularly in properties receiving EWI where air infiltration could potentially (and hopefully) be reduced through the measure, the project tried to ensure that such fans were installed to reduce risk of condensation build up. However, in some properties it was not feasible to install fans, even though it may have been desirable, due to lack of appropriate wall space available or the wall thicknesses being too wide for the specified fan housing to span them.

Under the project, 42 properties received HR fans either in the kitchen or the bathroom or in both. The sample covered all construction types considered in the pilot; traditional solid wall, cavity wall, Cornish Type II (refurbished with cavity walls and unrefurbished) and timber hybrid construction. Most of these households received the fans in addition to other retrofit works, including insulation measures, ASHPs, new oil boilers or PV systems. In kitchens the fan model used was the Vent Axia Lo Carbon HR25H with humidistat control. In bathrooms, the fan model used was the Vent Axia Tempra HTP that could either be operated by a timer linked to the light switch or by humidistat control.

10.2 Results

36 of the 42 households stated that they were utilising their fans during the interim survey in May 2013. 4 households did not answer the question, but for 2 of these data available from sensors indicates that the relative humidity (RH) in the house was generally within ‘comfortable’ limits below 65% over the measurement period. 2 households reported that they did not use their fans. Although not a question that was specifically asked, no households commented that the use of the fans made the room in which they were operating colder, which is often a concern with extraction-type fans.

Of the households that received HR fans, 27 had been selected to receive monitoring equipment that included temperature and RH sensors. General patterns could be seen across the range of monitored properties that indicate that towards the end of the summeri the relative humidity increased compared to the winter/ spring period from January to the end of May. Following this summer increase, the relative humidity levels in autumn were somewhat higher (between 5-15%) than the earlier winter and spring period. The temperature and RH profile for an example dwelling is given in Figure 12. Comparison with i Since this was outside the heating season the opening of windows for additional ventilation would be reasonable




data from the weather station that was located in the village for the duration of the project confirms that the average outdoor RH was higher for the period October to December (96%) than for the period January to May (90%). While this difference was not of the same magnitude as that seen in the dwellings, it does indicate the latter part of the year was wetter than the beginning.

Figure 12: Temperature and relative humidity profile for a solid wall dwelling with EWI

It was generally witnessed that the RH was starting to return to similar levels to those at the start of the year by the end of the monitoring period in December. It is proposed that this is a result of householders beginning to switch their heating systems back on towards the end of September/ early October, which then helped to gradually dry the house out and reduce the RH in the property.

It is generally accepted that ‘comfortable’ levels for indoor humidity lie between approximately 40-70% RH9. As seen in Figure 13, from January to May (covering the majority of the heating season) the living rooms of most properties (24) were broadly within this region (discounting some isolated spikes in RH). 3 properties regularly experienced RH around or in excess of 80%. These were of solid stone or Cornish Type II construction (though one of the Cornish properties had previously had the ground floor concrete panelised walls replaced with cavity wall) and all had reported significant condensation and/ or damp problems prior to the works.

Since more energy is required to heat moisture-laden air to a set temperature than ‘dry’ air, properties with high RH levels are likely to have an increased heating demand. Certainly it was reported in section 4 that energy usage had been higher than initially forecast in solid wall dwellings with EWI, assumed to be a result of reduced U values due to moisture in the walls and also due to the heating of moisture laden air in some instances.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec




Figure 13: Approximate living room RH of dwellings with HR fans

10.2.1 Comparison with previous state of damp Of those that said they used their fans regularly (36), 28 households said they suffered from damp problems previously and, of those, 20 stated when surveyed in May after the first winter that they had witnessed an improvement in the damp and condensation since the fans were installed (8 felt it had remained the same or they could not really notice an obvious improvement). By the December survey, 18 still felt that it was better but two mentioned that they were now experiencing damp in a single concentrated area. One of these households recognised that this was occurring in an unheated hall space and was looking into installing an additional small radiator in this location to overcome the problem. The other noted early signs of mould in the corner of their kitchen, but it was also observed that their HR fan did not appear to be moving into the ‘boost’ mode as it should. It is hoped that fixing the fan’s operating mode will help remedy this issue in due course.

It is noteworthy that one household that stated they did not use the HR fans due to concerns over additional expense reported that the damp situation in their home had become worse since the measures (EWI) had also been installed. RH readings suggest the property regularly experienced RH values of around 80% over the winter months in the main living space, rising to 90% at times in circulation spaces (where temperatures were generally a few degrees lower). This supports the proposition that adequate ventilation provision should be ensured when properties are receiving solid wall insulation in case natural leakage paths that may previously have been offering uncontrolled ventilation are closed off.

10.3 Discussion

It is apparent that some households feel they have benefitted more from the HR ventilation units than others. There are several factors that may influence their use:

• Some are reportedly not working, or potentially not working correctly, which is disappointing

• It is a relatively unfamiliar system and households (and installers) are not familiar with their operation. Many households simply switch them on and off manually rather than leaving them on constantly in trickle mode, which is how they will offer most benefit by constantly circulating air

• Fans may not have been set up appropriately for the rooms with regard to the sensitivity to the room’s RH, hence spending too long in boost mode or not moving into boost mode as necessary




• Some households are not comfortable with the fans running constantly either due to the noise they produce (although very quiet in trickle mode) or due to the thought they were costing money to run. However, households have subsequently been informed of typical running costs in the hope it would encourage their use (plus less energy would be used to heat ‘dryer’ air rather than moist air)

Overall the surveys suggest that the majority of households that received fans as part of their retrofit measures are using them regularly and monitoring data suggests the majority of properties measured remain within comfortable RH levels over the course of the heating season when it may not be desirable to open windows for additional ventilation.

Since nearly all dwellings receiving fans (and certainly all those with monitoring equipment installed) also received other retrofit measures, it is not possible to determine whether the use of the fans and in particular the heat recovery aspect of the fans helped homeowners save energy. It is suspected that the ‘heat recovery’ feature of the fans will have encouraged their use more than if regular extraction-type fans had been recommended. However, it cannot be ruled out that simple extraction fans with humidistat control may have provided a similar net benefit in helping to reduce the risk of condensation and damp problems.

10.4 Summary conclusions for heat recovery fans

Survey feedback, supported by the monitoring of relative humidity data in a selection of dwellings, indicates that the provision of improved ventilation generally helps to reduce potential problems of damp and condensation in dwellings. Ventilation is an aspect that should certainly be examined when considering any retrofit measures that could potentially reduce the uncontrolled air leakage from an existing building (e.g. EWI). Installation of ventilation fans in wet rooms would be a minimum recommendation, along with the provision of guidance to householders to advise of the risks of condensation and mould growth if such ventilation is not provided/ used.

The specification of heat recovery ventilation will likely have encouraged use of fan units in some situations where households will have been concerned about losing valuable heat through the use of regular extraction-type fans. Although benefits of such kind have not been quantified through this study as a direct comparison of different fans was not made, since the purpose of the Green Deal initiative is to improve comfort in homes and make dwellings easier to heat, the heat recovery aspect can only help in this regard. However, the relatively high cost of heat recovery units compared to typical units will likely drive users to favour traditional extraction-type fans, at least in the short term.




References

1 Weeks. C, ‘Penwithick Green Deal Pilot project: Selection of properties for refurbishment measures’,

BRE Report number 273 223.1, May 2012

2 Weeks. C, ‘Penwithick Green Deal Pilot project: Comparison of various energy modelling tools’, BRE Report number 283 724, Nov 2012

3 Hartless. R, ‘Penwithick Green Deal Pilot project: Green Deal and cost benefit analysis’, BRE Report number 284 814, Jan 2013

4 BRE News, ‘BRE begins major new research project into Britain's homes’, press release issued 04/04/13 on BRE website: http://www.bre.co.uk/news/BRE-begins-major-new-research-project-into-Britains-homes-867.html

5 Baker. P, Historic Scotland Technical Paper 10, ‘U-values and traditional buildings: In situ measurements and their comparisons to calculated values’, Historic Scotland Conservation Group, Jan 2011

6 Eaton. C, ‘Appendix G: Existing conditions detail monitoring’, Technical paper Appendices, Trinity College New Court Listed Building Consent application for refurbishment works, June 2012 (Study carried out by Natural Building Technologies Ltd, Oakley, as part of the consultancy team developing the Listed Building Consent application)

7 Rhee-Duverne. S, Baker. P, ‘Research into the thermal performance of traditional brick walls’, English Heritage, 2013

8 Building Regulations Approved Document F – Ventilation, Dec 2010 with Apr 2013 amendments. Available via the Planning Portal online Building Regulations resource at: http://www.planningportal.gov.uk/buildingregulations/approveddocuments/partf/approved

9 HSE, ‘Thermal comfort – the six basic factors’, Available via the Health & Safety Executive website at: http://www.hse.gov.uk/temperature/thermal/factors.htm#humidity

http://www.bre.co.uk/news/BRE-begins-major-new-research-project-into

http://www.planningportal.gov.uk/buildingregulations/approveddocuments/partf/approved

http://www.hse.gov.uk/temperature/thermal/factors.htm#humidity

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