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Very Low Energy Houses

November 2006

by Pascal Lenormand and Dr Anne Rialhe, AERE

email [email protected]

Abstract

With the ever-increasing attention on environmental protection and energy prices, theonce exclusive low energy dwellings are now getting more and more popular in Europe.

There are presently more than 6 000 such dwellings in Germany, Switzerland, and Austria

alone. Nevertheless, the term low energy houses covers a large variety of concepts and

technologies which need to be placed into their proper context. This is the subject of this

article.

Since the Rio Conference and the Kyoto Protocol, many have become aware of the problem

of global warming. Energy is the cause of 85% of all greenhouse effect gas emissions.

Efforts have been made, but two sectors keep increasing: transportation and buildings.

The current energy situation further strengthens the case for low energy construction.This article demonstrates that, although technologies and design play an important role,

individual behaviour has a great impact on two levels. The first is on the selection of

technologies, which is always the result of a human choice. The second is on the manner in

which the technologies are used day-to-day, in real life. It is therefore extremely important

to focus on the training of inhabitants in low energy houses.

Retrofit remains a critical point, since Europe has a very large number of older dwellings,

which are not at all efficient. NegaWatt mentions that, for France only, reducing energy

consumption in every pre-1975 building to 50 kWh/m2.y would require the retrofitting

of 450 000 buildings per year for 45 years.

One point remains unclear: the local capacity to build such low energy dwellings, as well

as the cultural acceptance by the building industry. We demonstrate that construction

materials and processes need massive improvement. How ready are construction compa-

nies to accept these changes in their work today? How can local regulations be adapted

to encourage best practice regarding energy, as has been done with electrical appliances

in the past?
mailto:[email protected]


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www.leonardo-energy.org Green Building

Contents

1 Introduction - The path towards very low energy houses 3

2 Variety of housing regarding energy 4

2.1 Types of Houses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Residential energy consumption in the European Union . . . . . . . . . . . 5

2.3 Various national labels for low energy houses . . . . . . . . . . . . . . . . . 6

2.3.1 PassivHaus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.3.2 Minergie R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3.3 LEED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.3.4 Comparison between PassivHaus, Minergie R and LEED . . . . . . 10

3 Residential Energy Use 123.1 Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1.1 Passive systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1.2 Active systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.1.3 Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.2 Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.2.1 Passive Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.2.2 Active Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

3.2.3 Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.3 Electrical Appliances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.3.1 Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.3.2 Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.4 Hot Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.4.1 Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.4.2 Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.5 Cooking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.5.1 Improved traditional cooking equipment . . . . . . . . . . . . . . . 29

3.5.2 Alternative energy cooking . . . . . . . . . . . . . . . . . . . . . . . 30

3.5.3 Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4 Benefits of Low Energy Construction 31

4.1 Financial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.2 Social . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.3 Political . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

5 Conclusion 32

November 2006 Page 2 of 33
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1 Introduction - The path towards very low energy

houses

With the ever-increasing attention on environmental protection and energy prices, the

once exclusive low energy dwellings are now getting more and more popular in Europe.

There are presently more than 6 000 such dwellings in Germany, Switzerland, and Austria

alone. Nevertheless, the term low energy houses covers a large variety of concepts and

technologies which need to be placed into their proper context. This is the subject of this

article.

Definition: what is a low energy house?

Although the basic concepts are widely known, research and development in different

countries have led to various interpretations of the low energy house concept.

Wolfgang Weiss, inventor of the PassivHaus concept, established his benchmark for low

energy houses using a comparison to the average energy consumption for heat. In Euro-

pean dwellings, this is around 200-250 kWh/m2/y.

0

50

100

150

200

250

existing "low energy"individualhouses

"low energy"collectivedwellings

Passive

houses

kWh/m2/y

Figure 1: Definition of low energy houses by comparing heating

Going much further than low energy houses in improving energy performance, passive

houses are defined as having a mean heat demand lower than 15 kWh/m2/y. This is less

than 10% of the average standard dwelling.

It is also necessary to mention the evolution of passive houses towards the so-called zero-

energy houses, or even positive energy houses. These are houses employing one or several

renewable energy production units added to a building so that the total energy balance



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(total annual production versus total annual consumption) is zero or positive1. This, of

course, only makes sense for a building that is already strongly optimized, if not passive.

In this paper, we will first have a look at the differences between buildings. This will

clearly establish the need for adapted solutions. There are a large number of possibilities,

but some, defined through the labelling process, have gained more recognition and offer

concrete guidelines for a project.

Having once established the overall framework, it will then be possible to discuss the var-

ious technologies that are available for each energy use in such very low energy buildings,

without losing sight of the important role played by individual behaviour.

In our conclusion, we will broaden our view by examining the various impacts (financial,social, and political) of a massive reduction of energy consumption in dwellings.

2 Variety of housing regarding energy

2.1 Types of Houses

The population of the European Union (EU-25) has been continuously increasing since

1945 to its present level of approximately 450 million people.

This population lives in 170 million dwellings for an average density of approximately 170

hab/km2. This is representative of a strongly urbanized structure. As a comparison, the

population density in the USA is 30.2 hab/km2.

There are different methods for classifying dwellings and they can be further divided into

individual and collective dwellings. This distinction, as we will see later, has an influence

on the construction techniques and energy systems that are available.

Another interesting way of classifying is by the age of the dwelling. The rationale for

this is that implementation of high performance technologies is relatively easy in newconstruction (based on financial and cultural considerations). This is clearly not the case

when retrofitting older dwellings.

1Usually, the embodied energy of the building materials, technical installations and renewable gener-

ation units is not included in the energy balance



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2.2 Residential energy consumption in the European Union

For direct information regarding residential energy consumption in the EU, we use data

from the Human Settlements Bulletin published by the United Nations Economic Com-mission for Europe.

As already mentioned, the dwelling stock in the EU today is around 170 million dwellings.

Figure 2 shows the spread in age of these structures (data extrapolated from 15 countries

to EU-25):

Date of construction for dwellings in Europe

0%

5%

10%

15%20%

25%

30%

Before1919

1919-1945

1946-1970

1971-1980

1981-1990

1991-2000

Construction Date

Percentage

oftotal

Figure 2: Age of dwellings in Europe

As we can see, around 50% of the dwellings were constructed before 1970, in times whenenergy was cheap and abundant and climate change was not a concern. This usually led

to high energy consumption. Moreover, around 27% of the dwellings were constructed

after World War II, with fast, but usually non-durable, energy consuming techniques.

We should also note that between 1993 and 2003, 12% of so-called new dwellings were in

fact retrofit dwellings, indicating the weakness of this activity, and partially explaining

the very large percentage of older dwellings in Europe.

These three factors taken together lead to the average 200 to 250 kWh/m2/y energy

consumption observed today in Europe (sources: www.passiv.de and La constructionecologique, ed. Terre Vivante).

Another important aspect to be considered is the evolution of stock. Figure 3 represent

the evolution of building stock, with regard to the number of dwellings and average floor

space.

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Total number of dwellings in Europe

159 000

162 000

165 000

168 000

171 000

174 000

177 000

180 000

1993 1997 2001 2002

Average living floor space(m2)

78

81

84

87

90

93

96

1993 1997 2001 2002Year

Surfaceinm

2

Figure 3: Evolution of dwelling stock since 1993

This clearly shows a significant increase for both parameters. This situation, if not com-

pensated for by tremendous improvement in construction techniques, will surely lead to

a constant increase in energy consumption, with all the associated drawbacks.

2.3 Various national labels for low energy houses

The necessity of improving the entire building process is readily apparent. Several coun-

tries have developed labels or design processes in order to standardize, control, and pro-

mote best practices concerning low energy demand dwellings. We will take a closer lookat three of these schemes: the German PassivHaus label, the Swiss Minergie R label, and

the American LEED label.

Official and detailed information about these three labels can be found on the following

Web sites:

PassivHaus: www.passiv.de

Minergie R: www.minergie.ch

LEED: www.usgbc.org/leed

2.3.1 PassivHaus

The PassivHaus Institute in Darmstadt, Germany is strongly focused on the energy aspect.

It provides the Passive House label for structures meeting its standards. The technical

definition of this label is very clear and straightforward for climate conditions between 40

and 60 degrees latitude in the Northern Hemisphere.

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More precisely, a house can be certified as a PassivHaus (Passive House) when the follow-

ing three criteria are met:

1. A comfortable inner climate can be maintained without the use of a central heatingor cooling system. The annual heat demand for such a dwelling must therefore be

set at a value lower than 15 kWh/m2/y in the project plan.

2. The comfort criteria must be respected in every room of the house, both in winter

and in summer. With this goal in mind, the label requires very precise levels of

insulation for every construction element:

Every external surface with U-values lower than 0.15 W/(m2K)

Every window with U-values lower than 0.8 W/(m2K), as well as strong re-

strictions on the relative window surfaceThere are also strong restrictions on orientation, surfaces, and opening and clo-

sure possibilities for each translucent element, depending on the orientation and

construction of the dwelling. Ventilation rates are strictly controlled.

3. The total use of primary energy for all uses combined (heating, hot water, and

specific electricity) may not exceed 120 kWh/m2/y. The calculation is included in

the project plan.

Every building is checked at the completion of construction, with particular attention to

the integrity of the hermetic sealing. The PassivHaus Institute also proposes a labellingservice for stand-alone elements (doors, windows, wall elements, etc.). This process guar-

antees that projects really meet all requirements when finished.

Since the 1980s, when the concept was created, more than 5 000 projects have been

realized in Germany, 1 000 in Austria, and, more recently, around 100 in the Benelux.

2.3.2 Minergie R

The Minergie R label, which is presently only available in Switzerland and Liechtenstein,

is quite similar in principle to the PassivHaus concept. It stipulates very precise energyusage levels, particularly in its Minergie-P R version. The Minergie version is applicable

to any kind of building (collective dwellings, hospitals, industrial buildings, etc.).

There are two different paths to obtaining a Minergie R certification. The first one is

to use the standard solutions. These are only applicable to individual houses. These

solutions cover three points:



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1) Very precise insulation values for every construction element

Construction element Value if in contact with

external environment, orburied less than 2 m

Value if in contact with non-

heated rooms, or buried morethan 2 m

Roof, ceiling

0.20 W/m2K

0.25 W/m2K

Wall 0.28 W/m2K

Floor 0.28 W/m2K

Floor with heating system 0.25 W/m2K

Windows 1.30 W/m2K 1.60 W/m2K

Doors 1.60 W/m2K 2.00 W/m2K

Table 1: Insulation requirements for Minergie R standard solutions

2) A choice among five technical solutions for heat production and distribution

Standard

solution

1 2 3 4 5

System Geothermal

heat pump

Wood boiler

+ solar water

heater

Automatic

wood system

Waste heat

(industry,

incinerator,

etc.)

Air-Water

heat pump

Table 2: Available technical solutions for heat and hot water in Minergie R standard

solutions

With all of these systems, the use of a double-flow heat exchanger with a minimum

efficiency of 80% is mandatory.

3) The additional cost for using Minergie R standard solutions may not exceed

10% of the cost of conventional solutions (15% in Minergie-P R).

The second way to obtain a Minergie R certification, which is in fact the only solution for

collective dwellings, is to utilize a control process on the buildings performances. These

are very detailed, but we should focus on some aspects of these requirements:

They are different for private houses and public dwellings

They are different for new buildings and renovation projects

They are adjusted to specific climatic conditions (mainly altitude)



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Building

type

Collective

dwellings

Individual

housings

Commercial

dwellings

Hospitals Industries Sport

installa-

tions

Maximalvalue (all

uses) in

kWh/m2/y

42 42 40 75 20 25

Table 3: Some requirements in the Minergie R scheme

The Web site www.minergie.ch reports more that there are approximately 5 700 structures

with the regular Minergie R label. Since the later Minergie-P R label does not as yet enjoy

the same name recognition, the institute has also recently launched a new premium label.

It is known as Minergie-Eco R and concerns the use of environmentally friendly materials

and processes.

2.3.3 LEED

LEED is the acronym for Leadership in Energy and Environmental Design. Its Green

Building Rating System R is a voluntary, consensus-based national standard for develop-

ing high-performance, sustainable buildings. The US Green Building Council developed

this framework, and seven labels were created; each label corresponding to a certain type

of construction project (LEED-H for houses, LEED-EB for existing buildings, etc.).

The certification process is based on a full list of criteria, which goes far beyond the use

of energy in the houses. Aspects such as transportation, visual impact on the neighbour-

hood, use of local materials, etc. are also taken into account. LEED uses the Energy

Star label requirements as the basis for the consumption of energy in houses. These claim

a 15% reduction compared to 2006 IECC (International Energy Conservation Code) reg-

ulations. These very detailed regulations are finely attuned to the local climate and

impose construction elements and techniques accordingly. Full information can be found

on www.energycodes.gov.

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Figure 4: Climate zones, as defined in IECC 2006

Some basic levels are mandatory for certification. Improved performance confers a bonus.

The final notation consists of four performance levels (certified, silver, gold, and platinum).

Although most projects have been implemented in North America, some are also located

in Europe.

LEED is a good example of a vision that is broader than just low energy building; taking

into account not only the energy uses inside the building, but also the entire cycle of

construction, activity, useful life, and demolition.

2.3.4 Comparison between PassivHaus, Minergie R and LEED

Since requirements for energy consumption, when they exist, vary according to climatic

conditions and specific project parameters, the simplest way to compare the labels is to

compare their technical requirements, particularly the required insulation values.

In the figure below, we compare some requirements, the EnergyStar being estimated for

Zone 5, based on the IECC requirements.



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Requirements on insulation (U-Factor) for three differentlabels

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,61,8

PassivHaus Minergie EnergyStar

Umax(W/m2.K

)

FenestrationCeilingWall

Figure 5: Comparison of requirements on insulation values

The great influence of fenestration (the arrangement and number of windows), widely

known in thermal construction analysis, is very clear here. The three labels have differ-

ent requirements, PassivHaus being the most demanding, thus allowing a relatively easy

comparison on heating energy.

Nevertheless, the work is more difficult regarding other aspects, since the scope of the

three labels differs.

Heating-

Water

Heating

Other

Uses

Natural-

Local

Materials

Transport Internal

Air

Quality

Water

Mgt

Training

Passiv

Haus

Yes No No No No No No

Minergie R Yes Minergie-

PR

Minergie-

EcoR

No No No No

LEED Yes Yes Yes Yes Yes Yes Yes

Table 4: Comparison of application field for three labels

Most of the aspects in table 4 have an energy dimension. Transportation is a good

example: a growing number of people are realizing that it is useless to build a low energy

house if one has to increase car use as a result.

Finally, it should also be noted that labels are only available through a monitoring orga-

nization, which may or may not be available locally. Minergie R, as one example, is only



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available in Switzerland and Liechtenstein. Nevertheless, the criteria and evaluations can

play a valuable role as inspirations and guidelines for any project.

3 Residential Energy Use

Labels define targets to be achieved in construction (new construction or renovation), and

sometimes give recommendations about technologies to be employed. Numerous energy-

efficient technologies can be used to improve the overall performance of any building,

based on its geographical environment and the pattern of use according to the cultural

habits of the users (especially how they dress in winter and summer).

Since technologies are nothing more than the tools used to convert an energy carrier intoa service, in this section we will provide a list of energy-efficient technologies classified by

end-use.

We will also introduce a sub-classification for these systems, referring to the kind of energy

input on which they are based:

Passive systems: intended to make optimum use of natural energy, without ex-

ternal energy input (whether electricity or any type of carbon energy)

Active systems: using external energy (whether electricity or any type of carbon

energy) Behaviour: although not traditionally considered to be technology, behavioural

actions (that is, modifying the interaction between inhabitants and the dwelling)

are a key element in low energy dwellings

For each of these systems, we will provide elements on the requirements of various labels

and a description of the implementation possibilities.

3.1 Heating

3.1.1 Passive systems

General considerations The best way to reduce energy consumption is to take ad-

vantage of all available natural energy. This is the purpose of bioclimatic design, which

is one path to a low energy house. The bioclimatic approach operates at two levels:

1. let the energy of the sun come in

2. do not let it out again



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The best passive devices to let the energy of the sun come in are windows. In low energy

houses, south facing windows act as energy absorbers. The entire building can be designed

so that this energy can be distributed from the south fa cade.

Figure 6: BedZed, with sun absorbing south facing walls

Implementing large, south-facing spaces is usually quite easy in the design process of a

new building. It can be more problematic in retrofit programs, in particular because of the

global orientation of the building. In such cases, a simple widening of existing windows

can still be a great help.

Some elements such as reflective blinds can also help let more solar energy into the house.When properly oriented, they can increase the energy input by 25% or more.

The second step in the bioclimatic process of maintaining satisfactory heat levels without

energy expenditure is to reduce energy losses. The list of possible measures is quite long,

but the most common are:

Reduce exchange surfaces: design compact buildings, the goal being to reduce the

volume to surface ratio (fig 7). The aforementioned labels do not mention compact-

ness in their criteria, although LEED does it indirectly in the two sections:

Land Use section: Optional Measures

5.1 Build homes with an average housing density of seven or more dwelling

units per acre of buildable land. (1 Point) OR

5.2 Build homes with an average housing density of ten or more dwelling

units per acre of buildable land. (2 Points) OR

5.3 Build homes with an average housing density of twenty or more dwelling

units per acre of buildable land. (3 Points)

Materials and Resources section



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Reduce heat losses through surfaces: use thick and efficient insulation on all surfaces

(walls, roofs, and floors); use efficient, double or triple glass windows. The labels

described above place the highest requirements on this aspect. Since materials are

normalized, and sold with a given insulation and performance value, this pointshould be easily achievable.

Avoid heat losses between surfaces: this aspect, which should be integrated by

selecting the right materials, is often ignored. In a well-insulated dwellings, the share

of ventilation losses in the buildings heating requirement becomes more important.

In passive houses, hermetic sealing of the building is as important as insulation.

Hence, the special requirement in labels like Minergie R and PassivHaus to use a

blowing door test, which is mandatory before the dwelling is certified

Figure 7: Same volume, variable surface



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Figure 8: Points for home size compared to average in the LEED notation system

Figure 9: Blowing door (www.fh-ooe.at)

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Influence of energy content One question that can be asked is whether the energy

content of the insulation is reimbursed during the lifetime of the material, i.e. whether

reinforcing insulation improves environmental performance. Figure 10 show a calculation

for glass fibre of density 12 kg/m3, =0.041 W/C.m and energy content 7.34 kWh/kg(source: ekoinventare for Equer, www.izuba.com, calculation AERE). The first graph

shows a comparison between the total energy content of the insulation and the total

energy consumption over the lifetime of the material. As long as the straight line is under

the curve, the energy invested in more insulation is paid back over the materials lifetime,

and is thus worth doing.

As seen here, for the conditions specified (lifetime 10 years, 2400 h heating period with

T=20C), with an insulation thickness of up to 47 cm (which, in this case, means

R=11.4 m2.K/W, 60% more than required in the PassivHaus label), the glass fibre reim-

burses its energy content over the lifetime of the project.

Total energy content compared t o total loss over l i fetim e

0

100

200

300

400

0,01 5 10 15 20 25 30 35 40 45

I nsulat ion thickness (cm)

Totalenergy(kWh)

Total energy content

(kW h/m 2)

Total loss on lifetim e(kW h/m 2)

Figure 10: Comparison of energy content and energy savings

Figure 11 presents the same data from another perspective: for a given thickness of

insulation, how much an extra centimetre of insulation will save over the lifetime of

the material, and comparing this to the energy content of this extra centimetre. We

can then calculate, for a given thickness, the reimbursement or payback time for an

extra centimetre. When this time exceeds the materials lifetime, then the cost is not

worthwhile.

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Reimbursement time (in heating seasons)

0,0

2,0

4,0

6,0

8,0

10,0

12,0

0 5 10 15 20 25 30 35 40 45

Insulation thickness (in cm)

Reimbursmenttime(insea

sons)

Reimbursement time (inheating seasons)

Figure 11: Reimbursement (payback) time of an extra centimetre of insulation

Here again, we can observe that the insulation can be increased up to 47 cm and still

reduce lifetime energy consumption.

The cost is not justified except in some extreme cases (extremely short lifetime, very short

and/or temperate heating season, etc.). The influence of energy content is also clearly

visible, showing the benefit of insulation materials with low energy content, like most

natural materials (hemp, cellulose, wood wool etc.). These materials provide the bestbenefit in terms of overall energy efficiency

Inertia Less known is the use of inertia. The idea here is to use massive materials or

thermal mass that can store heat in their structure, and release it when the temperature

drops. The positioning and dimensioning of such architectural elements has to be done

very carefully, so that the building behaves in harmony with its environment and the

needs of its inhabitants. This parameter, very important for summer comfort, also plays

an important role in the way the building manages passive solar inputs.

The best example of an inertial system is the Trombe wall, in which a massive elementis placed behind a window. As long as the sun is shining, the wall stores heat, and will

continue to release it even at night. In fact, massive elements play a regulatory role in

the same way as a dam on a river.

In some particular situations, it might be beneficial to plan inter-season heat storage

to increase the inertia effect. The goal is to store excess summer heat in a huge or

massive element (sometimes underground using the ground itself, sometimes in the form

of enormous water tanks).



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3.1.2 Active systems

Ventilation systems Once the heating demand has been reduced to a minimum through

proper overall design, a complementary heating system might be necessary, especially inrenovation programs or collective dwellings, where individual adjustments might be more

difficult to achieve solely through passive solutions.

An active system is already included in the passive house concept to reduce the energy

demand to a minimum. As we have seen, low-demand houses are very nearly airtight,

ventilation being assured by a HVAC (Heating Ventilation and Air Conditioning) system,

which is in fact an air-air heat pump working on extracted air, leading to an efficiency

of 75 to 80%. This particular heat-pump system is in fact a keystone It is mandatory in

Minergie R and PassivHaus systems, and a constant in all normalized low energy build-

ings. For additional efficiency, such a system can be coupled with an Earth-Air HeatExchanger (EAHX, often called a Canadian well in Europe). The fact that heat loss

through air renewal represents one third of the losses in classical buildings, and up to 70%

in well-insulated constructions, justifies the attention given to such systems.

Nevertheless, it must be noted that such equipment, although quite easy to implement

in new constructions, are more difficult to add to retrofitting actions, leading to heavy

works (installation of bi-directional ventilation system). However, they are used today in

a variety of contemporary buildings, both individual and collective.

Heating systems In the case of passive houses, theory says that an additional heating

system should not be needed. The basic concept has this as its primary goal and is able

to maintain comfort solely with its occupants and parasitic heat. Nevertheless, it must

be noted that Scandinavian Homes, a producer of serial passive houses, adds a 900 W

electrical resistance to the HVAC system as security.

For more traditional low energy houses, the challenge is that the heating demand is greatly

reduced and is therefore too low for most devices available on the market. As an example,

a 100 m2 Minergie R house with a demand of 35 kWh/m2/y will need 3 500 kWh during

the heating season. This is a nominal power of around 3 kW for an average French climate,and up to 6 kW for colder climates whereas small pellet furnaces have a typical power of

7 kW, and standard heating systems are rarely under 15 kW.

For individual houses, in fact, the question remains. As a reference, let us examine the

five standard technical solutions that are proposed in the Minergie labelling process. The

electricity mentioned in wood systems represents less than 5% of the total energy involved.



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Technical Solu-

tion

Energy input Primary en-

ergy

Global coefficient of performance

Geothermal

heat pump

Electricity Carbon,

nuclear,renewable

82-230%

Very efficient, needs sufficient

energy demand for economic

payback

Wood + Solar

(hot water)

Biomass

(+electricity)

Biomass 70-90%

Taking the energy service heating

largely off grid, but highly

dependent on the lifecycle ofenergy source

Automatic

Wood system

Biomass (+

electricity)

Biomass 70 to 90%

Highly dependent on the lifecycle of

energy source

Waste

industrial

heat

Undefined Undefined 85 to 95% at the point of use

District heating unlikely to beeconomical for low energy houses,

as the cost of distribution and

connection becomes too high

Electric + Solar Electricity Carbon,

nuclear,

renewable

30 to 92%

100% for solar, based on an IEA

convention

Table 5: Comparison between heating solutions

Biomass systems can be a best practice, depending on the lifecycle and including transport

of the energy source. Waste heat systems (based on heat distribution networks) can be

advantageous but they demand a high density of heat use to be cost effective, and are less

likely to be economical in areas with a high density of low energy houses. Considering a

90% reduction in heat demand with low energy houses, a combination of generating resid-

ual heat with a solar-electric combination becomes attractive and could be instrumental

in allowing a higher penetration of ambient generation in electricity systems.



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The performances of heat pumps depend greatly on local geology. Some structures

(argillaceous, sand, etc.) are not suitable for the use of such systems. The congruency

between the site and the technical solution must be carefully studied, and can, in the case

of a heat pump, sometimes lead to a situation that is not cost efficient. This helps makethe case for more versatile wood-based systems.

The problem is easier to solve for collective dwellings, where all these small remaining

needs can be accumulated, and a heat network can be built. Occupancy rate and distance

between houses have to be carefully studied since these aspects are more easily optimized

in compact collective dwellings.

On the other hand, a more conventional heating system (but of reduced size) can be

designed for compact collective dwellings. Here energy carriers can be combined (such as

solar + wood) in a manner that is difficult to carry out in an individual house becausedemand is too small. Since boilers have a limited optimal operating range, collective

heating systems have to be designed carefully.

3.1.3 Behaviour

The way inhabitants use their dwelling can greatly influence the thermal balance, and

thus the energy consumption. These influences can be classified in two categories.

Pure behaviour Fanger (1970, Thermal comfort, Copenhagen) has defined the con-

ditions of comfort for a person, and has shown that comfort depends directly on only six

parameters: ambient temperature, radiant temperature, humidity, air velocity, clothing

insulation, and activity level. It is indeed intriguing to observe the similarities in research

on low energy houses and human thermal comfort.

This clearly shows the very important interaction between inhabitants and interior cli-

mate: maintaining the balance when one parameter changes can be achieved by changing

another parameter. As an example, a decrease of one degree in the ambient temperature

in a house (a 5 to 10% economy) can be compensated by:

The installation of a radiant heating device (+5 to 10% energy)

The modification of the radiant temperature of walls - for example, by choosing a

low emitting material such as wood (a very common practice in northern Europe)

Increasing clothing (no cost, except for the purchase of additional clothes)

Parasitic heat Today, many of our activities within a building entail the use of electrical

devices such as a refrigerator, cooking devices, lighting, computers, etc. These appliances

generate a certain amount of heat. The total amount of heat generated in a house today



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is far from negligible. Compare the typical values listed below to the average 1.5 kWh

per day necessary to heat a 10 m2 room in winter in a Minergie R house.

Example of equipment use Heat generated inone day

Equivalentheated surface

TV on sleep mode (15 W) for 20

hours

0.30 kWh 2 m2

TV on (75 W) for 4 hours 0.30 kWh 2 m2

20 minutes ironing 0.30 kWh 2 m2

30 minutes oven baking 1.5 kWh 10 m2

Fridge (compressor + heat release

on condenser)

3.0 kWh 20 m2

PC and cathode screen on for 24hours (ADSL use 250 W)

6.0 kWh 40 m2

PC and cathode screen on for 8

hours (office use - 250 W)

1.75 kWh 12 m2

PC and flat screen on for 8 hours

(office use 125 W)

1.0 kWh 7 m2

Laptop on for 8 hours (office use

30 W)

0.24 kWh 2 m2

Table 6: Examples of heat generation for typical home appliances - Source Fracheur sans

clim- ed. Terre Vivante and AERE

With these values in mind, it is clear that these parasitic heat gains cannot be ignored

in the energy input, and should be incorporated when calculating the heat demand. In

office buildings, parasitic heat gains are large because of the heat generated by computers.

They may even need to be air-conditioned because of these heat gains. In the Minergie-P

labelling process, the choice of efficient electrical appliances (A, A+, or A++ categories)

is an inherent part of the low energy design process.

3.2 Cooling

The fact that low energy buildings are designed to let a lot of solar energy in, and not let

it out again, can cause overheating on sunny days. Therefore, the occupants behaviour

in the building during the summer needs to be carefully studied and cooling measures

taken as necessary.



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3.2.1 Passive Systems

General considerations The bioclimatic approach, which has already helped us a

great deal regarding the use of energy for heating, can also help us in keeping the buildingcool with minimal energy expenditure. Again, this is a two-step process:

1. prevent the heat from coming in

2. let the heat trapped inside escape

In Europe, warmer periods usually correspond to times when the sun is high in the sky.

Therefore, the use of correctly dimensioned overhead protection on south facing windows

works very well in avoiding excessive heating.

It is also important to reduce the number or area of windows on west and east facing walls(hence the limitation in the Minergie R guidelines). Where windows remain exposed,

the use of external blinds, or strategically placed trees can offer effective shading in the

summer, while letting light in during wintertime

Thermal Inertia Inertia is a property that has already been mentioned regarding heat-

ing. However, it is also a very important property for summer comfort. In fact, this is

the primary factor that will determine how long a house will take to warm up. Sufficient

inertia is therefore a guarantee in maintaining a cool interior.

The first passive houses, while strongly focused on insulation, neglected the impact ofinsulation materials on summer overheating. This design flaw has now generally been

corrected, but remains an important consideration. Below is a table of thicknesses nec-

essary to correctly insulate a house in winter (dependent on insulation) and summer

(dependent on inertia).

Material Conductivity Thermal Capacity Winter Summer

(W/m.K) (Wh/m3. K) thickness (m) thickness (m)

Mineral wool 0.04 4 0.173 0.815

Polystyrene 0.04 8 0.173 0.593High density cellulose 0.045 42 0.195 0.271

Sheep wool 0.04 10 0.173 0.535

Wood fibre panel 0.04 80 0.173 0.185

Table 7: Comparison of winter and summer thicknesses for various materials - Source:

Dr. Ing. Reinhard Geisler, Isolfloc (in La conception bioclimatique, ed. Terre Vivante)

The influence of the thermal capacity of materials (this can be generalized to every mate-

rial in the building) is clear. Materials such as mineral wool and wood fibre panels, which



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have the same effect in winter (insulation), have very different behaviour in summer (in-

ertia), with 4.4 times more mineral wool than wood fibre being necessary to create the

same thermal comfort in summer.

The use of night ventilation, already mentioned in the Behaviour Section, has a direct

consequence on the design of the house: it must be possible to open windows in every

room, to allow for sufficient cooling. This is another requirement in the Minergie R

labelling process.

Surrounding environment The area surrounding a structure has an influence in two

significant aspects:

1. Albedo, which is the ability of a surface to reflect more or less energy from the sun

2. Temperature evolution, related to the presence of grass or plants, which retain or

release water and water vapour

Since the surfaces surrounding a structure interacts with the building and influences the

energy input, it should be carefully designed with respect to orientation and building

design to help regulate the energy input.

Ground quality Surface temperature in summertime Albedo (reflection)

Asphalt 35C 7%

White asphalt 25C 90%Bare ground 25C -

Mowed grass 23C 20%

Uncut grass 21C -

Table 8: Examples of ground surface properties - Source Fracheur sans clim , ed. Terre

Vivante

3.2.2 Active Systems

The first and simplest cooling system is the Earth-Air Heat Exchanger (Canadian well).

By letting the air travel under the ground before coming into the house, its temperature

will drop several degrees, refreshing the inner atmosphere. Typical temperature drops of

3 to 5C have been measured.

A variant of this system has been in use for centuries in North Africa and the Middle East

(the Iranian badgir are an example), where filled amphora are suspended in the air flow

and evaporation creates an additional cooling effect. The use of evaporation - in home

fountains, for example - can still be a modern and efficient cooling solution.



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A more classical, but also more energy consuming, cooling solution is the air-air heat

pump. This device uses electricity to circulate a heat transportation fluid and transport

heat from the interior to the exterior. It should be noted that such a device should not

be considered as a heating system, because of very poor energy efficiency, particularly atair temperatures below 7C (Source: Etude chauffage electrique et pompe chaleur en

France - Greenpeace France).

In spite of a currently reported performance coefficient of approximately 2, we must

remember that A/C appliances work with electricity. To make an accurate comparison

of the total energy efficiency of such systems, it requires us to backtrack to the primary

energy source.

Origin of electricity Combined

cycle gas-fired power

station

Gas-fired or

coal-firedpower

Nuclear

electricity

Renewable

electricity

Ratio of heating/cooling

energy to primary energy

for low energy houses

1.20 0.60 0.80 0.72 2.00

Table 9: Ratio of heating/cooling energy to primary energy of an air/air cooling system,

depending on electricity production source and applied to low energy houses

Another aspect to be studied, since Europe is committed to the Kyoto Protocol, is the

amount ofCO2 emitted by the energy source.

Coal Fuel Combined cycle gas Cogeneration Nuclear, hydro, wind power

915 676 404 230-380 0

Table 10: CO2 emissions for electricity production, in g CO2/kWh - Source: Elements de

calcul des emissions de gaz a effet de serre dans les installations energetiques, J.P. Tabet,

C.Cros, 2000

Finally, a significant portion of the electricity generated in some countries is produced by

nuclear reactors. This leads to a production of nuclear waste of 8.64 mg/kWh (radioactive

waste with a short half-life) and 0.85 mg/kWh (radioactive waste with a long half-life)

(source: EDF).

3.2.3 Behaviour

The same considerations cited regarding comfort and heating can also be applied to

cooling. For example, reducing the temperature from 27C to 25C using an A/C



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system leads to an energy consumption increase of 10 to 20%, whereas the same result in

terms of physiological comfort is achievable by reducing clothing (no cost) or increasing

air velocity (inexpensive fan using significantly less energy).

In Japan, the CoolBiZ campaign in summer 2005 proposed setting A/C at or above 28C

(instead of the usual 22C) and invited people to work without a jacket and tie. The

results for 2005 led to a modest economy of 70 GWh, in a society with a high cultural

reluctance to changing clothing habits. The campaign has been relaunched in 2006,

together with a WarmBiz campaign in winter, setting the heating limit at 20C.

It is also important, in the case of a warm summer period, that the occupant of the house

be able to cool the building during a cooler period (at night, for example) by opening doors

and windows, and to protect the building from excessive overheating by using shades and

blinds. Here again, we see the direct link between behaviour and energy use.

3.3 Electrical Appliances

3.3.1 Technologies

Most labels insist on the initial choice of class A (or A+ or A++) equipment, in reference

to the European energy labelling for refrigerators, freezers, washing machines, dishwash-

ers, driers, ovens, and hot water heaters.

With the average European price for electricity around 0.10 e/kWh, a freezer will cost

about 65 e/year, although models costing around 200 e are not an exception. The

importance of good quality and high efficiency clearly lead to potential economies of

up to 40% and more. The same type of calculation can be made for every electrical

appliance, and should take into account the fact that many appliances consume energy

when on standby mode. Values around 10 W are current for TV systems; since there is

currently no regulation for sleep consumption levels, the initial choice is all-important.

3.3.2 Behaviour

Whereas choices in the power supply can automatically reduce the energy consumption

of appliances when turned on, behaviour remains a very important parameter. There are

still many appliances on the market that use more energy in standby mode than in use,

simply because the user leaves the appliances in sleep mode 24/7.



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Category Miscellaneous

Standby Power

Consumption

(kWh/year)

% of total con-

sumption

Cooling Appliances 12 5

Cooking 34 13

Audio, Video, Communication 108 42

Lighting 57 22

Table 11: Examples of standby power consumption - Source: Miscellaneous Standby

Power Consumption of household appliances, EU-DG XVII Brussels, Belgium

The total energy expense in Europe for standby equipment has been estimated at 53TWh/y. This is the production of eight large power stations. Simply unplugging or

turning off the appliances (which can be facilitated by an adapted design) could save a

large portion of this energy.

Among all specific electric uses, cooling appliances (fridge, cooler, etc.) are an important

focus, since they represent 30 to 40% of the total electric use. Placing them in a cool

room can provide significant savings.

Washing and drying machines represent more than 20% of all home energy use. They

consume large amounts of energy, around 1,000 kWh. This amount might never be

amortized when the appliance is used only two or three times a week; hence the value in

sharing this kind of appliance in collective dwellings. This is a very common practice in

countries such as the USA and Switzerland.

3.4 Hot Water

3.4.1 Technologies

General considerations The three labelling processes that we studied in the firstsection of this paper have a different approach regarding water heating systems. While

PassivHaus only puts a limitation on the total amount of primary energy used in the

building (max. 120 kWh/m2.y), the Minergie R solutions require the technical system

to be selected from the following list: heat pump, wood boiler, or solar powered systems

along with waste heat from the industry.

LEED does not impose any mandatory measures, but proposes variable bonuses for ef-

ficient distribution (loop sizes, insulation, etc.) and production (solar, gas or electric)

installations.



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A standard low energy water heating solution is the solar water heater, because it uses a

cost-free energy, and can supply up to 70% of the requirement.

Despite its very low consumption, it remains important to design and integrate the systemcarefully (the circulation pumps, in particular) in order to reduce total energy consump-

tion to a minimum.

Solar heating systems always need a complementary energy source to ensure that the

service is maintained on cloudy days.

Electricity

Fuel/Gas burner

Wood can be a good solution, but low power (12 to 15 kW) wood systems that

would be adapted to low energy individual housings are rare. However they arevery well adapted to collective dwellings.

Alternative solutions A new approach to water heating systems has been proposed

and applied in recent years. The system, called warm water, is based on very small

electrical water heaters integrated very close to the usage point rather than a single large

source. There are multiple benefits to such a solution:

Immediate response, leading to hot water consumption reduced from 10 to 40

Greatly reduced thermal loss in distribution system, leading to a 10% reduction inenergy use

Smaller, more insulated, and more efficient water heater (power from 3 to 20 W),

leading to 10 to 20% economy compared to traditional electric boilers.

Since these advantages are cumulative, a possible 50% economy on energy and water is

claimed. The distributor states that the savings on water and energy is so significant that

it makes installing a solar heater unnecessary. The entire energy for hot water can be

produced by a small area (from 2 to 5 m2) of photovoltaic panels instead.

Another solution that has been used in collective dwellings and the food industry is thereuse of drain heat. One of the distributors claims an economy of 34% on the energy bill,

and return on investment within 2 to 4 years.



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Figure 12: Principle of the warm water system - (Source: ets-concept.monsite.wanadoo.fr)

and principle of the GFXstar drain heat reuse system - (Source: www.gfxstar.com)

3.4.2 Behaviour

Two parameters define the amount of energy that is used in heating water: The temperature to which the water is heated: the heat capacity of water is 4.18

kJ/kg.K therefore heating 1 litre of water 1 C higher requires 1.16 Wh

The amount of water that is heated

The first parameter is easy to modify by correctly setting the temperature of the wa-

ter heating system. It is still very common to find hot water systems that are set to

80C, a level that results in useless energy expenditure. This also accelerates calcifica-

tion, leading to additional energy losses, and additional maintenance costs for de-scaling.

However, a temperature below 55C increases the risk of legionella. Setting the systemat approximately 60C is an optimal choice for residential systems.

The second parameter is also directly linked to behaviour, the question always being:

How much water do I need for a given service? (and equally important: How much of

this service will I consume?). A typical example is comparing taking a shower (20 to 60

litres of water in inefficient situations) instead of having a bath (min. 100 litres). Bathing

represents 39% of our consumption, and washing activities more than 25%.

It should be noted that Europeans consume eight times more water than their grandpar-

ents did only 50 years ago and that several countries in Europe have insufficient availability

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of fresh water, as shown on the map below.

Figure 13: Availability of freshwater in 2000. Source: World Resource Institute

3.5 Cooking

Cooking is an activity that uses energy in the form of heat. Although some attempts

are being made in Europe, the path to an energy-efficient cooking system is still long.

Nevertheless, it is important to note that, in the entire food activity cycle, the majority

of the energy is consumed in fridges and freezers, again making the choice of A, A+, or

A++ appliances particularly important.

3.5.1 Improved traditional cooking equipment

The traditional method of cooking, with a pot placed over a heat source (flame or electric),and no surfaces of the pot being insulated, is very inefficient (maximum efficiency of 35%)

and leads to significant heat loss.

One interesting attempt to improve this is the so-called Norwegian pot. This device is

nothing more than an insulated box, in which one places the hot pot before the end of

the normal cooking time. Then, the heat being conserved, cooking continues without any

further energy input, leading to an economy of 20 to 50%.

Is it possible to generalize this principle to all cooking activities? This remains an open

question today, since there is no mass production of such appliances.



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3.5.2 Alternative energy cooking

While the cooking process itself has seen little progress, some interesting attempts have

appeared recently concerning the energy source. Solar cooking is being developed insouthern countries (Africa, South America), with a great deal of success, especially for

long cooking processes (steaming, stewing, etc.). Its use in northern countries is still

sporadic, although about 1,000 solar cookers are currently operating in Switzerland.

In Africa and Asia, biogas production from human and animal manure is quite common,

and the gas (methane) is then used for cooking. Such a process has been installed ex-

perimentally in Freiburg, Germany for research purposes and it is noted in the document

Leben und arbeiten that Our research installation is too expensive to be reproducible in

another situation. On the other hand, the Kigali Institute for Science, Technology, and

Management has equipped six prisons of 5,000 persons each with methane productionfrom human excrement. The gas is then used in the prisons kitchen, leading to a 50%

reduction of fuel consumption.

Figure 14: Biogas production plant under construction in Kigali, Rwanda - detailed in-

formation on www.ashdenawards.org/winners/kist05

3.5.3 Behaviour

As with interior heating and cooling, cooking is an activity where inhabitants significantly

interact with the house. Without even discussing equipment and technologies, the method

of cooking itself has the greatest influence on energy demand. Behaviour is, in fact, the

most important single factor regarding energy demand for cooking.

For example, the use of a cover when cooking divides by a factor of 3.8 the energy demand

to maintain boiling water (calculation for 1.5 litres, 190 W instead of 720 W - Source:

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INFEL, ENERCO (Alain Gaumann))! Turning off the power at some point before the

end of the cooking process can save substantial amounts of energy. Cooking or baking

several dishes while the equipment is still hot also saves energy. Steam cooking is a very

efficient method. Some oven producers are now offering steam ovens. And, of course, rawfood does not require cooking energy and maintains the full nutritional value of the food.

4 Benefits of Low Energy Construction

4.1 Financial

It is often remarked that the construction of low energy dwellings costs more that tra-

ditional construction techniques, and might therefore not be financially advantageous.

However the way construction projects are executed varies significantly, especially in the

amount of DIY work. We note that the Scandinavian Homes company2 offers a standard-

ized passive house. The first house built in Ireland between March 9th and March 17th

has a surface of 230 m2 for a price of 1 130 e/m2.

We should also note that a label like Minergie R strictly limits the surplus costs (10% for

Minergie R S, 15% for Minergie P) due to the special construction techniques employed.

The French study Construction durable (available on www.constructiondurable.com)

has also demonstrated that the earlier the energy parameter is included in the project,

the smaller this cost will be. The HQE association in France, reports an additional cost

of only 5% if the High Environmental Quality parameters are taken into account early

enough.

It is worthwhile to again mentioned that, as explained in the The costs and benefits of

green buildings - a report to Californias sustainable building task force, the payback

on initial investment is relatively rapid. The savings on the total annual charges usually

reaches 3 e/m2/year, with an increase in the value of the building at around 8 e/m2. The

principal problem remains that the investor is often not the same person or organization

as the user.

4.2 Social

The same Costs and benefits of green buildings study discusses the financial benefits

of green constructions over their lifetime. These benefits break down as follows: 11%

consists of energy savings, 16% consists of reductions in charges, and 70% are savings on

productivity increase and reductions in health costs.

2www.scanhome.ie/passive.php

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While this clearly shows the importance of energy savings, with total economies going up

to 70%, there are also important side benefits. In fact, low energy buildings are usually

designed with a full quality procedure in mind, so that the benefits from energy savings

pull a lot of other benefits along with them. It is also important to note that, in the caseof collective dwellings, the reduction in charges varies from 1.6 to 3.4 e/m2/year. This

is a very important point for the low income population, who benefit from good quality

housing at lower costs with reduced charges on energy usages.

4.3 Political

Some cities and regions, such as Freiburg-im-Breisgau in Germany, have implemented a

full environmental approach, low energy construction being one element of the puzzle,

along with the elements of urban organization, transportation, waste management, etc.

The idea behind this approach is that dwellings are only one part of a global energy

system that entails massive waste.

The fact that political institutions have taken on the responsibility to lead such low

energy programs has limited the drawbacks of uncertainty and poor financial efficiency

on the initial experiments. The success of these programs, which are now performing well

financially, has greatly improved the image of these cities and countries, while at the same

time helping innovative local companies (like the now widely recognized Solar Fabrik in

Freiburg) develop.

5 Conclusion

Since the Rio Conference in 1992 and the Kyoto Protocols in 1995, many have become

aware of the problem of global warming. Energy is the cause of 85% of all greenhouse

effect gas emissions. Efforts have been made, but two emission categories keep increasing:

transportation and buildings. The current energy situation (between 2000 and 2006, the

price of oil doubled, the price of natural gas for individuals increased by 34%) furtherstrengthens the case for low energy construction.

We have also seen that, although technologies and design play an important role, indi-

vidual behaviour also has a great impact on two levels. The first is on the selection of

technologies, which is always the result of a human choice. The second is on the manner

in which the technologies are used day-to-day, in real life. It is therefore extremely im-

portant, as mentioned in the LEED procedure, to focus on the training of inhabitants in

low energy houses. A low energy dwelling with well-informed inhabitants can radically

cut its energy expenditure, a typical example being a 7 to 14% reduction on the heating

consumption for a 1C decrease on the settings.



33/33


Retrofit remains a critical point, since Europe has a very large number of older dwellings,

which are not at all energy efficient. NegaWatt mentions that, for France only, reduc-

ing energy consumption in every pre-1975 building (there are 17 million of them) to 50

kWh/m2.y would require the retrofitting of 450 000 buildings (which is the number ofbuildings put on sale annually) per year for 45 years.

One point remains unclear: the local capacity to build such low energy dwellings, as well as

the cultural acceptance by the building industry. As we have seen, construction materials

and processes need massive improvement. How ready are construction companies to

accept these changes in their work today? How can local regulations be adapted to

encourage the best practices regarding energy, as has been done with electrical devices in

the past?

References

[1] Fanger (1970, Thermal comfort, Copenhagen)

[2] Salomon - Aubert (Fracheur sans clim- ed. Terre Vivante)

[3] Miscellaneous Standby Power Consumption of household appliances, EU-DG XVII

Brussels, Belgium

[4] www.constructiondurable.com[5] PassivHaus: www.passiv.de

[6] Minergie: www.minergie.ch

[7] LEED: www.usgbc.org/leed

low energy house

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