Identifying the Best ofthe Walling Alternatives Presented By: Manfred Braune, Technical Executive GBCSAOn Behalf of: WSP Green by Design and ClayBrick.org
OPTIMAL WALLING SOLUTIONS FOR ENERGY EFFICIENT HOMES IN SA
The 130 m² House Model
Derived from CSIR Garsfontein Control House
? 130m² FootprintHallway, lounge, dining room, kitchen,
3 bedrooms, 2 bathrooms
Insulated brickJohannesburg(CR = 100 h)
Insulated brickDurban
(CR = 60 h)
Walls with Regional CR Specifications
Passive Case Thermal ComfortSingle Skin Walling ~ Upington
Hourly Predicted Mean Vote (PMV) ~ Values over a Year
Zero PMV line represents line of greatest thermal comfort.Deviation from it reflects increasing discomfort.
Wall 3.3: 140 mm Concrete Block, Bag and Paint both sidesPassive Case reveals nature of the materials alone.
CR Product Value of a WallJ = Joule (a measure of heat energy)
C = Thermal Capacity – the ability to absorb, store and release heat energy, or the heat energy needed to raise the temperature of the material by 1°C. (kJ per °C)
R = Thermal Resistance – from thermal conductivity, or the ability to conduct heat energy, or the heat energy lost per second for a difference in temperature on either side of the material. (J per °C.s),
C x R = 370.4 x 0.88 x 1000/3600= 91.54 hours,
the time constant property of the wall system
For every m2
Wall TypeDouble Brick
(DB)DB with 50mm
air cavity
DB with R=0.5Cavity
insulation
DB with R=1Cavity
insulation
DB with R=1External
insulation
Cact (kJ/m2.K) 139 149 157 162 270
CR (hours) 40 60 90 130 130
CR Product defined
Active Case EnergyHeating & Cooling Fan Energy use per Annum vs. External
Wall CR Product for 130 m² House as Modelled, Upington
Basis for Costing
Total cost comprises:
External walling construction External walling maintenance over a 50 year period and Heater and cooling fan energy use over a 50 year period
Discount rate for future cash flows 10 % / yr
Initial energy cost (start of year 1) 83 c / kWh
Year 1 energy escalation 25.9 % / yr
Year 2 energy escalation 25.9 % / yr
Remaining years energy escalation 7 % / yr
Maintenance expense escalation 7 % / yr
High Thermal Capacity Walls:
– moderate swings in daily thermal comfort
– reduce cooling fan energy (all S.A. climates)
Correlation agrees with CR theory:
- Heating and cooling fan energy minimised by high
CR walling e.g. insulated brick
Single Skin Walls (Low C • Low R)
- Poor choices for envelope walling systems in terms of energy use and thermal comfort.
Conclusions for all South African Climates 1/5
(Valid for 130m² house as modelled only)
Conclusions for all South African Climates 2/5
– .. Musina
– .. Durban
– .. Pretoria
– .. Upington
– 2nd Cape Town
– 1st Johannesburg
(Valid for 130m² house as modelled only)
Choice of external walling more critical in terms of absolute energy use and energy cost, as one moves through the climates in the following order:
Conclusions for all South African Climates 4/5
(Valid for 130m² house as modelled only)
Lightweight walls are not paying back high construction
cost with sufficient energy savings in this scenario.
• Cost
• Regulatory or Standards Compliance – SANS 10400, SANS 204, Green Star
• Thermal Comfort
• Sound Transmission
• Local Availability
• Aesthetics
• Preference
Conclusions for all South African Climates 5/5
(Valid for 130m² house as modelled only)
Different Selection WarrantedDepending on Actual Goals :
Questions for Further Study?
(Valid for 130m² house as modelled only)
• How does an air conditioning in a house with increased cooling energy use affect energy ranking of walls?
• How can active thermal capacity be used to gain further insight?
• What is the sensitivity of the costing to changes in the various parameters such as future electricity tariff escalation?
Low Cost House ~ 40m²
Percentage of Time Occupants Experience Thermal Discomfort ~ Johannesburg
LSFB not SANS 517 compliant
Low Cost House 40m²Low Cost House ~ 40m²
Monthly Cost of Heating Energy ~ Johannesburg
LSFB not SANS 517 compliant
66 c/kWh tariff assumed
Low Cost House ~ 40m²
Energy Required to Achieve Comfort on Winter Solstice ~ Johannesburg
LSFB not SANS 517 compliant
Low Cost House ~ 40m²
Monthly Cost of Heat Energy in the Different Climatic Zones66
c/k
Wh
tarif
f as
sum
ed
Low Cost House ~ 40m²
Monthly Heating Energy in Low Cost House ~ Average of 6 Climate Zones
LSFB not SANS 517 compliant
Low Cost House ~ 40m²
c
Increase in Annual Energy Consumption ~ Light Steel Frame & Clay Brick
LSFB not SANS 517 compliant
Low Cost House ~ 40m²
In Johannesburg, using two leaf brick as opposed to concrete block saves enough energy yearly to light the household for 55 days. 24 hours a day.
Heating Energy per Annum
LSFB not SANS 517 compliant
Low Cost House ~ 40m²
Carbon Footprint (Construction and Operational Heating Energy) ~ Johannesburg
LSFB not SANS 517 compliant
Low Cost House ~ 40m²
Construction and Annual Energy Costs ~ Johannesburg
LSFB not SANS 517 compliant
66 c
/kW
h ta
riff
assu
me
d
(Valid for 40m² house as modelled only)
Conclusions ~ 40m² Low Cost House
Single skin concrete block falls short of conventional clay brick in thermal comfort, electricity cost for heating.
Clay brick walls overall best performers.
Insulated ceilings should be mandatory ~ significant thermal benefit for reasonable outlay.