Designing and Building Passive Houses
Passive Houses are very well insulated and draughtproofed buildings whose annual space heat demand is so low that conventional heating system can be omitted. The small amount of heat still required can be delivered to the individual rooms by heating the air supplied by the ventilation system. This will work, when the space heating energy demand is up to 15kWh/m²a) (kilowatt-hours per square meter of floor area per annum). The construction of a Passive House is very demanding in terms of the performance of building components used. The following refference values apply to the Central European climate. The principles are valid in other climates as well.
- exterior building elements must have a U-value below 0.15W/(m²K)
- The external envelope must be constructed without thermal bridges
Simply combining appropriate components is not sufficient to construct a building as a Passive House – the integration as a whole is greater than the sum of the individual parts. The component interaction necessitates an integral plan in order to achieve the Passive House standard. This is the purpose of this Passive House Planning Package.
WHAT IS THE PASSIVE HOUSE STANDARD?
- A passive structure is a building in which “a comfortable interior climate can be maintained without active heating and cooling systems” (Adamson 1987 and Feist 1988)
- The house heats and cools itself, hence “passive”.
ENERGY CONSUMPTION – HEATING COMPARISON
- The average Canadian home consume 59% of total energy in heating
– 43,506 Btu/ft2 per year
– (137.2 kWh/m2 per year)
- Homes built to today’s Passive House Standard, consumes 6.4% of total energy in heating
– 4755 Btu/ft2 per year
– (15.0 kWh/m2 per year)
TOTAL ENERGY CONSUMPTION: AVERAGE HOME
ENERGY SAVINGS WITH PASSIVE HOUSE STANDARD
How to achieve these requirements?
→ high R-Values ≥ 38 (ft2*h*0F/Btu) / U-Value= 0.13 W/m2K
→ minimize heat loss trough surfaces
→ minimize air leakages to ≤ 0.6 times the house volume per hour
→ solar heat gain
High Energy Efficient Windows
→ U ≤ 0.15 (Btu/ ft*h*F)/ U(METRIC)= 0.85 W/m2K
ANNUAL HEATING COST COMPARISON
Average power cost (kWh): $0.08
Average Canadian home: $2039
- The average energy consumption in Canada for residential buildings for heating in 2006 was 137.2 kWh/(m²*yr) (43506 Btu/ft²*yr).
- Assuming average heated area of a home is 2000 ft2 (185.8 m2)
- Source: Natural Resources Canada
Passive House Standard: $222
By the standard, the heat demand for a passive house should not be higher than 15 kWh/(m²*yr) (4755 Btu/ft²*yr).
CONSIDERATION OF SOUTHERN EXPOSURE AND SHADING
- Passive use of solar energy is a significant factor in passive house design
- Most of the glazing should be facing south to get maximum heat gain during the wintertime
- Shading should be provided for summertime to avoid overheating
AIR TIGHTNESS/ BLOWER DOOR TEST
- Air leakage through unsealed joints and penetrations must be less than 0.6 times the house volume per hour under an under pressure and overpressure of 50 Pa.
- Minimize the risk of condensation → mould !!
HIGH ENERGY EFFICIENT WINDOWS
- Windows (glazing, spacer and frame combined) should have Ufactors (Imp.) not exceeding 0.14 Btu/h*ft²*F 0.80 [W/(m²K)]
- → R 7.1 (h*ft²*F/Btu), with solar heat-gain coefficients more than 50%.
- RFrame = 7.8 h*ft²*F/ Btu (U = 0,73 W/m2K)
- RGlazing= 9.5 h*ft²*F/ Btu (U = 0,6 W/m2K)
- ΨSpacer = 0,037 W/mK (factor linear thermal bridge)
- Solar Heat Gain Coefficient (SHGC) = 0.52
- RW Build in = 6.7 h*ft²*F/ Btu (U = 0,85 W/m2K)
EXTERIOR WALLS AND INSULATION MATERIAL
Wood fibre (loose)
Wood fibre board
Strawbayle (not structural)
HEAT RECOVERY & VENTILATION UNIT
Fresh air can be brought into the house through a ground source heat exchanger. This preheats fresh air to a temperature above 41°K (5º C), even on cold winter days.
Cold fresh air is heated up by the warm used air (without blending) by a highly efficient heat recovery cross-flow plate heat exchanger (efficiency min 80%) almost to room temperature
The rest of the maintaining energy in the exhaust air is taken from a highly efficient mini heat pump (1-3 kW) to heat up the domestic hot water
The compact unit can be combined with geothermal or solar if necessary.
BUILDING GREEN VS. GREEN BUILDING
Where do your materials grow?
Where do building material go at the end of their useful life?
MATERIALS – HIDDEN ENERGY COSTS
- More energy required for production
→ higher negative impact on the environment and climate
- “Grey” energy
→ Energy to produce the materials → no recovery!
→ Raw material to produce the materials → eg. Petroleum
- Waste and excess construction material