Buildings PassivHaus
How the standards compare
PassivHaus standard UK new-build common practice Acharacle Primary School
Compact form and All components of the exterior shell of a Limiting U-values of approximately 0.25 The school is single-storey and has a
good insulation: Passivhaus are insulated to achieve a U- to 0.35 W/m
2
/K. relatively high surface-to-volume ratio as
value that does not exceed 0.15 W/m
2
/K. it is spread across two wings. However,
the U-values comfortably exceed
PassivHaus targets: 0.125 for the roof,
0.128 for the walls, and 0.098 for the
floors. The building also achieves a
U-value of 0.8 for the windows com-
pared to the expected 1.8 using normal
building methods.
Southern orientation Passive use of solar energy is a signifi- Some consideration is given with regard Principle rooms (classrooms and
and shade cant factor in PassivHaus design. to north/south orientation, but the nursery) are oriented towards the south
considerations: improved energy savings resulting from to minimise heating requirement. Open-
passive site design are often overlooked. ings to the north are minimised. Fabric
roller blinds fitted to the outside of the
classroom windows minimise the risk of
overheating.
Energy-efficient Windows (glazing and frames, com- 1.8-2.2 W/m
2
/K typical. Windows (glazing and frames, com-
window glazing and bined) should have U-values not exceed- bined) have U-values not exceeding
frames: ing 0.80 W/m
2
/K, with solar heat-gain 0.8 W/m
2
/K, with solar heat-gain coef-
coefficients around 50 per cent
1
. ficients around 50 per cent.
Building envelope air- Air leakage through unsealed joints must Design air permeability of 7 to 10 m
2
/ Air leakage through unsealed joints is
tightness: be less than 0.6 times the house volume hr/m
3
@ 50 Pa. This is approximately a 0.27 m
3
/hr/m
2
@ 50 Pa – or approxi-
per hour (this is the equivalent of an air factor of 10 poorer than the PassivHaus mately 0.2 air changes per hour.
permeability value of less than 1 m
3
/hr/ standard.
m
2
@ 50 Pa).
Research has also shown that air perme-
ability values for completed dwellings
frequently exceed these design limits.
Passive preheating of Fresh air may be brought into the house The majority of new-builds do not There is no passive preheating of incom-
fresh air: through underground ducts that ex- achieve good enough air permeability ing fresh air. The moisture and thermal
change heat with the soil. This preheats values to warrant the incorporation of a mass of the building fabric contribute to
fresh air to a temperature above 5 deg C, whole house ventilation system – thus creating comfortable indoor environ-
even on cold winter days. trickle vents, extract fans, or passive ments in order to minimise the require-
stack ventilation is commonly used. ment for fresh air in the first place.
Highly efficient heat Most of the perceptible heat in the The school is naturally ventilated
recovery from exhaust exhaust air is transferred to the incoming throughout (with the exception of the
air using an air-to-air fresh air (heat recovery rate over 80 per kitchen and internal shower/toilets,
heat exchanger: cent). which require mechanical ventilation).
Energy-saving Low energy refrigerators, stoves, freez- Dedicated low-energy lights are provided The artificial lighting system uses low
household appliances: ers, lamps, washers, dryers, etc. are in a number of rooms in a new dwelling energy fittings throughout, and is fitted
indispensable in a PassivHaus. – if appliances are supplied they will be with daylight linking sensors in principle
generally C-rated or perhaps ‘Energy rooms and corridors. In addition, lights
Saving Recommended’ in some switch off after a predefined period. Low
instances (as these are widely available). energy electrical appliances have been
specified by the staff for the various
kitchenettes throughout the building,
though it was discovered that there is
currently no energy efficiency require-
ment for commercial kitchen appliances.
Total energy demand Less than 15 kWh/m
2
/yr. Typically 55 kWh/m
2
/yr. Less than 15 kWh/m
2
/yr: until the build-
for space heating and ing has been operational for 12 months
cooling: this figure is unavailable. However, it is
anticipated that the wind turbine may
produce more energy than is required by
the heating system. Only time will tell.
1
The Solar Heat Gain Co-efficient (SHGC) is provided as a guide; it can be adjusted for glazing on different facades. This can help either reduce heat loss on
sheltered sides/ north facing glazing, or alternatively help to reduce the likelihood of overheating when specified in conjunction with other features/strategies
(please note that the SHGC of a window usually decreases as the U-value improves).
Please note that the above information is for guidance only. Compliance with the PassivHaus standard must be assessed using the PassivHaus Planning Package.
Source: www.passivhaus.org.uk
www.cibsejournal.com July 2009 CIBSE Journal 31
CIBSEjul09 pp28-31 passive.indd 31 26/6/09 12:07:36
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