Super insulation. All elements of the external envelope of the building should combine to provide a U-value of not more than 0.15 W/(m2K)
Space heating. Conventional central heating is replaced by a combination of waste heat from appliances, heat recovery from ventilation as well as body heat from people. Ancillary heating can be provided through actively pre-heating incoming ventilation.
High volume to external surface ratio
Triple-glazed advanced window technology. Glazing and frames combined should have a U-value of not more than 0.8 W/(m2K).
Air-tightness. Air leakage through unsealed joints must be less than 0.6 x the house volume per hour ( or less than less than 1 m3/hr/m2 @ 50 Pa).
Whole house mechanical ventilation with heat recovery. The recovery rate should be no less than 80%.
Elimination of cold bridges. Use bridge-free connection details or calculate losses at heat bridges.
Some use of passive solar gain. In central Europe, solar heat gains are, on average, greater than heat losses, even in winter.
Some use of thermal mass to reduce summer overheating, maintain stable winter temperatures and reduce the possibility of overheating in spring and autumn. In practice, opinion is divided as to its benefit. Successful implementation will be dependent on the careful modelling of heating and occupancy.
Some use of renewable energy, particularly for water heating and electricity generation.
Some pros & cons
Low energy demand
Homogeneous internal air temperature
Good internal air quality
With the omission of radiators there is more ‘wall space’
Temperatures are slow to change
High occupier satisfaction recorded in Germany
Requires a mechanical ventilation solution (the alternative, passive ventilation, is too dependent on wind conditions)
Requires electrically driven fans and air heater
Health implications concerning drawing air through ducting
Embodied energy not considered
Emphasis on primary energy rather than carbon dioxide reduction
Thicker than conventional walls can give rise to floor area issues
Difficulties in achieving air-tightness using conventional construction techniques
Little practical expertise of required construction techniques
'Passivhaus' v 'Passive Solar House'
For many of us, the PassivHaus is a novel concept – particularly for those of us who have been brought up thinking that a low-energy house is one that is heated by the sun – the ‘Passive Solar House’. These two approaches are radically different. Whereas the ‘Passive Solar House’ looks to the sun to do all the work, the direction that PassiveHaus takes is to minimise the work to be done in the first place, through super-insulation.
The ‘Passive Solar’ concept continues to have its adherents. Indeed, it is a concept that can work well in sunnier climes and one that, if UK temperatures continue to rise, could be increasingly relevant here. However, a combination of factors, including our limited quantity of sunshine along with the increasing efficiencies of insulation, are making PassivHaus the more appropriate concept upon which to found future low-carbon buildings.
PassivHaus too, as we have seen above, is not without its problems. We are still translating a standard established around a middle-European climate and culture, into something that might become uniquely British. In the short-term at least then, we shall probably see attempts to marry our own traditional understanding of how a low-energy building should be designed with the newly imported ideas from central and northern Europe.
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