The house is heated predominantly by passive solar and internal heat gains from people, lights and appliances. A minimal space heating system is needed. One is only now being installed after living in the house since August 2012.
Some of the factors contributing towards its very low heat consumption include:
- High thermal insulation, respectively 450/300/200 mm in the roof/walls/floor;
- Draughtproof construction, around 0.4 air changes/hour at 50 Pascals in a ‘blower door’ test
versus 10 for a normal UK house;
- Passive solar features, plus a high thermal capacity structure;
- Mechanical ventilation with heat recovery (MVHR) including an earth-buried tube to preheat
fresh air in winter and precool it in summer.
Schematic cross-section through
the high-mass, externally-insulated
The result of modelling the building with
the Passive House Planning Package.
The ‘heating season’ in a normal year
is roughly four months long.
A high thermal mass structure surrounded by a thick layer of external insulation gives a thermally stable building. It reacts slowly to changes in the weather or to sudden solar energy inputs through the windows.
In a temperate climate, a relatively long thin and south-facing house; e.g., house A below, can actually have a superior energy performance to a compact, almost cube-shaped dwelling such as house B. House A has a slightly greater heat loss than house B but it gives superior daylighting and passive solar gains.
Which to build: house A or house B?