The beyond zero carbon performance is achieved by advanced passive solar design techniques;
- Orientation - the buildings are oriented south specifically to maximise solar gain so as to achieve optimum benefits in terms of space heating, ventilation and high levels of daylight.
- Super-Insulation – Insulation reduces the rate of heat loss from the building while increasing its capacity for retaining stored heat. The specification of premium performance rigid insulation creates elemental u-values vastly better than the minimum Building Regulation requirements.
- Natural Insulation – the earth around and over the building provides a good layer of further natural insulation.
- High Thermal Mass – the thermal mass (the concrete structure) is placed inside the insulation to provide a heat ‘battery’ to hold onto the heat gained. The internally exposed 'mass' works to stabilise the internal ambient air temperature by acting as a heat-sink.
- Layout – the buildings parabolic layout allows it to 'follow the sun' and so maximises natural light and heat into the living areas throughout the day.
- Fenestration Arrangement – by maximising the areas of glazing on the south elevation of the building, the opportunity for solar gains into the home are optimised. By reducing the glazing areas on the north, east and west elevations, the rate of heat loss from those sides of the building most prone to higher rates of heat loss is minimised.
- Ventilation – The layout of the building is designed to enable cross-ventilation by inducing the movement of air through the building from the south side to the north side using a passive venturi effect system.
- Courtyard Micro-Climate - the bunded courtyard induces a micro-climate that retains external warmth against the front of the buildings.
- Passive Heating – As well as the passive solar heat gains, human occupation and secondary heat from household appliances will provide the heat that these homes will require.
- Energy Generation - This is all supplemented by photovoltaic energy generation.
Concrete may not initially appear an ideal 'eco' building material (these homes are basically concrete rooms hidden underground) but a lot of the thermal mass can be made up of recycled materials and it is important to remember that concrete will be structurally sound for thousands of years (think of the Roman buildings and aqueducts that are still functioning across Europe). Ecological impact needs to be measured over the lifespan of the building. Although concrete may not have a low initial carbon footprint, when measured over the lifetime of the building it has a very good annualised carbon footprint.
Using all the above the three buildings, when built, have been calculated to be 7.7 tons per year 'Carbon Negative'. These aren't simply 'zero carbon', they are beyond zero carbon.