Passivhaus design ensures the construction of ultra-energy efficient buildings with little or no requirement for conventional heating. The highly insulated walls, roof, floor, windows and doors, ensure very low heat loss from the external surfaces of the building. Window positioning is carefully tested to maximise the capture of solar heat, and the building is air tight with a mechanical ventilation system, which ensures a high turnover of fresh air with minimal heat loss.
Passivhaus buildings create an exceptionally comfortable and healthy living environment based on a stable internal temperature of 20 degrees throughout the year, while achieving a 90% reduction in the energy needed to heat the house. The internal temperature is largely maintained through the capture of solar gain and the retention of heat generated within the building (appliances, body heat, bathrooms etc). The cost of heating a Passivhaus is extremely low.
Passivhaus achieves an exceptionally low heating demand with the use of mechanical ventilation heat recovery. Internal air is drawn from the rooms that require increased ventilation (kitchens and bathrooms) and is passed through a heat exchange to preheat the external air coming into the building. While the energy demand to heat the building is very low, there is an energy cost to running the ventilation system. Passivhaus buildings also have a tendency to focus on space heating and often rely on inefficient methods to provide hot water.
Greentithe homes use a combined mechanical ventilation and air heat pump unit to regulate both the space and water heating demand as efficiently as possible. The houses include a solar PV array sized to match the energy demand of both the space and water heating.
The nature of solar PV is that it tends to generate electricity when the energy demand of the house is low. PV generated energy is often exported to the National Grid, and payments for this energy through the Feed-in-Tariff has reduced significantly. The most cost effective solution is to use as much of the the energy generated on site as possible, and Greentithe is looking to include innovative energy storage technology, so the electricity generated can be used directly to meet the energy demand for space heating, hotwater and ventilation. While it is difficult to demonstrate complete self-sufficiency in terms of heating energy requirements, we believe no other houses go as far to achieve zero-cost-to-heat.
energy ratings and carbon zero
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