The energy efficiency and environmental impact of domestic mechanical ventilation systems in the United Kingdom.

Balanced ·mechanical ventilation with heat recovery (MYHR) offers, in principle, a way of reducing carbon dioxide emissions from dwellings. In order for such systems to produce a clear reduction in C02 it is necessary for the emissions from the low temperature heat saved to exceed those from the electricity used to drive them. This condition places a lower limit on the coefficient of performance (COP) of MYHR systems, which in the UK is around 3. The major variable in system performance is the electrical input to the fans. The electrical input required to drive MYHR systems available in the UK, based on manufacturers' literature, varies between 60 and 170 Watts. The lower end of this range implies a coefficient of performance just above 5, while the upper end of the range implies a COP below 3. It therefore appears that a number of systems currently on the market in the UK may fall below this limit, while the best are only just above. In contrast, theoretical calculations suggest that an electrical input as little as 10 Watts might be sufficient for a carefully designed system, giving a COP of 30. A three year project has been established in which detailed measurements of electricity use and energy dissipation in six domestic MYHR systems will be made, followed by the design and construction of a system with a significantly higher COP.