Mechanical systems require electrical power to operate, including power to the fans, any compressor(s) and transformer(s) and control and safety devices. The term ‘specific fan power’ is used to compare the electrical energy use for different ventilation systems as installed (i.e. allowing for system resistance).

Specific Fan Power (SFP) is defined by the Energy Savings Trust as: ‘The power consumption, in Watts, of the fan (plus any other electrical system components) divided by the air flow through the system, in Watts per litre per second (W/l/s)’

Specific Fan Power Calculation: Heat Recovery Ventilation (HRV)

For a small house with a Kitchen + 1 Wet Room the minimum extraction airflow rate is 21 l/s (Part F: Eng & Wales 2010). If the unit consumes 15 watts to achieve this rate of air flow then: SFP: 15 / 21 = 0.71 W/l/s

The Energy Savings Trust Best Practice recommendation for SFP is 1 W/l/s or lower. The aircycle 3.1 Heat Recovery Ventilation unit currently achieves a SFP down to 0.37 W/l/s, which makes it the market leader in terms of efficiency.