Question from Geoffrey Postles, via e-mail:
When installing an air source heat pump outside a building, are there any advantages to installing this on the sunny side of the building or even inside a small greenhouse in order to take advantage of the warmer air in these two locations?
Answer from Dave Lacey, commercial director in the UK and Ireland for Vaillant:
Generally speaking, an air source heat pump extracts heat from the outside air in the same way that a fridge extracts heat from its inside. The air is converted into energy via a refrigerant circuit. The warmer the air is, the higher the heat output and level of efficiency.
Normally, air at the north side of a building will be the same temperature at the south side. Any increase in CoP when the sun warms the air is very small and not even measurable.
I would not recommend installing an air source heat pump in a confined space, such as a room or a greenhouse. As the heat pump extracts energy from the air, the average air temperature in the greenhouse will reduce, cooling below the ambient level and resulting in a reduction in CoP.
For example, an air source heat pump with an output of 8kW would be required for a well insulated, new build property. This level of heat output would circulate 3,500 cubic metres of air per hour, so it would need to be fitted in a very large greenhouse indeed!
Furthermore, during nighttimes and the winter months – the main periods when you want additional heat – there is no sun in the sky anyway, rendering buildings such as greenhouses redundant.