The Air Source Heat Pump range comes in 2 clear technology groups: Air to Water heat pumps (eligible for the Renewable Heat Incentive) use the heat created by the heat pump to heat a water based central heating system. Air to Air heat pumps (not eligible for the Renewable Heat Incentive) use the heat created by the heat pump to blow in hot air into a room.
When deciding on whether you are suitable for a heat pump (or which technology you are suitable for) it is essential to understand what works and for whom. Air Source Heat pumps are more efficient when they are supplying heat at lower flow temperatures. A traditional Gas boiler will supply hot water to the radiators at around 60 degrees Celsius. A Heat Pump on the other hand is better at supplying heat at a more constant temperature of between 35 and 40 Degrees Celsius (i.e. they supply heat at a lower “flow temperature”).
It is for this reason that Air Source Heat Pumps work better with Under Floor heating. Under Floor heating also requires lower flow temperatures as it dissipates heat over a larger area (than a simple radiator). That is not to say heat pumps can’t work with radiators – they can.
When sizing a heating system you need to ensure that the heat can be emitted to the room efficiently enough to ensure the room gets warm. If a gas heating system was supplying heat at a temperature of 60 degrees to a radiator in a room and then you suddenly swapped to a heat pump you may find that the room will no longer get warm when the same radiator is only getting a supplied flow temperature of 40 Degrees. Here, what you would have to do is increase the size of the radiator (such as making it a double or triple convector).
However, many properties will find that the radiators were sized for that property when it was built and since then the property has been better insulated (double glazing, cavity walls, loft insulation) and therefore the radiator may have become oversized for that room. Therefore when you analyse whether to install a heat pump you may find most radiators are sufficient!!
It may seem somewhat confusing, but this is all part of a rigorous and professional design service that any good quality heating company should provide (indeed MCS standards require it)!
The lower flow temperatures of heat pumps also mean that they are more suited to well insulated properties. if you are supplying heat at a lower temperature, but the property is losing heat quite quickly (i.e. it is not very well insulated) then you will struggle to heat the property!
Finally, once you have sized what heat load the property requires, and whether the heat emitters (i.e. radiators) are sufficient, you then need to ensure that the heat pump can work throughout the year. The following Heating Curve and Coefficient of Performance Curve show how the efficiency and output of a heat pump vary with the outside temperature.
Note that the kWp rating of the heat pump is a laboratory test at 7 Degrees Celsius! So, at 7 Degrees Celsius the 13kWp heat pump provides 13kWp of heat. However, if the outside temperature drops to 0 Degrees Celsius then the heat pump will only provide 10kWp of heating (at a flow temperature of 35 Degrees Celsius) and this will not be enough to heat your property if you installed a 13kWp to meet 13kWp of demand! In addition, the efficiency of the heat pump changes from a CoP of 3.5:1 at 7 Degrees to 2.5:1 at 0 Degrees – a drop of nearly 30% in efficiency!