Air Source Heat Pumps (ASHP)

Air Source Heat Pumps

Air Source v Ground Source

Both Air Source Heat Pumps and Ground Source Heat Pumps use the warmth in the surrounding environment, whether that be by the air or the ground the warmer that temperature the more efficient the heat pump is. The temperature below around 1m is roughly consistent and this is the reason over the course of a year Ground Source heat pumps are more efficient. This consistency however comes at a cost, in the form of either a bore hole or a horizontal loop in your garden, which dramatically increases the cost of the system. In short if you have enough land and don’t mind the extra capital expenditure Ground Source is the way to go. The reality for most people is ASHP are the only viable option.


Air Source Heat Pumps design types: –

Monobloc – single outdoor unit

High temperature split – outdoor unit as well as an indoor unit

Low temperature split – Same as above but works

This can then come with or without a hot water cylinder and depending on the system you may have a separate buffer vessel.


Heat emitters and the need for a heat loss calculation

Heat pumps run at lower temperatures than conventional boilers and therefore the heat emitters in your house may not be big enough and will require a change. The best application is underfloor heating but oversized radiators work well, but must be correctly sized.

To ensure these are correctly sized for the heat pump a room-by-room heat loss calculation must be carried out to determine what output in watts is required.

It is also important to look at the size of the pipework.

The best way to save energy is always to insulate first and this will help with the size of the radiators required. A well-insulated house will likely only require an upgrade from single panel to double panel radiators, meaning the only change would be the depth of the radiator. It is also good practice to flush the existing system so the whole system is working at it most efficient.


SCOP Seasonal Co-efficient of performance

Heat pumps are rated by the SCOP, the higher this is the more efficient the heat pump.

In simple terms an Air Source Heat Pump with a COP of 3 means for every 1 unit of electricity that the heat pump uses it will produce 3 units of electric making it 300% efficient. The best gas boilers on the market are around 90% efficient. Its important to realise though that the outside temperature makes a big difference to this COP figure, although all heatpumps will still operate down to -15 or less, the efficiency of the heat pump will be far less than 300%. It is therefore important to look at the savings over the course of a year and not just in the coldest months or you may feel the system isn’t working.


Below is a typical schematic for Heat pumps used in conjunction with a backup boiler:-