Why choose ground source over ASHP
In general when looking at both technologies the more efficient is a ground source heat pump, simply put when installing a ground source your installing a loop underground which extracts the heat from the ground rather than extracting from the air. As discussed COP & SCOP for an ASHP the same applies for a Ground Source one unit of cost will produce 5 units of renewable heat, so slightly better than a ASHP, because the ambient temperature underground is around 10 Degrees annually (SCOP seasonal Co-efficient of performance) whereas the ASHP has to work in all types of temperatures. Realistically, for the installation of a ground source you need a lot of area or to install a bore hole. Also the ground needs to be tested to understand how much heat you could extract and a lot of ground work needs to be completed so the cost of aground source is substantially more expensive and the only extra benefit is the SCOP at 5.
Government Incentives are available for both technologies
ASHPS & GSHPS Incentives
The Government have been running the RHI (Renewable Heat Incentive) for many years and people have been taking advantage of this. As an example, if you install an ASHP you will benefit from the RHI paid over 7-years and on average you will receive 80% of the cost of the installation back over this period. Also, the Government is offering the Green Homes Grant which is available now of up to £5k upfront to help install either technology but the offer will only be available until March 2021. If your Boiler is old, then the cost of replacing this would be between £1600.00 to £2000.00 which would be the same if you installed an ASHP with the Government Grants.