day, negating any benefits a time-ofuse tariff should offer.

Comparative costs

In the majority of scenarios, the initial cost of an ASHP is typically lower than a GSHP, as the latter require the additional cost of drilling and groundwork prior to installation. The cost of installing a GSHP, for example, ranges between £10,000 and £20,000 depending on the scale and complexity of the project, while ASHPs typically cost between £7000 and £14,000. While this cheaper price may seem appealing in the short term, the prospect of higher running costs and lower efficiency can quickly eliminate any savings.

As GSHPs are installed safely within a building, they require minimal maintenance compared to ASHPs. Due to an ASHP’s constant exposure to the elements, units typically last for an average of 10 years before needing to be replaced – a figure which drops even further should it be installed in an undesirable location, such as on the coast. GSHPs, on the other hand, are designed to last as much as 20 years, with the actual buried pipe system remaining efficient and operational for over a century.

Efficiency competition

The coefficient of performance (CoP) of a heat pump is a figure which describes the efficiency of the system, in terms of the relationship between the power that is drawn out of the pump as heat, and the power that is supplied to the unit. The higher this value is found to be, the more efficient the heat pump system is. On average, the COP value of a GSHP ranges from between 3.5 to 4.5, meaning that for every kilowatt of power that is supplied to the GSHP, between 3.5 and 4.5kW of heat energy is produced. For ASHPs, however, this figure is a far lower– 2.5 to 3 –primarily due to the GSHP’s ability to tap into a constant temperature source and remain unaffected by adverse weather conditions.

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