High hopes: overcoming challenges with high-temperature heat pump integration

Retrofitting with high-temperature heat pumps can pose significant challenges if buildings are not properly investigated first.

Baxi’s Ryan Kirkwood navigates the highs and low of swapping boilers for heat pumps in hard-to-heat buildings

We all know the phrase ‘fabric first’. It means to design with good thermal efficiency in mind, to ease the burden of heating (and cooling) plant.

When we say ‘fabric first’ in the context of renewables, however, we are really asking what can be done to the building envelope to reduce heat loss. A reduction in heat loss means that a lower kilowatt (kW) capacity of heating plant is required, meaning lower capital and installation costs. It also means heat pumps can run more efficiently (see panel, ‘Why heat pumps suit fabric first’).

However, if heat losses are high because the fabric first approach cannot be taken, heat pumps will struggle to compete with the boilers they are replacing in terms of running costs. (Improving the fabric efficiency may not be possible if costs are prohibitively high or buildings cannot be altered for conservation reasons.)

So, what can be done if a building owner wants to decarbonise their heat and the existing building thermal envelope cannot be improved? One option, which is nearly always fast, affordable and efficient, is to design a hybrid system combining boilers and heat pumps – but this won’t do if the client brief is for full electrification of heat.

Many argue that high-temperature air source heat pumps (HT ASHPs) have been developed to solve this problem. However, the solution is not as simple as it is often made out to be. For anyone considering this route, it is essential to investigate the building and system to ensure an appropriate design and specification. 

This article considers possible solutions for high-temperature heat pump retrofits and looks at the key areas to investigate before undertaking such a project.