Recommendations from the UK’s largest heat pump trial

Results have been published from the UK’s largest field trial monitoring 83 heat pumps installed in UK homes. The trial has been undertaken to determine the key factors that impact the performance of domestic heat pumps.
Conducted by the Energy Saving Trust, one of the UK’s leading organisations set up to mitigate the effects of climate change, the field trial considered both technical parameters, such as system sizing and installation, as well as customer feedback and behaviour.
The findings show the heat pump performance to be highly dependent upon appropriate installation and integration with the building’s existing heating system, as well as appropriate control by the customer. As a result, the Energy Saving Trust is calling on industry to improve heat pump installation techniques to ensure they become a quality and mainstream technology for householders.
Results regarding overall system efficiency. The participating installations included 54 ground source and 29 air source heat pumps that were monitored for a full 12 month period. Overall, a number of heat pump installations performed very well, achieving an overall system efficiency (the amount of heat the heat pump produces compared to the amount of electricity needed to run the entire heating system, including domestic hot water, supplementary heating, and pumps) rating of three and above.
By type of heat pumps the trial found:

* Ground source heat pumps: The ‘mid-range’ of measured system efficiencies was between 2.3 and 2.5, with the highest figures reaching over 3.0. However, efficiencies were lower than those monitored in similar European field trials.

* Air source heat pumps: The ‘mid-range’ of measured system efficiencies was near 2.2 and the highest figures in excess of 3.0.
Conclusions and recommendations

Conclusions and recommendations from the first year of the trial include:

* Heat pumps are sensitive to design, commissioning and use. The field trial covered a variety of early installations, many of which failed to correctly design and/or install the heat pump. This result emphasises the need for improved training for installers.

* Keep it simple. There were many system configurations monitored in the field trial. In most cases, the simplest designed systems performed with higher efficiencies.

* The impact of domestic hot water production on system performance is unclear. Heat pumps can be designed to provide domestic hot water at appropriate temperatures, but more investigation is needed to determine the factors which have an impact on system efficiency.

* Heating controls for heat pump installations have to be comprehensively reviewed. There has been a failure to explain proper control requirements to both installers and heat pump customers.

* Responsibility for the installation should be with one company, and ideally be contractually guaranteed to ensure consistency in after-sales service.

* Further study needs to be undertaken on an installation-by-installation basis, to record what has been done wrongly (or correctly), what could be done better, and what exactly should be done in the future.
Next steps

The trial will continue for another year to enable further investigation into the factors that influence heat pump performance.

The Energy Saving Trust will also be doing work with trade bodies, heat pump manufacturers, the UK Department of Energy and Climate Change, and the Microgeneration Certification Scheme to identify improvements to heat pump installation guidelines and installer training.