A recent report on heat pumps published by the Energy Saving Trust suggests that the technology is not delivering the savings in terms of money and CO2 which are often claimed. The EST say they are now working with industry to improve installation of domestic heat pumps, following the largest ever UK heat pump field trial. The study looked at the performance of both air and ground source heat pumps, and found many installations were proving disappointing. They concluded that better installation practices and guarantees are needed to ensure promised savings become reality. The report follows the completion of the first phase of the most comprehensive field trial of the technologies ever undertaken in the UK, which studied heat pumps at 83 sites (54 ground source and 29 air source.). The trial began in early 2009 and monitored both technical performance and customers’ experiences for a full 12 month period.

Results showed that while some heat pump installations performed very well, achieving an overall system efficiency rating of three and above (for every unit of electricity put in there is an output of three units of heat), many were much less efficient than this.

The sample of ground source heat pumps had slightly higher measured system efficiencies than the air source heat pumps. The ‘mid-range’ system efficiencies were between 2.3 and 2.5, with the highest figures reaching over 3.0. The lowest figures for both types of pump were only a little over 1 - 1.2 - Of the air source systems studied, over a third (10 out of 29) returned figures below 2. The ground source pumps scored slightly better, but only 13% of all the pumps studied scored over 3. Interestingly, the system efficiency figures for the sample of ground source heat pumps were lower than those monitored in similar European field trials.

The report concludes that some of the blame for the poor performance of many of the systems studied is down to the conditions in the UK. The major difference between the UK and European field trial findings is that the UK has particularly old and inefficient housing stock. The British climate also tends to be cold and damp, rather than very cold and dry like Scandinavia. But as well as these predictable factors, heat pump performance is affected by the existing heating systems in UK homes, the attitudes and behaviour of heat pump users, and the quality of installations.

Many of the owners of the pumps in the survey were disappointed with the installation's performance. Running costs were one of the main negative factors affecting user satisfaction.Rather hopefully, perhaps, the EST concluded that 'dissatisfaction may be related to the substantial increases in fuel costs which occurred just before and during the project' (due to unusually severe weather). There were many more dissatisfied social housing residents
(42%) than private householders (13%).

They also concluded that 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. These results emphasise the need for improved training for installers.

Simon Green, Head of Business Development for the Energy Saving Trust, says: “We have a responsibility to make sure that customers’ investments are spent on measures that lead to the greatest potential to save carbon and reduce energy bills. This trial shows that when installed and operated correctly, heat pump technologies will save significant amounts of CO2 in the UK, when replacing oil or traditional electric heating.

“Over its lifetime, a high performing heat pump installed today will save CO2 even when replacing gas condensing boilers due to the planned decarbonisation of the grid. But there is no doubt that the results are more varied than were expected, with results showing both high and low performing heat pumps.

“We are securing funding to extend the trial, with the objective of defining the reasons for variation in performance levels so that we can inform industry about good practice and advise householders on exactly what to look out for.”

The Energy Saving Trust worked with the Open University to determine how customers’ behaviours impact on the performance of heat pump installations - many found the instructions and controls too complicated.

The Trust also worked with the UK government and industry experts to develop a comprehensive methodology which has been peer reviewed by leading European heat pump experts.

Roger Nordman, of the Swedish SP Technical Institute, who peer reviewed the methodology for the trials, says:

“Domestic heat pumps are a well established technology in Sweden and although there are differences in UK and Swedish applications, some of the best performing sites in this project compared favourably with what has been monitored in other European countries. The major difference is that the UK has particularly old and inefficient housing stock. The market is also more mature in the rest of Europe and installers have much more experience in installing the technology.”