Heat pump field trial: good or bad?
Posted by John Barker-Brown on 21 September 2010 at 12:02 pm
Heat pumps don't work, so scrap the RHI, or
Heat pump technology works well and we must pursue it.
These are the two completely opposite views generated by the Energy Savings Trust's (EST) Heat Pump field trial. The report, Getting Warmer; a field trail of heat pumps has finally been released to a very varied reception.
So what is the truth? The EST started the trial with good intentions, seeking to establish the performance of heat pumps when installed in a variety of properties and offering to comment on factors critical to the technology’s successful application. The problem is this is a bigger question than it first seems. The efficiency of any heat pump is very dependent on the building, the occupants and what you are asking the heat pump to do. All things that need to be quantified before you even get to the heat pump. I can take the same heat pump and place it in two different buildings and get two completely different results.
For example, the efficiency of any heat pump is dependent on its outlet temperature; the higher this is the lower the heat pump efficiency, so if generating domestic hot water (DHW) at 55oC its efficiency will be lower than if it was simply connected to the space heating. Add to this the insulation levels of the property, the location, the number of occupants, etc; you can see comparing one heat pump installed in one property to another is no longer simple matter.
This is why manufacturers will quote you a CoP at a fixed condition and to a standard EN14511, so it is possible to compare one unit with another. Ask a manufacturer to provide a seasonal performance figure for your application and it is almost impossible due to all the variables. In fact, the EST gave up trying to measure a seasonal performance figure and generated a new measurement which was the system performance figure (with the same abbreviation!)
It is too early to draw any performance conclusions from the results and it must be remembered that this is an interim report, with the EST planning to focus on why the results were not as expected in the second report. Comparing performance of air and ground source heat pump technologies on this report would be premature, given the significant amount of estimated data for air source heat pumps included in the report.
The EST has produced a number of sound recommendations in the report which are reproduced here and should not be any different (and certainly no surprises) to what manufacturers and suppliers are currently doing as a matter of course. The points echo what Kensa has been saying for years and all our sites within the trail fell within the top 18%.
One thing missing from the list which I think needs addressing and could explain some of the low performance figures is that a number of heat pumps contain in-built immersion heaters. Using direct electricity to heat the building will certainly lower the overall performance. In-built immersion heaters are not required if the heat pump has been sized correctly.
There is also the issue that the pumps were installed prior to the launch of the Microgeneration Certification Scheme. However, the governance of the MCS scheme, and its ability to protect consumers, must be refined to ensure sanctions are imposed on suppliers and installers not capable of delivering projects consistent with the trial’s best performing sites.
So overall, although the results are not quite as expected, there are no real surprises in the recommendations and nothing that shouldn’t be done already. The EST has acknowledged that further evaluation is required to understand some of the initial findings and I’m sure we will all look forward to reading the next report.
About the author: John Barker-Brown is special projects manager at British heat pump manufacturer Kensa Engineering.
If you have a question about anything in the above blog, please ask it in the comments section below.
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