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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.

Photo: Kensa

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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8 comments - read them below or add one


AnonymousComment left on: 1 February 2011 at 7:14 pm

@ Jdoddy. I have experienced similar problems with an air source heat pump (Back up immersion heater running for a lot of the time + out door unit icing up) this was all due to the unit being massively undersized. It was the first ASHP I had dealt with and left it to the supplier to size the unit... never again!

Thankfully the developer I was working for had told me to use the supplier and ended up getting a larger o/put unit free of charge since the supplier knew they'd screwed up and didn't want to lose the customer. 

What is the heat load from your house? If greater than 11kW then your GSHP is undersized. it should match or exceed the load on it.

What flow temperature is  it putting into the UFH? as the other comments have said, the higher the flow temp the less efficient (Lower COP)

What is the hot water load (Size of cylinder? ) and how often are you heating it to 65°C? If every day then you're using too much juice. it need only be heated to 70°C once a week to disinfect. Heating to 45ish would be sufficient for most Hot Water needs.

 There are plenty of other factors that can affect the GSHP Size and Depth of ground loop, spacing of trenches/boreholes etc etc. if this doesn't help you with your Queries then I strongly suggest you employ an independent consultant to look at the system, if it has not been designed/installed correctly it will never work correctly and you will be lumbered with high electricity bills (and CO2 emissions!) Sorry

Good Luck


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Kensa Heat Pumps

Kensa Heat PumpsComment left on: 1 February 2011 at 7:08 pm

The symptoms you are describing do sound like the heat pump is undersized although as ItalicSix mentions with the unprecedented cold weather at the end of the year may mean that the heat pump was operating outside of its design conditions and hence running continuously.

If it is undersized then there maybe a chance of the ground arrays freezing resulting in the heat pump stopping, and this can happen to all types of ground arrays.

If you want, I’m willing to take a closer look at the sizing and give you my opinion. If you could send all the details such as the SAP report, building drawings, site plan, description of system and what you need the heat pump to do, i.e. space heating, DHW, etc to I’ll take a look.

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ItalicSixComment left on: 1 February 2011 at 3:56 pm

Dear JDoddY

I certainly would not expect the fact that you property is 'drying out' to cause the electrical cassette to come on, although I would expect the compressor to be running fairly constantly at this time of the year. What make of GSHP are you using?

The electrical cassette should only come on when you are failing to extract enough energy from the ground. What kind of collection system are you using (horizontal collectors, slinky coil or bore holes) and how much do you have? If you do not have enough pipework down or the pipework is not spaced out enough (such as with slinkies or compact collectors) this could be the cause of the problem if the ground is freezing.

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JDoddYComment left on: 1 February 2011 at 1:11 pm

I have recently installed an 11Kw GSHP with UFH in my newly built house. It has all the benefits of being well insulated and a heat recover system throughout.

The compressor is almost always running and that in turn brings in the additional (electric) cassette which is driving my electricity costs literally through the roof - never mind being slightly excessive as some are reporting!

My manufacturer insists it is because the house is still drying out - a claim which has been disputed by my architect, builder and that company's own refridgeration expert!

I need an independant expert to check over my building and the installed equipment to either prove or disprove the fact that the system has been badly under-sized. If it hasn't help me work out why this is proving to be one of the horror stories you regretably hear about which tarnish the technology which, I believe is fundamentaly sound..

Can anyone help me please? 

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Kensa Heat Pumps

Kensa Heat PumpsComment left on: 15 October 2010 at 12:10 pm

I think you might be talking about CO2 heat pumps (eco-cute) which are available in Japan for DHW production only (I can't tell from your website, what type of heat pump you manufacture?!). The EST report dealt with R407C, R134a units which if you increase the outlet temperture then the efficiency will drop. No two ways about it. This means that if the heat pump is producing water at 35oC, for underfloor it is more efficient than when it is producing 55oC water for DHW.

CO2 heat pumps have high CoPs if the temperature difference between the load (i.e. space or DHW) is high. However if this is low then the CoP's will drop. So CO2 is good for the production of instantaneous DHW, but for space heating where the temperature difference is low (Delta T = 5) the performance and hence CoP is poorer than a standard refrigerent type of heat pump.

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" if generating domestic hot water (DHW) at 55oC its efficiency will be lower than if it was simply connected to the space heating. " While, as I know,  air-water heat pumps (to make hot water, not to heat space) have high COP. they're specialized for water heating.

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Kensa Heat Pumps

Kensa Heat PumpsComment left on: 4 October 2010 at 2:05 pm

Thanks Malcolm,

I think Steven also forgot to mention that the UK housing stock is a lot poorer than that in Europe. Houses in Europe tend to be better insulated and therefore heat pumps have an easier time. 

I know the Kensa units in the trial (even though they performed in the top bracket of the results) were not in what I would say ideal applications with the clients being advised to improve the insulation levels a number of times.

With regards to the installers, no doubt the technical level of these people could make a difference, but there are/were a lot of good competent installers around and with support of the manufacturer the installations should be fine. Even with MCS accreditation there are still good and bad installers and despite a number of compliants against installers from clients I have still to see a company thrown off this scheme for heat pumps.

With the method of calculating your CoP described, this seems fine for the performance of the heat pump in your property. However I believe the EST were trying to compare one heat pump in one property with another. (Even if they weren't this is how people/industry would read the results). This is where the results fall down, as you said in your post, one womens jam making affected the results, while in another, the daughter smoking did!

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malcolmcroComment left on: 1 October 2010 at 6:20 pm

As a recent purchaser of an Ice Energy heat pump I was disappointed with the EST 'Getting Warmer' Report. I was shocked to find ground source performance at COP 3 or below as I seem to be getting up to 5. I wanted to replicate their methods of measurement.

Steven Harris, Head of Low Carbon Technologies at EST kindly phoned me and discussed the methods they used.

It was indeed very thorough and agreed technically by the heat pump manufacturers and peer reviewed at every stage. Unfortunately the cost of monitoring each home for a whole year with £5000 of equipment could not be afforded by the average householder.

The results compared well with a similar German study for air source but their ground source figure was between 4 and 5 COP. He said the reason was that installers in Germany were of degree standard whereas ours had 1 week training.

I asked what the objectives of Phase 2 would be and he answered that it was to find out the reasons in each case for the poor performance. Anecdotally there were circumstances in the installation or use of the equipment which contributed in a minor or major way. Things like jam making raising the internal temperature but not being monitored. In another instance the daughter smoked at the open back door. Also pipes going to the wrong cylinder and ground loop kinks.

Surely there is a simpler way to compare heat pump performance. I have a water meter on my ground loop so I can measure how many litres circulate. I multiply that by the temperature difference to get the KW entering the home. My OWL measures the electricity being used, pumps and all, and my COP is between 4 and 5 at present.

True, I may not be using the heat well inside the house but that is a separate problem.

Let's have some methods we can all use!

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