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Thermodynamic panels: the UK's first independent test gets underway

Posted by Tom Bradley on 4 June 2014 at 9:40 am

Recently there has been an increasing discussion of a new heating technology, known as solar thermodynamic panels (or solar-assisted heat pumps). They are sometimes marketed as a “solar panel that works at night” to quote one manufacturer. Essentially they are a type of air source heat pump, which uses a flat plate evaporator to extract energy from the air and sun, whereas a conventional air source heat pump uses a fan drawing air over a matrix of finned tubes.

At Narec Distributed Energy, we became interested in the claims by different manufacturers, some of which seemed especially ambitious, particularly since none appeared to be based on UK test data for a thermodynamic panel system. As an organisation that carries out a wide range of tests of renewable and low carbon technologies, we thought it would be interesting to test a system and post the results publicly.

In April last year, we issued a challenge through our blog: a manufacturer would provide and install a system and we would test the system for free and post the results online monthly. A UK manufacturer took up the challenge and installed a system here in Blyth in December 2013. The specific system installed is purely for the heating of domestic hot water.

The purpose of the test is to quantify the Coefficient of Performance (COP) of a thermodynamic panel system under UK weather conditions, specifically in this case north east England weather conditions. The Coefficient of Performance is essentially the ratio of the energy used by the system (pumps, compressor, etc) against the energy delivered into the hot water load. 

The system is under test in our Thermal Test Lab at our office in Blyth. This lab has been used for various heating technology tests, including boiler efficiency, energy saving flow restrictors, and the impacts of integrating traditional solar thermal panels with combi boilers.

In order to ensure that the test is repeatable, and representative of a domestic consumer, we are using what is known as a tapping cycle to control how much water is drawn off, and when. The standards BS EN 13203-2 and BS EN16147 contain a number of different tapping cycles for the boiler and heat pump industries. We used Tapping Cycle no.2 or “M” for this test, which corresponds well with the domestic hot water load of a four-person household (estimated by the Energy Saving Trust at around 120 litres per day). 

The tapping cycle ensures the hot water load is 5.845kWh per day; the actual volume of water drawn depends on the inlet and outlet temperatures – if the water is heated from 10 to 50°C, this equates to 124 litres per day. This means the thermodynamic system will provide the same amount of energy every day.

In order to understand the efficiency of the water tank and immersion within the thermodynamic system, the test was run for four days without the panel input. This allowed us to measure the efficiency of the water tank alone, so that we could separate the impacts of the panel.

Since January 2014 we have posted the results on our website.  

So, what have we found out? Ultimately, it is still too early to pass judgement on the performance of the system, as we do not have a full winter/summer cycle recorded yet, but we have identified that the water tank used is particularly efficient. 

The thermodynamic system average basic COP for January is 1.02 rising to 1.36 in April. Taking tank losses into account, the average COP in March is 1.87, with a maximum of 2.64. Daily hot water tank temperature averaged 52.6°C. We have not seen the COP of 7 claimed by some manufacturers of thermodynamic panels.  

Even without the summer data, we can see that the thermodynamic panel returns approximately twice the energy of an immersion heater. Therefore it would be fair to say the technology may be suitable for people off the gas grid, although obviously there are other competing, more established low carbon technologies to consider such as solar thermal or biomass, instead.

With regard to properties on the gas grid, we still need more data to make a fair evaluation of how a thermodynamic panel compares with competing technologies.

So what are the next steps from this? When we have a full six-month cycle which includes summer and winter, we will be able to make a fair evaluation of the technology. There are improvements to be made, this is ultimately a young technology, and there is much that can be done to optimise it for the UK climate.

Update from Tom (9 June 2014):

"We have noticed there is some confusion over how the COP we have measured for the thermodynamic panel compares to that quoted for air source heat pumps. The thermodynamic panel system under test at Narec DE is for domestic hot water only, and is thus producing water at a temperature of around 50°C. Generally, air source heat pumps are used for space heating and produce water at a lower temperature (35°C to 45°C in the test standards). To put it simply, the higher the temperature produced by a heat pump (air source or thermodynamic), the lower the COP. Essentially, this means that comparing the COP of an air source heat pump used for space heating to the COP of a thermodynamic panel for DHW is not comparing like with like, and could lead to a consumer making the wrong choice."



More information

From the blog

Thermodynamic panels: your questions answered

Are thermodynamic panels eligible for RHI?

How can I future proof my heating and hot water?

More information about renewable heating systems from YouGen

YouGen guide to heat pumps

YouGen guide to solar thermal

YouGen guide to biomass boilers

YouGen guide to renewable heat incentive

YouGen guide to heating and hot water

About the author: Tom Bradley works for Narec Distributed Energy, which is part of the UK National Renewable Energy Centre group of companies.

If you have a question about anything in the above blog, please ask it in the comments section below.

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9 comments - read them below or add one

Andy in Hawick

Andy in HawickComment left on: 30 April 2015 at 11:17 am

This research is good but unless read very carefully it could be misleading. It raises as many questions as it answers, particularly about the test conditions and details like pipe run-off volumes.

I would like to see the results calculated against the datum of immersion heater performance as this is essentially the baseline against which one would typically compare.

It would also be interesting to see this technology tested for space heating as I would expect significantly higher COPs due to the larger, more even heat flow and the lower temperatures involved.

I am fascinated by the lack of correlation (day to day), or even inverse correlation between calculated COP and insolation levels. What else is happening here that alters that dynamic?

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Tom Bradley

Tom Bradley from Comment left on: 7 January 2015 at 12:45 pm

Thank you for the comments. We ran the test from Janaury to July, to test the system in winter and summer conditions. We appreciate that we have left the page as a stream of data, with no final update. We will write a summary in the near future, commenting on the results and comparing them to other technologies.

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Cathy Debenham

Cathy DebenhamComment left on: 6 January 2015 at 9:53 am

Hi bxman I haven't talked to Narec recently, so I don't know. You'd have to contact them direct to find out more.

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bxmanComment left on: 6 January 2015 at 9:50 am

Thanks Cathy


But there does not seem to be anything after July 2014 .

Was the evaluation concluded then and the experiment wound up?

cheers Patrick

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Cathy Debenham

Cathy DebenhamComment left on: 5 January 2015 at 9:21 am

@bxman Narec publish ongoing test results here.

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bxmanComment left on: 4 January 2015 at 8:04 pm

New here so may not looking in the right place .


But are there any more results on the Panels from June 2014  to date 

Hope there have not been any problems with them as it seems an exciting new technology and to eliminate some of the problems associated with ASHP's 


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Johnd44Comment left on: 28 December 2014 at 12:08 am

Hi all,

I have an "ENERGIE" system manufactured in Portugal. Unfortuneatly the installer went but 6 months after installation.

The system has not ben fault free but my guess is that the installer did not do a very good job. However so far since installation all my hotwater has been generated by the system. I have a problem now as I think that either the Gas refrigerent or the comperssor have failed so I am now having to use the electric for hot water, I also seem to have a pressuer release valve that is not up to the job. some more work to be done, and of course winter is here.

I hope to har more experiences. John.

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Tom Bradley

Tom Bradley from Comment left on: 9 October 2014 at 4:28 pm

Our test resuilts have not shown the theymodynamic panel system to perform well, with a COP varying around the 2.0 level. What COP have you found your system to perform at?

Please have a look at our test results at

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ScotsplumComment left on: 17 September 2014 at 11:32 am

I have this technology installed in my house in Scotland it has been in place for one month short of a year, I am a qualified plumber heating Engineer and have installed a number of air source heat pumps as well. Although I have never installed one of these thermodynamic systems myself I do not have an F-Gas qualification I have found that this system outperforms a traditional Air source system this I place down to the fact it uses a refrigerant in place of the normal water/glycol mix it certainly works better in lower temperatures. I had a gas combi boiler that was supplying our hot water and since switching to this system for our hot water I find it far more effective (sadly their is a finite supply of hot water in the tank so it cannot compete with the combi as for supplying the quantity) my heating needs are met by a wood burner, electricity is met during the day by PV (at night though I am on the grid) so my utilities demands are quite small. I really hope your test results back up the results I have found because I believe this technology is a real step forward and it needs MSC accreditation to become nationally accepted.

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