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Energy Performance Certificates and Heat demand

Jenny@ross · 2021-06-21T17:33:25Z

Since moving to our home in 2017 we now have 3 EPCs and they are all different. Each surveyor has had difficulty determining whether or not our home has (a) a timber frame or cavity walls; and (b) suspended floors or solid floors. Admittedly two of the surveyors didn't try very hard. The final surveyor was very comprehensive and contacted her accreditation body to confirm, finally, what kind of house we were likely to be with regard to these two aspects. This has a bearing on the RHI and also on whether or not we have insulation and what type. I am interested in the heat demand of our home, which determines the level of RHI (I think?). What I don't understand (and perhaps others on this forum can explain this to me) is what does a heat demand for space and hot water of 22,000 kW actually means in reality. The other aspect I don't understand is that our home is one of eleven on a private estate. All the properties were built to similar specs. Our home has by far the highest heat demand, and it's almost twice that of one of the properties which is slightly bigger than ours. Sorry to sound so ignorant but can anyone explain to me or suggest to me in simple terms why our heat demand is so high? Thank you :-)

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Air Source Heat Pumps (ASHPs)

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Derek M

(@derek-m)

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Joined: 5 years ago

Posts: 4427

25/06/2021 3:13 pm

Hi Jenny,

If I was considering an ASHP installation I would be looking at the following criteria and asking the relevant questions.

ASHP :-

What is the predicted Coefficient of Performance (COP) at the various ambient air temperatures +10C, +5C, 0C, -5C and -10C, or for a performance graph covering that range of temperatures. This will allow comparison of the efficiency of each ASHP against the other brands. This is also important to ensure that the correct size ASHP is selected for your particular situation. You state that you often experience temperatures of -10C, so you need an ASHP that will provide sufficient energy to fully meet your heat loss and total heat demand at this ambient temperature.

Does the heat pump compressor run at constant speed or does it have a variable speed drive? Variable speed drives are claimed to be more efficient and help reduce energy consumption.

What is the cost of the ASHP?

What is the manufacturer's specified Mean Time Between Failure (MTBF) for the selected ASHP? This is a measure of the anticipated reliability.

What is the manufacturer's warranty period and what if anything is excluded?

What after sales service is provided by the manufacturer?

Approximately how many of their ASHP's have been installed in the UK?

Designer/Installer :-

Why have they specified a particular manufacture of ASHP?

Show detailed information of how they arrived at the size of ASHP required for your property?

How many installations have they performed?

What warranty period and level do they provide?

What after sales service do they provide and at what cost?

Are they MCS registered and for how long?

What level of spares for your particular ASHP do they carry?

What is the cost of installation with an itemised breakdown?

Do they have any satisfied customer's with whom you could speak?

How long will installation take and what level of disruption is to be expected?

Obviously there are other questions that you or others may think of but I think the above covers many of the important issues.

If you would like clarification of any point then please get in touch.

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Jenny@ross

(@jennyross)

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Joined: 5 years ago

Posts: 63

Topic starter 26/06/2021 10:48 am

@derek-m Thank you for your detailed reply. I can see that I need to carry on with my research for a while longer!

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Mars

(@editor)

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Posts: 3678

26/06/2021 1:35 pm

@derek-m, that's a terrific check list - very detailed, and very helpful for others to work through.

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Derek M

(@derek-m)

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Joined: 5 years ago

Posts: 4427

28/06/2021 1:46 pm

Hi Jenny,

I have thought of some additional criteria, which although not essential are indeed desirable.

Does the ASHP system have any form of weather compensation, and if so, how does it function. There are two main aspects which affect the efficiency with which an ASHP operates. One is the ambient air temperature, since below approximately +5C the ASHP has to work harder to extract the same amount of energy from the ambient air. The other is how warm the central heating water needs to be heated by the ASHP, the warmer the water, the harder the ASHP needs to work. Correctly optimised weather compensation, should lower the central heating water temperature, particularly during the Spring, Summer and Autumn periods, to just meet the required heat demand. In this way the ASHP operates at maximum efficiency. If weather compensation is not available, then how easy is it for the end user to change the setting of the desired central heating water temperature?

Another desirable capability would be for the system to provide monitoring of energy consumption and operating parameters, particularly historical data so that operational performance can be assessed and optimised where necessary.

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JonnyD

(@jonnyd)

Active Member Member

Joined: 4 years ago

Posts: 4

30/06/2021 8:06 pm

@derek-m thanks for all your thoughts here. This is going to prove very useful for my heat pump journey too.

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Derek M

(@derek-m)

Illustrious Member Member

Joined: 5 years ago

Posts: 4427

30/06/2021 9:10 pm

Thanks JonnyD, it is always useful to get feedback, so that we can try to ensure that information is relevant and meaningful.

A further thought that I have had, is to ensure that the control system (thermostats, TRV's etc), provides the most efficient control and operation of your system, without adding unnecessary complication.

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