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ASHP in Hampshire

batalto · 2021-04-22T13:28:11Z

Hi all, Just wanted to talk you through our upcoming ASHP installation. We live on the south coast, just outside of Portsmouth. The house is a detached home of around 260m2 in footprint. The bottom floor was an extended bungalow and we added a second floor. The first floor is standard construction, brick cavity that's filled and double glazed. The upper floor is made of Structurally Insulated Panels (SIPs) with triple glazing. We had to use SIPs because they are lightweight and so wouldn't affect the shallow bungalow foundations. As an upside SIPS are also extremely efficient in retaining heat and have a very low U value, 0.18. The loft has 200mm of insulation in the middle beneath the floor and 400mm of insulation for everywhere else. We have 8.4kW of solar PV on the roof and 7kWh of battery storage (Pylontech batteries). We also have a Solic solar PV heat controller, which will dump excess solar power into the tank before we export. We've just had our EPC done and we scored very highly A (93) that also provided a heat demand of 34w/m2 which tallies with our ASHP assessment of 36w/m2. The ASHP is a 12kw Midea with a stated SCOP of 3.36 supplied and installed by J A Rees, sourced from Freedom Heat Pumps - total cost just under £10k. We will be replacing our current 32kW gas system boiler and hot water cylinder and using the green homes grant for £5k of the cost and I will paying the other £5k. We qualify for the highest RHI so would expect to get roughly £7200 back over the next 7 years. The boiler will be retained as a backup heating system and isolated from the ASHP system. We have been told this is fine with the RHI as its a backup and not hybrid. The heating is currently set to 45 degrees and we have had no problems. Our main living area has a large bifold door system and west facing. This means we have significant heat loss in the winter and for 2 months its very cold and this makes the room chilly, but not cold. All the other months the solar gain is significant, heating the room and the rest of the house. With the conventional boiler the room is chilly, so I am expecting issues in January heating up the room. We might need to come up with a plan for this room, possibly some thick curtains. The install will be next week and should be very straightforward. The ASHP will go on the drive next to the current power intake. The pipework will go straight through the wall into the current boiler room and tap into the current pipework. The tank will need replacement for one with a larger coil, but more or less everything else will remain the same. The aim is 2 days. Currently our gas is 2.5p and electricity is 14p and the current boiler is 58% efficient (according to the boiler) - this leads to a bill of around £1250 for both gas and electricity for the year. With the ASHP, boiler efficiency and assuming a worse SCOP of 2.7 on the current tariff we expect the bill to fall to just under £1,000 (34,000kw of gas to 7,000kw of electricity). This cost includes a standing charge for gas even though we wont be using it. My plan after we have got used to the ASHP is to upgrade the batteries and add 7kw extra, then move to a new tariff. Agile GO is very interesting as I could fill my batteries at night and expend them during the day. The batteries would store 11.4kw (14kW @ 80% Depth of Discharge). I have estimated this would further drop my bills down to £780

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Air Source Heat Pumps (ASHPs)

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HJD

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28/11/2021 8:07 am

40Kwh here yesterday (Nottingham) - CH only

This post was modified 4 years ago by HJD

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batalto

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Topic starter 28/11/2021 11:15 am

64kW used and 184kW delivered yesterday in total for CH.

COP 2.55

w/m2 244

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE

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Derek M

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28/11/2021 5:38 pm

Posted by: @batalto

@derek-m I think the sensors are integral. The only external sensor is in the hot water tank. Perhaps @grahamh can help. He seems to be the man who knows the Midea units better than anyone else

Hi Batalto,

Sorry for the delay in replying.

I have read through the Midea manual, and it would appear that you are correct, the water temperature sensors are located within the ASHP itself, though there is the option of installing an external water flow temperature sensor, but not a water return temperature sensor, which seems a little strange. Did you measure the water temperatures on your pipework and did they differ from the displayed values?

Besides making the operational changes that I have just suggested to Kev, one way that you could make your system more efficient would be to increase the heat output rating of your heat emitters, which should allow you to run your system at a lower water flow temperature.

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batalto

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Topic starter 28/11/2021 8:28 pm

@derek-m I did just have a look with my meat thermometer

On the ASHP controller it says I should be 43 and 37 on my inlet/outlet. From my science of stick the meat thermometer onto the side of pipe and wait a bit, I got 41 and 36 degrees. I am fairly confident that;

1) The meat thermometer might not be the best at measuring water flow temperatures in pipes, than say a chicken

2) Pressing it against a pipe under some lagging might not give the most accurate contact to measure from

3) The ASHP probably has its number close as dammit doesn't matter

4) I'm a better engineer than a scientist

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Kev M

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28/11/2021 9:10 pm

@batalto

but are you a better chef than engineer? ...

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batalto

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Topic starter 28/11/2021 9:14 pm

@kev-m given I use my meat thermometer to measure hot water pipes - I'm not convinced that I am perhaps good at either

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Derek M

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28/11/2021 10:27 pm

@batalto

No worries Batalto, I just thought that you would be getting better efficiency at those water flow temperatures.

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batalto

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Topic starter 28/11/2021 10:38 pm

@derek-m I imagine there are a range of factors which will affect it. Given how cold it currently is, I'm not too bothered. However a better COP would always be appreciated.

Perhaps I need to consider the next steps of how to make it better - bypass the low loss header etc

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Derek M

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29/11/2021 1:00 am

Posted by: @batalto

@derek-m I imagine there are a range of factors which will affect it. Given how cold it currently is, I'm not too bothered. However a better COP would always be appreciated.

Perhaps I need to consider the next steps of how to make it better - bypass the low loss header etc

Hi Batalto,

Rather than jumping in and making changes, I find the best approach is to think things through first.

Draw a schematic of your system, showing approximately where any sensors are located. With the system operating note down as much data as possible about the temperatures around the system.

Measure as accurately as possible, the inlet and outlet temperatures around your low loss header.

Then sit down and analyse what appears to be happening within your system.

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batalto

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Topic starter 29/11/2021 10:11 am

@derek-m after mapping my w/m2 (input, not after COP) to ambient I am getting fairly confident with the power demand expected from the ASHP. From the trend line its also pretty accurate with an R of 93.

Some more data will slowly fill in the gaps and give me a pretty good estimate for any given day and I can just multiply this by my house area (262m2) to get my expected kW demand. I can also now compare this to the heat loss given when the pump was installed.

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Kev M

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29/11/2021 10:38 am

similar ...

I had a couple of outliers where I got the house temperature wrong. I found an order 2 polynomial was a slightly better fit than linear. 😉

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Derek M

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29/11/2021 11:08 am

@kev-m

Thanks Batalto and Kev,

That is highly useful. It does indeed show, as suspected, that the heat loss is not a linear function against ambient air temperature, but does increase exponentially as the ambient air temperature falls. We obviously need more global warming. 😆

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