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Air Source Heat Pumps (ASHPs)
Last Post by batalto 2 years ago
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 HJD
(@hjd)
Estimable Member Member
Joined: 4 years ago
Posts: 43
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
(@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
(@derek-m)
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Joined: 5 years ago
Posts: 4427
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
(@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


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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 Kev M
(@kev-m)
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Joined: 5 years ago
Posts: 1276
28/11/2021 9:10 pm  

@batalto 

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



   
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 batalto
(@batalto)
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Posts: 1092
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


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
(@derek-m)
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Joined: 5 years ago
Posts: 4427
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
(@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


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
(@derek-m)
Illustrious Member Member
Joined: 5 years ago
Posts: 4427
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
(@batalto)
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Posts: 1092
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.

image

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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 Kev M
(@kev-m)
Famed Member Member
Joined: 5 years ago
Posts: 1276
29/11/2021 10:38 am  

similar ...

wm2ambient

 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
(@derek-m)
Illustrious Member Member
Joined: 5 years ago
Posts: 4427
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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