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System pressure and COP

 
Air Source Heat Pumps (ASHPs)
Last Post by ChandyKris 2 months ago
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 ChandyKris
(@chandykris)
Reputable Member Member
Joined: 2 years ago
Posts: 116
Topic starter 26/12/2025 3:42 pm  

A couple of days ago, I noticed that the pressure had dropped to nearly 1 bar. The installers had mentioned that the ideal pressure is around 1.5 bar. So, I re-pressurised to the appropriate level, and since then the COP has gone up slightly with respect to days comparable in temperature. For example, yesterday was very cold, around 2 degrees Celsius, but we still managed to reach a COP of 4 for the day, including hot water. On a similar day earlier in the month, we probably reached just around 3.5 COP. Does the system pressure matter for COP, or is this just a correlation and not causation?

 


16 * 435 watts PV
13 kWh Growatt battery
1 EV - Mercedes EQB
6 kW Aira Heat Pump


   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4290
26/12/2025 5:58 pm  

Posted by: @chandykris
↑

Does the system pressure matter for COP, or is this just a correlation and not causation?

Provided it's sufficient I can't think of any reason in physics why system pressure would affect cop


4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4290
26/12/2025 5:58 pm  

Posted by: @chandykris
↑

Does the system pressure matter for COP, or is this just a correlation and not causation?

Provided it's sufficient I can't think of any reason in physics why system pressure would affect cop


4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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 ChandyKris
(@chandykris)
Reputable Member Member
Joined: 2 years ago
Posts: 116
Topic starter 26/12/2025 6:01 pm  

Thanks @jamespa


16 * 435 watts PV
13 kWh Growatt battery
1 EV - Mercedes EQB
6 kW Aira Heat Pump


   
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