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Did anyone else's ASHP spend most of yesterday (Mon 21/11/22) in defrost?

 
Air Source Heat Pumps (ASHPs)
Last Post by Mars 4 years ago
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 AllyFish
(@allyfish)
Prominent Member Contributor
Joined: 4 years ago
Posts: 520
Topic starter 22/11/2022 11:35 am   [#605]

The worst possible weather for an ASHP - freezing fog! (?) No sooner had the evaporator defrosted than it had frozen up again. I guess there's not much can be done about that. My CoP went through the floor and my energy consumption went through the roof. I was tempted to switch it off and light the wood burner! Location - North East England.



   
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 Benseb
(@benseb)
Estimable Member Member
Joined: 4 years ago
Posts: 109
22/11/2022 12:54 pm  

Lower flow temps help avoid defrosts I think!

 

Can you run for longer at lower flow temp?


250sqm house. 30kWh Sunsynk/Pylontech battery system. 14kWp solar. Ecodan 14kW. BMW iX.


   
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 mjr
(@mjr)
Reputable Member Member
Joined: 5 years ago
Posts: 303
22/11/2022 7:40 pm  

Not all day here because the fog cleared, but a slight settings error saw our unit do 5 defrosts in the morning and only achieve a COP of 3.1 for the day.



   
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 6 years ago
Posts: 4950
23/11/2022 9:33 am  

We've not been too bad with the defrost cycles yet. We've found that the worst defrosting occurs when temperatures drop to between 0-3C and there's a lot of humidity in the air. This is one of the main reasons that we favour the hybrid approach, because the HVO can take over the heating in these instances, so we avoid horrible heat pump inefficiencies and countless defrost cycles. Two Christmases ago (when our heat pump was running solo), we had two back-to-days where the pump was in perpetual defrost mode, which affected our temperatures inside the house. We shouldn't experience that this year. 


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 AllyFish
(@allyfish)
Prominent Member Contributor
Joined: 4 years ago
Posts: 520
Topic starter 24/11/2022 10:45 am  

@editor Freezing fog seems to be an ASHP's nemesis. When similar weather is forecast I'll pop downstairs, light the log burner first thing and switch the ASHP off!



   
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 6 years ago
Posts: 4950
24/11/2022 11:53 am  

@allyfish, yes, freezing fog definitely isn't an air source heat pump's friend as it forces your heat pump to full speed during defrost cycles. 🤣 Your strategy to use the log burners make sense to maintain good internal temperatures so when the heat pump is turned back on it's got an easier job to do.


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Free UK shipping.
📗 Heat Pumps Explained
A Jargon-Free Guide for Homeowners
Rewritten and updated for 2027
📘 From Zero to Heat Pump Hero
🛠️ Bodge Buster
New to heat pumps?
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