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Air Source Heat Pumps (ASHPs)
Last Post by MPHB 1 year ago
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 JohnR
(@johnr)
Estimable Member Member
Joined: 1 year ago
Posts: 106
25/01/2025 9:07 pm  

I caught my Arotherm+ heat pump at the end of a defrost cycle this morning when the OAT was about 0C. I then checked the data provided by the Vaillant control box to see that the compressor power was ramping up steadily by about 1% every few seconds, so no sudden jump to a big load.

End of defrost cycle


   
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 Old_Scientist
(@old_scientist)
Reputable Member Member
Joined: 2 years ago
Posts: 357
04/02/2025 8:32 pm  

Posted by: @s_gatorator
↑

Posted by: @cathoderay
↑

More seriously, -7 to +5 degrees is really quite a large range, there must be places in Europe where the OAT is within that range for some if not much of the time. I wonder what happens there?

That's a very good question. I wonder if anyone on the forum has an idea, an interested contact, or experience of living the ASHP in such temperatures

 

I have seen mentioned two things that may help alleviate the effects of defrost cycles.

The first is having sufficiently large thermal mass within the system such that the amount of energy used, or taken out of the system for the defrost doesn't have a significant impact and is easily recoverable. The larger the system volume, the less the flow temps will drop during a defrost cycle.

The second is the size of the heat pump and how hard it is having to work. An otherwise oversized unit that is not working as hard may frost up less frequently? Similarly, a large two fan unit with double the surface area would presumably take longer to frost up than a unit half it's size delivering the same amount of heat? Sounds reasonable although I have no evidence to substantiate. Having an oversized heat pump also means the system has capacity to recover quicker from the inevitable drop in flow temperature, and without the system working flat out.


This post was modified 1 year ago by Old_Scientist

Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.


   
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 MPHB
(@mphb)
Trusted Member Member
Joined: 3 years ago
Posts: 31
05/02/2025 4:31 pm  

Bit late to the party maybe, but my Midea clone heatpump slowly raps up its electricity use at the beginning of a cycle. I have a designated Eastron SDM230 smart meter that I tend to - not very smart - look at every now an then. The HP draws 17W when standby and when the compressor is switched on the power gradually (50W steps give or take) goes to the required power demand (up to 2300W for my 10kW HP). What I have not yet witnessed though, is how power ramps up when the internal backup heater is switched on and I suspect that to me just a 3000W jump.



   
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