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Aerotherm 12+12kw cascade huge power utilisation

 
Air Source Heat Pumps (ASHPs)
Last Post by Hamish_mckay 8 hours ago
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 Hamish_mckay
(@hamish_mckay)
New Member Member
Joined: 9 hours ago
Posts: 1
Topic starter 14/03/2026 11:23 am  

Looking for a little bit of advice.

 

new install. Heat loss calcs in my newly built (580m2) house. With air permeability of 2.5 and a heat loss calcs of 18kw at -6 for flow temp 45 def and internal temp 21.

 

my system is as follows 

2 12kw heat pumps in cascade. 45mm copper 10m (internal - insulated run) to plant room into a three port valve to dhw or To heat exchanger (no glycol - antifreeze valves in place)

 

this then goes to 100l buffer piped correctly 

 

single flow out to ch pump which tees to ufh (down) rads up via 22mm pipe throughout home to 3 ufh manifolds with mixing pumps and upstairs rads tees off into 15mm pipework.

 

our system set up doesn’t allow me to see flow and return temps, but when going via dhw it easily gets up to 65deg for legio cycle. So I know it’s capable. 

I put an ebus adapter on for a bit and could see flow temps able to get 45-70. 

the ch temp probes show temps of low 30s unless I set the heat curves at 1.2-1.4 (both) which leads to an acceptable warm house, but burns through 140-150kw a day (which is clearly insane)

 

I also noticed on the ebus adapter that flow temp was lower than return which I think is probably a ebus communication error with the device I was using, altho my valliant app shows my cop anywhere between 0.85 and 1.8 one of which is likely impossible so possible that the sensors are factory switched by accident.

 

the heating engineers are going to remove the hex as it’s clearly pointless and loosing us 5-10deg heat exchange. 

the buffer. Would you push to loose it, would you put it an an inline volumiser or a side tee volumiser. 

I think the guys dont really know what they are doing, and unfortunately it’s been left to be and my wife to diagnose and suggest changes to get it working.

 

i also wonder if a few rads upstairs are maybe undersized but that’s another isssue. 

I suspect at 1.2-1.4 the heat pump flow is 60deg plus and we are only seeing 40deg on ch side so loosing 20deg accross hex and buffer. Solving this alone I would imagine would drop our heating bills and max efficiency

 

any help would be very greatly appreciated 


This topic was modified 8 hours ago 3 times by Hamish_mckay

   
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