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Is it KISS or constant – weather compensation vs. set flow temperature?

 
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Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 2 years ago
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 cliffhanger
(@cliffhanger)
Eminent Member Member
Joined: 2 years ago
Posts: 21
Topic starter 16/03/2025 9:38 am  

Away at present. Hence the delay.  Will get back asap.

Cliff



   
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 cliffhanger
(@cliffhanger)
Eminent Member Member
Joined: 2 years ago
Posts: 21
Topic starter 28/03/2025 8:53 am  

Okay. I have setup the system using just weather compensation.   There is something called 'thermal blockade' on my smart controller which turns off the stat rather than turn it to maximum.  

I'm going to video the heat curve but at the moment it starts at 18(20c) and runs to 45(-30).  -5c = 33c. The OAT is 10c and the system is stable at 19.5c.   I tried a lower curve but the pump cycled as expected, 25c is the lowest it will go.

What's struck me is how cool the rads are.  They don't feel they could warm anything!  But they do of course.  Now we are at the end of March the system's not going to be tested at lower temperatures which to me is the breaker.

To be continued

Cliff

 



   
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JamesPa
 JamesPa
(@jamespa)
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Joined: 4 years ago
Posts: 5573
28/03/2025 9:01 am  

Posted by: @cliffhanger
↑

What's struck me is how cool the rads are.  They don't feel they could warm anything!  But they do of course.  Now we are at the end of March the system's not going to be tested at lower temperatures which to me is the breaker.

Indeed.  Its weird at first but you get used to it and actually it is more comfortable because the temperature gradients are less.

There is a school of thought pursued by some installers that having cool radiators leads to call outs (which is probably true).  Thus some installers force a minimum FT of 37, which is roughly the point at which radiators feel warm.  This of course increases the cost to the householder.


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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 Old_Scientist
(@old_scientist)
Prominent Member Member
Joined: 2 years ago
Posts: 575
28/03/2025 9:20 am  

We ran our radiations at anywhere between 30-35C over winter. At 30C I struggle to tell they are on. If I place my face over the top of the radiator, I can just about feel warm air convecting on my face. At 32C I can feel they are warm to the touch, and at 35C they are (relatively) positively hot!

I still walk around touching the radiators to see if they are on - I just need to trust the room thermostat, which doesn't lie.


Samsung 12kW gen6 ASHP with 50L volumiser and large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW). Net Zero


   
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 Grantmethestrength
(@grantmethestrength)
Reputable Member Member
Joined: 2 years ago
Posts: 185
03/04/2025 3:09 pm  

I had to laugh at this as I do exactly the same thing, I read on here someone explain it well, the body is running at 36c so anything less will feel cold. As I explain to friends it is actually magic that heats my house! 

 


Kind Regards
Si
——————————————————————————
Grant Aerona3 13kW
13 x 435w + 13x 480w Solar Panels
Sigenergy 10kW Inverter
25kWh Sigenstor battery


   
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 cliffhanger
(@cliffhanger)
Eminent Member Member
Joined: 2 years ago
Posts: 21
Topic starter 14/04/2025 7:59 am  

Hi

Just as an aside.  My system is heating only.

What is the best way of turning a weather compensation setup off in the summer?   I thought of turning the stat back on to its lowest temp, in this case 10c.  Won't go any lower. 

Or setting the heating curve to its lowest?

Cliff



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 4 years ago
Posts: 5573
14/04/2025 10:40 am  

@cliffhanger Mine has a 'space heating off' setting!  Otherwise turn down thermostat if you have one and it's set up to call for heat


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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