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The Definitive Guide to Weather Compensation and Curves for Air Source Heat Pumps

 
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Air Source Heat Pumps (ASHPs)
Last Post by Tim441 1 year ago
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 5 years ago
Posts: 4794
Topic starter 28/10/2024 11:40 am   [#1809]

If you’ve been following our Homeowners’ Q&A podcast series, you might know that one of the most valuable takeaways has been around optimising the weather compensation curve for heat pumps. My discussions with experts – including a few off-topic conversations after the recordings ended – have highlighted just how nuanced and crucial this setting is for ideal efficiency. Since every home has unique requirements, setting the perfect weather compensation curve can be challenging but it's highly advisable that homeowners try to figure this out because it'll lead to cheaper running costs.

This thread is a space for sharing insights, experiences and questions around weather compensation settings.

For those starting out, I’ve attached the weather compensation curves issued with our Global Energy Systems 16kW Caernarfon heat pump to serve as a reference point. 

Throughout October and November, ours is set to 0.2 which results in a flow temperature between 32-35C, which has comfortably maintained most of our property at 21C (apart from the TV room – our index circuit).

Weather curves

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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 5 years ago
Posts: 4794
Topic starter 28/10/2024 11:41 am  

Please post your heat pump's weather compensation curves and data as a reference.


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Rewritten and updated for 2027
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bontwoody
 bontwoody
(@bontwoody)
Noble Member Contributor
Joined: 4 years ago
Posts: 1055
28/10/2024 3:05 pm  

@editor Im still experimenting with mine Mars, having made some changes to my house in the summer. My low end is 32C (at OAT of 15C) which is probably hotter than I need to keep the house warm but the minimum I can get away with before my heat pump starts to cycle as the radiators cant lose enough heat.

I suspect many people hit this problem.

My upper end will be evident after the winter 😉


House-3 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
10kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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 IRMartini
(@irmartini)
Estimable Member Member
Joined: 2 years ago
Posts: 80
28/10/2024 3:53 pm  

@bontwoody 

Exactly the same here.


“Anything worth doing, is worth doing right.”


   
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 DavidAlgarve
(@davidalgarve)
Reputable Member Member
Joined: 3 years ago
Posts: 248
29/10/2024 1:34 pm  

Hello Mars

4 bed large house in Portugal 16kW Mitsu. Still playing around and waiting to have buffer tank converted to volumiser.

Also pondering on PAR-WT50 wireless remote to let it do the thinking.

Weather Compensation

 


342sq m "Upside down" house in Algarve. Portugal
Mitsubishi PUHZ-120YUK 12kW ASHP
12 Solar Panels Growatt Inverter
2 x Growatt 7.5kW Batteries
Fronius EV Charger
Kia e- Niro 64kW


   
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 Judith
(@judith)
Prominent Member Member
Joined: 3 years ago
Posts: 548
30/10/2024 9:07 am  

We’re on Vaillant’s 0.55 curve which means 42C at -2C and around 30C at an OAT of 15C.

The pump cycles about once an hour once it’s warmed up the house after set-back. The house upper limit is set at 21C (expanded mode for occasional solar gain) and the rooms are mostly at 20C (bedrooms less).

IMG 3007

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with SCOP >4) open system operating on WC


   
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 Boycey
(@boycey)
Trusted Member Member
Joined: 2 years ago
Posts: 47
05/01/2025 8:35 am  

Is there a weather comp curve for ecodan?



   
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 5 years ago
Posts: 4794
Topic starter 05/01/2025 11:19 am  

@boycey the curves for your Ecodan should be published in your manual.


New to heat pumps? Take the Heat Pump Fundamentals course and use INTRO50 at checkout for 50% off.
Rewritten and updated for 2027
📘 From Zero to Heat Pump Hero
🛠️ Bodge Buster
🎧 Prefer to listen? Heat Pumps Explained – use AUDIO50 at checkout for 50% off.


   
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 Boycey
(@boycey)
Trusted Member Member
Joined: 2 years ago
Posts: 47
05/01/2025 11:49 am  

@editor I can't find any, any other ecodan users here have a mitsibushi weather comp chart?



   
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 Gary
(@gary)
Reputable Member Member
Joined: 3 years ago
Posts: 350
05/01/2025 3:19 pm  

The Ecodan WC curve doesn’t have presets like you see in other systems it’s fully customisable.  So you can set the high and low end at any OAT and change the gradient as you see fit between those values 

Like bontywood my low end doesn’t go below 32C to prevent cycling and is set at 45C at -10 which gives 37C at -2C

 



   
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 Gary
(@gary)
Reputable Member Member
Joined: 3 years ago
Posts: 350
05/01/2025 3:20 pm  
IMG 1017


   
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 5 years ago
Posts: 4794
Topic starter 05/01/2025 3:30 pm  

Posted by: @gary
↑

The Ecodan WC curve doesn’t have presets like you see in other systems it’s fully customisable.  So you can set the high and low end at any OAT and change the gradient as you see fit between those values 

I had no idea that was the case. Thanks for the clarification. 

 


New to heat pumps? Take the Heat Pump Fundamentals course and use INTRO50 at checkout for 50% off.
Rewritten and updated for 2027
📘 From Zero to Heat Pump Hero
🛠️ Bodge Buster
🎧 Prefer to listen? Heat Pumps Explained – use AUDIO50 at checkout for 50% off.


   
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