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Weather compensation climatic heat curves

 
Air Source Heat Pumps (ASHPs)
Last Post by davidm06 6 months ago
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 davidm06
(@davidm06)
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Topic starter 27/01/2025 1:20 pm  

We have a Grant Aerona3 R32 installed 3 years ago by a previous house owner hence we were not involved in the installation and are trying to work things out now. I have checked the install and weather compensation is enabled but I am a bit surprised at the heat curve settings and am looking for advice. The Maximum outgoing water temperature in Heating mode is set to 50C (Tm1), the Minimum outgoing water temperature in Heating mode (Tm2) is set to 45C, the Minimum outdoor air temperature corresponding to maximum outgoing water temperature (Te1) is set to -4C and Maximum outdoor air temperature corresponding to maximum outgoing water temperature (Te2) is set to 20C. To me, that is not much of a curve....  I appreciate this varies between installations. Unfortunately I have not been supplied with the heat loss calculations for the property but am trying to get it. It is an old house but reasonably well insulated. We live in the north of Scotland on the Black Isle, beside the sea, north of Inverness and aim for an indoor temperature of 18.5C 


   
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bontwoody
 bontwoody
(@bontwoody)
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27/01/2025 1:41 pm  

I think you assessment is correct. I would try and reduce the 45C end initially and see how the house feels. 

Also 20C OAT is quite a high setting particularly if you prefer 18.5 inside. I would knock that down a couple of degrees too. 

It’s a bit trial and error really to get the result that suits you. Just make small changes and see how that feels to get the lowest flow temperature you find comfortable. 

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 JamesPa
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27/01/2025 2:46 pm  

Those settings are crazy and barely do any weather compensation at all.  Perhaps they were set up by someone who thought that the radiators had to feel hot to be heating the house.  

If your target IAT is 18.5 Id start with the WC curve at something like 30 (FT) (or even less - maybe 27 or even 25) at 15 (OAT).  I would then slowly reduce the 'cold' end of the curve until your house just heats up enough.  Once the cold end is set up you can tweak the warm end a bit later in the season. 

Make sure that any external controls are permanently calling for heat.  This means turning up thermostats/TRVs to well above the desired point, and ensuring heating is timed to come on 24*7 except when the system is heating DHW.

That should get you to a near optimum setting.  Allow a couple of weeks, you can make bigger changes at first but once you are getting near change by only a degree every 24hrs. 

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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 davidm06
(@davidm06)
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Posts: 19
Topic starter 28/01/2025 1:31 pm  

Many thanks for that advice. I did think it was a bit crazy. The previous owners would not made these settings as they were in their 80s....

I have implemented and will report back...


   
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 davidm06
(@davidm06)
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Topic starter 02/02/2025 10:16 am  

There is one other setting in the Grant heat curve group which is the Hysteresis of water set point in heating and the default is 8C.  Am I right that this relates to the hysteresis of the hot water tank heating and not the central heating and says that the hot water will come on if the hot water tank heating will come on when programmed if the tank is 37C and switch off at 52C as the tank is set to 45C?

 

 

 


   
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 davidm06
(@davidm06)
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Topic starter 04/02/2025 5:25 pm  

I realise now that this hysterisis setting is controlling when the heating comes on e.g. Heating : Outgoing water temp ≥ Water set point (parameter 2100~2105) – Hysteresis (parameter 2141)


   
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 davidm06
(@davidm06)
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Topic starter 08/02/2025 5:27 pm  

@jamespa thanks for the advice. If I am tweaking the curve for low temps, should I first increase the Maximum outgoing water temperature in Heating mode (currently 45c) (Tm1) or the Minimum outdoor air temperature corresponding to maximum outgoing water temperature (Te1) - currently -4C. Maybe Tm1 to 45C or Te1 to -1C??


   
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 JamesPa
(@jamespa)
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08/02/2025 11:50 pm  

To tweak for low temps I would increase or decrease (as appropriate) the target flow temperature at the minimum outdoor temperature end of the curve.  

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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 davidm06
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Posts: 19
Topic starter 09/02/2025 12:34 am  

@jamespa many thanks. will do


   
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