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Any thoughts on control strategies for heat pumps?

 
Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 1 hour ago
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 Travellingwave
(@travellingwave)
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Topic starter 24/02/2026 1:46 pm  

Just wondering what thoughts are on different control strategies for heatpumps. And is there a winner?

To my knowledge the main options seem to be

1. Fixed Flow temp with on/off control via third party room stat- think we can agree not the way to go.

2. Weather compensation

3. Load or room temp compensation

4. Third party optimisers like Havenwise etc.

 

I have dabbled with all 4 but not really come to any conclusion.

Initially ran with weather compensation - seems to work ok but you have to tweek quite a bit.

This year have been running Auto Adapt on our Ecodan. As others have mentioned it seems to have better ability to keep the heatpump running constantly when running at low output. It does what it says on the tin - ie it will maintain the room at the temperature you set, as it can only see the temp of one room , the rest of the house relies on your rads to be balanced in order to get the temp you want in that room.(or TRV limiters not ideal)

My impression from watching it work is that it only controls based on room temp ie does not use outside temp as well?? Am I right? 
I also note it is quite aggressive in its action - ie if you increase the set point it will try to reach the new set point as quickly as possible by ramping up the flow temp. It would be nice to have an option to dial this down.Full access to PID parameters might be a recipe for disaster but maybe 3 or 4 response settings ranging from aggressive to very slow would be good,

Other brands may use a combination - ie primarily weather compensation with automatic tweaking of the curve depending on room temperature.

Is there any practical difference in running cost between the approaches?

I could imagine that sub optimal weather compensation would waste energy due to overheating?? Whereas room comp should find the correct and lowest possible  flow temp for room temp that you request.

I tried Havenwise - like the simplicity of the app - use the hot water optimiser since I presume it finds the best time to reheat based on outside temp?? For the heating control it seemed to lead to a lot of stop start running which seems to go against the low and slow philosophy. So to be honest I switched that bit off. I expect if you have time of use tariff it makes more sense.

Really like what Adia have done (in principle, have no experience with it). If it works brilliant bit of work , Must admit I like the idea of the TRVs optimising for lowest flow temp whilst achieving room temp, plus flagging undersized rads. Not so sure about the hydro box bit of it?? Do they have any plans to sell the TRV bit separately I wonder. 
Anyone tried it yet?

I have seen that it is possible to hack smart TRVs via home assistant to allow for PID (modulating) control rather than on/off control- this combined with some optimisation logic might be a way to DIY something similar to ADIA??

Also benefit of fixed speed v variable speed circulation pumps- Mitsubishi is fixed speed which definately seems sub optimal to me. I guess it removes a variable from the mix.


This topic was modified 2 hours ago by Mars

   
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JamesPa
 JamesPa
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24/02/2026 2:22 pm  

Posted by: @travellingwave
↑

Whereas room comp should find the correct and lowest possible  flow temp for room temp that you request.

Given your background, you will have come across control theory (you probably know more than I do!).  The fundamental problem with room compensation is the response delay.  The house might take 6-24 hours to react to a small change in stimulus or response, you will understand why this is a problem.  In a fairly static/predictable system this can as you infer be tuned out using PID, but the weather is very far from a static system and houses differ enormously, so adjusting PID parameters would be challenging to say the least, exacerbated by the fact that you can control upwards only.  This is perhaps why WC was invented, its simple and works (see below).  It is used for boilers elsewhere in Europe (mandatory in some countries), but we in the UK didnt generally adopt is.

Weather compensation gets around the delay because it senses the external stimulus, ie outside temperature, as soon as it changes.  This is the main driver of heat loss, which is what the heating must compensate for.  So correctly adjusted weather compensation will mean that the heating dumps into the house exactly as much energy as the house loses, at (more or less) the time its needed, and thus the house stays at the same constant temperature.

Many heat pumps (and boilers which also feature WC), including Mitsubishi and my Vaillant, have some sort of auto adapt which slightly tweaks the weather compensation derived value for FT according to room temp.  Its typically only a small tweak though, so not sufficient for set up.

In practice many here (including me) find that pure weather compensation without any reference to internal temperature gives the best comfort level (and much better than was ever achieved awith my gas boiler).  Actually I tweak very slightly - throughout most of the season I run pure WC, but in March and early April, when solar gain is sufficiently high that it can more than compensate for the loss, I run a limiting mode which stops excessive overheating due to the solar gain.

Posted by: @travellingwave
↑

I have seen that it is possible to hack smart TRVs via home assistant to allow for PID (modulating) control rather than on/off control- this combined with some optimisation logic might be a way to DIY something similar to ADIA??

I believe @editor has signed an NDA with a company that may be developing something along these lines (in addition to what Adia has said).  Its an obvious need, but the control aspects are probably quite challenging without some sort of central coordinator - how to stop the flow regulators on different rads fighting each other?

Posted by: @travellingwave
↑

Also benefit of fixed speed v variable speed circulation pumps- Mitsubishi is fixed speed which definitely seems sub optimal to me. I guess it removes a variable from the mix.

The question is what are the benefits of variable speed?  Its not actually obvious.  To first order fixing the speed at whatever the highest you can reasonably achieve is leads to the lowest FT required for any given rad output, which maximises COP.  As it happens doing this also means that a linear WC curve, which the majority of heat pumps have, is a bit closer to the 'ideal', taking into account that rad output is proportional to average rad temp ^ 1.3 not rad temp ^1.

Of course not reducing the speed when demand is lower means more water pump power consumption, so that's a trade off against better COP due to lower FT.  Its as yet unclear if there any other trade offs.  Some installers have said there are, but a coherent description of a mechanism for such a trade off hasn't yet been advanced on this forum so far as I know.  

 

Hope that helps, many of the questions you are asking have been debated (and sometimes even resolved) in past threads.


This post was modified 26 minutes ago by JamesPa
This post was modified 24 minutes ago by JamesPa

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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