Midea ASHP – how to set weather compensation

Curlykatie · 2023-01-20T17:15:11Z

After lots of help from @derek-m around balancing the system I am now looking for some advice on how best to set weather compensation. We have moved into a 4 bed new build with a Midea ASHP and underfloor heating throughout and individual thermostats in each room. I have looked at the manual and on YouTube but still rather confused as to the best way to set weather compensation. On the main panel I have found the option to select the weather compensation curves- when I click through it says ‘zone 1 high temp mode’ and ‘zone 2 low temp mode’- I have found the high and low temp curves in the manual but unsure which I should be selecting? I also came across a video on YouTube about setting for weather compensation within the serviceman settings? Thank for everyone’s kind help, Katie

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JamesPa

(@jamespa)

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03/09/2025 12:10 pm

Good summary.

Some comments: they will probably dispute that the buffer tank is too small and, even if they replaced it with a larger one, unless its controlled properly it will still mix. What you can ask them to avoid this argument is

how is the inevitable mixing (also called 'distortion') in the buffer accounted for in the design
have they checked that it works as they have designed it ie the temperature drop across the buffer is what they designed for

then await a blank stare or some BS!

Yes I would ask about the control. They probably wont understand 'controlling the buffer', perhaps the simplest way to put it is 'does the call for heat from the UFH also connect to the ASHP as a call for heat, or does the ashp charge the buffer independently? A look at the wiring or some experiments with the thermostats could ferret this out.

Posted by: @pash44pump

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(1) I believe the presence of a large container of glycol suggests that there are no antifreeze valves. I assume this is an installer decision that might be sub-optimal but something I have to live with.

Yes and yes unless they are prepared to swap it out or a/f valves.

That said this may be a design fault, the UFH was designed presumably to work with water which is both less viscous and has a higher heat capacity. If the UFH is marginal (which it seems it is) then this could be contributing to the deficit. You could ask them how they have accounted, in the design, for the fact that water has been replaced by glycol in the UFH given the increased viscosity and reduced specific heat capacity of the latter. Again await a blank stare or some BS.

Posted by: @pash44pump

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(2) Are there any leaks? Yes there is a small amount of leakage from the pipework in the following photo. What actually are those valves? How big an issue is this? I would raise this with the installer as another thing that needs resolving.

I think its just a tee'd flow meter. Very useful!

Posted by: @pash44pump

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You won't be surprised to know that the worst performance in the house are bedroom 1 and its en-suite

Do you happen to know where the pipe run is, any possibility its poorly insulated.

Posted by: @pash44pump

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Some posters have mentioned room thermostats as being negative but in a large house, how else do you control the temperature of zones that you don't want to be the same.

they are negative and should generally be set a couple of degrees above the target otherwise you may well not reach the target and the on/off switching contributes to system inefficiency.

In answer to 'how do you control', what you do is balance the loops, much like balancing radiators, so that when run 24*7 they emit the right amount of heat. There will be valves on the manifolds that allow you to do this.

I cant currently think of any other design faults but others may be able to comment and I would reserve your position until you have answers to the above, as those answers may reveal other faults.

Hope that helps

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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