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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10/09/2025 10:36 am

@cathoderay the dataloggers have been purchased and are on their way. The plan as per your instructions, is to leave one outside for OAT and one inside for the IAT. My wired controller is in a cupboard with the buffer tank and primary pipework but I've just put a thermostat in there with the door open to see if the temperature is in line with other parts of the house. If it is then I guess I can put the second datalogger there to measure IAT. The only thing that doesn't help with is the coldest rooms in the house which are at the other end of the house so I guess for now, I will have to just check the thermostat at that end during the experiment.

On a different note, I had the chance to talk to an ASHP engineer today as he was here to check my recent PV installation. I showed him my set-up and he suggested that my winter problem could be that the buffer tank could be receiving hot water from the ASHP at say 20 litres per minute and the flow rate out and back in to the buffer tank could be say 25 litres or more meaning that 5 litres of water that's cooled through the UFH and rads system is mixing with the ASHP water thus cooling it down and forcing the ASHP to work harder.

He suggested that once I've run the winter tests and if I have a problem, they could bypass the buffer tank and use it as a system volumiser with 2 separate zones for the UFH and the radiators. We then use the pump within the ASHP which is much bigger than any internal water pumps we might have. Sounds interesting and I think he knows what he's talking about. He was going to check with Freedom whether Midea controllers can do 2 zones - @cathoderay you may already know the answer to that question. At least that sounds like a better solution than to wire the buffer tank immersion into the system and give me a massive kettle to overcome the problem at high cost.

Another issue (you guys have started me off on a path of obsession) is that during the summer, the heating part of the ASHP is dormant. Not an issue I assume. In the winter, the ASHP will start up using WC and I will use that to control IAT with an open system. Here I am assuming that I just set the room thermostats to a high temperature to keep the system running at whatever flow temp the ASHP decides is right. Now what happens if (as is probable in a house that is long, thin and not compact) if some rooms reach the temperature I want and others are too hot? How do I tweak parts of the house where let's say the IAT is 3C more than I want?

Finally (for now) I have been reading the posts on setback. I took from those that setback probably isn't compelling given the extra work required to bring the house back to desired temperature (although I'm confused about how you do that when running WC anyway). We are often away for anything up to 2 months in the winter, a different kind of setback. It would make sense to set a different WC curve so that the ASHP flow temp is lower when we are away and the IAT is let's say 5 degrees lower than normal. But how do I get the house back to desired, normal IAT for when we get back? Can you program WC differently for different periods? I imagine not. In those scenarios, what I do is use the room thermostats that can be programmed to desired "away" IAT and to come back on say 1 week before returning at normal IAT. I know my energy use is way lower when I do that as I have daily KWh stats for the last 18 months and I can compare winter away and home months when the KWh usage is about 20-30KWh lower for away periods (adjusted for the fact that I am using no DHW, washing machine, oven etc). Is this the best solution or is there something else that would be optimal?

Many thanks

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