@jamespa thank you. You may well be correct regarding the downstream system being the issue. I can do what you suggest but my question - is this a test that will tell us what we need to know if the external temperature is currently 16C? I know the ASHP can produce sufficiently hot water in warmer temperatures but the problem arises in cold weather. I had a dialogue with the installer earlier this year when house was below desired temperature. At that time it was -1C outside. The Midea controller was set to 55C and the inlet/outlet temperatures were 38/34 so an enormous discrepancy. At 5C they were 46/41 and at 10C later in the month they were 50/46. These are the readings from the heat pump. Obviously the temperatures at the UFH manifolds were lower than those readings. 

I'm happy to try what you suggest though if you think that will give us useful information. How do I measure the temps on the four ports of the buffer (sorry don't know what that means). By measure temps at beginning of UFH loops do you mean as shown in attached photo where I have one of these gauges for each loop (so 2 of these

and one for each room?

On a different point, if I have UFH and rads then leaving the rads on in winter means I am running my ASHP at a flow temp of 55C. Doesn't that make the COP really inefficient? The rads are all in upstairs rooms that aren't used in winter. 

Thanks in advance

Posted by: @pash44pump

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At that time it was -1C outside. The Midea controller was set to 55C and the inlet/outlet temperatures were 38/34 so an enormous discrepancy. At 5C they were 46/41 and at 10C later in the month they were 50/46. These are the readings from the heat pump. Obviously the temperatures at the UFH manifolds were lower than those readings. 

This suggests that the heat pump was not running on weather compensation (WC) at the time you recorded these values. With WC you don't set the (flow) temp, you set each end of the WC curve and then the controller reads the flow temp from the curve and sets it to that value.

"These are the readings [for the inlet/outlet temperatures] from the heat pump" - are these from the Operational Parameter page on the Controller? If so, can you confirm which values you recorded? If not from the controller, where did they come from? The difference is about right, about five degrees or a bit less depending on any cycling. More to the point, if they were spot readings, the absolute temperatures will vary as the heat pump cycles.

I agree, you need colder weather to see what is going on.   

Posted by: @pash44pump

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I am running my ASHP at a flow temp of 55C

As we keep on saying, don't do it! That is non-WC running, which you do not want to use!

@cathoderay correct. I only just switched to weather comp after reading this forum and yes the values (Jan 2025) were from the Midea controller's operational parameters page. At the time I was increasing flow temp as I didn't know any other way to try and get room temperatures up. Mrs A was understandably not happy with an en suite at 13C!

I think what I will do is try and get installer out to check everything. Then if necessary run tests when it's colder. In the meantime, do you agree that I need to have my rads on upstairs when rooms are not in use? I mentioned before that my pipework from ASHP is external and not well insulated. Does the Midea controller take its inlet/outlet temps from inside the house or from the heat pump. The question is because I'm interested how much heat I lose running 4m outside when it's cold and whether I should reinsulate and box them or bring them inside (which is probably not cost effective because I can do the former myself and not the latter).

Thanks

Posted by: @tasos

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Weather compensation is a complicated and ineffective way to control heat pumps

That is just complete nonsense.

Posted by: @tasos

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I don' t think you are going to solve this problem on your own. I suggest you call a technician from the heat pump makers to try and see what is going on. 

Thw first part of this may be true.  However I doubt the heat pump manufacturer will be able to help as this is more likely to be about the way the downstream system is set up than the heat pump itself.

Posted by: @tasos

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Furthermore you cannot have more than one target temperature, unless you have mixing valves in each separate room.

That is true, assuming temperature refers to flow temperature.

Posted by: @pash44pump

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I think what I will do is try and get installer out to check everything. Then if necessary run tests when it's colder. In the meantime, do you agree that I need to have my rads on upstairs when rooms are not in use? I mentioned before that my pipework from ASHP is external and not well insulated. Does the Midea controller take its inlet/outlet temps from inside the house or from the heat pump. The question is because I'm interested how much heat I lose running 4m outside when it's cold and whether I should reinsulate and box them or bring them inside (which is probably not cost effective because I can do the former myself and not the latter).

If it were me, I would start with everything on/open, running on weather compensation, and take it from there (once the weather is cold enough to need the heating on).

Can you describe or better still post photos of you external pipework? It may be your installer has installed a garden heater...

I'm pretty sure the Operation Parameter values shown on the wired controller come from the heat pump, if only because the data cable runs from the wired controller to the heat pump, and doesn't go anywhere else. It may or may not also report the indoor air temp at the wired controller, but as mine is in the airing cupboard, I don't take much notice of that. The outdoor air temp is not what it says it is, it is instead most likely, though not 100% certain, the air intake temperature somewhere inside the heat pump, and is subject to various influences that at various times @jamespa and I have tried to understand. Nonetheless, this outside air temp is what the wired controller used to get the WC flow (leaving water) temp - but it is not the actual outside air temp. Go figure, as the say...

The wired controller (and modbus if in use, as it is in my setup) values I use for the flow (output, leaving water) and return (input, returning water) temperatures are on screen 4 on the wired controller Operation Parameter pages (see image below, the bottom two rows,  31° out, 27° in in the image) and are in modbus registers 104 (in) and 105 (out). The two sources report the same values.

Here is an example of WC in action from my heat pump monitoring (done over modbus) from earlier this year:

As the OAT (green line) falls overnight, both the set and actual LWT (flow, outlet) temps rise, as does the RWT (return, inlet) temp, then the reverse happens when the OAT rises in the morning. The room temp stays remarkably constant at around 20° C. During the colder overnight period there is some cycling, which are in fact defrost cycles, but that is a whole new can of worms to explore come the colder weather, as are the OAT spikes related to the defrost cycles (we can be pretty sure that is not what the 'real' OAT did...).  

My experience with installers is that they often have a poor understanding of weather compensation. And even if understanding wc often prefer to guide you to a higher than necessary flow temp (fixed or wc) simply as it is a simpler fix than explaining and setting WC properly.

We have had a heat pump in old building for 5 years.

First 2 years used 8000kwh on fixed temps.

Next 2 years used 5800kwh on weather compensation and actually warmer (with 24x7 operation)

I set up weather compensation myself (after 2 years) with helpful input from this forum and a user group on Facebook

I'm sure there are some great installers out there these days that CAN give great advice & help on weather compensation. Just don't assume it! 

Posted by: @jamespa

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Posted by: @jamespa

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Posted by: @tasos

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Weather compensation is a complicated and ineffective way to control heat pumps

 

 

That is just complete nonsense.

Which part of the sentence do you consider complete nonsense: "complicated" or "ineffective" ?

@tim441 That's very interesting. Thank you

Posted by: @tasos

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Posted by: @jamespa

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Posted by: @jamespa

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Posted by: @tasos

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Weather compensation is a complicated and ineffective way to control heat pumps

 

 

That is just complete nonsense.

Which part of the sentence do you consider complete nonsense: "complicated" or "ineffective" ?

Both actually, but ineffective in particular.

There is nothing complicated about WC if you choose to understand it, which isn't difficult. What I will grant is that it can be a little tiresome to set up.  Not difficult, just takes a bit of time.

Incidentally I think op may well be able to fix it himself if he is prepared to provide some info, follow the sensible suggestions and ignore the silly ones, and be patient and methodical.  He is clearly intelligent enough to understand it if explained (unlike quite a few installers, sadly) and none of it is rocket science.  It depends mostly IMHO on whether he has the will and determinatio..

@cathoderay the in/out temps I posted were from the same screen you showed. I only first got into these kind of screens this year after being fobbed off again by the installer. External pipework photos attached. Total run is about 4.5m

Posted by: @pash44pump

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@jamespa thank you. You may well be correct regarding the downstream system being the issue. I can do what you suggest but my question - is this a test that will tell us what we need to know if the external temperature is currently 16C?

The simple answer is probably not, it needs to be colder.

I will read your post and subsequent ones by @cathoderay and others, and then decide whether I can add any more until the conditions are right for experiments.  

@jamespa 😎