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? 

An eyeball on the wiring or some experiments with the thermostats could ferret this out and Im not sure I would trust what an installer says anyway without checking it myself!

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 in fact 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 likely 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  You could ask them how they have accounted, in the design, for the fact that water has been replaced by glycol in the UFH given the increased viscosity and reduced specific heat capacity of the latter.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!  Small leak not a big issue but best to fix it.

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 because in at least some circumstances it will switch off before the fabric has heated properly.  Furthermore and the on/off switching contributes to system inefficiency and risks crippling defrosts if there is insufficient system volume in loop when defrost takes place (that said the buffer tank should deal with this)

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.  In fact poor balancing may well be part of the problem.  How many water pumps are there in the system?

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

@jamespa thanks so much. Very useful

@pash44pump - @jamespa has already come up with some useful comments. At this stage all I would add is:

(a) yes, the analogue flow meter is very useful. It is reading about 17L/min in the photo (reading it the way i read them). The two tee valves: one can used for filling/topping up the system (at least that's what my installer did/does, can't remember which one of the two it is). Fixing the leaks may not be that simple a job as the system is full of fluid but worth attempting.

(b) the floor plans: were they in the scope document? It opened rather oddly here (Libre Office), with some blank pages. If so, there's the beginnings of a heat loss survey there (floor areas and maybe some window information) but it is certainly not the Full Monty.

Let's see what the installers come back with over the full heat loss calculation question.  

@cathoderay floor plans were in the scope document that I posted 👍

@pash44pump Since you will inevitably have to deal with controlling the pump, here is my advice.

Heat pumps produce hot water at a set temperature, which circulates around the house. The temperature of the water in the various parts of the house, varies, but comes from the one and only heat pump. So, if you want to properly heat your "coldest" room, you should control your heat pump, according to the temperature of that room, i.e the water temperature leaving the pump should be high enough for your "coldest" room.

So, how can you achieve this ?

The Midea pump is controlled by its wired controller, which houses the weather compensation curve (which is straight line, but ignore this) and its internal thermostat. These two should be operated in unison. The weather curve should tell the pump the outlet water temperature corresponding to a set of outside air temperatures. So at below zero outside temperatures, I should indicate maximum power (i.e. 60-65 C in your case). The internal thermostat should be at the required room temperature in the "coldest" room, say 21 C. This implies that you should position the wired controller in the "coldest" room.

In order for the above setup to work, you have to enable two settings:

1."Room thermostat" setting should be set to NO. This disables any existing thermostats from the previous installation, other than the internal one.

2. In "Temp. type setting", Room temp. setting should be Yes. This will enable the "coldest" room temperature sensor to stop the pump, in case the water is too hot for the instant climate conditions.

I hope I have not confused you more than needed.

Posted by: @tasos

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The Midea pump is controlled by its wired controller, which houses the weather compensation curve (which is straight line, but ignore this) and its internal thermostat. These two should be operated in unison. The weather curve should tell the pump the outlet water temperature corresponding to a set of outside air temperatures. So at below zero outside temperatures, I should indicate maximum power (i.e. 60-65 C in your case). The internal thermostat should be at the required room temperature in the "coldest" room, say 21 C. This implies that you should position the wired controller in the "coldest" room.

This simply isn't true. Midea heat pumps of the type we are talking about are controlled in one of two ways:

(a) using weather compensation (WC): the flow (leaving water) temp is set from the outside air temp (sensor is in the outside heat pump) using the WC curve (which I agree is a straight line, curve being used here as a generic term for a line on a graph). The internal (to the wired controller) thermostat is not used, nor any external room temp thermostats (beyond setting them high eg 30 degrees, ie always on and always calling for heat). The only exceptions are 'set-backs' and 'set-forwards' which we are not talking about here, and crude on/off switching ie turning the heat pump off for the summer by setting an external room stat low eg 10 degrees. In normal day to day running, all the control comes from the WC curve, which only uses the outside air temp.    

(b) using a fixed flow temp ie there is no weather compensation, in which case some sort of indoor thermostat is used, be it the one in the wired controller if it is in a sensible place (not always the case) or an external one. This mode of running is the same mode as normally used with fossil fuel boilers in the UK, and while it can be done, it is not the best way to run a heat pump.

@pash44pump a few observations which may or may not be of use, to add to the excellent and more technical advice from others.

You mentioned in your initial post that you turn the rads off upstairs as the rooms are seldom used. I know others have mentioned turning them on/turning up TRVs as one of the initial suggested steps. If you keep upstairs cold it will just draw the heat from downstairs. Zoning (for any heating in a domestic property arguably- not just heat pumps) isn't really effective and causes more problems than it solves. In our experience it doesn't even save any money. Your best bet with your general approach I would suggest is to try and get the envelope of the house i.e. the entire house, at the same, consistent indoor temperature including upstairs, even if you don't use it.

The same applies to setbacks as well. 14oC I would say is quite a significant set back and to then try and get the house back up to comfortable temperatures in the coldest weather is always going to be difficult. Again we just leave ours on.

Lastly I feel your pain with the Midea control panel and trying to get the readings you need from this to diagnose the problems. Part of the issue I think is that you have nothing currently that allows you to plot these parameters over time and indeed retrieve this data at your leisure, so outlet/inlet temperatures, IAT, flow rates etc. This might be a good initial step to consider as well, and there are relatively cheap and easy solutions out there to do this. 

@benson thank you. I am beginning to see that now and will be changing my approach thanks to what I have recently learned.

@cathoderay and others. The response from my installers regarding the question "Please send me the Formal Heat Loss calculation". 

They write - I am sorry but not sure what document you actually mean? My understanding is that the heat loss calculation per room is on page 5 and 6 of what I sent you.  That is the summary of the heat loss of each room. The details of each room are put in to a programme called Evergreen and that document is what is produced.

That's all

@pash44pump 

@benson is pretty much spot on.

We have been brainwashed by the controls industry into thinking that microzoning both in time and space is a good thing.  Mostly it isn't, particularly with heat pumps but also with boilers.  It is unlikely to save much money if any (and may well cost more) and any zoning reduced comfort levels.  

The key thing to bear in mind is that houses continue to lose heat when the heating is off, at more or less the same rate unless the temperature drops dramatically.  This has to be made up and making it up is less efficient, which may wipe out any saving or worse.  The exception is a very lossy house where micro zoning in time, space or both may make sense.  Yours is pretty much the opposite end of the spectrum so it almost certainly doesnt.

Posted by: @pash44pump

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I am sorry but not sure what document you actually mean? My understanding is that the heat loss calculation per room is on page 5 and 6 of what I sent you.  That is the summary of the heat loss of each room. The details of each room are put in to a programme called Evergreen and that document is what is produced.

No surprise TBH.  Most will use a program to do the calculations.  What they should be able to produce is the data they put in.  Whether they can or will is another matter.  All the other questions remain valid but dont hold your breath for answers.  Self help is often best help for this sort of thing, sadly.  They should definitely fix the insulation however.

Posted by: @pash44pump

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They write - I am sorry but not sure what document you actually mean? My understanding is that the heat loss calculation per room is on page 5 and 6 of what I sent you.  That is the summary of the heat loss of each room. The details of each room are put in to a programme called Evergreen and that document is what is produced.

Oh dear. Evergreen appears to be a quick shot spanner plumber to heat pump planner toolkit from an outfit called EasyMCS. That rather sets the tone. I'm not even sure they know what a full formal survey based heat loss calculation is, given their reply. This raises he possibility that their heat loss assumptions are somewhat, possibly even completely, out of whack. That might explain rather a lot.

You do have their heat loss tables. I have not been able to find out how the EasyMCS Evergreen calculator determines heat loss. It might be worth doing a formal heat loss for one or two rooms, and seeing how those results compare to the Evergreen results. Maybe start with the living room, as the largest room, and then the kitchen. You already have some of the measurements required. The Freedom calculator is still available eg here.

@cathoderay nice one. That's what I was doing when I saw your message. Will revert