Posted by: @pash44pump

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plus the compressor pic appearing on the heat pump controller

That is a fairly good indication it is running! As a further check, when the compressor appears to be operating, go to Menu > Operation Parameter and scroll down through the screens. Screens 3 and 6 will give you more useful info. Note that on screen 3 'Power Consum' is lifetime energy in (used) in (k)kWh, the one above (Heat Pump Capacity) is the current power out (in kW). Screen 6 has compressor info, current (draw) and frequency, both will be zero when it is off and non-zero when it is on.

Posted by: @pash44pump

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What do you mean by primary pipework?

The pipes that run from the heat pump into your property. If you know where they end up inside the property, that is the best place to determine whether they get warm or not.

Posted by: @pash44pump

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I don't have design details so I don't know if heat loss and emitters match but I think I can get these from the installer.

This should have happened at design/quote stage, bit of a red flag if that didn't happen. Get what you can from the installer now. Forget the EPC, it's a comedy exercise at best, a damn nuisance at worst. Mine had errors as well.

Initially I thought you had weather compensation on (where you say "turn it on, leave it on" which is how you run weather compensation, plus this thread is about weather compensation) but it ("turn it on, leave it on") could also apply I think to fixed flow temp running, ie no weather compensation (which is simply adjusting the flow temp based on the outside air temp, higher flow temp when it is colder outside and vice versa). Do you know what your system is using? 

@pash44pump 

I'm going to leave this mostly to @cathoderay as he has a midea and I don't.  However...

Just a guess but one quite likely reason for the nighttime firing up is that it's cold outside so the WC curve instructs the heat pump to fire (we don't yet know how it's set up by your installer so it may instruct it to fire even if the outdoor temperature is quite high).  It depends on how the thermostats (which ideally you shouldn't have, or if you do should be set a couple of degrees above the desired temperature) are set up and what they are set to, as well as whether the heat pump has been configured to take any notice of them.  Fwiw my heat pump, which works very well, would be firing up now at night if I hadn't told it to stop heating altogether (just as I did with my boiler in summer!).

Alternatively many heat pumps and boilers fire up their water pump daily to stop it seizing, although this wouldn't account for 1.5kWh.

Do either of these make any sense in relation to what you observe?  If not please can you tell us a bit more about the 'call for heat'.  How do you know that there is none?

Can I also suggest you read this introduction to help a bit with the terminology and how heat pumps differ from boilers in the best way to operate them.

@pash44pump - @jamespa has anticipated my next steps but before looking into those details (including the effect of 'turning off' upstairs) (a) we need the heat loss etc calcs and (b) we need to see what the wired controller displays when the heat pump is doing one of its rogue runs. Posting a photo of the wired controller main display (home screen) during one of these rogue runs would be very helpful. The weather compensation settings are behind a password protected screen (screen 'For Serviceman' password '234') but you need to understand how weather compensation works to make sense of and if necessary adjust those settings. The introduction @jamespa linked to above covers the basics.     

@cathoderay I have weather comp running thanks to the excellent explanations on this thread!

Prior to that it wasn't using weather compensation even though the installers told me it was at the last service.

I have been sent the calcs now by the installers and these are attached. I will have to wait for a rogue run again to look at what's happening on the controller.

Regarding JamesPA's points - nightime firing due to cold outside can be discounted as this was happening when we had 20C plus night temperatures earlier in the month. I have thermostats in multiple zones - probably too many on reflection and my understanding is that a call for heat is if any thermostat is below set temperature. At the moment they are all set low enough to effectively be off (15C) when house is 20C+ everywhere at the moment. Also if I look at my wiring board for the actuators, any calling for heat would turn on a red light and I haven't seen one on for quite some months. 

Re water pump daily firing, how long would you expect that to run for? 

Thanks for responses so far - appreciated.

Posted by: @pash44pump

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Regarding JamesPA's points - nightime firing due to cold outside can be discounted as this was happening when we had 20C plus night temperatures earlier in the month.

I don't think you can discount on this basis alone, it would depend on the WC curve settings and the system design

For example if you have a secondary pump and buffer tank (do you?) the call for heat will likely turn this secondary pump on and off, while the heat pump does it's own thing (and thus will come on whether or not there is a call for heat from the thermostats if the WC curve instructs it to do so, until the buffer tank is warmed up)

Posted by: @pash44pump

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. I will have to wait for a rogue run again to look at what's happening on the controller.

Sensible, perhaps also note other conditions, how long it lasts etc.

Posted by: @pash44pump

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Re water pump daily firing, how long would you expect that to run for? 

A few minutes at 50Wmax hence why it wouldn't account for 1.5kWh.

The oversize factor of 3.1 indirectly tells us design room to rad deltaT namely 21C implying an ft of around 44.5 for a room temp of 21 and a flow return deltaT of 5.

Is there a buffer tank or something else between heat pump and emitters?  Is the ufh running at same temp as rads or is there a mixing valve?

Posted by: @pash44pump

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I have been sent the calcs now by the installers and these are attached.

They look decidedly skimpy to me. A proper heat loss estimation (which is all they are - see many posts passim) uses a survey of all surface areas and materials, and sums the loss for each at the design outside air temperature, and then adjusts for other factors like air changes (ventilation). Your installer appears to have used only room area in metres squared x watts/metre squared (with no indication of where those numbers came from), while the emitter list only has two emitters!

Your property seems to be on the large side (6 bedrooms) which may be one factor affecting total heat loss but other factors like construction and insulation also play a large part. Can you give us a bit more detail about the property, and rough location (because that affects the design outside air temp)?

@cathoderay thanks. House is large (3700+ sq ft) and is a converted barn made of solid brick with internal insulation, which assuming it met building regs and based on photos of the build project (before us) was 100mm of Kingspan between battens. I'm convinced that they ran out though because one end has definitely only got 50mm of Celotex having had a camera look behind the plastered wall (this is the end where the coldest rooms are in winter). Roof has also got only 50mm of Celotex above ceilings - all upstairs rooms are converted to living space (done by first owner not us) so there is no loft void to lag. Lounge is double height so a very large space to heat (but we do have a wood burner to supplement the UFH there). Heating is via wet UFH. 2 sets of UFH manifolds. One set very close to heat pump and another set at other end. 3 rooms upstairs have rads but as mentioned before rarely used rooms and rads not usually on in the winter.

Total length of property is close to 40m so there is a lot of distance to pump through. Property is in Wiltshire.

Not surprisingly, the end of the house nearest the heat pump stays warmer than the far end. Having tested the far end for heat loss in cold weather, it performs significantly worse than the rest of the house and I'm fairly sure that this is a combination of distance and less appropriate insulation at that end.

I know the scope calcs for the heat pump used 45C flow temp at -1C. That doesn't cut the mustard at that flow temperature setting (but now I have weather comp on)

Regards

@pash44pump - the installers heat loss calculations appear to indicate a total heat loss of just under 9kW, which seems rather on the low side for the property you describe. I have a smallish old leaky 3 bedroom property, and my pre-installation heat loss (done using areas and U values) was just over 12kW, while my actual measured heat loss is if I recall correctly around 9kW (see many posts passim for discussions on the discrepancy). That said, your heat pump is set to 16kW, meaning it will probably put out something like 13-14kW in cold weather (see the Midea Engineering data manual for the actual outputs), so you do have something in reserve.

Before I forget - the fact the installers left the system running on fixed flow temp rather than weather compensation is another red flag.

For now, you need a better estimate of room by room (and total) heat loss. Assuming you have basic spreadsheet skills, you can do this yourself, a tedious and boring but necessary exercise (use one of the many downloadable spreadsheets*). You can also, if you have detailed enough records, do an empirical (measured) heat loss estimate, based on how much fuel/energy you used in the past, again see many posts passim on this.            

* Edit: thread with some useful links available here.

Posted by: @pash44pump

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I know the scope calcs for the heat pump used 45C flow temp at -1C. That doesn't cut the mustard at thats flow temperature setting (but now I have weather comp on)

Something isn't right here, you don't design ufh to work above 45C, you would burn your feet.  Normally it's designed for 35C or thereabouts.  This may not be a heat pump problem!

Who specified the ufh?  Did they take into account the actual insulation, or what was supposed to go in?  Are long feeds insulated or not?

We really need a plumbing system and control diagrams or at least a description to make sense of this but if you don't have one then:

• Buffer or no buffer (or anything else between heat pump and emitters)
• Mixing down for the ufh or not?
• How was the ufh designed, against what loss specI
• I assume it's run 24*7
• When it's 'not cutting it' are the radiators switched on or off?

are probably the most important starting questions.  I agree with @cathoderay you may well need another loss calculation but that's a fair amount of work and we may be able to home in if we know more about the system.

Ps in case posts crossed I answered above re the switching on during summer, there are some more questions to answer before we can rule out the most likely cause.

@jamespa thanks

Surely the 45C number is just the water temperature that the ASHP is being asked to produce initially. The UFH wouldn't be at 45C unless you had a loss-less system. The UFH was here when we bought the house. No information available to us.

Buffer yes. Mixing down. I think yes. UFH spec - no idea. 24/7 yes. When not cutting it - all rads off

I think it is an ASHP issue. Before installation we were on oil and never had an issue with room temperatures

Regards

Posted by: @pash44pump

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I think it is an ASHP issue. Before installation we were on oil and never had an issue with room temperatures

I think this is very unlikely indeed.  If the water is being mixed down for the ufh then it starts off hot enough when it leaves the ashp (and 45C is certainly hot enough assuming that the ufh is correctly designed) and there is no way the temperature should be falling by 10C between ashp and emitter due to loss (and if it is it would be heating the house, albeit perhaps in the wrong place).  

Although I think this is very unlikely indeed that the fault lies with the ashp, it is likely kely that it is linked to the fact that the heat sourced was changed to an ashp, and that needed some downstream adjustments/adjustments in how the heating system is operated, which may or may not have been made.

It maybe to do with the adjustment of the mixing valves or the way you are operating it which may not have been adapted for the lower temperature produced by the ashp, or it may be the way the buffer is set up (buffers are generally bad news) or a pump issue, but it's unlikely to be to do with the ashp itself.  Also turning the rads off upstairs isn't helping, you may not be using the space but it's still losing heat which has to be made up by the ufh which therefore has to work harder.  Turning up the flow temp from the ashp is unlikely to be the solution, getting the commissioning of the downstream system right is most likely what needs fixing.

From what you say the installer of your ashp may not have adjusted the downstream system to suit when he installed it.

My suggestion (ie what I would do if this were my house), in the absence both of a system diagram and load calculation and if the installer won't come back to finish the job, is a reset and some measurements to find out what the system is capable of of you remove all the external constraints that can be easily removed;

1 Turn all mixing valves up to max

2 Turn all thermostats up to max

3 Turn rads on

4 Operate 24*7

5 Measure the temperatures on the four ports of the buffer.

6 If you can, measure the temperatures at the beginning of the ufh loops

I would do these sequentially leaving a day between changes.  4, 3, 2 altogether first.  Then 1.  If you can do 5 and or 6 at each stage that would be good.

The first four may well fix it (with some further minor tweaking), the last two will tell us more if the first four don't fix it and give some diagnostic info to improve efficiency (if that's a concern).

I should stress that this is NOT the ideal way to go about things, ideally we would have a lot more info about the system and take several temperature measurements in addition to the above, but based on what you have said so far that seems unlikely without a site visit.  What it is is an educated guess of things which are easy to do, reversible and might either contribute towards fixing the problem or to our understanding of the problem.

One possible alternative is to try running at a fixed temp of say 55 (or with a WC curve that sets ft to 55+ at -1) or whatever the max your system will do.  This comes close to simulating what the downstream system would have seen from the oil boiler and so again may tell us something.  It's not the same, because of the buffer (I'm guessing this was added with the ashp but please confirm).  Also it's very inefficient so not recommended long term but again might tell you something.  Personally I would take this route further down the path not now, but you may think differently.

Ps.  Given you have a buffer it's quite likely that my explanation of what you observe in summer is in fact correct, see above for details.  Without a control diagram it's impossible to be certain but it's definitely very likely indeed.

Weather compensation is a complicated and ineffective way to control heat pumps. Your house was OK when you were on oil, because oil heater control depends on internal thermostat. 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. 

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