Posted by: @pash44pump

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From experience what is the rate of flow change per turn of the lockshield valve as I've never done this before?

@jamespa is right, typically they are far from linear, with most of the change in flow rate happening near total closure. Do be careful not to over-close them, though, as I mentioned before this can unwittingly throttle the system. Once you have found what you think is the right position (by trial and error), make a mark to identify the position, then fully close and then open again to the marked position, to confirm that it isn't all but closed. If it is, then start the process again (yes, it can be tedious! But worth it).

Posted by: @pash44pump

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On a different note, @cathoderay I read somewhere that you had advised someone on how to schedule DHW on the Midea. If I do that I think you said that the DHW will not run at any other time other than that programmed and will only run to schedule if the DHW temp is 10C below what is set. Is that correct? Can the 10C tolerance be adjusted somewhere? I think last night there was no DHW cycle but then this morning I see DHW at 40C which is 2 degrees below my 52-10 setting so I have to adjust manually which is not what I want to be doing every day. Any advice?

Yes, you can put the DHW heating on a timer, and reading between the lines you have already done that, if not it is done via the Schedule > Timer menu and for once is reasonably intuitive: tick checkbox, set start and end time and set mode got DHW. Using my setup (timed to 1300-1400 daily to use what may be the warmer part of the day, DHW set temp 50°, drop to trigger reheat 10°) as an example, what this means is:

(1) left untouched, my DHW heating will only come on at 1300 when the tank is at less than 40°. In practice, it turns out it doesn't always happen at 39°, sometimes it needs to be a bit lower. When it does come on, the heat pump works flat out, LWT approaches 60°, and the reheat to 50° typically takes 30-40 minutes, during which time the space heating is off. If the tank is already above 40°, nothing happens.

(2) yes, you can adjust the drop from set temp to trigger a reheat value, via For Serviceman >  DHW Mode Setting > Item 1. 6: dT5_ON. The default is 5°, mine is set to 10°. Don't forget that going into and out of the For Serviceman menu will usually turn any current heating off, just turn it on again on the Home page.

(3) if you want to trigger a reheat outside the timed period, you can do thins manually by turning on the DHW heating on the Home page. To trigger the DHW heating when you do this, the DHW tank actual temp must be below whatever the trigger temp is - it won't just go into DHW heating regardless. If you want a reheat when this condition isn't met, then the easiest way I have found to trigger a reheat is to increase the DHW set temp on the Home page. For example, if my DHW is currently 41°, I set the set DHW temp to 55° and because 55-41 > 10, the DHW heating comes on when I manually turn the DHW on. I then wait until the DHW reaches the temp I want, and then, on the Home page, turn off the DHW heating manually, and then finally set the DHW set temp back to 50°.

To avoid having to do manual adjustments all the time, try to find a combination of set DHW temp and drop to trigger reheat value that works most of the time for you. There will always be exceptions, but most of the time the system will look after itself.      

@cathoderay thanks for that. I have set up daily schedule for 13.00-14.00 when I usually have PV power and OAT is higher on average. My controller shows the 7 day timer schedule as a calendar icon. The DHW though is showing off - I'm assuming that it stays off and only comes on at scheduled times (which is why I'd have to do a manual boost if needed outside scheduled hours). Have I understood all this correctly?

Thanks

Posted by: @pash44pump

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I have set up daily schedule for 13.00-14.00 when I usually have PV power and OAT is higher on average. My controller shows the 7 day timer schedule as a calendar icon. The DHW though is showing off - I'm assuming that it stays off and only comes on at scheduled times (which is why I'd have to do a manual boost if needed outside scheduled hours). Have I understood all this correctly?

Mostly, I think, but with some caveats. 

I set the TIMER option (left most tab) on the Schedule Menu, not the WEEKLY SCHEDULE, just checking you have done the same?

In the image of the wired controller, the space heating is on (sun symbol in centre panel with ON, plus squiggles above rad symbol on the left, circulating pump is on (bottom of mid panel) but compressor has yet to start, when it does the petrol pump (hullo???) symbol will appear in the bottom of the left panel. This appearance is what I would expect to see a minute or so after turning the space heating on, either from 'all off', or switching from DHW heating to space heating, or alternatively during a cycle, ie the actual LWT is either at or a bit above the set LWT, so compressor is off. That may be the most likely explanation, given the OAT of 18°.

However, I also note the time shows 1330 today but your DHW tank temp (right hand number) is 42° ie there hasn't been a DHW reheat at the time the photo was taken (unless maybe you have just had a bath!). I think this is because although 52-10 = 42, ie you should get a DHW reheat, as I mentioned before, the Midea controller makes up its own mind on the borderline, and today it decided it wasn't going to do one. The other possibility is you set the timer during the 1300-1400 period, and I've noticed when I do that, it does not have immediate effect, it only kicks in the following day, at 1300.

If you need to do a manual DHW reheat, I suggest do it as I said before, temporarily increase the DHW set (target) temp, manual turn on etc.

You may also find you can drop your normal set DHW temp a bit, 52° is on the hot (scalding) side plus of course needs a bit more energy to get there, plus even modern DHW tanks are not that well insulated, they still lose heat, albeit usually to the inside of the house. I have mine set to 50°, others I know have theirs set to the high 40s.           

@pash44pump Referring to the problem of rooms with different heating demands, I would use a recently available option which is thermostatic valves with remote thermostat control. Such a device is  Sonoff TRV ( https://help.sonoff.tech/docs/trvzb). These devices regulate flow in a radiator, based on a thermostat located in some appropriate spot (this of course in addition to the embedded thermostat). Many other useful options are also possible, such as for example open window detection. Their app eWeLink can of course control any of their other smart devices. 

The advantage of this approach is that you don't have to experiment with finding the correct position of classical TRVs. 

@cathoderay and others. Latest update

Heat Loss Survey Weds afternoon. Will be interesting if nothing else, to see what assumptions are made and compare end result to my calculations. Engineer Thursday to redo the insulation. Will also ask lots of questions raised here to test his knowledge of all things system design.

I am now recording OAT and IAT with data loggers. System running fully open and room temperatures now good with WC tweaked down to 27C at 15C OAT. So far so good.

I have though been reading back through the forum now that I understand things better. One thing that strikes me is that the scope document states that the system should provide a COP of 4.01 at 45C flow temp with OAT at -1C. If I compare that to the Midea output table that @cathoderay supplied, that shows that at 45C flow temp and OAT of 0C the norm output shows at 9428 at a COP of 3.0. Where the hell does a COP of 4.01 come from and should they be held to that?

I do now think that my main bedroom en suite struggles to get to desired temperature because it is very weather-exposed, a long way from the heat pump and has a small UFH footprint. I don't want to run the whole house at a higher LWT just to get the en-suite up to temperature (especially as it really only needs to be hotter than the bedroom when we get up and go to bed). What do you think the most cost-effective additional heat source would be? Additional electric UFH (thinking no as what we need is a short blast), ceramic wall heater, fan heater? Any advice appreciated

@pash44pump We have a dual fuel towel rail and this augments the K2 radiator in the bathroom; we are possibly not a typical case though as we like our abluteing department to be at ~25 degrees C, this works for us. The electrical supply to the towel rail is switched on for 3 hours in the evening via our Eddi diverter and this works well for the summer and shoulder months. During the winter, I close the valve during those 3 hours and allow the ASHP to heat the rail the other 21 hours each day. I have wondered whether I should have a motorised valve for this purpose but have not explored the practicalities yet (3 years nearly now)  Regards, Toodles.

Posted by: @pash44pump

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One thing that strikes me is that the scope document states that the system should provide a COP of 4.01 at 45C flow temp with OAT at -1C. If I compare that to the Midea output table that @cathoderay supplied, that shows that at 45C flow temp and OAT of 0C the norm output shows at 9428 at a COP of 3.0. Where the hell does a COP of 4.01 come from and should they be held to that?

Do they mean scop?  SCOP of 4 at 45 is reasonable.

Posted by: @pash44pump

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-effective additional heat source would be? Additional electric UFH (thinking no as what we need is a short blast), ceramic wall heater, fan heater? Any advice appreciated

If you just need a short blast then something that heats the air quickly, eg a fan heater.  Keep the ufh on so background heat present.  It's also cheap to try.  Wall mounted fan heaters for bathrooms certainly used to exist.

@pash44pump - I think the COP of 4.01 comes from the 'scope' document, and if so it is a SCOP:

which they say comes from the 'MCS HP SCoP Table below' which looks more like part of their EasyMCS software output, though it may get its data from MCS. In any event, I suspect it is rather optimistic, to get a SCOP of 4.01 means having periods of very high COP values during milder weather, to offset the lower values when the OAT is colder.

The cooler than you would like en-suite - and I don't like cold bathrooms either! - could you add a radiator, fed from the radiator pipe work above?    

@cathoderay I also note in that spec. that the DHW COP is well below 2; is it me or is this particularly low? I note that Adam Heat Geek often claims performances in excess of 3.5 or even higher - are they measuring the same requirements I wonder? Curious, Toodles.

Posted by: @toodles

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I also note in that spec. that the DHW COP is well below 2; is it me or is this particularly low?

I noticed that too and thought the same thing, but then thought the DHW is only a small part of the overall energy use. The note alongside it suggests that it comes from the default value from SAP2012, which may be a clue (it is a default generic value). Typically my calculated energy out/energy in DHW COP values for my system are between 3 and 4 for the period in which the heating was running in DHW heating mode, occasionally a bit higher or a bit lower.

@cathoderay and everyone else. Latest Update

Installer came out and redid the insulation on the external pipework - not a bad job but not as good as I really wanted. They did use the right insulation, put the Munsun rings outside the pipes etc but still used cable ties and there were some gaps because not all the joints were sealed. I improved things by taping the joints and then I did a little woodwork project - boxed all the pipes in and lagged the pipes with mineral wool. Finished it yesterday.

As you know, there was also a new Heat Loss Estimate at their expense as my calcs (thanks to the Freedom Heat Pumps model that @cathoderay shared, came out with 12.9kW). Today, I got a call from the installer as I chased the new HLE up and lo and behold. The new HLE shows a requirement of 14kW and I have a 12kW Midea. Apology issued - I do believe them when they tell me this hasn't happened before but they have agreed to redo everything from scratch with probably a 17kW Grant ASHP or 2x10kW ASHPs. 

They are visiting next week to start the redesign phase. Thanks to all for your immense help - I would not have got to this position without you - albeit 4 years after the initial installation.

So now the question has changed completely. What should my new system look like? Obviously, bigger ASHP, no buffer tank just a system volumiser, pipework inside rather than outside (I've never liked it outside), different location for the ASHP? I really want to make sure the revamp is 100% right. Anyone have "what an ideal ASHP system should look like"?

Another point, I'm thinking that if I've been running an underpowered ASHP for 4 winters, I have probably used way more power than I should have as my COP has probably been well below what it should have been. Any reasonable way I can quantify that? Also not sure what happens regarding my grant as the RHI always ask whether the system has been changed.

Feeling relieved that they have at least seen the light!

Regards

Posted by: @pash44pump

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Also not sure what happens regarding my grant as the RHI always ask whether the system has been changed.

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If I were in your situation I would personally be straight with them and get in touch. Given the changes are being made by the original installer, because of longer term experience of living with the heat pump (think of it like a warranty claim), is not offering additional or changed functionality and is, in fact, increasing the efficiency (i.e. RHI's aim), I would like to hope they'd be entirely supportive.