Posted by: @cathoderay

I too have recently (beginning of this February) had a Midea ASHP installed (14kW), in my case in an old leaky building (yes, I know) in Sussex but not on the coast. Most of the rads have been upgraded to K3s. I'm interested in the weather compensation settings too, but for an additional reason beyond economy, getting the maximum number of kWs out of the unit.

My installer (who has been very helpful throughout) said he doesn't have much experience of different weather compensation settings beyond Freedom's 55@-2/37@15 setting. I tried contacting Freedom's tech dept and they have been rather unhelpful, to say the least.

The reason I want to get the maximum number of kWs out is that the 14kW unit is marginal for the building's heat loss. Elsewhere I came across Midea's technical and engineering data, and have plotted out the unit output at different flow temps (LWTs) and external ambient temps. The chart looks like this:

As others have pointed out, it turns out that a nominal 14kW unit is far from a 14kW unit except when it is operating in ideal and warm ambient temp environments, when of course you don't need the maximum output!

My idea is that if I set the max LWT to maybe 45 degrees at -2 degrees (instead of 55 degrees) and leave the lower LWT at 37 degrees at 15 degrees, then the heat pump will output 12kW (or more) until it gets very cold outside. With a max LWT of 55 at -2, the output drops to nearer 11kW (pale blue line, 55 on the x-axis), which is below the buildings heat loss of just over 12kW at -2 degrees outside.

My questions are:

(1) does my proposed way of eeking the maximum output from the unit make theoretical sense (I'm guessing it works something like this: at high flow temps, a bit more power does in, but COP falls sharply, so we get something like (simple made up example) 55 degree flow, 5kW in, COP 2, 10kW out cf 45 degree flow 4kW in, COP 3, 12kW out) and, if the theory is correct, is it likely to work in practice (unlike the economy side of tuning the weather comp settings). I can of course try the settings and see what happens, but with constantly changing ambient conditions it is hard to be sure what actually happens without very close monitoring, and I don't have the kit to do that. 

(2) if it works theoretically and practically, how - this is really just curiosity - does the unit deliver more kWs to the building at lower flow temps? Perhaps a faster flow rate (l/m) in the primary ASHP to house circuit?    

Very happy to start a new thread for this, but it also seems to fit here in this currently active thread, so have posted here for now. 

cathodeRay

gutted to hear the tech guys at freedom have been rubbish, im a shareholder at freedom. I used to run the tech department but ive been gone a year now.  setting the weather comp up is really simple, there is a video here its me in the video.

i chose your settings when i wrote the book. its a simple logic, if they set the weather comp upnice and warm you dont call about cold rads. you need to remember the engineers agenda is not the same as that of the homeowner. you can set the weather comp anywhere you lie. it makes not a massive difference ive found. if you save 10-15 % you are doing really well. 

all heat pumps give fictional outputs on the side of the tin, it drives me mad, i blogged about it here https://www.linkedin.com/pulse/lies-damn-heat-pumps-why-kw-always-graham-hendra/

not sure the run it colder longer theory will work but you can try, there is no harm playing with the unit. one of the mideas best tricks is if you break it you can just reset it and start again. here is my manual.

enjoy

Posted by: @grahamh

I used to run the tech department...

I was hoping you might see my post, and, having read many of your posts, dared to hope you might reply, as you have written much interesting stuff, here and elsewhere, so thanks very much for doing so. I had also come across your video, and so become familiar with the 55@-2/37@15 degrees to keep the homeowners happy logic. I am however 'OK' with cooler rads because that's how ASHPs work best. One of the (hopefully) plus points about an old leaky building is that it has a high thermal mass, so when it does heat up, it will retain the heat better.

I have no idea why Freedom now refuse to speak to end users, it's a very old fashioned way of doing things and has no place in 2022, all the more so when I have made it clear I have done my best to understand as best I can how heat pumps work, and am asking what I hope are intelligent questions. 

The manufacturer's 'nominal' kW output (and the air 7 water 35 'for comparability' between different units/brands figures) are bordering on the misleading. It's analogous to a car manufacturer advertising their car as doing 60mpg and omitting to say that's downhill on a motorway with a following wind, round town you'll be lucky to get 30mpg. I agreed to the 14kW unit on the basis of those figures in Midea's literature, and it was only after the unit had been installed, and I came across the data in this thread

https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/measuring-your-cop/paged/6

and plotted the output for the 14kW unit that I realised that in colder outside temps things will be very marginal, hence my wish to be able to extract the maximum number of kWs from the unit at low outside temps, and the chart suggests 45 (max) flow is the sweet spot to get the most kWs, at higher flows the output drops below 12kW.

I'm still finalising the balancing of the rads, once that is done i will set the curve to 45@-2 (and leave the other end at 37@15) and see what happens when (if, it may not happen this heating season) we get a spell of colder weather (today is OK, ambient outside is about 10 degrees, so it is running on the purple/circle line on the chart, need the colder weather to have more testing conditions. At the moment, the heat pump is more like the car on the motorway going downhill with a following wind, what will happen when it has to go uphill into a head wind?).

cathodeRay

Hi @cathoderay 

Whilst I commend your desire to reduce your energy consumption, the starting point should initially be with improved insulation and draft proofing.

For optimum efficiency with a heat pump, it should be operated at the lowest water flow temperature possible that meets the heat demand, which in turn is predominantly due to the heat loss of the property. It is not a matter of getting the maximum heat energy output from your heat pump, but more a matter of matching the heat output to the heat demand, in the most efficient manner.

There are four main variables which affect required water flow temperature that meets the heat demand. The effect of the first two, the desired indoor temperature and the actual outdoor air temperature, are fairly obvious, the lower the outdoor temperature the greater the heat demand, and the higher the indoor temperature the greater the heat demand.

A third parameter is the calculated heat loss for the property, with the fourth being the specified heat output capacity of the combined heat emitters within the property.

I have attached a copy of a spreadsheet that I produced for a 14kW Midea unit, where the above parameters can be set to match your particular system. By adjusting the parameters highlighted in green, to match your system, the data produced in column 'D' is the estimated resultant at the specified outdoor air temperatures.

The top value in column 'D' is the COP, the middle value is the required water flow temperature, and the bottom value is the estimated electrical energy consumption.

The calculated water flow temperatures should hopefully be fairly close to those required for your system to operate in true weather compensation mode. If you have active thermostats or TRV's within your system, you may find that they interfere with the operation of the weather compensation algorithm, and hence reduce the efficiency of the overall system.

Hi @derek-m

I was also hoping you would see my post and have something to say, as I have seen some of your other posts, and the impressive work you have done.

I absolutely agree limiting energy consumption is paramount where possible, and I am doing this, but there are constraints, as the building is listed. 

Your spreadsheets are wonderful. If I set the row 1 variables to my particular circumstances (heat loss 12,500kW at -2 ambient, room temp 19 (which is an average as not all rooms at same temp) and emitter loss at delta T 50 of 23,000 (this is the delta T 50 loss, not the loss at the lower ASHP delta Ts) I get a LWT in col D of 50.3 when it is zero degrees outside (and a COP of 2.26...) but when I look at the cells to the right (the various flow temp columns), the coloured cells go red at 50 and above flow temps, but are green at flows of 45 degrees and less, with the exception of 35 degree flow, which perhaps appears to be some sort of anomaly: 

The colouring of the cells to the right of column D appears consistent with my reading of the Midea data as shown in the chart in the original post, ie when you get to higher LWTs, the efficiency (ie COP) falls substantially, and the unit can't output enough kWs, so you actually need a lower LWT to get more kWs (along the lines of the simple made up example in the original post of 55 degree flow, 5kW in, COP 2, 10kW out cf 45 degree flow 4kW in, COP 3, 12kW out). Another way of approaching it: if you look at the light blue and burgundy lines on the chart (0 and -5 ambient), you need a LWT of 45 degrees or less to get an output of 12kW (and a bit more at lower LWTs).

This is the crux of what I am focusing on: the on the face of it paradoxical observation that the way to get the maximum kWs out is to lower the LWT (I think because the although the power input goes up by X, the COP falls by more than X, so the net effect is less kWs out, if that makes sense). This then becomes critical in a marginal case, like mine, at lower ambient temps around zero.

Hi @cathoderay 

Using your data, I'm afraid that you cannot just set the water flow temperature at 45C and expect the indoor air temperature to remain at 19C. In this situation it is not the heat output of the heat pump that is the limiting factor, but the heat output of the heat emitters. To maintain an indoor air temperature of 19C, with a water flow temperature of 45C, it would be necessary to either increase the size of the heat emitters or reduce the heat loss.

Hi @derek-m

I agree the heat loss needs reducing as it is high, and there is scope for lowering it, even within the listed building constraints eg draft proofing, secondary glazing etc, improvements which are already, albeit slowly, in hand. The emitters should I hope be OK, they are all replacements (bar one in a utility room), mostly larger K3s replacing smaller K2s, all sized to meet the rooms heat loss and a bit at design temps with a ASHP delta T of around 30 degrees, though this is with higher flow temps so they might be borderline at lower flow temps but possibly still OK because of the 'and a bit' element in the sizing. But I may be wrong (depends now much 'and a bit' over-size they are, varies between rooms). I will have a look at the emitter calculations again tomorrow and see how it looks.

Thanks again for your input.

cathodeRay 

@cathodeRay, 

If your house heat loss is 12kW @ -2, why has your installer designed a system with an ASHP that can't deliver that amount of heat at that outside temperature?  Have you asked them?  What does your MCS calculation say (I'm assuming your supplier is MCS certified)?  

You may be able to increase output as you suggest and Derek's suggestion of insulation/draught proofing will always help.  But it does sound like your supplier may have got the design wrong. Either way, you shouldn't have mess around trying to eak out the last kW out of your ASHP just to heat your house.  It's extremely misleading for Midea to label their ASHPs like this but your supplier, as the expert, should know this and should design your system accordingly.       

BTW I'm not a heating engineer so apologies if I've misunderstood any of this.

Apologies in advance - this is a very long post...

@derek-m - you are of course right, as I feared you would be. The rad sizing was based on the higher (55 degree) flow temp, and when the flow temp is dropped to 45 degrees the rads become too small. At 50 degrees flow, they are 14% undersized, at 45 degree flow they are 34% undersized. Even if the heat pump delivered more kWs at lower flow temps, the rads would not be able to emit the extra kWs, and the system will fail to reach design temperature.

The building is most attractive but not only is it old, leaky and listed, it is also small. This means limited horizontal wall space, and furthermore, the ceiling heights are low in most rooms, with a knock on effect that the floor to window sill heights are also small in many rooms. The new larger K3 rads just about fit, with some juggling, but, as can be seen by the percentage shortfalls above, considerable increases in rad sizes would be needed to get sufficient emitter output, and the installation would start to enter the realms of the absurd, with huge rads dominating every room. For example, a current K3 600 x 1200 would need to be increased to K3 600 x 2000 to get sufficient output. Such increases in size are not trivial in a small building. Underfloor heating is not really an option, as the cost and disruption would be prohibitive. So basically, to use the vernacular, I'm stuffed.

@kev-m - you too are onto something. The installation from start to finish has been something of a 'difficult journey' that has taken over a year to complete. I have no doubt that without the determination I ended up having to apply, the installation would have fallen by the wayside, and I would have reverted to using oil CH (we're off mains gas here). I suspect this is one reason why ASHP installation are so rare, they are just too much hard work. One has to raise a wry smile at the government's ludicrously ambitious installation targets over the coming years. Some 'highlights' from my 'installation journey':

1. Initially I approached over a dozen installers, 50% failed to reply, some replied but failed to quote, meaning I finally ended up with 4 quotes, an attrition rate that is probably normal. All the installers, including particularly those who finally produced quotes, were MCS/Trustmark etc approved, and they were all working with the same data, and yet they all produced different designs. No two heat loss calcs were the same, and two of the four considered I didn't even need to change the old small K2 rads for larger ones. I underline, these were all MCS approved designs, insofar as they were produced by MCS approved installers. I learnt something during that process... 

2. Being listed meant no permitted development, so I needed both Listed Building Consent and Planning Permission. That nearly failed because of the dreaded bat problem (which wasn't a problem, but initially the planners thought it was).

3. Initially, funding was going to come from the GHG voucher scheme and the RHI, then the former got shut down abruptly last spring, and I ended up on the so-called LAD (local delivery scheme). This is generous, but it meant more bureaucracy, and using yet another (and so yet another different heat loss/design result) 'preferred installer' who turned out to be hopelessly incompetent, so much so I had to say I wasn't prepared to let them within a 10 mile radius of my house. I reverted to my original chosen installer, who had stood out for his calm and sensible approach to the design and installation. Quote prices varied widely, his was in the middle.

4. The incompetent installer wasted the best part of six months on not doing the installation, and the LAD scheme has a closing date (31st March this year), and so by the time I got rid of the incompetent installer, in December last year, things need to happen swiftly. In addition, my chosen installer (a small family firm) had long standing plans to travel to Australia for six weeks over Feb/March, leaving even less time to get the installation done. It is fair to say he has pulled out all the stops, and did everything he could to make it happen. At this stage, up until shortly before the installation (late Jan this year), the heat pump was a Midea 16kW unit, and it met MCS requirements at high flow temps. A Midea unit was chosen because it is one of the few, perhaps even only, low profile unit at these output ranges, ie wider than it is tall, greatly lessening the visual impact on a listed building, and was 'baked into' the Listed Building and Planning consents.  

5. Literally days before the installation was due to start, the heat pump supplier (Freedom) announced no stock of 16kW Midea units, apparently their had been a rush on other brands after Mitsubishi's supply chain packed up. Earlier it seemed the 16kW unit was available, but I suspect the installer didn't order one because at that point we were still waiting for LAD grant funding approval for him to do the installation. Freedom did have a 14kW Midea unit in stock, and the installer and I agreed it should be sufficient, if close, based on Midea brochures. A little over 12kW heat loss, 14kW unit, what could possibly go wrong? Even the very technical looking performance data in the brochure indicated all would be well: outputs 14.5kW at A7/W35 (ambient air 7 degrees, water flow out 35 degrees), 14.1kW at A7/W45 and 13.8kW at A7/W55. All seems to the uninitiated comfortably above the 12 and a bit kWs needed. No mention that these figures were the downhill on a motorway with a following wind figures, and presenting only them hides the fact that things are very different at lower ambient temps. 

6. The lead time for a 16kW unit was weeks/months, and because of the time constraints there was a stark choice: go with a 14kW unit, or nothing, and have the whole year long process collapse into nothing, and forcing me back onto fossil fuel heating. At the time the decision had to be made I had no inkling that the output would be far less at the critical lower ambient temps, I had the above figures and all seemed OK. Curiously, the 14kW unit does not seem to appear anywhere in Freedom's own Midea brochures: had it done so, we might have seen the '-2/50' output figure (ie A-2/W50 output), which might or might not have been an alert, but we didn't see it, because it isn't listed. The supplier one presumes must have known the figures, even if they didn't list them. The installer, who I have found extremely helpful throughout, and do not want to criticise, is, I think, like most installers, an installer rather than an engineer, and like most installers, only knows so much (@grahamh, I think this has been a theme in some of the things you have said). I am the end user, perhaps more involved than some in the installation, but still at the end of the day the amateur in all this.

7. I am the amateur, but a meddlesome one. I discovered Freedom's calculator (v2.4, which is the one we were using at the time) had a lot of hidden cells, and if these were exposed, there was some Midea 14kW output data, and, after making the necessary changes, the calcs could be done and the system was just MCS compliant (101%...): 

The heat loss from the Heat Loss Calculator sheet is 12.3kW, and at 55 degrees flow and -2 ambient (see the chart) the heat pump output is 12.4 which is just under the loss, and the system is shown as MCS compliant: 'Will the system qualify for MCS? Yes'. To appreciate the urgency of the situation, bear in mind I did this check on the Friday before the Monday on which the installation was due to start. My comment at the time to the installer was "a 14kW should be OK, but if your supplier can be persuaded to find a 16kW unit, it would definitely be better". In the event a 14kW unit arrived. 

8. I knew it was borderline, and furthermore there is a candid note in Freedom's spreadsheet: "the midea figures are mostly made up ** had to average them", though the fact they were there at all suggested there had to be some basis for them, and, at the time, they didn't stand out as being obviously wrong. Nonetheless, knowing it was borderline, I started searching on line over the following days, and in due course (after the unit had been installed) came across this forum, and the posts on Midea data (including links to Midea's own technical data), and @derek-m's spreadsheet, and it became apparent that the true (assuming Midea's own data is correct...) output that the 14kW units output at 50 and 55 degrees flow and around zero degrees and less ambient is less than 12kW... (eg 11.691/11.599kW at 50/55 flow and zero degrees ambient, see screen shot of spreadsheet in earlier post). It seems very likely the system is 'set up to fail' in lower ambient temperatures... 

I've posted the details as a salutary lesson: even an informed amateur can end up with 'a situation', so what hope is there for Mr and Mrs Not-Informed? Remember the two out of four installer who were not even going to change the rads that are obviously undersized for an ASHP. These designs (unsurprisingly) had lower heat pump outputs (12kW and less) that we now know could never have been adequate. It's an appalling dreadful mess. What happens next? I don't know. The heat pump is managing fine today, in ambients around 10 degrees, rooms (bar one) are at design temps, exactly as expected. But will things also happen 'exactly as expected' given we now have Midea's full data, when its zero or less outside? Will the rooms fail to reach design temps? I rather expect so, but will only find out when it gets colder, which may not happen until next winter. In the meantime, I can approach the problem from the other end, and do what I can to reduce the building's heat loss, which brings us back to where we started, there are two parts to all this heat loss out, and kWs in.

Lastly, manufacturers and suppliers need to clean up their act, as others have said, so I am just adding my voice. Calling a unit a 14kW unit sets an expectation in the mind, and is frankly misleading (that is the polite word) when the 14kW unit will deliver less than 12kW when it matters, and will never ever deliver a steady 14kW (when it can, at higher ambients, it won't because it will cycle on and off, because the buildings heat loss and so demand will be dramatically less). MCS, not the most agile of organisations in my view, is also part of the problem: by focusing on SCOPs in their product certification, they omit the all important output data at lower ambient temperatures. And then there is the regulatory problem, the MCS approved installers who design systems that are bound to fail in practice (no replacement rads) - how on earth do they get these designs past MCS's processes? It seems to me MCS are failing consumers...

Like I said, all a bit of an appalling and dreadful mess.   

I wrote that excel heat load tool. I'm impressed you cracked it open. The reference to "i made it up" was because we have to extrapolate from incomplete data. No manufacturer tests at every single air temperature. 

I agree that the numbers on the tin should relate to the real output but they dont, its nothing to do with mcs. The manufacturers are obliged to test at a ridiculous condition of 35c water in 7 degree ambient. god knows what moron thought that up but its life, its never going to change so we have to build tools to size at the real outputs. 

first you need to talk to your installer who is responsible for the installation, the sizing the spec and the set up, they should be advising you how to use the unit etc. Only they will know how they sized it up and designed it. 

At 101% its tight but it wont leave you cold. I blogged about this this week on linked in. 

if your really worried about capacity why not upgrade the unit from a 14 to a 16, its a simple job, flick a switch in the outdoor unit and it becomes a 16kW, the units are identical, inside the cover it even tells you how to do it. 

my advice would be leave the thing alone. The best systems are the ones which are left to get on with the job. Years ago I had a laptop on my Samsung unit and tweaked it constantly, I managed to get an extra few percent out of it, what a waste of time that was. There are more interesting things to do and thats coming from a heat pump guy.

good luck 

@grahamh cracking open that sheet was fairly easy to be honest. I think it took me around 5 mins.

@grahamh - its a very impressive spreadsheet, how you managed to keep on top of all those lookup formulas is beyond me. I did wonder if gh was you, but couldn't know, there might be another gh at Freedom, and even if it was you, I wasn't going to disclose it on a public forum!

I'm not blaming MCS for the manufacturers' behaviour (and how could MCS have any affect on a huge Chinese manufacturer?) but MCS could improve their data, what they have on their website. If they had the output data as well as SCOPs on their product data pages, then it would be relatively easy to see (and compare) outputs for different units. They could do that in the interests of transparency, and folks would soon see better what is going on. The manufacturers (deliberately, no doubt) do not make the full data readily available, I only found the Midea data via this forum, and I am not a complete clown when it comes to finding things online.

I've read some of you linked in blogs and found them very interesting and enlightening. I'll look for the one you mention.

My installer was very willing to explain heat pumps and their design ways with me (one of the reason I liked him and felt comfortable with him doing the installation), discussing the design etc as we went along, so I already have a a good idea of the design thinking etc. Our mistake, if it was our mistake to make, was not to delve deeper and then deeper again into the output data (this is why I say the manufacturers need to be more honest with their data, not hide it away where it is very hard to find). 101% is tight, but is nonetheless a pass, but it relies on the data in Freedom's spreadsheet which you extrapolated (interpolated?) from the data you had, giving 12.4kW at 55 flow and -2 ambient, whereas the buried, now discovered, Midea data show it is going to be more like 11.3kW (from screengrab in earlier post: 55 degree flow 11599W at 0 degrees ambient,  11144W at -5 degrees ambient). I think you (always?) factored in the defrost cycle effects at these temps, not sure whether Midea do. I think they might (see shape and positioning of curves in the original post chart, bearing in mind that chart is not the same as the chart in your spreadsheet, it's output (y-axis) at various ambient temps (the lines) for various flow temps (x-axis)).

I think it will struggle at these lower ambient temps, but agree the first thing to do is leave it alone, and see how it actually gets on in the real world once things get cold. That may mean a wait, as we are now into March. At the current higher ambients (its been 10-12 degrees outside here today) it is keeping the house warm (bar one room on the end of a run, which probably has a partial blockage that flushing hasn't cleared) no need to fix something that is working.     

Very interesting to hear the Midea 14 and 16kW are the same unit, just with different settings. It's rather odd Freedom didn't point that out, given the installer (and I) wanted a 16kW unit. Nonetheless, it takes a huge weight off my mind, as it provides a simple fix if the 14kW setting does turn out to be inadequate. But again, no rush, I have to know there is a problem before I fix it, and I'm pretty sure a 16kW setting will use more power in than a 14kW setting, so no reason to up the setting unless it is needed. I guess if we do need to do it, my installer and/or I will will have to get Freedom's approval first, otherwise they will claim we have just torched the unit's guarantee. 

PS while writing this post, I see a comment has been added by @batalto about opening up the spreadsheet. I agree, it isn't hard if you know how, and in a way it is a good thing (provided it is done with good intent) because it increases transparency, and improves general understanding of how these things work, which is in everyone's interest.

cathodeRay