hi everyone

I dont get involved with after sales and problems anymore, those days are long behind me, I got bored of people asking my advice then ignoring it, so ive moved on to speccing units before installation.

just to try and clear up a load of points:

The Freedom Heat loss includes defrost figures, I know, I wrote it.

The plate is rated at 60kW if it came from Freedom, we used it for everything, I sized and specced it years ago to be 100% oversized.

the comment that people only used midea because they couldn't get Mitsi is a bit harsh. The Mitsi unit is pretty mediocre, you are much better off with a midea. 

if you are worried its the wrong unit or not big enough its pretty easy to prove. The heat load calculation you get with your mcs pack should perfectly match the house. I believe you can protest to mcs if you think you believe you have been had. Its very unlikely anyone would undersize the kit, if you do the heat loss calculator wont let you have any figures, it was designed like that. But if the house info has been input incorrectly it could be wrong.

Sounds like you need someone to come and do the heat load calc again, check the rads, give the system a once over and make sure its actually balanced across the plate and in all the rooms. Pretty simple stuff. there are loads of good people in the area, freedom would be worth consulting as to who they recommend to do this. (not me)

should be a synch now, weve all got a 7 week holiday we were not expecting. 

Posted by: @grahamh

the comment that people only used midea because they couldn't get Mitsi is a bit harsh. 

I wasn't meaning to be harsh (and note that I chose a Midea over a Mitsubishi, for various reasons, including it must be said its low profile design but also its long guarantee among other things). I was only quoting my installer, and the impression I meant to give was that many installers normally use Mitsubishi, but when faced with the shortage of Mitsubishi units, they turned to other brands, including Midea.

Posted by: @grahamh

Sounds like you need someone to come and do the heat load calc again

These have been done many times by many people, me in the 1980s for the original CH, then again recently, plus at least five installers who provided quotes. Errors were common (there is a lot of data to enter, typos happen, also some installers don't know how to record/enter the measurements, and even the final heat loss calc submitted to MCS had a typo, 2.3m external wall for the kitchen when it is actually nearer 12.3m) but I think we now have as good an estimate of heat loss by room and total as we are ever going to get. Let's say it is 12.4kW give or take. It's an old leaky building (it is in the title of this thread).

One of the crucial bits of information about my installation is the rush on Midea units meant there were no 16kW Midea units available at the necessary time, late Jan/early Feb 2022, and none were likely to be available in time to meet the LAD grant deadline of 31st March 2022, 16kW being the size specified in the quote/pre-installation calculations. 14kW Midea units were available, and so the question was would 14kW be sufficient and with a ~12.5kW load we thought it would be. What we didn't know then, but do know now, thanks to @derek-m's research, is that a nominal 14kW unit is actually a ~11.5kW, maybe even less, unit at zero degrees ambient/55 degrees flow, and so when it is needed the most, the heat pump output is not adequate. 

I have to tread carefully here, because I know you designed the calculator, but a critical problem is that the Midea heat capacity estimates at low ambients are slightly higher than Midea's own quoted figures. A slight difference normally wouldn't matter, unless it just happens that the difference straddles the actual heat loss, and that is what happened. The calculator estimates capacity at just over the demand (101% on one version, but hey ho, anything over 100% is MCS +ve) but with Midea's own figures the capacity is under the demand at low ambients. This only came to light after the installation, obviously had we known beforehand we would have done things differently, which might even have included not installing an ASHP at all, given the constraints imposed by planning/LBC (Midea low profile unit baked into the consents), the unavailability of a 16kW unit, and the LAD grant deadline. 

Lord Sugar/Apprentice question: who is to blame for the failure of this task? Both my installer and I relied heavily on Freedom's calculator. It is true I unlocked the v2 version to expose the Midea 14kW data and make it available (it is available in v3, but up to and at the start of the installation we were using v2, for historical reasons, the original quote was done in Feb 2021, when v2 was current) and the bottom line is that we relied on the supplier telling us the right information. Yes, there is the hidden note about the Midea figures, but the figures are nonetheless there. There was intense pressure to make a decision: if the Midea estimates were credible enough, then go with the 14kW unit, if they weren't, cancel the whole ASHP project. After over a year of battling to get one installed, I was not in a mood to give up at the moment just before installation could happen.

We could just say it was an unfortunate confluence of events, and sometimes things just do go wrong. But that leaves me with inadequate heating in cold weather, when I need it most, and, because it is grant funded, the tax-payer has paid for something that went wrong. My own opinion is that the greater share of the blame rests with Freedom, for having a spreadsheet available for use that contained incorrect data, with some. but mostly hidden, and inadequate flagging, that the data might be critically wrong. My installer, and I, both relied in good faith on the supplier to know what their products can do. My installer and I did check the installation would be adequate, which is about as much as we could do, using the calculator, and were then tripped up by the fact the data in the calculator was wrong. I also can't emphasise enough the misleading effect, something I know you agree with from what you have written elsewhere, of calling an effectively 11.5kW unit when it matters a 14kW unit. 14kW is the headline, the thing that sticks in the mind, that's they way people read it. 14kW covers 12.4kW, everything is hunky dory. The whole industry, and that includes Freedom, need to be far more honest about real world outputs, because the problem is, if you mislead people, people end up misled, and things are likely to go sour. 

There is an additional complex question of where the responsibility should lie. There are several players: the manufacturer (Midea), the supplier (Freedom), the installer (my installer), the end user/consumer (me) and the payer (the LAD grant system), and even the certifier (MCS). Who of these players should be responsible for getting things right? 

Rant said, I have every hope that there is a relatively simple solution to the inadequate capacity problem (there may also be other flow problems), first suggested by you: uprate my 14kW unit to a 16kW unit using the dip switches. Others have suggested I just go ahead and do it anyway, but I am mindful of the fact the installation is very recent, and still well within guarantee, which I might void by 'tampering' with the unit, and furthermore I think it would be far better all round if I work with my installer and Freedom to sort this out. Jaw jaw is better than war war and all that. 

The interesting and puzzling thing from reading the thread is that the system can’t reach design temperature at 3degC ambient. Even if the 14kW unit is inadequate at 0deg and below, it should cope at 3deg, but it appears miles off.

Posted by: @cycleneil

The interesting and puzzling thing from reading the thread is that the system can’t reach design temperature at 3degC ambient. Even if the 14kW unit is inadequate at 0deg and below, it should cope at 3deg, but it appears miles off.

Exactly, that is why I am increasing thinking it is a compound problem, both the heat pump capacity is inadequate at low ambients and the heat that is produced isn't efficiently transferred to the house. 

Early indications suggest it might be doing better with the secondary pump set to max constant flow, but at the same time outside ambients are now in double figures again (currently 12 degrees) so maybe that is why its a bit warmer inside.

Hi @cathoderay

To save me having to search, do you have the specified output capacity of each of your radiators at a delta T of 50C?

Let me explain the objectives of the various proposed tests.

Assuming that the supplied data from the Midea controller is reasonably accurate, it would appear that your heat pump was producing approximately 6kW of heat energy. Within its operating range the heat pump will produce the required amount of heat energy to meet the demand.

This heat energy is getting to the PHE and is being transferred to the secondary water circuit, but at colder ambient temperatures is inadequate to heat your home to the desired temperatures. The fact that the temperature of the water coming out of the secondary side of the PHE is close to the inlet temperature on the primary side, would indicate to me that there is insufficient flow on the secondary side. The temperature of the water in the secondary side of the PHE is being raised by between 11C and 16C, which would indicate that the flow rate is between approximately 50% and 35% of that within the primary side.

Since the weather is reasonably mild at the moment, I suggest that you close the TRV's on all the radiators except for one, and then measure the temperatures and flow rate over a period of time. If my theory is correct then you should find that the temperature of the in service radiator will increase. You could then repeat this test on each radiator in turn.

The Mitsi unit I've got may be mediocre but it's heating my house, while @cathoderay's Midea isn't heating hers... but maybe the unit's worse while their calculator or installation manual doesn't have a problem at low ambient temperature?

I hope this story will have a happy ending. I can't imagine how horrible it must feel to be spending £330+ a week on heating.

Posted by: @mjr

The Mitsi unit I've got may be mediocre but it's heating my house, while @cathoderay's Midea isn't heating hers... but maybe the unit's worse while their calculator or installation manual doesn't have a problem at low ambient temperature?

I hope this story will have a happy ending. I can't imagine how horrible it must feel to be spending £330+ a week on heating.

I would always prefer to buy Japanese designed equipment to Chinese, which I have often found have internal components which barely meet the required specification. I think that you will find the majority of the ecodan owners on the forum experienced problems with how their system was installed and commissioned, rather than the quality of the units themselves.

Comparing the manufacturers published data, the Mitsubishi would appear to be far superior to the Midea.

Posted by: @derek-m

To save me having to search, do you have the specified output capacity of each of your radiators at a delta T of 50C?

The rads are actually Ultraheat branded, and the output per size varies slightly between different manufacturers. My installer went with a certain supplier who had K3s in stock in the needed sizes (or very close, see below), and it just turned out they were Ultraheat rads. Reviewing the list, I am reminded there were also three last minute minor changes, to accommodate what was in stock (because of the urgency of the installation): two rads 750 height to 700, which was still >100% of the room's heat loss in both cases, and another 1600 wide to 1800. Here are Ultraheat's quoted outputs at delta t 50 for my rads as installed: 

K3 700 (was 750) x 1400: 4059W
K3 600 x 1200: 3101W
K3 600 x 1800: 4651W
K2 700 (was 750) x 600: 1260W
K3 500 x 1800 (was 1600): 4030W
K3 500 x 800: 1791W
K3 500 x 1000: 2239W
K2 500 x 1600: 2590W 
K3 900 x 400: 1379W

I think I understand the logic of what you are saying. The heat pump is 'smart', and modulates it's output to match the demand. But only 6kW of demand is showing up, so it only supplies 6kW. The bit I struggle with is how does it 'know' there is only 6kW of demand? Difference between LWT and RWT (little or no diff = low demand, big diff = big demand)? Now add in the PHE: the drop in primary circuit is in turn determined by the 'demand' from the secondary circuit - and this is where I start to get confused. On the face of it, a high room demand would cool the water as it passed through the rads a lot, and vice versa, so here again a big diff between flow and return = high demand, little or no diff = low demand. But as you noted, the diffs are actually quite high (aren't they?) indicating high demand - but it isn't being seen as high demand? And wouldn't higher flow rates mean less apparent demand, because the water has less time to cool as it passes through the rad?

The other anomaly I can't get my head round is (from yesterdays minute by minute readings) the difference in secondary out 40 rising to 45 degrees, and the typical average rad temp of around 30 degrees. The secondary in makes sense, it is about 30 degrees, ie the rads average temp. But what happens to the secondary out? It leaves the PHE at 40-45, but only appears at the rads at an average of around 30 degrees. Where did it lose 10-15 degrees?      

Posted by: @derek-m

The temperature of the water in the secondary side of the PHE is being raised by between 11C and 16C, which would indicate that the flow rate is between approximately 50% and 35% of that within the primary side.

Is that because the drop on the primary side is around 5 degrees, and it is a simple linear relationship between temp drops and differential flow rate eg is primary drops 5 degrees, and secondary goes up 10 degrees, then secondary flow (in cubic metres/hour) must be half that of the primary flow? Likewise, if the flow rates were equal, then under ideal conditions, temp drop in primary would equal temp rise in secondary? The Midea controller reports the primary flow rate, is there any way of estimating the secondary flow rate from the readings we do have?

But I still struggle to understand: how does the secondary circuit signal there is a high demand to the primary circuit (and so indirectly to the heat pump)? By losing a lot of heat as the water goes round the circuit, so on that basis the slower the better, because it will be progressively cooler as it gets back to the PHE? But that's counter-intuitive: sluggish flow can't carry/transfer a lot of heat (low current/amps = low power from my earlier analogy)... 

Sorry to be so thick.  

I really do appreciate your input and help and explaining, and will run the tests you suggest ASAP. It is just that it is 'that time of year', when everything starts happening, and I need 30 hours in a day, but only have 16, so it may be a day or two before they get done.    

Posted by: @mjr

I hope this story will have a happy ending. I can't imagine how horrible it must feel to be spending £330+ a week on heating.

Thanks for the support, much appreciated, and I too hope all's well that ends well, but I am relieved to be able to say it is 'only' about £100pw, still painful, but mercifully not £330+ a week (the 334 figure is kWh ie units). 

Sorry if it’s an obvious question, but how is the HP sensing the room temperature to compare against demand? Is there a Midea controller with temperature sensor located in the main room to be heated?

@cycleneil - no, its controlled by an on/off room stat in the kitchen, currently set to 21 degrees, kitchen design temp is 19 degrees, so most of the time, sometimes all of the time eg over the recent cold spell, the room stat is calling for heat, and so is effectively on 24 hours/day.

Posted by: @cathoderay

Posted by: @derek-m

To save me having to search, do you have the specified output capacity of each of your radiators at a delta T of 50C?

The heat pump is 'smart', and modulates it's output to match the demand. But only 6kW of demand is showing up, so it only supplies 6kW. The bit I struggle with is how does it 'know' there is only 6kW of demand?

I don't think it does.  If you are using on/off stats, all the ASHP 'knows' is whether or not the target flow temp is reached; either a fixed one or whatever your weather compensation says.  I'm not sure exactly what the algorithm is but my mediocre ASHP seems to literally test the water.  When it starts up it starts low then ramps up over a few minutes.  I assume it compares actual flow against target, works out how much power to give, gives it, sees what happens to the flow and adjusts.  On a cold morning it delivers its maximum rated power (14kW or more) for a while then drops off as the target flow temp is reached. I don't think yours will be much different. But the PHE is a complication.

If the ASHP were targeting a room temperature using its own logic then it might be different; then I would expect it to adjust the weather compensation and keep going at higher power/flow until the target room temp was reached. 

Posted by: @cathoderay

Thanks for the support, much appreciated, and I too hope all's well that ends well, but I am relieved to be able to say it is 'only' about £100pw, still painful, but mercifully not £330+ a week (the 334 figure is kWh ie units). 

That will teach me to read too fast! I'd been away and only just managed to pass that horrible insulting discriminatory "are you a human?" test (I know my eyesight is poor: that's why I wear glasses. I don't need to be called inhuman too!) to be allowed back on this forum.

I still hope the story ends happily.