Posted by: @derek-m

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Unless it is an RNI that is glued to the exchanger you can remove the thermal insulation from it. The nameplate is on the front cover where the 4 connections are.

I think it may well be glued to the exchanger, it is certainly glued to itself, ie top to sides, and because of the way the exchanger has been installed, jammed between tome floor boards, and destructive removal of the thermal insulation is going to almost impossible to replace. I have tried to coax enough of the top layer of insulation off but still intact to be able to see the nameplate, but is starting to tear, and so I have stopped.

The dip switches: after much careful thought, I decided now is not the time to flip them, precisely because it is so cold. What if I inadvertently somehow mess up the system? I then find myself without heating, with temperatures below zero, and forecast to remain that way for the next few days. It is not a risk worth taking. The time to test flipping them is in a period when if necessary I can manage without heating, and it all all works as expected, then put them back to 14kW, knowing that if/when it gets cold again, I can switch to 16kW if needed.

More draught proofing work done on the kitchen, with three windows, three doors and three outside walls, it is a draughty room, but a little less so now.  

Some conclusions from last week's figures. It was an interesting week, insofar as the ambient temp was at or very close to design temp for a sustained period, meaning we can test the design predictions and ASHP manufacturer/seller's claims against actual results.

1. Total heat pump energy use: 554kWh (£210.52 at the price cap). This figure comes from the external meter, which is more accurate than the app. DHW use (according to the app) was 6kWh (I don't use much hot water) or 1.08% of total use, and can effectively be ignored, as in round numbers 99% of the energy use was going towards heating. 

2. Total heat energy output (this is from the app): 1476kWh, giving a COP of 2.66. The lesson here is that heat/energy use vs ambient temp isn't linear, so you use disproportionately more energy when it is cold. Put another way, when it is twice as cold, you use more than twice as much energy, because your COP has fallen. You get a double hit: more energy because it's cold, and then even more energy because your COP has fallen. The fact this will happen should be in capital letters on page 1 of any guide to ASHPs so prospective purchasers know what they are in for. It's called managing expectations.

3. For the last four days, the average ambient temp has been at design temps, ie -1 to -2 degrees. According to my heat loss calcs, the heat loss is 12.4kW, or a total of 297.6kWh over 24 hours. To meet this, the heat pump put out an average of 236.75kWh a day over the four day period, which gives a real world power output of 9.86kW. If we assume the heat pump was working flat out (which it no doubt was, see next point), the real world power output significantly lower than Midea's claimed 11.3kW, and far far far lower than Headroom Heat Pump's made up figure of 12.4kW. Conclusion: you cannot trust neither the setters not the manufacturers of heat pumps to tell you what the real world output of your heat pump will be. This fact should be in capital letters on page 1 of any guide etc etc

4. During the four day period, the upstairs rooms were mostly at design temps, near enough not to quibble, but the downstairs rooms were consistently below design temps, on average 4 or 5 degrees below design temp. This is a clear MCS fail. Furthermore, the actual LWT never reached the set LWT, being on average about three degrees below what it should have been. The heating was on standard weather comp settings, room stat set very high so always on, very close to standard weather comp curve (55@-4 / 30@15) and so far as I can tell, the heat pump was running flat out, insofar as the compressor icon was always on whenever I looked. Given the downstairs rooms never got to design temps, and the actual LWT never reached the set LWT, I think we have to assume that this was the best the heat pump could do, ie it was going flat out, but still couldn't reach it's targets. It was running at max capacity, and it wasn't enough.

5. I did wonder about setting the LWT ludicrously high, say 60@-2, but decided against it because (a) the COP would drop through the floor at a time when I was using vast amounts of energy and (b) the fact of the matter is, the heat pump couldn't reach lower set LWTs, making it extremely unlikely it would meet a higher set LWT (c) it was not a practical real world experiment, insofar as I am never going to run the heat pump at that set LWT.

The bottom line is that the Midea 14kW heat pump is insufficient at design temps. When it is milder, I will have a trial run of setting the heat pump to 16kW output, and if that works, then I have the option if/when the next cold snap happens of upping the output. I say option, because I have to expect that if I do that, my heating bill will go even higher. But maybe not by too much, if running the unit as a 16kW unit does indeed improve the COP a bit (see posts passim). Only a real world experiment will give the definitive answer.  

@cathoderay given upstairs is much warmer than down, have you considered balancing the rads again to push more heat downstairs?

@allyfish 

we also have a grant ashp

based on what you have said… always on, always calling for heat

i am considering putting me flow temperature at 35, weather comp off, and setting the thermostats high… would that be right?

@batalto - they are as balanced as I can get them (mostly by lockshields, starting full open then closing in stages in turn, then final tweak where needed using TRV), upstairs is at not above design temps, so if I push more water downstairs, yes, downstairs will get warmer, but upstairs will get colder.

PS I should add, I favoured upstairs because I spend most of my time indoors upstairs, I use one of my bedrooms as a study. 

@cathoderay I don't know, given heat rises, might that offset some of the heat lost to upstairs rads? I need to do the same, my upstairs is much warmer than downstairs. I think I might try a quarter turn on every rad upstairs and see what effect it has down.

@cathoderay i've just been round and tweaked my rads with a quarter turn tighter (upstairs). Lets see what effect we get in a few hours

@batalto - one of the upstairs rads is 2 degrees warmer than the others which are all within half a degree of each other. I tightened the hotter one by one sixth of a turn, and will monitor and minimally adjust the others and see what happens, and report back in due course. Maybe the rads are more fussy about being balanced in cold weather, in milder weather things just sort of even out. 

Great to see people getting support on this thread. 

Having had an ashp for 6-7 weeks now, I deeply regret getting it installed. It has started to give me anxiety. The first thing I do in the morning is check how much my energy bill for the day before is. Usually I’m horrified. For the last week or so it’s been anywhere between £26-31 a day. The real kicker is that the house feels like a fridge. A couple of the rooms (below loft space) don’t get above 14 degrees and the others (even downstairs) hover around the 18 mark. They just won’t go higher. 

Heating is only meant to come on for a couple of hours early morning and in the evening but since the thermostats can never hit target temperature  the heating comes on automatically. 

I am at a loss. If anyone lives in around South London and is familiar with the Grant ashp I would be in your debt if you could visit and show me how it works. 

thank you

@lucgw I'm sorry to hear about your problems. I suggest you make another thread about your system specifically to not get it confused (or maybe @editor can split it).

A couple of questions from me to hopefully get you on the right track:

1. When you had the heat pump installed, did you have your radiators changed? Or perhaps did they install underfloor heating (often shorted to UFH)?
2. What temperature is the water generally coming out of your heat pump once heated? This is also called flow temperature and leaving water temperature (LWT) to help with your controller. 
3. Does the flow temperature change with the outside temperature? This is called weather compensation or something similar. I think I even linked to a Grant manual above with where to find this setting. 
4. When you say the heating is meant to come on for a few hours, but it comes on "automatically", do you mean it stays on all day? 
5. What is the heat loss figure that was given to you when someone came round to measure your house for the heat pump?  
6. With the above you will probably also have been told a designed flow temperature. This is the flow temp for when the outside is basically as cold as it goes which in your area might have been about -2C. What's that design flow temp? 

Some general observations about air source heat pumps that might give you something to think about:

1. The lower the flow temperature to keep your house warm enough, the better. All other factors including the intricacies of your pipework, heating emitters, valves, buffers or whatever are all worth considering basically because of this point, to reduce that flow temp. That means though that you can start today without changing any of the setup. If you can lower your flow temp from 55C to 40C even if that means having the heating on all day every day, you will save money assuming the indoor temperature is the same. 
2. When it gets cold, as this week, not only does your house need more heat, but there is less heat in the air for a heat pump to extract. This means much higher running costs than when it's warm. This is somewhat unfortunate, but should balance out across the year with big savings in warmer months compared to other forms of heating. 

@oswiu 

thank you for responding. I’ll reply to each of your points above:

1) all got changed to UFH. Bathrooms and ground floor are all tiles and the rest on the house is engineered wood. We put an undelay under the wooden flooring as the company we bought from assured us that it was compatible with UFH.

2) how do I check the flow temperature an LWT? Are these the same? Sorry I find the whole pump, cylinder, pipes, manifolds and thermostats overwhelming. 

3) the weather compensation is at 0 degrees. 

4) I think as it’s trying to reach a target temperature it does come on when it’s not meant to in the day. I’ve tried to lower the target temperature in each room to either 17 (or in some rooms 14) as the temperature just won’t get above those levels.

5) I’m not sure. But we have spent a small fortune or putting new double glazed Aluminium windows around the whole house as well redoing the lofts and putting more insulation in them. Where there is no wooden boarding in the loft it’s 270mm insulation, where there is boarding there’s 200mm.

Thank you for the advice too.

@lucgw Hi, I'm quite new to this forum and an finding a similar problem.

We had 2 10kw grant Aerona installed last January with 11 new oversized radiators.

Since November our usage has gone up dramatically anywhere between 30-80kw per day in November, and 60-140kw through December.

Through the summer the system had been a dream used primarily for hot water with the flow set at 60 degs (since turned down to 45) Our use has also risen so much due to EV needing more frequent charging due to the freezing conditions.

The house is warm with the heating on manual and thermostat set at 20 (tweaked from 22 in the last week).

What I did discover was that my use was spiking after my water heating schedule finished as I was heating my cylinder overnight on a cheaper tarrif to top up for an hour through the day. I've adjusted this since to heat water more frequently (as suggested by somebody on this forum), for shorter periods, thus hoping there's still enough ambient heat that I don't get 2 or 3 kw spikes the following hours for heat. So far I think this is helping...

I am fortunate to get RHI and awaiting SEG from the PV which should reduce my bills anually £2200 for the next 7 years for so far yearly use of approx 17000 kw! 

On reflection I do wonder if I should have invested in more PV, diverters and a decent battery size and installed infrared panels to heat individual rooms instead to have more control over my heating.