Posted by: @batalto

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@cathoderay three other courses of action for you might want to try?

1. More loft insulation?
2. Swap the rads for more efficient ones? e.g K3 type
3. Remove the heat exchanger and go direct from pump into the house

Thanks, in fact much of this is already done or in hand:

1. Loft insulation: already part done, rest ready to go in once I have removed old cold water and central heating header tank.

2. K3s (strictly speaking not more efficient, just more output per metre squared of wall space taken up). All but two are already K3s, part of the design.

3. Remove PHE (and flip the dips) both of these are more radical option, and possibly not without unintended consequences eg even higher running costs if I flip the dips. The PHE is in a very tight space in the 'airing cupboard' and removing it will mean disturbing quite a lot of pipework. It is not something I want to rush into now, while it is cold, if at all. I do however note your results after removing the LLH. But a LLH is not a PHE...

The other thing I am doing is adding secondary glazing, which will also reduce draughts, which are not insignificant. It is slow work, because the frames typically need repairs, and then redecorating, before fitting the secondary glazing.

@cathoderay if you are doing something more extreme you could consider insulated plasterboard? Something I will 100% if we come to replaster

Posted by: @batalto

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if you are doing something more extreme you could consider insulated plasterboard

This definitely comes at the very extreme end of the scale for me, very disruptive eg fitted kitchen (I have sometimes also wondered whether fitted units are themselves a sort of insulation, but don't get included in heat loss calcs) not to mention awkward shaped walls, and expensive, and may well come up against listed building consent buffers. 

Posted by: @cathoderay

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Posted by: @benseb

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You might be more successful at a lower temp.

I doubt it, the system was designed with a flow temp of 55 degrees. Lack of available wall space for rads was a major constraint, necessitating a higher than ideal flow temp, But, as designed, the system needs these flow temps, any lower and the rads will not put out enough heat.

I agree it is absolutely a whole system thing, ASHP => circuits => emitters, as I have said many times. Each part of the system needs to do its bit. As designed, the rads can put out enough heat at 55 degrees flow, the weak link in the system is the heat pump which does not put out the 12.4kW plus headroom claimed by Freedom. It's going flat out, and doesn't get the system up to design flow temp.

For anyone wondering whether I am going to flip the dips, the answer is not yet, because doing so is bound to increase consumption, and as I am already using ~100kWh a day, I really don't want to push that up any further. I'd rather put on an extra layer of clothing. The point under discussion here is whether the heat pump as part of the designed system is adequate or not, not what I do if it turns out it isn't adequate.    

It looks like that, at the design ambient temperature, the ASHP is unable to achieve the design flow. It certainly sounds like your ASHP is under-powered. Were potential losses from the PHE factored into the calculations?

On flipping the dips, it's hard to say whether this will result in higher energy consumption without knowing exactly what happens when you do (and I'm not sure how you could find out).  What I do know is that with my ASHP (the average/mediocre one), for all models, the COP tends to drop as they approach their maximum capacity.  It's not 100% consistent but the tendency is there. See attached.  Do you have any similar data for Midea?  

Posted by: @cathoderay

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Posted by: @benseb

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You might be more successful at a lower temp.

I doubt it, the system was designed with a flow temp of 55 degrees. Lack of available wall space for rads was a major constraint, necessitating a higher than ideal flow temp, But, as designed, the system needs these flow temps, any lower and the rads will not put out enough heat.

I agree it is absolutely a whole system thing, ASHP => circuits => emitters, as I have said many times. Each part of the system needs to do its bit. As designed, the rads can put out enough heat at 55 degrees flow, the weak link in the system is the heat pump which does not put out the 12.4kW plus headroom claimed by Freedom. It's going flat out, and doesn't get the system up to design flow temp.

For anyone wondering whether I am going to flip the dips, the answer is not yet, because doing so is bound to increase consumption, and as I am already using ~100kWh a day, I really don't want to push that up any further. I'd rather put on an extra layer of clothing. The point under discussion here is whether the heat pump as part of the designed system is adequate or not, not what I do if it turns out it isn't adequate.    

It looks like that, at the design ambient temperature, the ASHP is unable to achieve the design flow. It certainly sounds like your ASHP is under-powered. Were potential losses from the PHE factored into the calculations?

On flipping the dips, it's hard to say whether this will result in higher energy consumption without knowing exactly what happens when you do (and I'm not sure how you could find out).  What I do know is that with my ASHP (the average/mediocre one), for all models, the COP tends to drop as they approach their maximum capacity.  It's not 100% consistent but the tendency is there. See attached.  Do you have any similar data for Midea? 

Posted by: @kev-m

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Do you have any similar data for Midea? 

@kev-m - thanks. I would normally think it is a given that if you have two units (or in this case the same unit running at different outputs) running flat out, then a higher powered unit will always consume more energy (and also put out more energy). At lower outputs it may be less obvious, but I think a difference will still be there. But with heat pumps, nothing is ever that simple.

We do have data for the Midea unit, but it is in tabular rather than graph format, and COP does fall as output increases. This raises an interesting possibility. What if (these are nominal not actual numbers to illustrate the idea) the 16kW unit operating at 14kW is actually more effcient than the 14kW unit running at 14kW, because the 16kW unit is not running at 100% capacity (better COP) where as the 14kW is at 100% capacity (worse COP). I will dig out the tables and if I can plot the relevant data.

Shocking COPs from these Midea units in the current climatic conditions. For comparison, here's a samsung gen6, running without a buffer or LLH, on the samsung controller. Rads sized for 35 degree flow temp:

http://emoncms.org/samsung5kw

@hughf a couple of points on that. Firstly I think my midea is way more efficient than it gives itself credit for in the app. For example the other day I measured the power draw for the it at 1.3kw, but it rounds up, so it recorded 2kw as its used power. Across a whole day that's the difference between 31kw and 48kw consumed. If I had a COP of 3 off the app, I might actually have a COP of 144/31 = 4.6    - these differences are insane, and I've raised that with Midea about their app. It doesn't count decimals and it seems to then count the rounded numbers in its total. A key example is this morning, at 5am to 6am my max power draw was 4.5kw across the hour, in reality it peaked at 4.5kw but lets assume that was static for the whole hour. The Midea unit registered its use at 5kw <--- not possible.

My ASHP said it used 82kw yesterday, but I only only purchased 72kw and I generated 17kw - that makes 89kw total a difference of 7kw. There is no way with lights, cooking, the tumble dryer and washing machine I used 89kw. The only logical answer is that the Midea unit over eggs its actual use. 

Second, my flow temp is way higher than 35 degrees as its 45 at -3. I could probably clamp a proper meter on it, but I know its wrong from my fuse box which is logging actual power consumed total from the ASHP. 

@batalto Interesting.... Any Mideas with level 3 monitoring floating about that we can have a look at?

@hughf yeah its annoying its not accurate. At the moment I am using the figures as a gauge to see how the system is working. I considered using emconpie - but I cant be bothered. Realistically lower flow temps = more efficient and its that simple. Unless someone wants to send me the kit, then I'll install it.

Posted by: @hughf

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Shocking COPs from these Midea units in the current climatic conditions. For comparison, here's a samsung gen6, running without a buffer or LLH, on the samsung controller. Rads sized for 35 degree flow temp:

http://emoncms.org/samsung5kw

I'm guessing you'll have seen it, but for anyone else the video the guy whose data this is made on his install is well worth a watch https://www.youtube.com/watch?v=Hyv_vQEvHgo

Posted by: @oswiu

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Posted by: @hughf

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Shocking COPs from these Midea units in the current climatic conditions. For comparison, here's a samsung gen6, running without a buffer or LLH, on the samsung controller. Rads sized for 35 degree flow temp:

http://emoncms.org/samsung5kw

I'm guessing you'll have seen it, but for anyone else the video the guy whose data this is made on his install is well worth a watch https://www.youtube.com/watch?v=Hyv_vQEvHgo

 

 

Yep, Glyn did a good job of that install. He followed the Midsummer wholesale wiring instructions and has a PWM controlled primary pump.