Turning our heat pump off over summer and a general moan

[RogerH]

JamesPa I don’t really understand.

I suppose what concerns me about connecting cylinder to heat pump is the cost of paying someone to do it, and who would do it, then complicating a system, that we understand. I need to know that the change would yield a good result. At the most we could save about 260 kWh pa. Because I don’t have the technical skill or knowledge I would be relying on someone else and trusting them. So far the installer(s) used have not been that knowledgeable or trustworthy.

The solar panels ,house batteries, solar diverter and car charger have worked out fine after many workings out with technicians over the phone. The heat pump not so much. With that I feel we are trying to make the best of an oversized pump for at least seven years because financially we are tied to it it with the RHI payments. After that we will think again.

in general it seems that there are no whole house retrofit experts (near us anyway) who know how all the bits work together and thus exactly what the best options are. The heat pump engineer who installed the mixergy tank did not understand the solar diverter so wouldn’t connect it up. The solar installer (initially) couldn’t design the system to work with the solar diverter and car charger, and seemed reluctant to talk to the company who installed the car charger. No one seemed to be able to work out easily where to put the ct clamps, for example. The heat pump installer was utterly unresponsive about anything until NAPIT got on his back. No one seemed to be able understand the work I’d done already, for example that we had so much insulation that we really don’t  need radiators upstairs or that our max heat loss at minus 3 really is under 3kW and therefore a 6kw heat pump won’t be able moderate low enough and thus we are left with cycling and thus a COP of 2.4. All this stuff we have had to learn ourselves.

 

as far as MELCloud goes I will contact Mitsubishi.

 

 

 

[SteamyTea]

23 minutes ago, Marvin said:

You miss the point. Quite surprising for you SteamyTea. Perhaps it me.

May have.

 

[JamesPa]

7 hours ago, RogerH said:

Hi All, this is my first post. We have a 6kw ecodan installed to radiators in dec 2021. We have hot water taken care of with a mixergy tank and solar PV and octopus go so not connected to heat pump. Therefore we have no need for it over summer. It looks like the pump uses about 20 kWh of energy over each of the summer months. I only noticed when I was looking back at the ‘consumed’ monthly figures in the ftc. In summer there are consumed figures but nothing ‘delivered’ . Our total kwh consumed by pump for 2022 was 1560 kwh so quite a bit of that, about 120 kWh was from it ‘doing its own thing’ in the summer. Can I safely turn it completely off in summer? 
Also I have been taking daily readings from ftc recently (of delivered and consumed energy), how accurate do people think these figures are for the purposes of determining COP? ( Also the Mitsubishi app is hopeless). If the consumed kwh for summer have not delivered anything then they have to be deducted from the total delivered figure to get an accurate COP. Also if I want to really get on top of our COP is it worth doing something like open energy monitoring? By the way our COP for 2022 was 2.4 so I am working on ways to improve it., also the installer has gone bankrupt!
BTW we have been through all the NAPIT complaints procedure to no avail. They think the pump was installed properly. 

In general, the installer was hopeless and now non existent , MELCloud hopeless, NAPIT hopeless. But we did get RHI and we don’t use much energy because we have done a deep retrofit (37 kwh per m2 for space heating), not because the pump is working efficiently. 
And relax.

 

 

 

 

 

In fairness this thread has gone down a bit of a rabbit hole about the summer consumption, which is a minor part of the story.  Having established that its as per spec, about 25 W, and yes you can turn it off, and furthermore, given you have solar PV, your DHW is heated nicely by your solar diverter in summer and most probably autumn and spring also (so heating it from the ASHP in winter would be nice, but not essential(, perhaps its time to think about the bigger picture ie 1560kWh per year.  You say that the house is 37W/sqm, how big is it/whats the estimated annual heating requirement, what flow temp is it running at and has weather compensation been properly adjusted?  

[ReedRichards]

Off topic but what does this message mean?

• Quote

  5 hr Nickfromwales changed the title to Turning our heat pump off over summer and a general moan

[JamesPa]

... Further to the above it would also help to know how its controlled eg is everything just left to the ecodan controller or is there also one or more roomstats/TRVs and if so are they actively controlling the system most of the time or set above the desired temp as 'iimiters' .  Given this information and the information above it might be possible to work out whats going on

[SteamyTea]

14 hours ago, RogerH said:

By the way our COP for 2022 was 2.4 so I am working on ways to improve it

That does seems to need improvement.

Edited January 19, 2023 by SteamyTea

[Marvin]

10 hours ago, RogerH said:

All this stuff we have had to learn ourselves.

Hi @RogerH

 

You have my sympathy. We have had to do the same. The mix of technologies now being installed in homes has only recently started to come together and the biggest hurdle I see, in trying to make it all work together, is that the answer can change for each individual property and its use.

 

As for turning off the ASHP:  You are fine turning off your ASHP, however consider this when turning back on:

 

If the outside temperature has been below 5 Centigrade in the last 12 hours the liquids in the compressor in the outside unit could be too cold for the unit to work properly. If this is the case you need to leave the system on standby for 12 hours for it to warm up.

 

I do not know which Ecodan you have but here is an Ecodan instruction manual. See section 7: Test run.

 

https://library.mitsubishielectric.co.uk/pdf/book/Ecodan_PUHZ-_H_W_Installation_Manual__BH79D532H03_#page-7

 

Different ASHP have different ways to solve this technical problem so check with your own model instruction manual.

 

As @JamesPa has started asking, to help with the question of how to improve your ASHP efficiency, we would need to know a lot more about what system has been installed. Personally I would have started with the physical aspects in detail.  

 

What is the make and model of your ASHP

Is the ASHP connected to a buffer tank.  If so, what size in litres, where is the buffer tank in the building, how long is the pipe distance between the ASHP and the buffer tank. Photos would help

 

What is the ASHP feeding. Obviously not water, radiators? underfloor heating? If underfloor heating what thickness is the insulation under the floor and what type. 

 

ASHP efficiency is related to the principle of low and slow: Low heat, slowly warming the property. If you do the opposite your COP will drop dramatically. Bearing this in mind any little leak of heat becomes important to avoid. The main pipes from the ASHP I have insulated to within an inch of their lives!

 

Good luck

 

M

 

 

 

 

 

 

Edited January 19, 2023 by Marvin
tidying

[PhilT]

15 hours ago, RogerH said:

By the way our COP for 2022 was 2.4

An estimated COP of 2.4 from the controller or MELcloud could be based on bad data. Given this uncertainty I would get a second opinion from Mitsubishi tech, who can see the data remotely if you give them permission, although not sure why the data they see would be any different from what you see, but worth a try anyway!

[jack]

3 hours ago, ReedRichards said:

Off topic but what does this message mean?

 

Most likely correction of a typo or formatting in the title.

[PhilT]

13 hours ago, Marvin said:

I would recommend checking out a solar diverter to anyone who has PV and a hot water tank with an immersion. 

I did give this a lot of though and decided against as I get 15p fixed SEG, my heat pump is doing better than COP of 3 for DHW, so at my current variable electricity rates 33p it would cost me 4p/kWh to use a solar diverter instead of the heat pump, or cost me 8p/kWh assuming "Cosy" rate 21p/kWh, and that's before taking into account the up front cost of the diverter (a few hundred quid?). Have I got that logic correct or am I talking complete cobblers?

[RogerH]

Sorry that this has become a rabbit hole. I didn’t know how much help to expect from the forum. Thanks for all you replies. 
est heat demand Pa from heat loss survey:7356 (actual delivered energy from heat pump (2022) 3744), pleased but not sure why there is such a difference 

area of house: 100m2 

model: PUZ-WM60VAA

no buffer

straight to radiators

1 room thermostat in living room supplied by Mitsubishi

in heating season we set back temp on stat to 18 degrees and then to 19.5 daytime

flow temp 38 degrees (didn’t spend much time using adaptive mode)

not tried wether comp yet

[SteamyTea]

24 minutes ago, RogerH said:

straight to radiators

Are you using TRVs.

Have you checked that there is enough volume in the smallest circuit.

[RogerH]

Not using TRvs except that they. Are always open . Smallest circuit?

[RogerH]

Sorry,typo. All rads have TRVs and they are all open. We don’t use them.

[SteamyTea]

19 minutes ago, RogerH said:

Smallest circuit

If your system is zoned, one of the water circuits will have the smallest volume.

If that volume is smaller than the ASHP can reliably handle, then you will get a lot of short cycling of the ASHP.

 

Get rid of the TRV in the summer, they are not needed.

[RogerH]

We only have one zone. What do you mean by ‘get rid’?

 

 

[JamesPa]

2 hours ago, RogerH said:

Sorry that this has become a rabbit hole. I didn’t know how much help to expect from the forum. Thanks for all you replies. 
est heat demand Pa from heat loss survey:7356 (actual delivered energy from heat pump (2022) 3744), pleased but not sure why there is such a difference 

area of house: 100m2 

model: PUZ-WM60VAA

no buffer

straight to radiators

1 room thermostat in living room supplied by Mitsubishi

in heating season we set back temp on stat to 18 degrees and then to 19.5 daytime

flow temp 38 degrees (didn’t spend much time using adaptive mode)

not tried wether comp yet

OK several thoughts:

 

The difference between calculated demand and measured could be real or not.  If its real then the most likely explanation is pessimistic assumptions about air changes or building materials, or just that you have the house colder than the design 21C.  All the calculations for my house says it needs about 11kW continuously to keep it warm when the external weather temps is -2, actually the measured value during the cold spell earlier in the season was 7kW.  I am pretty certain that's due to a combo of lower than assumed air changes and  slightly better than assumed fabric, plis we aim for 20 not 21C.  But it could be that your measured output is underreported by the Ecodan.   Difficult to tell unless you have an independent way of determining the actual load.

 

Assuming that the measurement of delivered heat is correct, the efficiency does seem poor.  I would suggest that as a starting point you get weather compensation going.  As it is currently operating it must either be cycling a lot (other than at the coldest design temp) or the TRVs or the main thermostat must be shutting down to compensate for hotter than required flow temp.  Weather compensation has been mandatory in Germany for decades (and Im talking gas boilers which don't benefit anything like as much from WC as do ASHPs), but of course our government deems the British (or British installers) too stupid, lazy or ill-educated to cope, or is too influenced by developers protestations about the extra cost (a few £100).   Fundamentally (in the physics) the efficiency of an ASHP is linked irrevocably to the difference between the source air and the flow temp, so keeping this as low as possible at all ambient temperatures is rule no 1 for efficiency.  Ideally the ashp should be running and heating the circulating water continuously with all the zone valves/TRVs (if any) open whatever the ambient temperature, delivering water continuously to the radiators at a temperature just sufficient to get the room to the temperature you want.  Neither the TRVs nor the thermostat should be doing anything at all, other than to limit the heating if there are exceptional conditions eg high solar gain.  

 

Then, as others have pointed out, you need to consider (short) cycling (ie cycling on and off with a short on perios eg <10mins) because of the limited modulation depth of the machine (ie the extent to which it can turn down when the the heat demand is low).  You cant avoid cycling when the heat demand is lower than the minimum output of which it is capable (guess  - around 2kW, its somewhere in the spec), but its better if the cycles are long.  That is achieved principally with sufficient thermal mass, ie volume of water in the system (radiators plus pipework).  Do you happen to have an estimate of your system volume.  If you have only small radiators it could be quite low and its possible that you would benefit from additional volume from a volumiser/buffer tank, but I wouldn't personally conclude that until you have eliminated other causes.

 

One other thing you might do by way of diagnostic is to look at the figures during moderately stable periods of low, medium and high ambient temperature.  That might give you an idea of whether the problem lies in a particular part of the temperature range.   Unfortunately we dont often have stable temperatures for an extended period (although we did back in December have a stable period of very low temperatures followed by a stable period of unseasonably high temperatures - perfect for testing Central heating systems)

 

I don't know if that makes sense or helps.  Keeping the message simple - get weather compensation going and see if it helps, get an estimate of your system volume to see if short cycling is likely to be a problem.

 

 

 

 

 

 

 

 

[RogerH]

Thanks James, I will start to use weather compensation. The rads were enlarged to suit the heat loss survey carried out by installers. We found that the living room was not getting warm as quickly as the other rooms and I read some stuff somewhere about the importance  of volume of water, and because we have no buffer we doubled the rad size in living room. So far perhaps slightly better COP but it only happened 2 weeks ago. No I don’t know how to estimate water volume in system and then use that info. No room for buffer tank in house so I’d have to build a box for it outside if it came to that.
I do wonder whether it is a good idea to invest in some more accurate way of determining what is happening. Not sure I am geeky enough to get into open monitoring and more cost though.

The  other issue that has been noticed by the NAPIT technician who came to the house is that there are a lot of 90 degree bends between the ASHP and the rads. All the pipework is squeezed into an under stairs cupboard. I really don’t know how significant this sort of thing is.

[JamesPa]

1 hour ago, RogerH said:

The rads were enlarged to suit the heat loss survey carried out by installers. We found that the living room was not getting warm as quickly as the other rooms and I read some stuff somewhere about the importance  of volume of water, and because we have no buffer we doubled the rad size in living room.

its worth watching the heetgeek videos on 'balancing'.  Basically adjusting the flow through the radiators so that, with the TRVs set to max (or the head removed) so they never close down, your rooms heat to the same temperature (or alternatively so that the temperature drop across each radiator is the roughly same - much easier but arguably less accurate).  Its not exact, but making some effort at balancing is a good idea.  You do this using the lockshields or, if you have TRVs - eg Drayton, with the ability also to apply a fixed restriction - the restriction adjustment on the TRVs.

1 hour ago, RogerH said:

No I don’t know how to estimate water volume in system and then use that info

The manufacturer data on the radiators tells you how much water is in them (sometimes for each radiator, sometimes per metre).  If they are all the same height and type (11, 20, 21, 22 etc) then you can just add the lengths together to get the total.  No need to do it exactly, +/-20% gets you in the right ballpark.  Then you add something for the pipework the volume of which is calculable using pi r squared times length (which you can estimate).

 

1 hour ago, RogerH said:

The  other issue that has been noticed by the NAPIT technician who came to the house is that there are a lot of 90 degree bends between the ASHP and the rads.

I had nightmares about fluid dynamics at uni, so I cant comment 'from first principles'.  maybe there are plumbers on this forum who can,  My understanding is that bends basically add resistance which means your pump will need to work a bit harder.  Thats unlikely to be significant unless there are lots more bends in the route to one radiator than others.  Balancing sorts this unless its an extreme problem.

 

1 hour ago, RogerH said:

I do wonder whether it is a good idea to invest in some more accurate way of determining what is happening

Very possibly, but just watching (and recording) the behaviour in various periods of different stable outside temperatures might suffice.  Of course sophisticated monitoring would be nice.

 

1 hour ago, RogerH said:

I will start to use weather compensation.

It should definitely improve things.  Whether its enough to get the system up to expectations is another matter (quite probably not), but best first to eliminate the obvious shortcomings before exploring the obscure.

Edited January 19, 2023 by JamesPa

[SteamyTea]

Wot @JamesPa says.

 

It is worth getting an IR thermometer and you can get fairly good weather data for your region from WeatherUndeground.

 

[RogerH]

Thanks everyone. I will act on the advice given and report back in the future.