Posted by: @profzarkov

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Hello folks,

It's still early days with my new install. I'm impressed with the ASHP as it keeps the whole house cosy. Having come from a coal fired stove. I've set the thermostat to 19°C pretty much all day from 0530 to 2300. And setback between that to 17°.

I'm lucky in having solar & a Powerwall 3, so the battery is charging up at 8p/unit at 0030 and powering the whole house during the day.

Any suggestions on changing the stats? The pump is adjacent to our bedroom so I didn't want it blowing all night. There is a quiet mode and this can be scheduled...what is actually do....

Cheers 

Prof

Welcome to the forum, Im sure you will find people here, who are happy to help.  Its also good that you like your ASHP!.  As far as the forum is concerned no question is too silly, just ask.  A 3C setback at night is a good approach in many cases

Can you answer a couple of questions to give us some context:

What pump have you got?

When you speak of a thermostat, is it external or the heat pumps native controller.  If the former, what model?

@jamespa Hi 

I left detalles in my profile:

Retired physics teacher 

New Eco4 install 

Samsung 8kW ASHP

Neomitis & Hive thermostats

12x425W solar installation= 5 kW

Powerwall 3 installed and working well. Don't use the zone two neomitis thermostat. Just the hive...easier to monitor and tweak 

Using the Hive may be a bad idea. 

Fundamentally the primary control of heat pumps should be the heat pump's own controller, and in particular weather compensation.  This adjusts the 'flow temperature' to be as low as possible consistent with heating the house, based on measurements of the outside temperature (which as a physics teacher, you will know is the principal determinant of the energy lost from the house, which must be replaced by your heating system).  WC matters because the thermodynamics say that heat pumps get more efficient as FT falls, by 2-3% per degree C.  By adjusting the WC curve correctly you should be able to maintain a very even temperature at minimum cost.

Its possible to 'layer' a temperature sensor on top of that, either by setting it a couple of degrees higher than the target so it switches off the heat pump when there is eg solar gain, or by adjusting the WC curve a degree or so above  the ideal and then using the thermostat to 'tweak'  The latter results in a slightly sub optimum efficiency (perhaps 2-6% penalty), but is better than not using WC at all.  The temperature sensor/thermostat, if you use one, must be simple on/off, not one that applies a PWM signal as the temperature approaches the target, which some 'smart' stats do.  I don't know what Hive does in this respect.

Mitsubishi heat pumps feature an 'adaptive/learning' mode (I cant remember exactly what they call it).  This starts with the WC curve but then learns about your house and tweaks it.  To enable this you must be using the sensor in the heat pump controller (or possibly an external sensor connected to the controller) and certainly not an external stat such as Hive.

Finally TRVs should be used sparingly.  The ones in the main living area should be either fully on or set 2C above the desired temperature so they act as limiters but not controllers.  In a sufficiently large house its possible to use the TRVs in eg bedrooms to throttle the heat.

You may need to rethink for optimum control, the cost of not enabling WC is about 20-30% in many cases.  Correctly adjusted WC will also improve comfort, as the thermal gradients (both in time and space) are reduced.

Finally your installer should have set all this up properly and explained it to you!  Perhaps they were put off by encountering a physics teacher who (depending on the quality of the installer) is probably capable of a deeper understanding than they have!

BTW weather compensation is nothing new, many boilers have featured it for years and in some more enlightened countries its mandatory.  Although the efficiency gains in boilers aren't quite as much, they are still present.  Sadly our, somewhat backward, heating industry shunned WC for boilers and, as a result, we have almost all being paying 10% more for our heating than we need to for about the last 10-20 years (basically since condensing boilers were introduced).

Hello

And thanks for that.

I think the Hive does have a program that gets the system to the target temp by the target time but I don't use that. It's just an on off stat but one I can see and monitor on my phone , at home or away.

We have no trv's.

Small bungalow with 8 rads .

WC was set and I have adjusted it, I think it's -2 & 45°, 14 & 32°.

I'll check that then amend my profile.

I've lowered the water temp down to 45° too.

Are you implying that I should set the stat to a much higher temp, in the day and just leave the ASHP to do it's thing. If it's too warm, adjust the WC settings?

Early days & very impressed so far.

Energy costs are about £3-4/day. Whereas coal & oil we're £7.

Prof

Posted by: @profzarkov

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Are you implying that I should set the stat to a much higher temp, in the day and just leave the ASHP to do it's thing. If it's too warm, adjust the WC settings?

Yes, the minimum cost will (almost certainly) come if you get the WC adjusted so it just heats the house to temperature so the lower you can get it while still heating the house the better (by 2-3% per degree C).  Obviously to do that you need to have the thermostat well above the target temp, so its doing nothing.  Low and slow is the mantra with ASHPs.  The theoretically 'ideal' way to run them is 24*7 with the ASHP continuously drip feeding the house with energy at exactly the same rate as energy is being lost from the house.  Tweak, but start from there, certainly when its cold outside.  Its all in the Carnot equation - basically the efficiency gets better as you reduce the difference between flow temperature and outside temperature.  You dont have control of the latter but you do have control of the former.  Once you get to the shoulder/ends of the season the simple theory might be overtaken by fixed loads (eg pumps and electronics) in which case timed working may prove more efficient in practice, depending on your house. Also of course if you have a ToU tarriff you want to pump it up a bit during the cheap periods.

@jamespa thanks.

Yes, I'm on a weird combo of Octopus Go & outgoing Lite.

Which gives me 5 hrs (0030-0530) of 8.5p import. Then it's the std 25p during the day with a flat rate export of 15p !

I'd be very surprised if we export any at this time of the year.

We have a Tesla Powerwall 3 which I charge up at 0030 fully, and then it runs the house almost all day.

Posted by: @profzarkov

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@jamespa thanks.

Yes, I'm on a weird combo of Octopus Go & outgoing Lite.

Which gives me 5 hrs (0030-0530) of 8.5p import. Then it's the std 25p during the day with a flat rate export of 15p !

I'd be very surprised if we export any at this time of the year.

We have a Tesla Powerwall 3 which I charge up at 0030 fully, and then it runs the house almost all day.

at 8.5p per kWh its probably not worth spending too much time optimising for efficiency unless you want to enter into the top of the SCOPs competition that takes place on heatpumpmonitor.org!  If, during sustained cold periods, the battery capacity is insufficient then a good strategy would be to pump energy into the house overnight using the heat pump.  Otherwise follow the basic principle of getting FT more or less as low as possible consistent with heating the house, when its cold leave the ASHP on 24*7 or thereabouts, and enjoy bountiful, cheap comfort!