Apologies can't answer your question but your posts have been really useful for me to follow - thanks. 

Hi Kev M,

You are indeed correct that it would be more efficient to produce your hot during the day time when the outside temperature is higher. As the ambient air temperature falls quite low at night at this time of year, it is beneficial to reduce the heat demand on your ASHP as much as possible when it is operating at its least efficient.

I am assuming that you do not have solar thermal or solar PV with which to produce your hot water.

Regards,

Derek.

@Derek-M, thanks, I'll have a play with the HW settings.  No we don't have solar PV or thermal (yet) but will have a look at the numbers.  

We have been living with the ASHP for one month now so here are some numbers for anyone interested.  The ASHP controller provides various simple summaries, including a month by month breakdown. This table is for the whole month of April, including my total electricity consumption from my meter (I must speak to Mrs M about the tumble drier!)

Overall I'm happy.  It's hard to compare exactly but my October kWh for E7 (which was exclusively my heating and HW) was 1925. I don't think October 2020 was colder than April 2021 but I'm not sure.  But 860 is a lot less than 1925.  In terms of money it's not quite as big a saving as 100% E7 is (obviously) cheaper than my current mix but April 2020 ASHP electricity cost about £70 less than October 2020 E7. 

The daily ASHP average was about 29 kWh per day with a low of 17 and a high of 39.  That's keeping the house at average temps (19-21 deg).  The ASHP was left as installed, with max heating output and HW both at 50 deg and on weather compensation.  

It hasn't been really cold and I expect efficiency (and cost savings) to dip when it is.  As it gets warmer there is less scope or reason to tinker but I may have a play with the heating and HW timings and temperatures.

I also need to think about tariffs.  I am on an E7 tariff atm and I used a surprising amount of E7 - about 60/40 Normal/E7.  I think this is because I have the thermostat set so that the ASHP comes on early morning during E7 when it's coldest and least efficient.  But that's OK if E7 is cheap enough; in fact it might be worth getting the house fully heated up to temperature entirely on E7 before more expensive day rates kick in and leaving HW until the middle of the day when it's a bit warmer and the ASHP is more efficient.  It will depend on the tariff though; I'm currently on 11.6/7.6 but this is only for a couple of months more.  

Anyway, so far so good.  We have a much better heating system, it looks like it's cheaper to run and the taxpayer will be paying for most of the installation. 

Hi Kev M,

Thanks for the energy figures, it is always good to see some positive data with relation to ASHP's.

Even for E7, your present tariff is excellent, even the daytime rate. Our present tariff for electricity, which ends next month, is 14.7p/kWh.

Reducing ones carbon footprint, without emptying ones bank account, is a continual balancing act. It is therefore necessary to spend a little time  looking at how we heat our home and provide hot water in the most efficient and cost effective manner. From the point of view of assessing your system and how it operates, it may be useful if you could split the day into 6 or 8 hours periods and make a note of the energy consumed during each period along with the time of day and weather conditions. This should give you some idea of the most energy hungry periods during the day and how it varies under different weather conditions. We have had quite a number of fairly warm sunny days this April, accompanied with fairly cold nights. Our Solar PV system has generated considerably more than it did during April 2020, which means we have also received a higher amount of solar gain. (if you are not certain what I mean then please read my recent article 'How to train your Enthalpy).

Having Solar PV along with an ASHP is certainly beneficial, in that on many days it will provide some, if not all, the electricity required to power your ASHP during daylight hours. Obviously it is not cheap to install Solar PV. Any excess generation can be used to provide hot water.

If my understanding is correct, a cheaper option is Solar Thermal, which is much more efficient than Solar PV, but of course only provides hot water. Even so it should reduce the load on your ASHP and hence save energy and reduce costs. You would need to confirm, but I do believe that you can claim RHI payments for Solar Thermal.

I hope this is of use.

Regards,

Derek.

Nice one Kev M. How do you derive the “delivered” numbers?  Do you have MMPS?

We’ve so far used 93kWh in 12 days. I will have to see if, by pressing buttons on the Daikin internal unit, I can get delivered heat.

Thank you and I’m glad the ASHP is working out

@julianc, no MMCP yet but our ASHP gives the delivered and consumed numbers through the Ecodan control panel. I don't know how accurare they are but they look in the right ballpark.

93kWh in 12 days seems very low.  That's less than 8kWh per day; are you sure that's right?  

We only have a consumption meter. Just checked, we’ve used 103 kWh in 12 days or 8.6/day. I guess bony running too much. H/w will be partially heated via Solic 200 diverter from solar PV.

I hope it continues to be economical. 

Hi JulianC & Kev M,

Julian, just to clarify the figures you quote, are they imported power derived from your electricity meter or power used by your ASHP?

Like me, you also have a 4kW Solar PV system which will have contributed towards running your ASHP and also possibly provided some hot water. You also have a lot of glass, so will have benefited from Solar Gain. This will have reduced the amount of electrical energy imported from the grid.

Because you have a lot of glass, do you find on sunny days the temperature increases in your home to the point where the heating shuts down and only comes back on as the Sun goes down?

It is important that we look at all the different ways in which we can utilise the free 'green' energy available for much of the year.

Derek, you are correct on the one hand. We get good solar gain when the sun is low in the sky (winter). In the summer when it’s high, the roof glass has a solar reflective coating to reduce gain by 90%. It used to get too hot. 
The meter shows additional electric used by the ASHP, so there could be a bit from the PV. But. Think most of that heats the water. 
Agree with your point on get green energy where you can. 
I think the house stays reasonably warm anyway. We are protected by a wall. And we wear jumpers in the house 😄

I think April has been colder this year than last. I’m sure the oil boiler was off this time last year

Another update.  As expected, usage is down and COP is up as the weather gets warmer.  It's changed from 25-35 kWh/day and COP of 2.5-3 on cold spring days with overnight frost, to 12-15 kWh/day and a COP of >3.5 in the warmer May weather we're having now.  Everything else is working well and I haven't tinkered with any of the settings yet.  The heating is still coming on in the morning and evening but it's not got as much to do.

I've decided to go ahead with MMSP; I'll get more than 1/2 my money back right away, the rest after 5 years and make a bit in the last 2.  It'll also make analysing numbers and tinkering easier. 

While our usage is down from April, I cannot believe that we've used 477kWh in May for heating and hot water. It's mid-May. Last year, in the whole of May we used 440kWh. The weather has just been so cold.