We have a 9kW Grant Aerona which has been in 5 years now. House is about the same size as yours but detached (so worse for heat loss). We did a full refurb so were able to install underfloor heating upstairs and downstairs.
We have the system set to 19 degrees downstairs (it always settles at 20) all year round. The staircase is open to the living room so heat leaks upstairs and tends to maintain about 17 even though the thermostats are set below that. This works for us as we don't use upstairs except to sleep when we prefer a cooler room. On sunny winter days the radiant heat makes the house feel warmer anyway. It's only on dull winter days that 20 degrees can sometime feel a little chilly if you are just sitting rather than moving around. We can supplement with a wood burner but that's mostly for show rather than regular use.
I too am only able to measure total electricity usage and this was a low of 16kWh per day in July peaking at 75 kWh per day in January. Since January (which, even allowing for the very cold weather, was a ridiculous level) we've had the configuration of the sytem changed and our YTD figures (apart from January) are now better than the previous year. I'm expecting total electricity usage for 2021 to be about 13,000 kWh. I expect to reduce this further in 2022 to under 12,000 KWh, assuming there is no repeat of January. The configuration problem we had was that the pump was trying to heat the house and the water at the same time. It's now set to turn off the heating during periods when it's heating the water.
With the benefit of hindsight our heating system was not designed or installed optimally (although MCS compliant) so I don't think it will ever run as efficiently as it might. But I'm reluctant to tinker with it any more as I'm yet to find a local heating engineer who really understands ASHP installations. Since joining this forum I've become a much better informed end user who, next time(!), would ask a lot more of the right questions of our installer. But this highlights one of the problems of the ASHP market - that customers shouldn't need to be so well informed. It doesn't bode well for the mass market roll-out of ASHPs envisaged by the government.
Having been stung by last winter's experience I am now all over our electricity consumption. I take daily usage readings and also have a Max-Min thermometer to monitor outside air temperature. I've been able to compile some useful graphs of usage, YTD, rolling 12 months and monthly comparisons with the same month in previous years. My wife rolls her eyes whenever I share the latest month's numbers with her. But being nerdy with this saves a lot of money, especially at current electricity tariffs.
What you needs is a 'man cave' at one end of your home and a 'woman cave' at the other end, that way you cannot see her eyes rolling. Works well for us.
I would be very interested to see the data you have compiled. The more data that is available on the forum, the better informed members may be about what to expect from their system, or highlight areas in which their system may be improved.
Do you have any idea of the heat loss of your home and the efficiency of your heat pump? With some optimisation it may be possible to reduce your energy consumption.
The COP rating on the label on back of the pump is given as 2.66 based on Air at 7 deg and water at 55 deg.
The total heat loss given for the whole building on the MCS certificate is 7.21kW
Interestingly that also shows annual energy figures of 14,400kWh for heating and 6,200 kWh for water which is more than my current total electricty usage. I guesss that the MCS figures are based on worst case.
Are these the relevant numbers - I'm good with spreadsheets but my technical knowledge of heat pumps is very thin?
The COP rating on the label on back of the pump is given as 2.66 based on Air at 7 deg and water at 55 deg.
The total heat loss given for the whole building on the MCS certificate is 7.21kW
Interestingly that also shows annual energy figures of 14,400kWh for heating and 6,200 kWh for water which is more than my current total electricty usage. I guesss that the MCS figures are based on worst case.
Are these the relevant numbers - I'm good with spreadsheets but my technical knowledge of heat pumps is very thin?
Mike
Hi Mike,
For maximum efficiency it is best to operate an ASHP at the lowest water flow temperature that meets the heat demand. At an ambient air temperature of 7C, but a water flow temperature of 30C, rather than 55C, you should expect to achieve a COP in the order of 5. Almost twice the efficiency. If you have a copy of the Grant Aerona3 - Air to Water High Efficiency Heat Pump Range (UK DOC 0136 Rev.2.0 September 2020), I can guide your through some simple checks to hopefully see how your system is performing. I have just remembered that your system is 5 years old, so please let me know what documents you do have to hand.
In your manual there may be a section labelled '10 Servicing', though not necessarily with the same page number. Under this section there may be a sub-section labelled Monitor Display Function.
Using the remote controller, follow the instructions given and see if you can obtain the information listed in table 10.3
Then please send me a copy of the data obtained. If you cannot obtain the data then please let me know.
If you would like to read a reasonably detailed description of how the internals of an ASHP, performs the task of stealing energy from the ambient air, then have a look page 1 of the thread labelled 14kW Mitsubishi Ecodan ASHP on the forum.
I very much enjoy using spreadsheets, I think they are one of the most useful tools to have been developed.
I haven't forgotten this, but am busy with work and it will take me a while to dig out the documentation.
If it's possible to improve the COP why do manufacturers not set the default to a higher level anyway? Is it like cars - you can often tune then with a simple ECU remap (with no adverse consequences) to well above their manufactured level.
I haven't forgotten this, but am busy with work and it will take me a while to dig out the documentation.
If it's possible to improve the COP why do manufacturers not set the default to a higher level anyway? Is it like cars - you can often tune then with a simple ECU remap (with no adverse consequences) to well above their manufactured level.
Mike
Hi Mike,
It is not so much to do with the ASHP itself, it is more to do with how it is installed and operated. To use your analogy, you can tune cars for optimum performance, but if you drive then badly you get poor fuel economy.
The COP rating on the label on back of the pump is given as 2.66 based on Air at 7 deg and water at 55 deg.
The total heat loss given for the whole building on the MCS certificate is 7.21kW
Interestingly that also shows annual energy figures of 14,400kWh for heating and 6,200 kWh for water which is more than my current total electricty usage. I guesss that the MCS figures are based on worst case.
Are these the relevant numbers - I'm good with spreadsheets but my technical knowledge of heat pumps is very thin?
Mike
Hi Mike,
I have just been reading through the previous posts to get back up to speed on your particular situation and I think that there may be a need for clarification.
I may be wrong, but I think that the 14,400kWh for heating and 6,200kWh for hot water, relate to required heat energy. Even if your ASHP is operating with a COP of just 3, the electrical energy consumed would be 1/3 of the above values.
Sorry for the delay but I've now read the remote control
My instruction manual is May 2016 but I think table 10.3 is the same.
Here are the numbers:
00 Circ Water temp 29 deg
01 Compressor freq 0
02 Discharge temp 35 deg
03 Current consump 400
04 Fan Control 480
05 Defrost temp 9 deg
06 Outdoor temp 11 deg
07 Water pump rotation 2900
08 Suction temp 9 deg
09 Circ water flow 38 deg
Mike
Hi Mike,
Thank you for providing the data. It is probable that your system is working on weather compensation, but it may be necessary to fine tune the settings for optimum operation.
How familiar are you with adjusting the settings on your controller? The other question would be, are you controlling the indoor temperature using thermostats and/or TRV's?
An easy way to check how well the weather compensation is functioning, would be to increase your thermostat setting by 1C. If the indoor temperature increases by 1C, then the weather compensation curve is incorrectly set and requires adjustment.
