Posted by: @ecoste

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@sheriff-fatman Thank you. Like you I am not chasing a particular COP, I am using COP to demonstrate the poor efficiency and hence the high cost. I have tried Havenwise but I found that their control reduced the COP and did not work well with the 12kWHr of battery storage that I have. The "maximum demand from the heat pump"  approach tended to fully drain my batteries in just over a couple of hours.

I currently have a COP of 1.3 for water heating across the 2 months since installation. I checked the initial power draw for water heating yesterday, it was 6.5kW. 

Do you have a problem with the Mitsubishi Energy Data updates, mine are very intermittent, sometimes 3 days between updates and sometimes one per day, but never more than one per day?

Thank you for the offer of more stats, I'll come back to you. I have a visit from my installer tomorrow.

I don't have any obvious issues with the MELCloud data updates, other than the fact that energy usage stats are only available on the following day each time (so anything for 29th currently reports as zero).  The hourly reports are updated to within the minute, but only show temperature data, rather than energy usage.  Of all the available reports, I find the Operation Mode one the most useful in terms of getting a snapshot of what's going on over the previous 24 hours, or 7 days.

I've got similar battery storage to you (2 x 5.3kWh Sunsynk batteries for now, with a 3rd one due to be added soon).  I've seen how quickly they can drain in the colder weather but, now that the heat pump is consuming over 20kWh per day, they are going to get depleted at some stage regardless of the profile in which the energy is used.  The PV generation is variable at this time of year, but I'm typically getting to the early evening at the moment before I'm on grid power for the rest of the day and the 3rd battery will assist with that.

I hope your visit from the installer provides you with some answers, but happy to provide more comparative info if otherwise.  From a hardware perspective, our systems seem to be very similar overall.

Posted by: @sheriff-fatman

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Posted by: @ecoste

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@dgclimatecontrol I am on an Octopus Intelligent Go Tariff, so I tend to heat my water when that starts and then heat the house for the remaining duration of the low cost time. There is very little temperature drop (2C max) in the water by next morning when I need it.

There is an immersion heater but I am not aware of any other back up heaters, where would they be located?

I have the same 10kW R290 heat pump as you, installed in June, and currently being run via Havenwise on the same Intelligent Go Tariff.  I see similar power draws to yours by the heat pump, but for limited periods of time and with an overall COP of around 3.0 at present.  For the last week, which has included the first sustained cold weather, Havenwise shows a CoP of 2.3 for DHW and 2.9 for heating.  MelCloud shows that over the last 7 days, the pump has spent 29.1% of its time doing heating, 3.7% doing DHW, 63.2% of its time in stop mode, 3.6% in Freeze Stat (which I believe kicks in below 5C OAT) and 0.3% of time running a fortnightly Legionella cycle.  To date, I've equated the relatively low CoP figure with the fact that it runs harder for shorter periods of time, hence spends a lot of the time sitting idle (and the experience living in the house is that the heat provided is constant and comfortable in all rooms, so it's doing exactly as I'd hoped from that perspective).

Having just done some analysis on the costs over the last month, I've calculated the cost of the heat pump energy draw as £8.39 for DHW and £34.03 for Heating from 28th Sep to 27th Oct, which compares to a gas bill of £117 for the same period last year, so I'm getting the expected overall cost efficiencies from the system, despite the reported CoP not being as high as many people report from their systems.

The peak power draw, as with your system, occurs when the once daily DHW cycle kicks in during the cheap rate period and, like you, I see usage spikes at times showing upto 5kW power draw for brief periods attributable to the heat pump, and usually as it starts either a heating or DHW cycle.  Total energy consumption for the past week, per Havenwise reporting from the MELCloud data, has been 21.6kWh for DHW and 134.2kWh for heating, neither of which looks excessive to me compared to circa 400kWh of gas consumption on last year's gas bill for the same period (based on a monthly consumption of just under 1,600kWh on that bill).

Ultimately, I'm more interested in cost savings than SCoP chasing, and I've attributed the low CoP scores (admittedly nowhere near those you have calculated on your system) with short periods of harder running that Havenwise has chosen to use as the optimal mode of operation, and this seems to be being delivered so far.

It might be worth you signing up to Havenwise for their free 30-day trial, to see whether this gives you any additional insight on performance.  There's no obligation to continue after this but the app will provide you with a weekly summary of CoP for both DHW and Heating during this time, using the MELCloud data.

Happy to provide more info on my stats, if this will assist.

 

Are you using Havenwise for Hot Water? I have seen it uses the "boost now" maximum power, highest speed and lowest efficiency method of re-heat so the CoP hit is expected

I run mine on the Eco DHW mode & controller schedule - so 32Hz maximum for longer (allowed up to 120min run time) and CoP is around 4.1

Heating can be tweaked with the controller max/min flow temperature and Thermo Diff setting to reduce cycling