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My ASHP is not performing as well as I’d hoped: COP just over 2

Morgan · 2024-04-12T09:55:10Z

Let me start by saying I'm happy with what the ASHP does and how it keeps the house at a nice constant temperature. However, it uses an incredible amount of electricity and, even in this mild weather barely scrapes a COP of just over 2. The house has cavity wall insulation installed in the summer of 2021, double glazing throughout and good loft insulation. The ASHP is a Mitsubishi Ecodan 11.2KW retrofitted to a 1950s 3-bed detached house. Complete new installation with new pipework to new radiators in a single zone. No wet central heating was present when we moved in. Installed in November 2021 and commissioned in January 2022. Initially with Heatmiser thermostat that I had the installer replace with the Mitsubishi wireless controller. The system is set to run 24/7 in Auto Adaptation mode. I have spoken with the original installer who is confident that his installation is sound. The system is a single zone with radiators only upstairs and downstairs.10 radiators in total. No underfloor heating. I think, having read through threads on forums that my system can probably be made to run more efficiently and cost-effectively. Hence the consideration for a third-party overview. For example, I have read that Honeywell valves are not ideal in an ASHP environment. TRVs should only be in bedrooms. As it is all my downstairs TRVs are left wide open. I have read of similar installs obtaining a COP far exceeding my figures. My COP barely goes above 2./2.5. My usage of the heat pump is, for central heating, Auto Adaptation mode, 24/7, with the Mitsubishi wireless room controller set to 20 degrees C without any setbacks. DHW is set at 50 degrees C with a reheat at 42 degrees C. The cylinder is a Tempest 250 Litre. It was recommended to me that I contact a certain installer who might inspect the installation and, in all probability, make physical changes to some components such as the Honeywell valves and pumps which might make the system more efficient. i.e. get a third party overview. Over the course of an email conversation, he asked for pictures. Having seen the pictures he replied: "I can not see a buffer, volumiser or low-loss header in the cylinder room, if it does not have one it’s incorrectly installed.A sufficient volume of water must be made available above the system volume itself for de-frost mode.Or it will remove pre-heated content from the system every time it does this, which means that has to be feathered again, causing additional power usage, the heat pump can also cycle too which all uses additional energy. I would be asking the installer where the volumiser is." I have been reading the thread regarding buffer tanks and LLH (link below) as a result of which I am utterly confused.

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HarriUp

(@harriup)

Reputable Member Member

Joined: 4 years ago

Posts: 108

15/04/2024 3:24 pm

@hcas - exactly so. I did read one other persons similar experience but the overshoot was lower if I recall correctly. I can only make this comparison because I have an electric meter just on the cable for the heat pump, but as it is not close the FTC unit I cannot connect an output from it to the FTC which would then replace the unit's own guesstimate with the metered value. This is what most people who have invested in metering will have done.

Mitsubishi EcoDan 8.5 kW ASHP - radiators on a single loop
210l Mitsubishi solar tank
Solar thermal
3.94kW of PV

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Morgan

(@morgan)

Noble Member Member

Joined: 4 years ago

Posts: 624

Topic starter 28/04/2024 4:19 pm

Have been incommunicado for a while. Now back online and will revisit this thread asap.

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
14 x 500w Monocrystalline solar panels.

2 ESS Smile G3 10.1 batteries.
ESS Smile G3 5kw inverter.

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Toodles

(@toodles)

Illustrious Member Contributor

Joined: 3 years ago

Posts: 2054

28/04/2024 4:35 pm

@morgan Did you need a passport to go there? 😉

Toodles, he heats his home with cold draughts and cooks his food with magnets.

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Morgan

(@morgan)

Noble Member Member

Joined: 4 years ago

Posts: 624

Topic starter 28/04/2024 4:40 pm

@toodles No. But I wasn't forced there either and The King had nothing to do with my trip LOL.

Just when I returned I had no internet which has now been resolved.

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
14 x 500w Monocrystalline solar panels.

2 ESS Smile G3 10.1 batteries.
ESS Smile G3 5kw inverter.

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