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My Mitsubishi ASHP has used 1078kWh from 25 November to 31 December – Help please

Sarah · 2023-01-26T14:41:26Z

Hi, I have a mitsubishi ASHP and have now had it for 7 years. I am genuinely confused with some of the stats I'm seeing of people's running costs - and how much cheaper it is. My own experience of underfloor heating in an approx 60 square metre new build with the ASHP is sky high energy bills, right from the start. So much so, that I called the engineer back a few months after it had been commissioned as the bills were so high....and this was 7 years ago. I have 3 zones - bathroom (set to frost setting), bedroom (set to 14 degrees) and sitting area (set to 15 degrees) - any higher and I simply cannot afford to pay the bill. I have contacted the installer to see if there were some settings I could change - possibly related to the SCOP (but I've no idea what to do with this!!) - I've looked at the manual as I'm not a stupid person, but that is not particularly easy to follow either. My energy usage (at standard rate of electricity 34.5 with Octopus) for 25 November to 31st December was 1078Mwh - yes MEGA !! Again this is just for the floor space I have described. For 1 January to 24 January 573Kwh - there will be another week to come - so approx 750Kwh. I could understand if I'm heating up to a balmy 18 degrees but, believe me, the bathroom is COLD !! Any thoughts/ideas would be gratefully received.

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Air Source Heat Pumps (ASHPs)

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SUNandAIR

(@sunandair)

Honorable Member Member

Joined: 4 years ago

Posts: 569

16/03/2023 11:14 am

Posted by: @harriup

↑

At the bottom of page 6 it states the water flow rate range is 10.0 to 24.8 l/m. Similar to mine, though I have also seen the tank installation manual be a bit more specific that the flow rate should be 24l/m. Not sure what to make of that difference. There is discussion in other threads about altering the flow rate to manage the difference between flow and return temperatures to 5°C, but if the manifold temps of 28 and 21 are typical then you have a slightly too large difference, which is to be expected if the flow rate is lower than it is meant to be.

Hi @Harriup

i thought I ought to add some comments on this for Sarah to consider.

Theres a good reason why there is a flow rate range quoted, and probably other reasons too.
It was generally believed in an earlier thread (Keystone COP) that Ecodan does not have an internal pump to regulate deltaT so there are 2 things that can control it. 1. Adjusting the flow rate via the circulation pump of the primary flow and primary return and 2. The internal modulating electronics which cannot regulate the circulating pump. In other words the ecodan operates at a constant flow rate depending on the chosen set pump speed.

A flow rate must therefore be measured on the return primary pipe since that is precisely en-route back to the heat pump and will give a near accurate measurement of flow through the heat exchanger. (I would say it’s essential to check this before any adjustment of flow rate)

another thing to point out is that a 28 to 21 differential is only 7c which is quite common when the hp is still settling down. I’ve noticed it fluctuates all the time between 3c and 8c and when it starts up it can be more.

So a flow rate of 13LPM is within the acceptable band of the ecodan 8.5 provided it is being measured in the correct place in the circuit. But if the temperature difference never settles close to 5c then a slightly faster pump speed will lower the temperature difference. However there are other issues such as balancing flow rates between the primary loop and other heating circuits so this kind of adjustment really needs to be done by a professional.
Hope this helps

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Sarah

(@sarah)

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Joined: 4 years ago

Posts: 79

Topic starter 16/03/2023 7:30 pm

@sunandair hi - yes that does help and again makes sense that it's set by the gauge on the pump itself - i.e. that is the maximum it will flow. I've had a manic week this week - but I need to look at the manifold on a regular basis for the living area to see what the return is. The thermostat is set to 18 for the living area - but rarely gets to that, unless there is solar gain - for the past two days it is still 17 degrees at 18:00 - when it was 16 degrees at 09:00. In all honesty this could be what I have to live with and it doesn't feel cold. The other 2 zones always get up to their set temp - although their set temps are 16 (bathroom area) and 17(bedroom area). Everything generally is SO MUCH BETTER since I first found this forum 🙂

👍

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