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Do I have a bad install and what can I do to improve it?

Air Source Heat Pumps (ASHPs)

Last Post by batalto 3 years ago

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Rich

(@rich)

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Topic starter 13/10/2022 10:03 am

Hi all

We finished our house last year and were so glad to be in we just let the heating system be however it did seem expensive to run.

The system installed is a Mitsubishi EcoDan 8.5 (PUZ-WM85VAA) this is connected to the pre plumbed 210L tank (EHPT21X-UKHDW) The house is only UFH. The downstairs is in screed upstairs is tiled in bathroom and low tog / underlay carpet in bedrooms. after seeing the HeatGeek YouTube channel and finding this forum more things about my system are starting to concern me.

One of the concerns I had during install was the fact the pre plumbed cylinder has pumps for the heating zones however this just pumps to the manifold that has mixing valves and its own circulation pump? at the time I was told this was normal and fine however I could never understand the point of two pumps and the mixing valve.

downstairs is fully open plan however they split this into three zone each with a thermostat to control it, I have since wired this so one central stat controls all of downstairs as the old system ended up with noticeably hot and cold floors.

upstairs every bathroom bedroom and the hall have a thermostat, I think this caused us problems as the 3rd bedroom always felt cold and this one room was always calling for heat, looking at the manifold another thing that concerns me is all zones have been opened right up 4l/min and I can see no real temperature difference on the flow and return.

Any advice you have would be great

Thanks

Richard

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batalto

(@batalto)

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13/10/2022 1:32 pm

How does your heat pump run and at what temperature?

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE

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Rich

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Topic starter 13/10/2022 6:16 pm

Thanks for your reply,

I only have the standard MELcloud app for reference until today it has been on the standard weather curve this would heat downstairs fairly quickly and turn off.

unfortunately the app wasn't setup until April this year, I do remember when the one bedroom was the only room calling for heating seeing the heatpump cycle Alot. (I'm not sure how often it should cycle in an hour but the graph of flow and return temperatures was very spiky)

after looking through the forum I have adjusted the weather curve today this had a flow temperature of about 31C this morning while heating.

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Kev M

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13/10/2022 8:04 pm

@rich It's normally better to avoid too many zones. As you've found out, this can lead to only one room being heated at a time. As well as potentially causing unwanted cycling, it's inherently inefficient. BTW 3 cycles per hour is OK, much more isn't.

The flow and return temps should be about 4 degrees difference. It's easy to tell this by touch so it's worth having a feel of the rad pipes to confirm that (or otherwise) if Melcloud is reporting correctly. It's important the temp probes are installed correctly (mine weren't).

One thing you could try is to turn all stats up full and see what happens, e.g, do some parts of the house end up warmer than others This will also allow you to tweak your compensation curve so that it works without the room stats.

This post was modified 3 years ago by Kev M

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Mars

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13/10/2022 8:09 pm

Posted by: @kev-m

The flow and return temps should be about 4 degrees difference. It's easy to tell this by touch so it's worth having a feel of the rad pipes that to confirm (or otherwise) if Melcloud is reporting correctly. It's important the temp probes are installed correctly (mine weren't).

How did you figure out your probes weren’t installed correctly @kev-m?

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Mars

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13/10/2022 8:17 pm

@rich, welcome to the forums. Is your house adequately warm and what’s your heat pump efficiency like?

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Kev M

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13/10/2022 9:28 pm

Posted by: @editor

Posted by: @kev-m

The flow and return temps should be about 4 degrees difference. It's easy to tell this by touch so it's worth having a feel of the rad pipes that to confirm (or otherwise) if Melcloud is reporting correctly. It's important the temp probes are installed correctly (mine weren't).

How did you figure out your probes weren’t installed correctly @kev-m?

Hi Mars,

I suspected because I thought the rads were hotter than the compensation curve was set at. I bought some cheap aquarium thermometers and confirmed that the flow was actually 4 degrees hotter than the comp curve said it should be. I got the installer to fix it when they were fitting my MMSP and it's OK now.

👍

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Derek M

(@derek-m)

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13/10/2022 11:29 pm

@kev-m

Did you ever get your MMSP working correctly?

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Kev M

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14/10/2022 6:31 am

@derek-m yes I did thanks. They came back and fitted the energy meter properly and it's up and running. I also managed to apply for and get the extra RHI. I can now see energy used and delivered by the minute, which will be useful for this winter's tinkering.

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Rich

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Topic starter 18/10/2022 10:03 am

sorry for the slow reply I was away this weekend.

in regard to the house feeling warm it does and can easily become too warm, the heating isn't really in use yet as the house is saying warm via large windows and evening sun. The smallest bedroom did struggle last winter overnight but I am going to check the insulation when it the temperature drops as I think this room is losing a lot more heat than any other.

Efficiency is harder to tell not having access to detailed figures, The apps estimated figures also record about 2Kwh per day even when not in use. looking over the info I have it looks like 2.5COP at my best guess

The system was probably cycling about 5 or more times when just the smaller bedroom was calling for heat so less than ideal.

The downstairs manifold shows a nice temperature drop however the upstairs looks to be only 1c or 2c drop. I think on the above advice I will buy some cheap aquarium thermometers and check everything out.

When the temperature drops, I will try putting all the stats up at the moment it would just overheat the house. Based on last year I would guess downstairs will overheat and upstairs will feel a bit cooler

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batalto

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18/10/2022 10:39 am

@rich if your house is overheating when you whack the stats to full your weather curve is set too high, or your flow temperature mixer into the underfloor is too high. I think this time of year is just a time when things will cycle.

You can see below the heat pump cycling on and off over night and then not working at all during the day. Its not ideal, but its just the nature of cold nights and mild days.