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How to best configure my Mitsubishi heat pump to work effectively?

CheshireCat · 2022-11-29T15:40:12Z

Hi, I've a Mitsubishi 14kWh Ecodan which has just been fitted ( commissioned at the end of last week). We have the room stat (Mitsubishi) and FTC. Our house is around 180m2 with a variety of ages of the house. (Some parts 1840, some early 00's - with varying and questionable insulation in some parts - though we're working on that). Installers commissioned the system, but I would say in a way that is very reflective of a twice on/off a day system with a heat curve where the lowest flow temp is 25 deg c - even at an indoor temp of 20 dec c. It's a Mitsubishi FTC controller - but it doesn't currently have energy monitoring ( annoying and hopefully to be resolved shortly). The heat pump is cycling off and then throwing hot water through the rads - so I need to get a more even temp. Installers set combo of curve and room stat - but the crazy heat up/ off cycle is still happening. So - how do I get this to stop happening? I adjusted the curve, which has helped a bit in some parts of the day, but still getting lots of cycling. I have the Mitsubishi app - but it's not very user friendly and I'm at a total loss to know what it's trying to tell me. I've tried switching weather comp only on - but the system stayed at 18 overnight which was far too warm for comfort. (I think this is because the app is set at 18 - it seems to have overridden the controller and I don't know how to get that back...) I know the set back needs to just be a couple of degrees but the commissioning engineer put the set back at 10 degrees and I KNOW that's not correct. I tried following a reset the curve at 8 degrees from Heat Geek, the cycling is less, but still present. I'm aware that this is not an easy ask, but I've no confidence that the installers will give me advice that works correctly for an ASHP as they seem quite determined to give me a set up that reflects my old boiler!Help is much appreciated.

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Air Source Heat Pumps (ASHPs)

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HughF

(@hughf)

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Joined: 3 years ago

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05/12/2022 8:09 pm

Posted by: @derek-m

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Posted by: @hughf

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@derek-m

One way around it is to use a PWM controlled pump on the secondary circuit too, piggybacked off the ASHP control boards PWM signal (provided it is available, mine is).... But if you're going to do that, you might as well ditch the buffer in the middle.

You have a Samsung ASHP, which does not have an internal water pump, hence the need for the PWM control signal, whether it is used or not, to control an external water pump. I'm not certain if other manufacturer's provide a speed control signal for external water pumps.

I’ve got a Cool Energy unit actually, I’ve just read a lot of the Samsung manuals over the last week.

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

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CheshireCat

(@cheshirecat)

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Joined: 3 years ago

Posts: 18

Topic starter 05/12/2022 8:47 pm

In reply to an earlier comment, I don’t appear to have a low loss header.

I have a hot water tank with two pressure vessels in the system, I have a filter and I have two grundfoss pumps which as has been pointed out have a few settings.

There is a pump speed setting buried in the FTC somewhere, I’m nervous to dig around too much as it asks me if I want to switch off the system when I press certain buttons.

The Mitsi certainly seems to put heat over economy in the room adaptation mode. I’m keeping a close eye on it and I think I’m probably unfortunate in having the ‘learning’ days where we get to know the heat pump in the cold, as the tweaks cost more the longer it takes to get it right.

I’m confident I can get the consumption down though.

I can see boiler flow/ return and another set of temps flow/return- which should have the 5 deg plus loss?

This post was modified 3 years ago 2 times by CheshireCat

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HughF

(@hughf)

Noble Member Member

Joined: 3 years ago

Posts: 489

05/12/2022 9:43 pm

Typical ecodan plumbing schematic is attached. Very simple, no buffer, no LLH

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

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Kev M

(@kev-m)

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Posts: 1276

05/12/2022 9:44 pm

Posted by: @cheshirecat

↑

In reply to an earlier comment, I don’t appear to have a low loss header.

I have a hot water tank with two pressure vessels in the system, I have a filter and I have two grundfoss pumps which as has been pointed out have a few settings.

There is a pump speed setting buried in the FTC somewhere, I’m nervous to dig around too much as it asks me if I want to switch off the system when I press certain buttons.

The Mitsi certainly seems to put heat over economy in the room adaptation mode. I’m keeping a close eye on it and I think I’m probably unfortunate in having the ‘learning’ days where we get to know the heat pump in the cold, as the tweaks cost more the longer it takes to get it right.

I’m confident I can get the consumption down though.

I can see boiler flow/ return and another set of temps flow/return- which should have the 5 deg plus loss?

It's the other flows, not the boiler ones you should be looking at. I think 'boiler' = immersion in Mitsubishi.

Don't worry about the system off warning if you want to have a look around. It's just a standby mode not a hard power down. You start it up again with the round button on the right. I haven't changed the pump settings on mine though.

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