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advice on excessive shortcycling and overall efficiency

RMY · 2025-02-22T23:33:05Z

hi, I've had to learn about heat pumps in the past 2 months due to my own bad experience with my currently installed system, and this forum has been of great help so far. a brief about the setup before i ask for advise, i bought the house with the Midea clone 12KW ASHP already installed, so i have no info on why it was setup the way it is , but i do know the original installers are of horrible quality and totally dishonest so i wont be contacting them again. I live in madrid spain so the weather is very mild, with only couple of weeks per winter when the temperature will consistently drop below zero, the system is only for heating , as there is a separate system for sanitary hot water. the heat pump consists of a large outdoor compressor unit connected to an indoor exchanger, the house is heated via 11 fancoils ( i dont know the exact term used but they are simply fancy radiators with a radial fan ), the house is 2 floors 240 M2, with decent insulation. i have configured it with a weather compensation curve simply on water flow temperature so no room thermostats, there are no zones as well. during most of the time . the compressor will run for less than ten minutes and then switch off, and will switch on again as soon as the minimum configured time has elapsed between runs ( i have i increased that from 5 mins to 10 mins) , i attached a graph of the electricity consumption of the heat pump ( i installed a smart interrupter that measure and sends the data to Home Assistant). i had recently a Midea service technician do an inspection, and his suggestion was to install a buffer tank as he doubts that the volume of water circulating is below the minimum recommended ( unfortunately i have no way to know the current volume). i 've attached a picture showing the installation, it shows every single part except for the outdoor unit. the other picture shows how many times the compressor runs for a 2hours period, along with indoor and outdoor temprature any advise on where to start or what do to about this?

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Air Source Heat Pumps (ASHPs)

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 4 years ago

Posts: 5573

25/02/2025 5:09 pm

As you say should be straightforward, good luck with the work!

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 4 years ago

Posts: 5573

27/02/2025 4:30 pm

Some further thinking on where to connect the buffer is emerging on this thread https://renewableheatinghub.co.uk/forums/postid/43152

The key take away is to put it beyond the DHW/Space heating diverter valve so that, outside the heating season, it is not engaged needlessly when heating the DHW.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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RMY

(@rmy)

Active Member Member

Joined: 2 years ago

Posts: 8

Topic starter 27/02/2025 5:12 pm

@jamespa thank for sharing this, i just went through it, but in my case the system is not used for DHW as there is a separate self enclosed system for that ( another sign the original installers just wanted to sell all they could without caring for actual value)

but it brought to my mind an idea (a rather silly one maybe), if my understanding that the goal is to add volume . regardless of where , then my idea as as following:

on the upper flow i have a very large storage closet just next to one of the fan coils, can i install the volumiser tank inside the house and just add a T Splitter valve on the fancoil connection that goes into the tank (so that would be option D or E from the hand drawn diagram in the other post you shared but i have a single circuit/zone for all fancoils), in a way the tank will act like another emitter but with a much bigger volume than the rest, what do you think about this possibility ?

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 4 years ago

Posts: 5573

27/02/2025 5:36 pm

Posted by: @rmy

↑

on the upper flow i have a very large storage closet just next to one of the fan coils, can i install the volumiser tank inside the house and just add a T Splitter valve on the fancoil connection that goes into the tank (so that would be option D or E from the hand drawn diagram in the other post you shared but i have a single circuit/zone for all fancoils), in a way the tank will act like another emitter but with a much bigger volume than the rest, what do you think about this possibility ?

If it is in series (ie both ports connected to the flow not one to the flow and one to the return) I cant see why not. Its not really like another emitter in this case, just a fat piece of pipe.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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RMY

(@rmy)

Active Member Member

Joined: 2 years ago

Posts: 8

Topic starter 27/02/2025 5:43 pm

@jamespa thanks for clarifying the connecting in series, didn't think of that and it obviously makes sense, I think this setup I can do on my own as I won't interfere with the main pipes of the system hence no risk of screwing something up and obviously saves money by not having to redo the main pipe work

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