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Advice needed on hybrid system - ASHP not reaching flow temperature

Air Source Heat Pumps (ASHPs)

Last Post by AllyFish 3 years ago

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Parmstar

(@parmstar)

Estimable Member Member

Joined: 3 years ago

Posts: 51

Topic starter 21/01/2023 5:20 pm

Hi, hope you’re all keeping well.

We had a Mitsubishi 11kw ASHP installed a month or so ago and we struggled to heat our house during the last cold snap we had. We made the decision to install a gas boiler alongside the ASHP to run on the colder days. Looking at the charts the specified flow temp of 50c for space heating has never been reached, it gets to around 45 degrees. The pipe runs are all insulated and i have even increased the compensation curve to the maximum. The flow temp for the hot water seems to reach 60 degrees but it doesn’t on the space heating side. I have attached a diagram of our setup at the moment. Please note that the gas boiler isn’t yet up and running as we are waiting on a sensor from Mitsubishi.

Thanks in advance.

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AllyFish

(@allyfish)

Noble Member Contributor

Joined: 3 years ago

Posts: 493

21/01/2023 7:31 pm

Is it the radiator side of the LLH that's not reaching temperature? Or does the heat pump monitoring show it's not achieving 50degC supply temperature? It clearly can if you're getting 60degC on your hot water, so if the primary side isn't allowing 50degC in heating, I guess some setting or parameter is overriding your climatic curve setting.

But if you're getting 50degC on the primary side and not getting that on the secondary side, the finger of suspicion points at the LLH?

Have you got balanced even flow on primary and secondary sides? Higher flow on the secondary radiator side compared to the primary side will pull return water through the LLH, mix with the higher temperature flow from the ASHP, and cause a lower radiator supply temperature.

If you've not got flow valves on both sides to balance flow, you can do it thermally with some temperature sensors. These are cheap and cheerful, and when cable tied to the copper pipe under insulation will give a reasonable indication of what's what +/-0.5degC or so.

This post was modified 3 years ago 2 times by AllyFish

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Parmstar

(@parmstar)

Estimable Member Member

Joined: 3 years ago

Posts: 51

Topic starter 21/01/2023 7:44 pm

Thanks for getting back to me ally - I am not sure where the thermistors are which are giving me the readings on the melcloud app.

there doesn’t appear to be any balancing valves installed.

all I know is that the flow temps are showing around 45c on the app despite it been set to 50c on the comp curve. Does the piping layout look ok to you from my diagram?

do you think it could be a setting on the controller somewhere?

worthwhile mentioning that there is a pipe run of around 15m from the ASHP to the llh around 10m of this is outdoors

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Kev M

(@kev-m)

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Joined: 4 years ago

Posts: 1276

21/01/2023 8:25 pm

There is a setting on the Ecodan FTC to limit flow temp. I know because I lowered mine a few days ago. It's in the maintenance menu, Operation Settings, Heating Operation, Flow Temperature Range. In case you don't know, pass key is (probably) 0000 and it'll ask you to shut the system down (which is fine as it will start when you exit).

My flow thermistors are physically just above my (non-Mitsubishi) HW tank. The sensors are attached to the flow and return copper pipes like those on Ally's thermometers and the other end disappears into the FTC.

👍

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Parmstar

(@parmstar)

Estimable Member Member

Joined: 3 years ago

Posts: 51

Topic starter 21/01/2023 8:37 pm

@kev-m thank you, just checked and mine was set to 50. Increased to 55 - let’s see if it makes a difference.

will take a look for those sensors a bit later

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AllyFish

(@allyfish)

Noble Member Contributor

Joined: 3 years ago

Posts: 493

23/01/2023 9:40 am

@parmstar Great, les us know how you get on. Piping on your circuit is simple enough, and with a hybrid bivalent system I can see the LLH being of benefit. I would suggest flow monitoring/setting valves on both primary circuits, one on the ASHP return, one on the boiler return, and one on the secondary flow return. They all need to be in balance. Fired boiler design flow might be lower than ASHP design flow, but I guess you've considered that and how to handle that.

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