Fine tuning your ASHP performance

MarkC · 2021-10-28T07:25:03Z

So you have had your ASHP installed and the installer has spent 2 minutes running you through the controls, which you promptly forget as soon as they leave the property. A quick YouTube search refreshes your memory and you realise there are so many options for controlling your system. Internal thermostats, weather compensation curves, flow temps. But which one is the most efficient for your setup and how can you find that out. I did start logging weekly performance data from the MMSP (Metering and Monitoring Service Package), changing room temperatures one week, flow temperatures the next but quickly realised that a simple comparison between weeks wasn't enough as outside temperatures were not the same. I did have a quick look at compensation curves but was left unclear as to whether this was relevant to UK usage. I currently only have 8 months of data. My MCS certificate stated a SCOP of 3.52. Not sure if that was the min, mean or max performance I should expect but it's currently bubbling around between 2.7 and 3.0. (October average outside temp is 13ºC, internal set to 22º with a flow temp of 50º) So that is the subject of this topic. How can you systematically discover the optimal setup for your system? Any suggestions welcome, and thanks.

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Peterr

(@peterr)

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Joined: 4 years ago

Posts: 67

05/04/2022 11:57 am

@markc

An interesting read and sounds like a good result in your swap from LPG to ASHP.

It sounds as though we have a very similar system to you, UFH downstairs and radiators upstairs, just wondering if I could ask you a few questions:

1. Do you get much thermal gain, if so how does your system respond?

2. Do you notice much cooling effect on the internal temperature due to wind/rain?

3. What coverings do you have over your UFH?

We have solid oak flooring over our UFH in all rooms except the kitchen. It was installed when we first moved in and were running an LPG boiler. The kitchen has ceramic tiles and generally seems to hold a more consistent temperature. The rest of the downstairs rooms fluctuate a lot more if the outside temperature drops. I am thinking that the insulating layer of wood increases the latency of the UFH. We are also running with weather compensation, but I am still tweaking it occasionally to try and get the curve right - currently 43C at -3C ambient going to 20C at 18C ambient. I am beginning to wonder if the lower end could be dropped if we didn't have the wooden flooring!

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MarkC

(@markc)

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Joined: 4 years ago

Posts: 97

Topic starter 05/04/2022 12:24 pm

Posted by: @peterr

@markc

An interesting read and sounds like a good result in your swap from LPG to ASHP.

It sounds as though we have a very similar system to you, UFH downstairs and radiators upstairs, just wondering if I could ask you a few questions:

1. Do you get much thermal gain, if so how does your system respond?

2. Do you notice much cooling effect on the internal temperature due to wind/rain?

3. What coverings do you have over your UFH?

We have solid oak flooring over our UFH in all rooms except the kitchen. It was installed when we first moved in and were running an LPG boiler. The kitchen has ceramic tiles and generally seems to hold a more consistent temperature. The rest of the downstairs rooms fluctuate a lot more if the outside temperature drops. I am thinking that the insulating layer of wood increases the latency of the UFH. We are also running with weather compensation, but I am still tweaking it occasionally to try and get the curve right - currently 43C at -3C ambient going to 20C at 18C ambient. I am beginning to wonder if the lower end could be dropped if we didn't have the wooden flooring!

1. Do you get much thermal gain, if so how does your system respond?

Yes, we have 6m of glazed sliding doors on the south facing elevation of the property. So when it's sunny approx 1/5 of the main living area gets a bathed in sunlight. Pushes the room air temp up to 24/25ºC.

I imagine the system responds by stopping as the return flow will not be cooler than the flow out.

The ASHP is located on the north elevation so constantly in the shade.

2. Do you notice much cooling effect on the internal temperature due to wind/rain?

No, however we are surrounded by trees so the effect of cold wind isn't as pronounced as it might be on an exposed property I suspect.

3. What coverings do you have over your UFH?

We have a 60mm slab of screed covered with ceramic tiling. Yes I suspect the wooden floor is insulating and also not able to retain the heat as well as a screed floor can do. I suspect this is why I'm able to run the heating 24/7 for the same cost as compared to turning it off over night and then having to reheat the slab.

With my 'curve' (actually a slope) I do have to manually adjust the heating down as the outside temp increases.

-5ºC to 10ºC outside the room temp is a stable 22ºC but as the outside temp goes over 10ºC I adjust the FTC. In this last spell of 20ºC daytime outside temp I was running the system at -6. Probably the solar gain effect.

👍

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MarkC

(@markc)

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Joined: 4 years ago

Posts: 97

Topic starter 16/10/2022 7:32 am

A quick update.
After running the system for a full year with weather compensation my actual annual ASHP energy usage is 5280kWh.
That's for both heating on 24/7 @22ºC indoors and hot water @48ºC.

👍

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