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Flow temperature & weather compensation. Impact on efficiency

Air Source Heat Pumps (ASHPs)

Last Post by AllyFish 3 years ago

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Tim441

(@tim441)

Honorable Member Contributor

Joined: 3 years ago

Posts: 398

Topic starter 14/01/2023 12:10 pm [#744]

Having had my heat pump for about 18 months I have gradually got to grips with understanding the controls and functions. I'm sure everyone's experience is different as it depends on so many factors including property efficiency, whether lived in all day, wfh, geographic location and more.

The most simple conclusions I came to are that the setup has best efficiency/cost with: Lowest flow temperature possible which is best managed with weather compensation. This requires a different mindset from my previous Oil central heating experiences! Target room temperatures are mostly around 21deg in main living room and kitchen but much cooler in secondary/less used rooms & bedrooms.

I came across a very useful tool that allows comparison of the impact on SCOP (Seasonal Coefficient of Performance) of different flow temperatures.

In my case using the exact model LG Therma V HM161M.U33

I can see the impact of the flow temperature and added benefit of using weather compensation. I am now using both and see that the flow temp is often as low as 30deg! But the house is reaching and holding the target 21deg without difficulty. The house is very old & generally inefficient but with underfloor heating and modern extension. At night I drop the temp just 1 degree (if more it would take a long time to warm up and/or need higher flow temp)

As can be seen in the screenshot the efficiency is around 375% at 35deg with weather compensation down to 200% at 55deg without weather compensation.

A very graphic and clear view of why flow temp should be as low as possible and weather compensation functionality should be used.

Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
3 x 8.2kw GivEnergy batteries
1 x GivEnergy Gen1 hybrid 5.0kw inverter
Manual changeover EPS
MG4 EV

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LG Therma flow temp weather compensation

Tim441

(@tim441)

Honorable Member Contributor

Joined: 3 years ago

Posts: 398

Topic starter 14/01/2023 12:30 pm

trying to add link again!

https://tools.bregroup.com/heatpumpefficiency/index.jsp

👍

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AllyFish

(@allyfish)

Prominent Member Contributor

Joined: 3 years ago

Posts: 518

14/01/2023 7:33 pm

@tim441 this is really useful info and a great find. Your experience of converting from oil to ASHP mirrors mine. I'm only 3 months into the journey however. My system design temperature was 50degC but I'm finding with climatic compensation on, a maximum of 42degC flow at 0degC ambient and 30degC flow at 20degC ambient is providing efficient operation. I'm using hugely less energy than I was when I had CH and HW from kerosene, hugely less emissions, and saving around 20% on my fuel bills over the most expensive and energy intensive months. As the days draw longer and the weather warms, the ASHP efficiency and solar PV should really start to kick in and save energy.

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