ASHP heat output monitoring

Carlo · 2025-08-02T06:56:51Z

Hi, I'm a new member from Italy, with a new LG therma V ASHP with an abysmal COP (about 1.6). For now I'm basing my calculations from the information given by the heat pump panel, but I would like an independent way of measuring, ideally integrable with Home Assistant. I already put in place a Shelly to measure the power consumption, but I need something to measure the heat output. I need two temperature sensors and a flow meter, but the ready made kit I found, such as the OpenEnergyMonitor ones are a tad expensive. I wonder if there are other kits around or some guides to DIY it with cheaper components. I will probably also open a topic on my specific installation but right now I want to be able to collect evidence to better argue with the installer. Thank you

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Air Source Heat Pumps (ASHPs)

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JamesPa

(@jamespa)

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14/08/2025 1:54 pm

Posted by: @tim441

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@jamespa I run 24x7 with weather compensation. So flow temps will normally increase at night

Thats true. Ideally the FT could go up a bit further ie above the level required simply to sustain target indoor temperature, but not all heat pumps support this; fortunately with a night time cheap rate the tarrif lows and the consumption highs coincide naturally!

Posted by: @tim441

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As my ashp was a retrofit I use simple digital thermostats to manage the target temp increase overnight.

As it works for your case that's great. My only reservation (in the more general case) is if thermostats are causing daytime cycling. That's why the recommendation is generally to set them a couple of degrees above the target so that they act as limiters not controllers.

Everything in this game is a bit house and person specific, the best general approach is almost certainly to start somewhere generically sensible, and tweak if there is a good reason. Unfortunately plenty of heat pump setups reported here (which of course is a distorted subset of the total population) dont start somewhere sensible!

This post was modified 5 months ago by JamesPa

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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Carlo

(@carlo)

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Joined: 5 months ago

Posts: 10

Topic starter 14/08/2025 8:38 pm

@tim441 Out of curiosity, how big and how well insulated is your house? And do you have any idea of how many of those 16kW you actually use at peak?

I tried quiet mode (it is still in it) and I also put the current limiter. Before that when it started it had peaks of 6(!) kW, now only 4.5.

10kW PV
14kW LG Therma V ASHP
Induction heater

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Tim441

(@tim441)

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Posts: 386

14/08/2025 9:09 pm

@carlo the 16kw rating refers to output.. afaik?

So we might expect COP around 3.5 and therefore draw around 4.5kwh?

I think I occasionally see that sort of draw in winter - especially if heating DHW to higher temperatures. But I believe my "normal" usage running the heating on AI is running around half that - or less.

I can see my annual use is 5800kwh for heat pump as it has a dedicated meter. Peak months around 1000kwh so perhaps averages 30kwh per day. But of course coldest days if freezing temps day and night we might use say 80kwh?

I don't monitor day by day - only monthly. We are in SW England where winter is generally relatively mild.

House is complicated! Total 200 sq m. Half is ancient building of stone, single glazed with poor insulation. Half is modern with excellent insulation. We heat the modern part to 21 deg as well as kitchen in old part. Remainder is heated to much lower temps as not needing higher.

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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