the cost quoted above is for imports only. So net cost is approx £900

export at risk of cut to tariff but not much I can do about that!

Another way of looking at things:

I was previously using oil for heating & hw. Likely 15000 to 20000 kwh/yr? At say 6p equivalent kwh = £900 - £1200

Plus elec for ev & general usage say 3000kwh/Yr = say £400 (Agile) to £750 at standard rates so total £1300 - £1950 per annum

N.b. daily standing charge not included above

Posted by: @tim441

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ASHP metered usage: 5741kwh
Interesting to note that the heat loss calcs from 2020 was for total energy usage 27597 kwh/yr

This appears to be another example of heat loss calculations over-estimating heat loss significantly, something that old buildings appear to be prone to (U values for old walls too high plus too many air changes per hour).

I take it your total estimated (from heat loss calculations) energy usage of 27597kWh/yr is actually the energy needed to match the heat loss, it it is actually the calculated heat loss, and the energy needed to balance that is the energy out (delivered to the house), not energy in (usage). Assuming you don't have (so much the better if you do) actual energy out (delivered to the building), then at a (S)COP of say 3, the energy out is energy in x 3 = 17223kWh per year, which is a lot less than the calculated 27587kWh per year. If, as I say, your LG heat pump records energy out, so much the better, you can determine what the actual energy out was (and that way also get a SCOP). 

Amply covered in other threads, but I think it is fair to say that in general an empirical heat loss derived from actual energy in/out values is likely to give a more accurate result than a spreadsheet calculation which at the end of the day is a classic exercise in whatiffery (what if my wall U values are X and my air changes per hour are Y?).   

@cathoderay sadly LG heat pumps of my vintage have very poor info extracts. I think they're a bit better now and capable of integration with 3rd party apps etc.

1. We heat much of the old part of the house to a lower temp than the calcs would've used but have very successfully brought the temp up if needed. It would be easy to imagine that saves us something like 4000+kwh/yr on comparable inputs. So maybe a fair heat loss comparison would be based on say 23500kwh/yr
2. The heat pump does not cycle significantly afaik and we are able to use a low weather compensation (AI) curve. 
3. At a guess I think our SCOP may be nearer 3.25 to 3.5 which 5741kwh used would indicate 18500 to 20000kwh/yr. 

But of course much guesswork involved.

Overall I was pretty happy with my installers. They made much more accurate heat loss calcs than any other quotes - detailed measurements and info on construction, insulation, etc 

Only significant complaint was that they setup controls for fixed temps. Later, when asked about weather compensation, they said they don't use it to avoid callbacks! Awful! Through forums including this one and Facebook LG user group I think I've got WC working well for last 2 years.

Our 2024 year end summary: 1992 EPC C house (76%) 155m2. 10kW ASHP primary CH & DHW, 5kW wood stove secondary heating for colder winter evening use. All electric, no gas or oil. 20 wet rads designed for 50degC flow temperature but now set to 45degC max flow temperature on weather compensation.

EPC energy consumption estimate: 16684kWh and £2025/annum cost. MCS energy requirement estimate 20162kWh. Make what you will of the large difference between EPC and MCS!

Electricity imported in 2024: 6800kWh + approx. 2600kWh from 3.6kW solar PV array = 9400kWh consumed.

Total energy Cost on Octopus Agile in Summer plus Cosy in Winter around £1100 incl. standing charge. Average 16.1p/kWh cost for imported energy. The big saving for us is Cosy in winter and load shifting 80% of our import to low rate tariff import to charge 13kW of battery storage. Batteries set to charge whenever the rate is low, currently 3x a day. ASHP heating is on 4am-9pm every day in the heating season: October through to March incl. The inverter and batteries get a proper hammering in the winter, charging and discharging constantly, but they are there to be used, and we have a 30degC airing cupboard (great for drying) due to the inverter losses, which are about 10% round trip.

Logs: we get through about £300 of hardwood logs a year, this is a luxury however. The house would heat to 21-22degC average space temperature without, but we would probably import a little more electricity over the winter. We do use a 3kW immersion in the low loss header to energise during defrost cycles to help the ASHP recover target flow temperature quicker - that burns through extra electricity, so we sacrifice some efficiency for comfort. We've found frequent 'all-day' defrost cycles results in target LWT and indoor temperature falling short by a few degC - the immersion boost during defrost largely mitigates this.

SCOP: a tentative estimate by me would be between 3-3.5 for CH & DHW combined, based on regularly seeing what the ASHP is up to and using my look-up instantaneous COP charts in the airing cupboard! OK for a medium LWT temperature all wet rad system.

£1200 (£100 a month direct debit) covers all our import energy costs, inclusive Jan 2025 price rise. If we were still on oil CH and DHW and having the heating on all day every day as per now, we would be well over £2000 a year. I never dared put the heating on all day when we had oil - we relied much more on the log burner and didn't heat unused rooms. Now all the house is fully heated and it's soooo much more comfortable 🙂

Good reminder on EPC energy forecast.

Our EPC was done for ashp purposes to get the RHI grant so was done with reasonably detailed measurements.

• 19,242 kWh per year for heating
• 2,997 kWh per year for hot water
• Total 22239.

Perhaps gives a fair estimate. But also needs huge pinch of salt!

Posted by: @tim441

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I think they're a bit better now and capable of integration with 3rd party apps etc.

That suggests a possible modbus connection. If you have or can get a service manual for your particular heat pump model, you might be able to find out what is and isn't available on your heat pump. I'd be surprised if there is no 'for serviceman' type interface at all. As you rightly say, without knowing output you can't know (S)COP, and any number you come up with is at the end of the day a guesstimate. It is worth noting short term COPs are quite sensitive to current conditions, which is of course why we have SCOPs. My short term COPs for example vary between around 2 in cold weather and around 4 in mild weather. That is a not inconsiderable variation!

If you have the means and inclination, you could add third party monitoring kit. Failing that, see what your heat pump can tell you. For example, I have two ways I can get the energy out over time. The first is the heat pump keeps a running total of kWh produced. Subtracting yesterday's 0900 reading from today's 0900 reading gives me the last 24 hours output. The second way is to calculate it from basic parameters, flow rate, LWT/RWT delta t and specific heat of the circulating fluid. The first two are available over modbus (and independently, flow rate from an analogue inline flow rate meter, temps from thermometers on pipes, but these are less accurate) and the specific heat is a constant depending on the circulating fluid. Having different routes to the same information provides some crude error checking.

Posted by: @tim441

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We heat much of the old part of the house to a lower temp than the calcs would've used

This certainly matters (and is another example of whatiffery leading the numbers astray - what it the whole house is heated to design temps, when in fact it isn't). You could redo the calcs using the actual room temps you have, but at the end of the day it is just more whatiffery...

Posted by: @allyfish

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If we were still on oil CH and DHW and having the heating on all day every day as per now, we would be well over [£XXXX] a year.

This is important, and I think often over-looked. I went from oil to a heat pump (via a period of no central heating, horrible!), and in so doing went from timed heating to mostly always on heating (there are times when I run with an overnight setback, but these need careful management if the house is to be up to temp during the day, and the savings are less impressive than may be imagined, see posts passim). The house is more comfortable, and there is almost no window condensation (used to be a major problem), but of course keeping the house warm all the time does use more energy, and that, along with different cost per kWh for each fuel, risks wiping out the heat pump efficiency savings. In other words, it is not a given that a heat pump will save you money on your heating bills.

I think it is a given that most EPCs are produced using random number generators. Mine certainly was.  

@cathoderay thanks for all the useful comments & thoughts.

Yes, current data from LG is minimal. They have an expensive WiFi dongle that connects to an app and I'm watching in case I can find a low cost one on ebay etc. However most people say the outputs are not great so it's not a silver bullet.

I think modus is an option and I hope to follow up via user group on how best to do that and then connect into 3rd party app/kit.

Posted by: @tim441

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I think modbus is an option

I think you are in luck. I found this in a LG Therma V manual:

Register 30003 looks like the RWT (returning water temp), 30004 the LWT (leaving water temp) and 30009 the flow rate. From the 'Value explanation' column, we can see these values are stored as integers by multiplying by ten (a common wheeze to simplify the numbers as it removes the decimal part), to get the true value you divide the returned value by ten eg if the LWT comes back as 355, actual value is 35.5 degrees. 

I also came across various pages where people have managed at least some sort of modbus connection to an LG Therma V. It will very likely be a very simple two wire connection, you just need to identify the two terminals, normally but not always called A and B, sometimes A+ and B-, but in a Midea heat pump they are labelled H1 which is the B terminal and H2 which is the A terminal (this information is in the Midea manual). I have in fact written up much (but not all) of how to do this on a Midea heat pump, which is what I have. If you haven't already come across it, it starts here. I even briefly  mention LG heat pumps! The basics of modbus connections are generic, in principle they apply to any heat pump that has a modbus connection to registers holding the data.

Be prepared for various confusions eg getting zero and one based counting mixed up but one way or another I am pretty confident you can get accurate energy out data from your heat pump. Others appear to have done this, or got close, using Home Assistant. I use python scripts running on a mini PC, and unfortunately the scripts are the part of the write up that I have yet to post! Perhaps I need to get a move on! 

As I'm on the case...

It looks like these are the LG modbus wire connection terminals, from this HA thread:

@cathoderay many, many thanks for the input and advice.

I think it's enough to push and inspire me to have a go! Will not be quick I suspect but will report back in due course...

Posted by: @tim441

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I think it's enough to push and inspire me to have a go! Will not be quick I suspect

Great, and good luck! Do take your time, the old think three times, measure twice and cut once routines. If you have any questions, don't hesitate to ask.