Optimizing LG Therma V Controller settings

[SteamyTea]

2 minutes ago, dpmiller said:

I've no doubt there's some map in it that you could alter to improve things at the frost-point

Probably been thought of, and as it is not a main stream, well published feature, probably just not worth it.

Easy and quick to take, what may be just half a kWh (about 10p), and pump it around till the unit drips.

[J1mbo]

1 hour ago, Hogboon said:

My aversion to having the heat pump on 24/7 is not entirely on, as it turns out, fallacious grounds of economy, but also partly due to the noise waking me up

 

The controller has a noise reduction setting, see page 38, "Low noise mode time". 

[J1mbo]

1 hour ago, Hogboon said:

does your calculation take into account the fact air temperatures at night tend to be lower than those in day time?

 

Partly - I've shown the heat loss impact but not the COP impact. The latter is far more difficult to model. Clearly on the occasion that it's -2°C then 12°C the following lunchtime it's better to wait. But the software for these units is all quite limited and really meant to configure a 'best average' use-case. If it's an R290 or R32 based product it will pump out 70°C water all day long (except defrosts) but it will cost a fortune to do so. There's a direct trade-off between system responsiveness and running cost with outdoor unit noise and room temperature stability all in the mix as well.

[J1mbo]

1 hour ago, Hogboon said:

The other detail that strikes me is that even given my wayward requirements, the perverse behaviour of the system is not explained. There are occasions early in the day on 27 and 28 Nov [and again today] when the heat pump squirts out sufficient heat to raise the house temp by 0.4º If it did that consistently starting from say 16º C at 07:00 it would reach the target temp in about 5 hours rather than the 9 hours it is averaging at present. 

 

Modeling the way the room temperature changes is complex. Presume the radiators are set to and do reach a specific flow temperature - say 50°C - relatively quickly (i.e. low water content system). When the room temperature is 16°C the output of the radiators is nearly 20% higher than when the room temperature is 20°C. So the radiator output is reduced somewhat as the room temperature rises if the flow temperature remains constant.

 

Secondly the thermal mass of the structure will absorb more heat as the air temperature rises further away from the general temperature of the structure, increasing the resistance to further rises (by absorbing and storing the heat). And as the structure temperature rises so does it's heat loss to the surroundings.

 

So basically we end up with the temperature rise curve being like a car acceleration curve: starts quite steep in 1st gear (16°C) and then rate of change tends to fall off until eventually it's flat where supplied heat = heat loss.

[SteamyTea]

16 minutes ago, J1mbo said:

There's a direct trade-off between system responsiveness and running cost with outdoor unit noise and room temperature stability all in the mix as well.

Need to throw in system size as well.

There is a big difference in suppling, say 55°C water, from a 5 kW unit and a 15 kW unit, regardless of weather.

[SteamyTea]

1 minute ago, J1mbo said:

So basically we end up with the temperature rise curve being like a car acceleration curve: starts quite steep in 1st gear (16°C) and then rate of change tends to fall off until eventually it's flat where supplied heat = heat loss.

We can thank Isaac Newton for that.

 

[dpmiller]

4 hours ago, SteamyTea said:

Need to throw in system size as well.

There is a big difference in suppling, say 55°C water, from a 5 kW unit and a 15 kW unit, regardless of weather.

 

It's more about the DeltaT tho isn't it?

[SteamyTea]

8 hours ago, dpmiller said:

 

It's more about the DeltaT tho isn't it?

Generally yes, if everything else is kept in proportion.

The main thing with heat pumps, like cars, is to not use them at maximum capacity too often.

[Hogboon]

16 hours ago, J1mbo said:

 

The controller has a noise reduction setting, see page 38, "Low noise mode time". 

 

This was on my list of 'Things to Ask.' Presumably no-one sets out to manufacture a noisy machine so if there is a 'quiet' mode the trade-off is presumably a loss of efficiency - the machine running slower therefore taking longer to reach target temp and concomitantly using more electricity. Or am I wrong? If right, is the trade-off penalty so slight as to be negligible? B.t.w. I am poised to go 24/7 to assess grid consumption on my installation.  And thanks for your other answers J1mbo. I only absorb such detail slowly but hopefully, like the tortoise, I will get there in the end.

Edited November 30, 2021 by Hogboon
addition

[dpmiller]

night mode is likely to mean reduced output rather then any less efficiency.

[J1mbo]

6 hours ago, Hogboon said:

 B.t.w. I am poised to go 24/7 to assess grid consumption on my installation.

 

If you are looking to monitor the consumption, have a look here: Heating & Cooling Degree Days – Free Worldwide Data Calculation

 

This will be essential in monitoring performance. Look for a weather station somewhere vaguely local, select heating, Celcius, 20°C, Daily, Past Month. This will provide a CSV. The first two columns are date and degree-days.

 

One degree-day would mean that for the 24 hours in question, the outside temperature was an average of 1 degree less than the heating temperature, presumably 20°C. So similarly, 20 degree-days would mean on average it was 20°C less than 20°C, i.e. 0°C. The heat pump energy consumption will be directly proportional to the degree-days for any particular day and this will enable you to monitor any changes you make. Bear in mind, it needs some time to build averages as the previous day impacts the energy demand the following day to some extent, especially where there is a swift change of temperature overnight.

 

It occurred to me that tracking total energy demand (compressor energy consumption + environmental yield) and plotting this against average temperature, knowing the desired compressor run-time the exact weather curve can be determined for the property by plotting the required radiator surface temperatures against each day to produce the energy demand. November is a good month as the temperature varies so much. This is the analysis I've done on my own system:

 

 

I'd broadly gotten to 28-45°C by spending far too much time with trial and error but maybe this might help somebody else trying to work out what the weather compensator curve settings should be.

[SteamyTea]

34 minutes ago, J1mbo said:

If you are looking to monitor the consumption, have a look here: Heating & Cooling Degree Days – Free Worldwide Data Calculation

You can use it to work out the DHW energy consumption as well.

 

HDDs are not perfect as each house is a bit different, but they are useful as a sanity check.

[SteamyTea]

36 minutes ago, J1mbo said:

 

Would it have been better to you an exponential or log curve matching for the Demand as then extrapolation is more accurate.

[ReedRichards]

On 28/11/2021 at 22:44, Hogboon said:

I altered some of LG’s Controller Installer settings as follows:

 

Outdoor temp for auto mode: min -10º max 15º changed to -1º/15º

Indoor temp for auto mode: min 16º max 21º changed to 18º/23º

LWT for auto mode: min 20º max 50º changed to 30º/50º

 

 

This struck me as odd.  You have the option to set the Temperature Sensor to be Air or Water or Air + Water.  If you have a Hive room thermostat then selecting Air or Air + Water would surely cause the Hive to "fight" the LG controller as they are both trying to set/control an air (i.e. room) temperature.  So, I think, the only sensible option is to select Water (being the leaving water temperature) as the parameter used for control.  If so then the Indoor temp for auto mode is irrelevant (or N/A as it says in my installation instructions).  You can set whatever values you like but it should not make any difference.  

[Hogboon]

J1mbo: “The house is being allowed to cool too much. Set the hive, if you must use that, to 18 degrees between 10 and 7…

“This is where things get interesting. If the heat supply was a gas boiler then of course it will be cheaper to heat it for 15 hours. It will use less energy and cost less.”

 

Done. I have just finished two x 4-day regimes for comparative purposes to test J1mbo’s assertion that “…the amount of electricity required is actually more when operating the shorter heating period than just leaving it on 24 hours”

 

Spot on! Here are my figures. The ‘benchmark’ data [26-29 Nov] are for my previous schedule i.e. turning the heating and hot water OFF between 22:00 and 07:00

 

Date	Time ON	AI	kWh consumed	£	average
26 Nov	15 hrs	+1	25.4 =	5.01
27 Nov	15 hrs	+1	29.6 =	5.84
28 Nov	15 hrs	+1	32.4 =	6.40
29 Nov	15 hrs	+1	22.0 =	4.34	£5.40

 

The comparison figures are for leaving the heatpump ON for 24 hrs save that the target temperature between 22:00 and 07:00 is 18º rather than 20º. Thus the system must heat the house from 18º to 20º between 07:00 and 22:00

 

Date	Time ON	AI	kWh consumed	£	average
4 Dec	24 hrs	+1	24.08 =	4.75
5 Dec	24 hrs	+1	23.08 =	4.56
6 Dec	24 hrs	+1	28.42 =	5.61
7 Dec	24 hrs	+1	25.35 =	5.00	£4.98

 

Which basically means I am a 24 hour ‘continuous’ convert. The improvement in kWh consumption and thus cost is in line with J1mbo’s prediction of 7% - in my case slightly under 8½% by my calculation. But I include the £ as they mean more to me than kWh.  Domestic consumption across the two series was comparable as was the weather – hovering a few degrees above zero.

 

I'm wirh ReedRichards when comes to oddity. "If you have a Hive room thermostat then selecting Air or Air + Water would surely cause the Hive to "fight" the LG controller as they are both trying to set/control an air (i.e. room) temperature.  So, I think, the only sensible option is to select Water (being the leaving water temperature) as the parameter used for control.  If so then the Indoor temp for auto mode is irrelevant (or N/A as it says in my installation instructions).  You can set whatever values you like but it should not make any difference." 

 

It is set to ‘WATER’ alone.

 

The coolant I believe is R32.

 

What continues to perplex me about my system is the seeming unpredictability of the heatpump’s performance - let alone my ability to control it. For example yesterday the heatpump failed completely to raise the house temp to the required 20º for no apparent reason. The house got there in the end but only after the log-burner was lit.

 

I am now running a similar 4 day schedule essentially the same as the previous  24 hrs regime [4-7 Dec] but with AI set to +5 and will post the results here when completed.

 

[ReedRichards]

1 hour ago, Hogboon said:

What continues to perplex me about my system is the seeming unpredictability of the heatpump’s performance - let alone my ability to control it. For example yesterday the heatpump failed completely to raise the house temp to the required 20º for no apparent reason. The house got there in the end but only after the log-burner was lit.

 

 

I also have an LG Therma V and I had the same problem the first time I used the AI mode.  However I tried AI again a few months later and the problem has not happened again since.  Either it's a (lack of) learning thing by the LG controller and/or the room thermostat.  Or you have the temperatures for auto mode set incorrectly.  With the parameters you are using if the outside temperature is +3 C then the maximum leaving water temperature will be 45 C.  Perhaps that's not enough?  

 

If it happens again I suggest you switch from AI mode to direct temperature control and set the Leaving Water Temperature to 50 C.  If that does not work then there is really something wrong.    

[ProDave]

I once tried turning on weather compensation on mine and the thing promptly switched to cooling mode.  I just turned it off again, a project for another time.......

[Hogboon]

Thanks ReedRichards and ProDave. I will persevere with the current A1 at +5 for 4/5 days but after day 1 it's not looking promising! Next up will be a similar 4/5 day continuous 24 hour run with AI 'off' and use the alternative 'Heat' mode. Such fun!   

[ReedRichards]

One of the annoying things about the Therma V is that it does not show the outside temperature (anywhere that I can find) so you cannot tell what the maximum Leaving Water Temperature is supposed to be in AI mode. 

 

Another annoying thing (and this may be typical of ASHPs; I don't know) is that it takes a very long time to get going, running the pump for several minutes before it gets around to switching the outdoor unit on.  So once the controller demands heat you need it to keep demanding for at least 15 minutes or more even if the room temperature is fluctuating around the set point.  The best way I could find to do this was to tell my controller it was running an oil boiler.  More recently a Heat Pump option has appeared but it actually invokes the same settings as oil boiler.      

[J1mbo]

@ReedRichards using native controls will eliminate that problem. Even on oil setting, typically 3 TPI cycles per hour are allowed and obviously that can introduce short-cycling in the scenario described.

[J1mbo]

16 hours ago, Hogboon said:

What continues to perplex me about my system is the seeming unpredictability of the heatpump’s performance - let alone my ability to control it. For example yesterday the heatpump failed completely to raise the house temp to the required 20º for no apparent reason. The house got there in the end but only after the log-burner was lit.

 

Was it windy? It could be additional ventilation losses?

[ReedRichards]

1 hour ago, J1mbo said:

@ReedRichards using native controls will eliminate that problem. Even on oil setting, typically 3 TPI cycles per hour are allowed and obviously that can introduce short-cycling in the scenario described.

 

That's a bit easier said than done.  I presume I would have to change the control settings from "Water" to "Air + Water" and set my 3rd party room thermostat to a temperature higher than I wanted so it did not interfere.  Do you think this is correct and all that is required?

[Hogboon]

It very possibly was windy - fag end of Arwen or early onset Barra? - but I don't take note of any met. conditions other than outdoor temp. I agree with ReedRichards and find that LG's 'cutting edge technology' needs help from a recently acquired thermometer costing £1.50 from the garden centre. [Same with the so-called electricity 'smart meter' which is incapable of recording input to the grid from my pv roof panels.] 

 

In view of the MASSIVE sums of money to be earned from heatpumps - especially retro fitting them - the technology and support for end users such as myself, who am neither plumber nor engineer - is utterly inadequate and beyond belief. I have no experience of any make of heatpump other than LG so whether they are particularly bad I don't know, but as things stand at present if someone told me they were thinking of installing an LG I would say DON'T! [at the top of my voice!] 

 

Meanwhile, as a spot check today, with outdoor temp around 4º C and AI at +5 running 'continuously' the 07:00 starting temp of the house was 18º and by 08:00 was 18.7º and at 09:00 it was 19.1º so it looks like it should get to 20º by about 11:00. Fingers crossed...        

[ReedRichards]

@Hogboon have a look at your MCS Compliance Certificate.  This should tell you what leaving water temperature your system was specified to run at, what external temperature your system was deigned for, what the total calculated heat loss of your house is and other useful snippets of information.  If I were you I would then forget about AI for the moment, set your leaving water temperature at the value stated on your certificate and check that you have no problem reaching your desired room temperature.  Learn to walk before you try to run.

Edited December 9, 2021 by ReedRichards