LG Therma V mono block Air Source Heat Pump

[ReedRichards]

My hot water timer is off at night, 50 C from 06:30 to 10:00, 40 C from 10:00 until 17:00 then back to 50 C until it goes off at 22:00.  If it was reasonably sunny the previous day then that should lead to no demand on the heat pump to heat the hot water (we don't typically use a lot of hot water in the evening so the tank will still be above 50C on the morning following a sunny afternoon).  However if not then the water will be heated hot enough for morning showers etc.

 

My buffer tank has an unconnected immersion heater.  Would it be sensible to heat that with spare solar PV electricity once the hot water cylinder is at temperature?   

[1not24get]

I have an issue with my new therma V monobloc.  When the unit is in heating mode it will not power the contactor powering the UFH pump.  (0 volts between ext pump blocks on PCB)  The air temperature in the data logging section of the installer menu of the control panel shows the air temperature to be 122-127.5 degree C which is obviously wrong but the display temperature on the contrler is correct at 22.5 degree C.  Using the LG cable to connect the controller to the outside unit. The system is using the temp sensor in the contoller (RS3) My installer is looking into this but has not come accross this before.  Any thoughts?

Thanks

[ReedRichards]

Remind me how to access the logged data and I will check what mine says.

 

Oh, found it.  My air temperature seems to vary around 100 degrees, from 92.5 up to 107.5.  Obviously this is wrong but not always the same amount of wrong so it must be measuring something.  

Edited May 1, 2021 by ReedRichards
Added info.

[ReedRichards]

The gas boiler in my old house was pretty smart.  It could do weather compensation and also load compensation.  I have only just discovered the technical term for this but the way it worked was to modulate the boiler to run harder when there was a big difference between the temperature measured by the room thermostat and the set temperature.  Conversely the boiler would modulate down when the room was at temperature.  Having lived with this for 20 years I think of it as the way any heating system should operate.  Now the LG Therma V can supposedly do weather compensation but is there any load compensation capability?  Given its fondness for cyclic operation I suspect not - which would be a pity because it is a missed opportunity for greater efficiency.   

[Ronny]

I am new to buildhub, and have read all 7 pages of this thread, twice as there is so much to digest. I have a 7kw therma v installed via the green home voucher grant. Installed just before christmas so straight into high energy use. I found in the very cold weather, it was easy to burn £6 a day which seemed very high. However now that the weather is warmer the cost is in the region of £1.40 to £1 80. I have also changed to Octopus energy tariff with 5 p a unit for 4 hours in the early morning. I have now timed my hot water to go off at 15.45 so i can take advantage of the cheap rate to heat the water, coming back on at 00.30. I would guess over the year i will be very close to the same running cost as i was with the combi boiler. The gas meter has been removed and an induction stove installed instead of the gas one. This also helps as there is only one standing charge instead of 2. Depending on the daily charge, this can easily save £60 per year. By the way the house is 2 bed ex council about 5 miles from Durham. As i slowly learn how to set the controller i will experiment with various settings, but at the moment anything i have changed has not made any great difference. I have it set at present on Auto (AI) and timed to come on at 07.45. It brings the house up to about 19.5 deg and hardly comes back on all day. Thanks to all for the very interesting thread.  

[ReedRichards]

Hello and welcome.  My Therma V was installed a week or two earlier than yours.  So far it has used about 5.2 MWh of electricity.  I expect the running costs to be broadly in line with what I was paying for my oil combi boiler but you'll do well to switch from gas and not pay more.  I have just gone back to trying the AI setting as I could not get that to work in winter (the room did not reach the set temperature).  

[markc]

11 minutes ago, ReedRichards said:

Hello and welcome.  My Therma V was installed a week or two earlier than yours.  So far it has used about 5.2 MWh of electricity.  I expect the running costs to be broadly in line with what I was paying for my oil combi boiler but you'll do well to switch from gas and not pay more.  I have just gone back to trying the AI setting as I could not get that to work in winter (the room did not reach the set temperature).  

Thats going to be one hell of a Bill

[Ronny]

6 hours ago, ReedRichards said:

Hello and welcome.  My Therma V was installed a week or two earlier than yours.  So far it has used about 5.2 MWh of electricity.  I expect the running costs to be broadly in line with what I was paying for my oil combi boiler but you'll do well to switch from gas and not pay more.  I have just gone back to trying the AI setting as I could not get that to work in winter (the room did not reach the set temperature).  

Like you i could not get the AI setting to keep the house warm enough. I am now experimenting with it and it comes on in the morning and gets the house up to about 19.5. If i increase the setting to +1 it goes up to 20 deg. My first account from Octopus energy was from the 17th Feb to 8th May. 291 kwh @ 5p and 1304 kwh @ 12.93p Total 1595 kwh. Total cost £203.42 including standing charge of 81 days @ 25p a day. Since just before christmas i have used 2573 kwh`s. Since the end of February it has included  cooking as we no longer have gas. It will be interesting to see the costs after a full year. I still think my costs will be close to what it was with the combi, or is that wish full thinking. If it costs more i will still be happy so no problem. You mentioned in a previous post the data logging temp. i have the same readings as you, so i don`t know what this reading refers to. This ex council house was built in 1937 and is insulated as good as possible without spending a fortune to improve it any more. I also like it to be warm as we lived in Africa for nearly 40 years, so are used to the heat. Now i pay for the heat instead of paying to cool the house down. You can`t win.

[ReedRichards]

13 hours ago, markc said:

Thats going to be one hell of a Bill

 

Say 15p per kWh so £150 per MWh.  5.2 x £150 = £780 used since early December.  Before the ASHP I had an oil boiler that cost me £910 per year in oil.  We've just had a cold winter and spring but I won't be using nearly so much electricity in summer.  I reckon I am on target to match the oil boiler for running costs.   

[Chris Bottomley]

Ronny, Hello and welcome.

We have had a 12Kw Therma V installed for a year now running a 15 radiator system and small underfloor loop in a reasonably well insulated 1960s chalet bungalow.  As an indication our  ASHP has used around 7800kWh over the last year with peak daily usage of of around 80Kwh on the really cold days.  When heating the ASHP was set to run all day with a target internal temperature of 20 degrees during the day and 19 overnight.  It is also providing hot water.  The running costs are comparable with our old oil boiler feeding the heating and stored hot water.  The ASHP consumption will vary dramatically with the outside temperature, as it gets colder the system has to provide more heat to the house but its efficiency also decreases as the outside air temperature goes down.  Don't look at your smart meter on very cold days!

 

I am hopeful of being able to reduce the running costs for the future by around 20% from what I have learnt in the use of the systems and controls in the first year.  I hope that the efficiency improvements will come from:

- Using the AI mode rather than a fixed temperature, this runs the radiators at between 35 and 45 degrees depending on the external air temperature rather than at 50 degrees all the time in normal heating mode as set by the installer.

- Leaving the system running all day when heating to maintain the house at a set temperature.  The ASHP has to run quite hard to increase the temperature of the house by one degree and it can take an hour or two to do this depending on the outside temperature.  The controls have to be used on a very different way to the oil boiler as it could raise the house temperature farly rapidly.

- When heating is not required over a period of time turning the heating off at the ASHP controller rather than relying on the timer thermostat.  We have a heating buffer tank and the ASHP spends a significant amount of energy keeping this at temperature even when there is no heating demand.

-  Timing water heating to coincide with maximum sun energy, we have a solar panels.

[Ronny]

13 hours ago, Chris Bottomley said:

Ronny, Hello and welcome.

We have had a 12Kw Therma V installed for a year now running a 15 radiator system and small underfloor loop in a reasonably well insulated 1960s chalet bungalow.  As an indication our  ASHP has used around 7800kWh over the last year with peak daily usage of of around 80Kwh on the really cold days.  When heating the ASHP was set to run all day with a target internal temperature of 20 degrees during the day and 19 overnight.  It is also providing hot water.  The running costs are comparable with our old oil boiler feeding the heating and stored hot water.  The ASHP consumption will vary dramatically with the outside temperature, as it gets colder the system has to provide more heat to the house but its efficiency also decreases as the outside air temperature goes down.  Don't look at your smart meter on very cold days!

 

I am hopeful of being able to reduce the running costs for the future by around 20% from what I have learnt in the use of the systems and controls in the first year.  I hope that the efficiency improvements will come from:

- Using the AI mode rather than a fixed temperature, this runs the radiators at between 35 and 45 degrees depending on the external air temperature rather than at 50 degrees all the time in normal heating mode as set by the installer.

- Leaving the system running all day when heating to maintain the house at a set temperature.  The ASHP has to run quite hard to increase the temperature of the house by one degree and it can take an hour or two to do this depending on the outside temperature.  The controls have to be used on a very different way to the oil boiler as it could raise the house temperature farly rapidly.

- When heating is not required over a period of time turning the heating off at the ASHP controller rather than relying on the timer thermostat.  We have a heating buffer tank and the ASHP spends a significant amount of energy keeping this at temperature even when there is no heating demand.

-  Timing water heating to coincide with maximum sun energy, we have a solar panels.

Hi Chris,

I have been running on AI for the last couple of weeks as using this setting during the winter did not appear to be doing what i wanted, never warm enough.  At the present time, the heat is set to come on at 07.45 every day and is on until bed time. We are long retired so always at home. I was looking at how to limit the temperature of the radiators, but had been unable to do this in the settings. After noting your comments re the radiator temperature in AI settings i had a look at the data logging and i see the max temperature of the radiators has been 44 deg. This is what i wanted so you have helped me there. The problem with the controller is there are settings i do not fully understand, and even googling them does not turn up any help. If you have used 7800kwh with your set up this indicates to me that my running costs will be fairly comparable with the combi boiler. I do note your comment not to look at the smart meter. What i was missing was the fact the kwh used, drops dramatically after the very cold weather. I pay attention to all the posts as i am learning a lot from them. Many Thanks to all.

[ReedRichards]

On 21/05/2021 at 23:14, Chris Bottomley said:

- Leaving the system running all day when heating to maintain the house at a set temperature.  The ASHP has to run quite hard to increase the temperature of the house by one degree and it can take an hour or two to do this depending on the outside temperature.  The controls have to be used on a very different way to the oil boiler as it could raise the house temperature farly rapidly.

 

I'm curious about this as there is no obvious reason I can think of why it should be true.  Or rather the obvious reason is that your old radiators were oversized for the water temperature of your oil boiler whilst your new radiators are well-matched to heat pump.  So the response speed has nothing to do with the heat source and everything to do with the radiators.  Could this be true?  

[SteamyTea]

28 minutes ago, ReedRichards said:

So the response speed has nothing to do with the heat source and everything to do with the radiators.  Could this be true?  

It will be a combination of the power that the ASHP puts out, the CoP it is trying to run at (if this is a settable parameter), the power the radiators can deliver at and the temperature differences between the indoor air temperature and the radiators, and the overall heat losses of the building.

It may also be a mismatch between the ASHP, buffer and radiators.

And that is before variable weather is taken into account, this can affect the CoP and the building losses. A cold but sunny, still day will be very different from a blustery, rainy day.

Usually combustion boilers have a greater power output as a ratio of mean power needed, this can mean they may heat up a building faster, but they do it at the cost of efficiency.

[ReedRichards]

Any "boiler" has to raise the central heating water to the specified operating temperature and then keep it there.  Unless it is ridiculously cold outside my ASHP has enough power to keep the water at temperature.  It may do this at the expense of a very poor CoP when its very cold outside but using my Therma V in the basic (non-AI) mode it managed to achieve this throughout the last winter. 

 

Once the heating water is at temperature then the rate with which it can heat the house will depend on how much heat the radiators give out compared to how fast the house is losing heat.  That's true of any radiator-based heating system.  So one reason an ASHP could be slower to heat the house than an oil boiler was is that the radiators give a smaller output at their specified operating temperature.  That would most likely be disastrously true if you did not replace the old radiators when you got the ASHP but might still be true anyway.  Once you reach the specified operating temperature for any boiler then it must be all down to what the radiators can achieve.

 

So then the other aspect of response speed it how fast the "boiler" can increase the temperature of the heating water.  I did a back-of-the-envelope calculation comparing my ASHP with my old oil boiler.  My oil boiler could heat the water faster but had further to go to reach the operating temperature so my conclusion is that there is not much in it.

 

In the real world of my house I have not noticed any difference in speed of response, except in the kitchen where I kept the old radiator and paid the price.  Its output is 30% below the calculated requirement and it is indeed slow to warm up in the morning.  But I knew that would happen and I know the reason why so I get very puzzled when people assert that there is some fundamental difference in response speed between an ASHP and other types of "boiler".

 

 

 

   

[dpmiller]

One point that you didn't note is that ASHPs like to run at a much smaller in-out delta so it's not quite as simple as running at 100% to get to setpoint. They're (internally) continually juggling flow/temp/ gas pressures and temps to try and maximise the production. Just because (say) the HP can deliver 55c water  doesn't mean it's aiming to do that when turned on from cold...

[ReedRichards]

Gas pressures???

[SteamyTea]

35 minutes ago, ReedRichards said:

Gas pressures???

When the pump modulated the pressure in different areas of the circuit varies.

PV/T stays as a constant though.

[dpmiller]

ASHPs tend not to have an orifice tube or thermo expansion valve, instead they use a servomotor driven expansion valve. So between variable speed drives and this, the actual load and efficiencies are very configurable.

[Chris Bottomley]

Going back to the note in my post about the time for the house to warm up and to reinforce SteamyTeas's comments.

 

We had most of the radiators replaced when the heat pump was installed.  The sizes were selected based on a full house thermal survey and in most cases the radiators were doubled in size.  The slower house warm up time is probably based on two factors, the oil boiler was around 30Kw output, would run more or less continually while heating and ran the heating circuit at around 80 degrees.  If nothing else the radiator temperature meant the house started feeling warm quickly. 

 

The heat pump is rated at 12kw and from the data I have probably very rarely runs at that output probably due to the reasons noted in the posts above and is running the radiators at say 35 to 45 degrees so at a delta of 16 to 26 degrees above nominal house ambient temperature. 

 

I know from the monitoring setup I have that the heat pump takes around one to two hours to raise the house temperature one degree.  I don't know how quickly the oil system raised the temperature but looking back subjectively it felt that it could warm the house up much quicker.  We would have the oil system on for three or four hours in the morning and again in late afternoon to late evening.  It could warm the house within about an hour and recover the over night temperature drop.  Using the heat pump to have the house at a comfortable temperature the most we feel we can get away with is to drop the demanded temperature by one degree overnight.

 

This is not an issue, I was expecting the operation to be different when I installed the system and to be fair the installer's advice was to leave the heating on all the time.  The point is that you have to run the system differently from an oil system and experiment to get the best balance between comfort and energy usage.

 

With regard to the ASHP warmup time with our system is the heating is turned on and set on a schedule the heat pump will maintain the temperature in the buffer tank.  This means that it will run approximately once an hour to warm up the tank even if the heating is scheduled to be off at that time.  This gives you a quicker startup when heating is demanded as there is hot water in the buffer tank to pump around the radiators.  The downside is that if the demand for heating is low there is a significant energy cost in keeping the buffer tank warm.  I therefore turn the heating fully off once the outside temperature gets to the point that the need for heating is marginal. In theory this should be early April as we are in the South West but this May has been a bit of a challenge!

[SteamyTea]

8 minutes ago, Chris Bottomley said:

Going back to the note in my post about the time for the house to warm up and to reinforce SteamyTeas's comments

You may also find that the oil burner was heating the house up from a lower temperature, this could also give the impression that it is 'heating quicker'.

 

 

But comparing a 30 kW and a 12 kW heater will probably make the biggest difference.

After efficiency losses, the ASHP is about half the output.

Edited May 24, 2021 by SteamyTea

[ReedRichards]

I throttle back on the temperature overnight, setting it at 17 C after being at 20.5 C (target) from 18:00 to 22:30.  I have solar panels and my inverter keeps a log of the house energy consumption.  Once in a blue moon there is a blip or two of usage in the middle of the night but the norm is no activity (hot water is also off).  I wonder why I am different to @Chris Bottomley  who experiences hourly activity to keep the buffer tank at temperature?

 

I appreciate that a 30 kW oil boiler (mine was 25 kW) is capable of a lot more power that a 12 kW ASHP but under what circumstances does it get to use all this power?  It may use it to heat the domestic hot water; my old cylinder used to have a coil with a smaller surface area or it might be a combi boiler.  But the calculated heat requirement of my house to maintain temperature is 10.5 kW .  If the rooms are colder than their specified temperature they will derive more heat from the radiators than when the rooms are at temperature.  But the radiator output depends on the temperature difference so its' never going to be that much more.   So I would expect a 30/25 kW boiler to rapidly get to the point where it has to cycle in order not to overheat the central heating water.  I don't doubt that @Chris Bottomley  is right that his ASHP heats the house more slowly that his oil boiler used to but I'm not convinced that comparing maximum heat output capacities provides the explanation.   

[SteamyTea]

23 minutes ago, ReedRichards said:

I wonder why I am different to @Chris Bottomley  who experiences hourly activity to keep the buffer tank at temperature

Could be size of buffer as a fraction of energy required.

 

 

[dpmiller]

38 minutes ago, ReedRichards said:

 

I appreciate that a 30 kW oil boiler (mine was 25 kW) is capable of a lot more power that a 12 kW ASHP but under what circumstances does it get to use all this power? 

 

Every.Time. you turn it on.

[ReedRichards]

I have just found the calculation I made comparing the heat output from my old radiators assuming delta T = 50 C with the MCS calculation for my new radiators.  My old ones gave 30% more heat output and that should certainly raise the house temperature faster.  I don't know if they were actually operating at delta T =50 but my condensing boiler produced copious quantities of vapour so it can't have been too high.

[ReedRichards]

6 minutes ago, dpmiller said:

 

Every.Time. you turn it on.

Yes, but no.  If you turn it on, it runs at 30 kW for X minutes and then has to turn off for a while to prevent overheating so on average you don't achieve the full output.  It's like driving through a big city, you may always drive at 30 mph but you won't travel 10 miles in 20 minutes because you will keep encountering traffic lights and other obstacles.