LG Therma V mono block Air Source Heat Pump

[ProDave]

I have started this thread to discuss all aspects of the LG Therma V Air Source Heat Pump that I am just installing and in particular a control strategy for it.  I have the 5KW monoblock version of this unit.

 

But first I want to talk about water flow rate requirements.  This is an essential subject, but one completely overlooked in the installation manual, and I could not find anything searching on the internet, so feel it is time for some simple clear and concise information.

 

When I first connected my heat pump and tried to run it, it almost immediately tripped on a "CH14" error which is water flow rate. The installation manual does not quote a minimum or a maximum water flow rate which I find an astonishing omission.

 

Before I did anything else, I went and bought a flow meter and installed that so I had a measure of the water flow rate that I was achieving, and that came back with a figure of 14 litres per minute.

 

It then took an email exchange with LG technical to be told the flow switch is "Set to 10 litres per minute plus or minus 3"  So I guess my 14 l/m was just failing to trigger the flow switch.

 

In my case I solved this by adding a second circulating pump external to the heat pump, and that boosted my flow rate to 20 litres per minute and the unit then sprang into life.

 

During my email exchange with LG technical, they sent me a copy of the service manual for this unit. I won't post that for download, but if anyone wants a copy I will send it by email if you send me a PM.

[PeterW]

Is the internal pump set to MAX..? Installation manual has a series of graphs and says to only use MAX or MED. 

[ProDave]

And now onto the subject of how to integrate this into a whole house heating system and how to control it.

 

The unit comes with a "Remote controller" which is it's own user interface. The idea is you are supposed to use that to control the whole house heating system and that alone.  BUT it is a fiendishly complicated thing, I am only just beginning to scrape the surface of how you program it and use it.  I remain to be convinced that this is the only user interface I want to have to control my whole house heating system.  I have some ideas that I will discuss in due course.

 

As well as being the heating programmer, this remote controller gives access to many setup parameters to vary some aspects of how the heating system works.  The first of these that has jumped out at me as being "odd" is the default parameters for hot water heating.

 

When I first turned it on, it heated my water tank for 30 minutes then shut down. It had not reached it's target temperature.  Looking through the parameters, it seems there are some timers set up.  The first  sets how long the heat pump heats the hot water for at one time, and is set to a default of 30 minutes.  The second sets how long it stops heating the hot water for, and is set to a default of 180 minutes.

 

I can only assume this rather odd timing is because when heating hot water, it stops heating the rooms. and someone felt that turning the room heating off for more than 30 minutes might cause an issue.  For the moment I have set both timers to 30 minutes so when heating the hot water it is now 30 minutes on, 30 minutes off. That might mitigate against defrost cycles when conditions are poor?

 

There is a third timer parameter relating to hot water heating, and that is a time delay before it turns on the immersion heater in the HW tank.  Again I assume this is done to speed up HW heating?  But I don't want it to use the immersion heater except for anti legionela heating. There are other parameters that affect the operation of the electric heaters that require further investigation.

 

What I want to end up with, is the supplied remote controller being just a tool to set up the unit, and day to day operation controlled by a 3 channel central heating programmer, so I can set times for upstairs and downstairs heating, and hot water heating, and quickly and simply turn any one on or off using a simple standard programmer.  I have some ideas, and also some challenges ahead to implement that, more of which I will discuss later.

 

[ProDave]

20 minutes ago, PeterW said:

Is the internal pump set to MAX..? Installation manual has a series of graphs and says to only use MAX or MED. 

Yes pump was set to max.

[PeterW]

Ok that’s odd as the flow rate on a Wilo at MAX is more than 14 l/min - is this direct into a floor or into a buffer ..??

[ProDave]

15 minutes ago, PeterW said:

Ok that’s odd as the flow rate on a Wilo at MAX is more than 14 l/min - is this direct into a floor or into a buffer ..??

That was direct into the HW tank, a 300L Telford UVC with the high capacity heat pump input coil. The motorised valve for the tank held in the manual overide position (controls not yet fully wired) It can only be the length of pipe limiting flow rate.  I haven't yet tried driving the UFH, that might re open the flow rate issue.

 

One particular issue I am expecting is the manual says "motorised valves must operate within 90 seconds" yet it appears the unit will trip out of the flow switch does not trigger within 10 seconds.  That sounds like a problem, particularly with the time delay of the thermal UFH manifold actuators.

[dpmiller]

sounds like you want your stats/programmer to operate the motor valves and the microswitch to then command the ASHP?

[ProDave]

2 minutes ago, dpmiller said:

sounds like you want your stats/programmer to operate the motor valves and the microswitch to then command the ASHP?

That is what I am thinking. However the "correct" way to wire it all is the heat pump controls the motorised valves, presumably so when it switches from room heating to hot water heating on it's own timers, it swaps them over.  The question is , is there any intelligence to allow for the time for the motorised valves to operate?

 

This is why I need to think carefully about a scheme to control the whole lot in a sensible way.

[PeterW]

Just put a bypass valve in and set the pressure so it opens at a lowish pressure and there is no problem then

 

I think some of the thermal control heads are really slow - the Wunda motorised ones are ideal as they just open nearly instantly and also manage the flow rates too. 

[ProDave]

I do have a bypass valve but I briefly tried it by shutting the HW motorised valve and even with the bypass valve on it's weakest setting, the thing tripped on low flow, but of course I didn't even have time to run down and see what the flow meter said. More work to do.

[Stones]

@ProDave our system (albeit it was an out the box preplumb system) is controlled entirely via the supplied master controller / thermostat. We have additional thermostats in the bedroom which activate actuators on the UFH manifold so we can shut off the heating in those rooms. Otherwise the house temp is centrally set and the system operates quite happily by itself to maintain the set room and DHW. Obviously you would have to wire for pumps and valves etc as required, but may still be worth considering the supplied controller rather than adding something else in?

[ProDave]

I have now fitted a Grundfos pump as my secondary pump, and that, in conjunction with the Wilo pump inside the ASHP gives a slightly higher flow rate.  I have now also found a setting on the ABV that gives sufficient water flow rate even with all my motorised valves shut. So hopefully that issue is now resolved and I can concentrate on connecting the controls over the next few days / weeks (this is a background job for me at present)

[ProDave]

My suspicion about the supplied controller was confirmed today.  I ran the unit for about an hour doing my pump tests, heating the HW tank in that time. Then I turned it off at the controller.  A little later SWMBO says to me "why is it still on"  Sure enough, in spite of it's controller being "off" it was most certainly on and running.

 

So it's supplied controller remains somewhat of a mystery with a mind of it's own, reinforcing my desire to integrate some proper controls so I can be sure when I want it off, it will be off.

 

Part of my desire to have full control over how and when it operates stems from the eventual desire to install solar PV so as far as possible I want to ensure the heat pump operates in daylight, when there is a reasonable chance of PV generation, and does not operate at night, except perhaps in the darkest depths of winter when it might have to operate longer to keep up with heating requirements (when there won't be much PV generation anyway)

[newhome]

20 minutes ago, ProDave said:

I ran the unit for about an hour doing my pump tests, heating the HW tank in that time.

 

How long does your HW tank take to heat using the 5kw heat pump? Temperature from and to and volume please? 

[pdf27]

8 hours ago, ProDave said:

Part of my desire to have full control over how and when it operates stems from the eventual desire to install solar PV so as far as possible I want to ensure the heat pump operates in daylight, when there is a reasonable chance of PV generation, and does not operate at night, except perhaps in the darkest depths of winter when it might have to operate longer to keep up with heating requirements (when there won't be much PV generation anyway)

It's a bit hard to tell without the manual to hand, but I **think** that unit is classed as "SG Ready" (although the only link I can find is in Polish - https://www.klimatizace-topeni.cz/_data/Files/LG-Therma-V-Split.pdf). That means you've got a couple of contactors somewhere in it that essentially turn the thermostat up when they're closed - pretty easy to do with any number of PV systems when a given export level is reached. This has the added advantage that you're splitting the problem of "is electricity cheap/free right now" from "am I cold", and with a low energy house even an increase of internal temperature of a degree or so will mean you don't need more heating for quite a long time.

[ProDave]

11 hours ago, newhome said:

 

How long does your HW tank take to heat using the 5kw heat pump? Temperature from and to and volume please? 

When I dirst ran it up a couple of days ago it was about 2 hours in total to heat the 300L tank to 55 degrees which was plenty hot enough.  We then each had a shower, did some washing up etc.

 

Yesterday after the tank had been off for a few days it was only on for 1 hour and when I turned it off it had reached 45 degrees. That was still hot enough for washing up, and the bath had it's first use last night from that.  I have now set the heat pump hot water temperature to 50 degrees which should be plenty for normal use and leave lots of headroom for solar PV to heat it further when we eventually get that.

3 hours ago, pdf27 said:

It's a bit hard to tell without the manual to hand, but I **think** that unit is classed as "SG Ready" (although the only link I can find is in Polish - https://www.klimatizace-topeni.cz/_data/Files/LG-Therma-V-Split.pdf). That means you've got a couple of contactors somewhere in it that essentially turn the thermostat up when they're closed - pretty easy to do with any number of PV systems when a given export level is reached. This has the added advantage that you're splitting the problem of "is electricity cheap/free right now" from "am I cold", and with a low energy house even an increase of internal temperature of a degree or so will mean you don't need more heating for quite a long time.

By default, this unit has a "room thermostat" input and when that is enabled it ignores any timers you have set and just operates the heating on demand from that thermostat contact, so that is my route to controlling the heating how I want it from my own timer and the UFH manifold controllers which will give a call for heat to the heat pump when any zone calls for heat.

 

LG do sell a "dry contact" kit but as far as I can tell that just gives you one global on / off input so I can't see much use for that.

 

The only bit of the controls that I can't see a tidy solution to is hot water heating.  It controls the hot water to a set temperature with a thermistor probe in the tank.  There is no other input associated with that.  My only quick and dirty scheme I can think is when I want to turn the hot water off, switch with a relay from the temperature probe to a fixed resistor that gives a high temperature reading so it thinks the hot water requirement is satisfied.

[pdf27]

6 hours ago, ProDave said:

The only bit of the controls that I can't see a tidy solution to is hot water heating.  It controls the hot water to a set temperature with a thermistor probe in the tank.  There is no other input associated with that.  My only quick and dirty scheme I can think is when I want to turn the hot water off, switch with a relay from the temperature probe to a fixed resistor that gives a high temperature reading so it thinks the hot water requirement is satisfied.

If you're trying to maximise PV, the better route would presumably be to turn up the tank setpoint when the electricity is available (say by shorting another resistor across it so that the heat pump stops trying at 55°C rather than 45°C normally). That way it will run whenever PV is available and the tank can take any more heat, and if PV isn't available it will still ensure that you have hot water.

[ProDave]

41 minutes ago, pdf27 said:

If you're trying to maximise PV, the better route would presumably be to turn up the tank setpoint when the electricity is available (say by shorting another resistor across it so that the heat pump stops trying at 55°C rather than 45°C normally). That way it will run whenever PV is available and the tank can take any more heat, and if PV isn't available it will still ensure that you have hot water.

I could do that. I would first have to take a couple of readings at different temperatures to determine what thermistor is used, then see what parallel resistance would modify the curve correctly.

[ProDave]

Today I have enabled the room thermostat input and have the downstairs under floor heating working, just 1 room at the moment.

 

I have set the water flow temperature in heating mode to be 30 degrees.  It seems to run with a 3 degree hysteresis (a parameter you can change) so stops heating the water until it drops to 27 degrees.

 

I have also adjusted the blending valve on the UFH manifold.  By removing the knob, rotating it a bit on it's splines and putting it back on, it now goes lower than it's default minimum of 35 degrees.  I will have to experiment a bit later (with the water temperature set higher) to see how well it regulates at low temperatures.

 

I have now just turned the hot water back on and am watching to see how it divides it's time between heating and hot water and how it switches between then.  It seems to do as set, do 30 minutes of water heating then switch back to room heating for 30 minutes.

 

So far, 4 little "niggles" discovered:

 

1) Any paramaters you change, including even the day and time set in the clock, are lost if you power down overnight.

2) when powered up, even with no heating demand from the thermostat, it keeps the heating motorised valves energised. They only ever seem to get turned off when it switches over to hot water heating.

3) It tries to turn on the immersion heater when heating hot water. I presume the logic here is to heat the water quicker?  I don't yet have the immersion connected to the heat pump so it is not doing that, but I have found no way to disable it doing this, just a parameter to give a delay before the immersion turns on.

4) The default when heating hot water was turn on the internal willis heater as well as the heat pump. I assume this was again done for speed of water heating?  I have disabled this as I want the maximum COP rather than the quickest time

 

Now I have disabled the internal willis heater, the unit is consuming about 7 Amps at 240V so consuming about 1.7KW while heating the hot water tank.

[PeterW]

8 minutes ago, ProDave said:

2) when powered up, even with no heating demand from the thermostat, it keeps the heating motorised valves energised. They only ever seem to get turned off when it switches over to hot water heating.

 

Assuming this is a standard zone valve you are using..?

 

If so, you can swap to a normally open valve and a normally closed valve. Wire the motor to the NO valve through the microswitch of the NC valve and you never have a closed circuit. Alternative is if you have a 3 way valve to swap the head to a diverter head as that is only powered when open and springs closed. 

[PeterW]

10 minutes ago, ProDave said:

3) It tries to turn on the immersion heater when heating hot water. I presume the logic here is to heat the water quicker?  I don't yet have the immersion connected to the heat pump so it is not doing that, but I have found no way to disable it doing this, just a parameter to give a delay before the immersion turns on.

 

Its how it gets the water to 50c or higher as the flow rate through the PHE to get a delta increase per cycle drops away - you may only be getting 0.1-0.2c per cycle at higher temperatures. To combat this, a lot of ASHP either have an inbuilt immersion or trigger an external immersion to take the temperature up quicker. This is also what hits the CoP as its a direct 1:1 electricity to heat relationship.

 

Some ASHP manufacturers actually state this in their product data as it can spike the current flow

[ProDave]

Still having a problem.

 

The thing ran fine today, doing some heating and some hot water heating. All seemed to be behaving.

 

Then I turned the hot water off at it's own control panel, and turned the room heating off at my programmer, so the heating would not be calling for heat (via the thermostat contacts)

 

Since then, 4 times it has tripped out on a "CH14" (low flow) error.

 

I can't see this is really a flow issue. Nothing is demanding heat or hot water. It should just be sitting there doing nothing. The pumps have not tried to start. So why is is tripping out?

 

One to throw back to LG I think.  This does seem to be giving more than it's fair share of issues, and if someone asked me right now, I don't think I would be recommending this particular heat pump to anyone.

[ProDave]

9 hours ago, PeterW said:

 

Assuming this is a standard zone valve you are using..?

 

If so, you can swap to a normally open valve and a normally closed valve. Wire the motor to the NO valve through the microswitch of the NC valve and you never have a closed circuit. Alternative is if you have a 3 way valve to swap the head to a diverter head as that is only powered when open and springs closed. 

It would be a bit of a pain and expense to change the motorised valves (all 2 port NC)  But I can't see I want to leave them sat there energised almost 24/7, sitting there getting quite warm.

 

One simple fix would be a small relay, only energised when the UFH is on, as an additional switch.  Still seems a lot of unecessary buggering about to fix a flawed control system.

[PeterW]

You can get a NO head for the valve from memory 

[ProDave]

I took a second reading from the thermistor at a different temperature, and concluded the best fit to the curve is what is known as a 6K thermistor (6K at 25 degrees)  From that about 510 ohm seemed a likely bet for my "temperature satisfied" resistor.  So I have tried it with a 560 ohm resistor and that gives an indicated temperature of 85 degrees.  So I will be using a relay to switch from the thermistor, to this fixed resistor, when I want the hot water heating off.

 

I have just ordered 3 relays from CPC as I didn't have any with 240v ac coils. One will be used to do the HW switching, and the other 2 will be used to spare the heating motorised valves being energised when the heating is off.