LG heat pump problem

[back2space]

Well hello guys, previous post was about remote sensors, these are coming in January and are on order from LG so will be fitted then, until then we are compensating by having the set points a degree higher.

As you can see from my previous posts I have 1 x FM25Ah outdoor multisplit unit connected to 2 x MV12AH (3.5kw) indoor convertible units, (lounge and bedroom)

The outdoor unit is RATED at 1990 watts going down to 1194watts (maintaining setpoint) when both indoor units are on cooling when maintaining setpoint (inverter ramping up and down). This is as per the product specification databook based on certain operating conditions outdoor ambient etc. This figure is pretty spot on though and very accurate.

However in heating mode its a diff situation totally. It says that to have both units turned on in heating and set point of 20C outdoor ambient 7 which is what it has been last few days here in Leeds that the outdoor unit is rated at 2280W, dropping to 1368W (i assume when only maintaining set point)

I checked this yesterday and today and it only ever gets to 1368W if one unit is operating maintaining setpoint. WHich apparently if only one unit is operating it should drop to 800w. It doesnt seem to be ramping down to the 800w so the unit cycles when mainting setpoint. It cycles in cooling but am not bothered because it is costing next to nothing to run.

If both units are running at max power on heating i.e room temp diff of 3C (inverter ramped fully up) the quoted max rating of the outdoor unit is 2500W however its registering on my energy monitor as 2900W even when only maintaining set point, this drops perhaps to the rated input when its maintaining setpoint.

When only one unit is operating in heating mode the max it will ramp down to is 1300W when its maintaining setpoint. This is no where near the 800w mark that is quoted in the specs? So im dissapointed as yes its cheaper than electric heaters but having checked with the energy meter its using more than I was expecting it to. Cooling is very cheap and within the specs quoted, heating is always like 2280W when both units are on and maintaining set point. No where near the 1368W quoted for the min input on the sheets.

We pay 18p per unit of electric and were putting in about £5 a day in coins when were using it both units, and prob about £3 when using just the one unit.

To say an electric heater uses 2kw well this is using an extra 500w when both units are on (yes it heats the whole flat using 2500w as apposed to one room but I want the quoted specs. The units are oversized a little but all doors are left open so it also heats our large hallway so the doors are never closed. Its like it doesnt ramp down early enough so it goes overset point. Cooling mode it sometimes maintains setpoint of .5C but in heating it seems to always be 1C before it clicks back in and 1C oversetpoint before shutting off its not as precise. When its 1C off setpoint it should be pretty much ramped right down but it still doesnt seem low enough for it to go over set point. Once its reached the set point point it stays on until its gone 1C over but doesnt seem to slow down.

For instance it just cycled back on in both rooms and was using 2300W but then cycled back off and didnt seem to ramp down.

Can any one shed some light on this for me? Have tried settng fan speeds from high to low to see if the space was heating up too quickly and in low fan speed its exactly the same, seems to use a lot of power even if just 1C off set point.

The installer who put it in did it as a favour and i got it a lot cheaper than normally but I feel if i keep asking him out and saying its not performing properly in heating that im being a bit ungrateful really. he has connected his ampmeter to it and he says its running properly but I dont think he left it long enough he only measured it on 30C flat out which I think is still using more than it should.

The link is here to the specifications data book. Scroll to my model of outdoor (FM25AH) on the combination tables and you can see the figures for heating and cooling below the cooling. http://mylg.co.uk/data%20for%20site/multi%20f%202008%20outdoor.pdf

Any help appreciated as always guys.

[Thermatech]

The cheap kit from Korea like LG is cheaper than other eqipment for a number of reasons.
They can easily copy metal & plastic parts & make the unit look any other but its more difficult to copy the control stratagy & control circuit boards. So you will tend to find that the control circuit boards are simplified & control stratagy is basic.
This helps to make the kit cheaper to manufacture.
They tend to sell most volume in very hot parts of the world. So the design department at the factory are not so focused on heating performance & heating control stratagy.
The product is basically a cheap cooling system with heating as a bonus.
The koreans brand the product very well but its never going to be as energy efficient as other brands unless they develop the product with more advanced contol. But that would make it more expensive & they would loose sales.

Look on the Eurovent web site & compare the data of this product with others & you will see that its not the most energy efficient kit in the world.

Hendra will give another spin on this but then his job depends on maximising sales of the product.

[Thermatech]

So for instance

Quite a few split systems have a minimum compressor run time of say ,,, 3 mins. This is programed into the system control stratagy.

On older fixed speed compressor units that had no oil seperator at the outdoor unit the manufacturers opted to make a minimum compressor run time to ensure oil return as the oil had to go all the way arround the system & back to the compressor.

Unfortunately if the unit was oversized which is common for heating mode when the system has been selected for max cooling duty, then the unit could overshoot the set temp before completeing the min comp run time.
Ofcourse this is not an issue on larger VRF systems which have oil seperators which are 99% efficient. But manufacturers of budget split systems need to keep cost as low as possible so the compulsary min run time is an easy option rather than install oil seperator.
I did overcome this problem a few times by fitting a time delay relay to the compressor contractor.
The min compressor run time is based on the max allowable pipe lenght & so if you have short pipe lenght then you can risk a shorter min comp run time by fitting the time delay relay so the comp will only run for 2 mins instead of 3 mins.
Ofcourse this makes the warrantee invalid & you risk stuffing the compressor.

You might find that your unit will run the compressor for a fixed speed for a number of mins. At the end of this period the circuit board then looks at the return air temp & the indoor coil temp & makes a decision what to do next. If the temp is near to set point then it may ramp down the comp. But if its has already reached set temp or overshoot then it will stop the comp.
So in this part load situation the compressor never gets to ramp down.

I dont have detailed info on LG units control stratagy so this might or might not be whats happening on your system but it is something I have seen a number of times before on a number of different types of split system.

Unfortunately with inverter systems it would be difficult to overcome this unless the manufacturer has some dip switch or function setting options & with budget a/c kit thats not very likely.

[Thermatech]

And for instance

Multi split systems tend to incorporate a safety feature which prevents the accumulation of liquid refrigerant & oil in any indoor unit not heating.

It works like this.

Any indoor unit which is off or thermostat off at set point will not completely shut the liquid line LEV valve. So a small volume of hot gas passes through the indoor coil.
This makes the indoor unit produce a small amount of heat & in a small room this can provide some heat to the room even though the unit is off.

This control stratagy prevents hot gas from condensing in the indoor coil which would make the system seem short of gas & trap some oil also.

This might seem to be incorrect operation to the end user but it is the control stratagy programmed into the electronic control to prevent compressor failure from trapped liquid & oil at any indoor unit at off.

[back2space]

Thermatech I have read all your comments and it seems that it is possible that its not getting chance to ramp down. Average compressor run times per cycle is about 10-15mins so its deffo not the min run time thing kicking in. It doesnt short cycle in the sense of starting then shutting off straight away, it actually has to work to bring the room temp back upto set point. The concern is that it surely winds up to the capacity it needs to be at based on room temp. If thats just one degree below set point does it really need to run at full speed to get the temp back up. I was sent something from LG that said that if the temp is 3 degrees lower than set point then it runs at full speed and as it comes to set point starts slowing down. There is no way the room temp is going over the set point in 3minutes it takes about 10mins in this weather before it reaches the set point then carries on going at full speed for another 5minutes until it runs over the set point.

[Thermatech]

For most inverter split systems once near set point the compressor will ramp down & hold room temp within 1 deg of set temp.
It should only switch off compressor if at minimum speed the heat input to the room still makes the return air reach set point.
If the compressor carries on at high speed until it hits set temp & stops then its working more like a fixed speed compressor unit.
If it overshoots then perhaps the return air sensor is reading a bit low the manufactuing tolerance for the sensors will only be + or - 1 deg C at best.

The remote sensor option with sensible sensor location might help.

Dont expect too much from this type of equipment.
Keep the fan heater ready as backup.

[back2space]

Really is it not that reliable. I am told by the installer and some other people that LG isnt that bad equipment and has vastly improved.

Do you think the remote sensor will communicate with the outdoor unit better?

The return air sensor has been checked in both units, one of them was faulty originally and we tested it and it was about 1C out so if the set point was 20, it was cutting out at 22.

Now they are both accurate to 1C so if set point is 20 its cutting out at 21 which is correct. Surely the 3C margin that is giving for compressor to start ramping down should start when the return air is climbing past 18C on a set point of 20C, Or does it only start ramping down when it gets to 20C to try hold thte 20C? As its currently shutting off at 21C with no evidence on the meter to show its ramping down at 20C, as it is continuing to stay on for another 5minutes at 20C until it reaches 21C.

[Argus]

.

Notwithstanding all the posts, why are you on a pre-payment meter?

You are paying far more for your power that way.



.

[back2space]

Because the flat is rented from a private landlord and he has them on a coin meter. I know we will be paying more but the wattage still goes through the energy meter the same, im not really looking at the cost im looking at the actual wattage consumption.

[Thermatech]

I was just thinking that some floor mounted indoor units can also be installed horizontally on the ceiling.
In this case the heating diff has to be activated for the high ceiling application & deactivated for the low floor mounted application.

[back2space]

Ah yes we have already done this, one of the units was setup for high ceiling when first installed and it was heating up 3C higher... was boiling!

Any more ideas?

[Thermatech]

No


To go any further it would be helpfull to have detailed explanation of the heating operation control stratagy & any heating operation safety functions ( if there is any )

But the information in the product data manual & the service manual is very limited & does not give detailed technical details of the control stratagy or any details of any heating safety function.

If you had that information yourself you would not need to post this thread as you would be able to workout what it is doing yourself.

Perhaps some engineers who have been to the LG training accadamy in Slough have been given some more detailed technical information which they can use to assist.

[back2space]

Im not an engineer so I wouldnt know what it is doing. I have a good knowledge of it being in the business that im in but im afraid I no nothing about safety cut outs and pressures etc. Only the basic running of the systems.

[Thermatech]

Well

Generally we would expect the system to have some sort of compressor start up stratagy where it gradually ramps up over a period of time to a traget speed. But what dictates that target speed ?
Indoor unit size ?
Outdoor temp ?
Indoor temp & diference from set temp ?
How long is the start up stratagy ? 1 min , 2min ??

Then following the start up sequence we would expect some sort of Target sub cooling control stratagy to control compressor speed & LEV valve refrigerant flow based on

indoor unit coil temps ?
Outdoor unit discharge temp ?
difference of return air from set temp ?

How often does the indoor unit look at the data & make adjustment to the LEV valve opening & compressor speed
once every 30 seconds ?
once every 1 min ?
once every 2 mins ?

This type of electronic control stratagy can be very basic as is often the case withlow cost budget systems or it can be more complex as is often the case on more expensive premium products.

Unless your service engineer has access to this detailed control stratagy information he will not be able to assess if the units operation is correct or incorrect & then move on to locate the problem.

If there are any LG experts in the world that can explain this type of detail information & help you to resolve this problem

NOW WOULD BE A GOOD TIME TO POST A COMMENT

[back2space]

Thermatech and everyone so far thanks for your help.

What are the chances of there being someone on the forum is clued up on the LG kit?

[back2space]

Gary... just shows how you learn something new every day!

HIgh fan speed too noisy!

[Thermatech]

Valid point Gary

Heating mode
Indoor unit is the condenser
Low fan speed
Higher discharge temp
Higher discharge pressure
More amps

We get alot of problems with heat pump systems comissioning at this time of year.
Today in London was 3 deg C & Foggy.
Indoor temp was 10 deg C.

So discharge temp & pressure very poor about 20 bar on R410a.
Drop fan speed to minium & discharge pressure & temp improved = more heat into the room.

[Gary]

Today in London was 3 deg C & Foggy.
Indoor temp was 10 deg C.

So discharge temp & pressure very poor about 20 bar on R410a.
Drop fan speed to minium & discharge pressure & temp improved = more heat into the room.

Keeping in mind that heat is a measure of both temperature and volume, lower fan speed gives you higher temperature air, but less heat into the room, because the air volume is reduced more than the temperature is increased.

[Gary]

So discharge temp & pressure very poor about 20 bar on R410a.
Drop fan speed to minium & discharge pressure & temp improved = more heat into the room.

If I'm converting bar to psi correctly, the SCT would be about 34C/93F. Given 10C/50F air entering the coil, that would mean the condenser TD was about 24C/43F, which if anything seems a little high, not low.

The lower than expected pressure/temperature was a result of the 10C room air entering the condenser. This would no doubt improve as the room came up to temp and it would get there faster with high fan speed.

[back2space]

So its gonna remove more heat from the outside air if the indoor unit is set to low fan speed but the disadvantage of this is higher wattage used?

Surely more airflow though with higher fan speed is better to bring room temp up?

[Gary]

So its gonna remove more heat from the outside air if the indoor unit is set to low fan speed but the disadvantage of this is higher wattage used?

No, less heat is removed from the outside air with low indoor fan speed... and the wattage is higher.

[back2space]

Sorry for all the questions? Its so confusing!

[back2space]

Ok have tried putting on high fan speed and monitoring the energy usage and were looking at 150watts less if its on high fan speed compared to if its on low fan speed. Still no where near the quoted ratings in the specs. My question is why doesnt the inverter ramp right down if it knows that the indoor is on low fan speed so as to not have to gather as much heat. Or is it using more power when the compressor is having to compress the vapour back into a liquid because it hasnt all turned back to a liquid due to it still retaining some heat? Or am i missing a point here?

[Thermatech]

Well

Generally we would expect the system to have some sort of compressor start up stratagy where it gradually ramps up over a period of time to a traget speed. But what dictates that target speed ?
Indoor unit size ?
Outdoor temp ?
Indoor temp & diference from set temp ?
How long is the start up stratagy ? 1 min , 2min ??

Then following the start up sequence we would expect some sort of Target sub cooling control stratagy to control compressor speed & LEV valve refrigerant flow based on

indoor unit coil temps ?
Outdoor unit discharge temp ?
difference of return air from set temp ?

How often does the indoor unit look at the data & make adjustment to the LEV valve opening & compressor speed
once every 30 seconds ?
once every 1 min ?
once every 2 mins ?

This type of electronic control stratagy can be very basic as is often the case withlow cost budget systems or it can be more complex as is often the case on more expensive premium products.

Unless your service engineer has access to this detailed control stratagy information he will not be able to assess if the units operation is correct or incorrect & then move on to locate the problem.

If there are any LG experts in the world that can explain this type of detail information & help you to resolve this problem

NOW WOULD BE A GOOD TIME TO POST A COMMENT

Still waiting for all those LG experts to help this fellow.
Afterall LG make big about how much airconditioning equipment it makes & sells.
You would think there must be some expert technical service engineer on this planet who can expain what this unit is doing ?

[back2space]

Yeh with both units on and set to 30C and max fan speed the unit is pulling 3268Watts.

The unit shouldnt be drawing any more than 2730watts!

[back2space]

I dont suppose someone could ring LG technical on my behalf could they. IF i ring they tell me they cant speak to me and to direct questions to the installer who I dont like to keep contacting.

[paul_h]

I told you they draw over rated watts with a high differential.
Yes there may be something wrong also, but it's normal for them to draw over rated consumption when the setpoint versus indoor temp is greater than ~7C.
I've seen inveter a/cs of many brands do that, ie rated for 3A draw 4A when set to heat and 30C in a 20C room.

[back2space]

Ok 1 unit operating, set point 21, room temp 20, diff of 1C, unit is pulling 1589 watts on low fan speed, in high fan speed unit is pulling 1310 watts.

Still no where near what it should be pulling at the stated 800watts. It just dont seem to ramp down enough.

[back2space]

SPoke to LG who said that it should be ramping down when it gets near the set point. THey also said if i want them to come out to it its gonna cost £400 plus vat! They didnt have a leaflet on the control strategy but first said my unit wasnt an inverter till I corrected them! THey say that the unit should be ramping down a lot lower than it is and the unit should be avoiding cycling off by doin this. It is not!

[SteinarN]

Have you tried to let the dors or window open so the temp doesnt rise so fast? Maybe it gets time to ramp down then without shutting down completely. Just for a try to see whats might happen.

[back2space]

Yeh we have done this, we also leave hte internal doors open as the units heat the hallway and other rooms of the ground floor flat and the unit just then seems to ramp up even faster!

[Electrocoolman]

What is the accuracy of your Wattmeter?

Is is one with a clamp on current sensor, and you have to enter the voltage figure manually?

[back2space]

Yes its the WATTSON, it is very accurate, we have done several tests. Its accurate to perhaps 5-10watts which we are taking into consideration.

[back2space]

GUys managed to get this from LG that shows the control strategy. Notice that it says in heating the unit runs the comp at full capacity even if its at set point. Tried to upload the attachment but its too big, tried compressing it and still too big! So copied and pasted it there were a couple of graphs but these havent pasted.



How does it work?

Cooling Operation





The Multi F and FDX products have quite a complex way of working.

The inverter compressor always starts first.
On compressor start up the compressor speeds up to its target frequency (we will talk more about this later). The refrigerant flows through the 4-way valve (de-energised in cooling) into the condenser where it condenses to a liquid. The liquid refrigerant passes through the electronic expansion valves where it partially expands and leaves the condenser to the fan coil via the field pipe work. The refrigerant continues to expand in the fan coils and returns to the condensing unit as a vapour. The vapour then returns to the compressor via the 4-way valve.
NB solenoid valve 1 is always open on start up and stays open to allow oil return.
As the capacity is increased the fixed speed compressor is needed this will happen when all indoor units are running with all EEV’s fully open.

How this inverter compressor speed controlled?

This unit has a dc compressor (digitally controlled) which is used to vary the cooling or heating capacity to meet the load required. The compressor has several speeds available, it is almost impossible to measure the speed of the compressor with a normal multi meter.

Compressor Target Speed

In normal conditions the compressor is controlled using the indoor units return air thermistor and the capacity. The indoor units measure the room temperature using the return air thermistor; this is compared with the set point temperature on the controller. The fan coils tells the condensing unit what its capacity is and what this delta t figure is. The condenser then calculates what the target compressor speed is.


It can be seen that if the room temperature is more than 3 degrees higher than the set temperature and the outdoor capacity is equal to the capacity of the fan coils then the compressor will be told to run at full speed.

When is the target speed over ridden?

Once the system starts some other parameters are measured to ensure the unit does not operate outside design conditions or operate in a condition which will cause the unit to fail see below:

Ambient temperature

The outdoor units return air sensor is used to protect the compressor in either high or low ambient temperatures, this will over ride the target speed of the compressor.
i.e. if the outdoor temperature is below 24ºC or above 54ºC the compressor target speed will be reduced causing the compressor to slow down.

Indoor unit frost prevention

If the indoor coil temperature falls below 6ºC there will be a risk that the indoor coil will freeze up causing liquid to return to the compressor. The indoor coil thermistor is used to measure this temperature. At 6ºC the maximum operating speed of the compressor is reduced to step 4, if the coil temperature falls to 3ºC the maximum operating speed of the compressor is reduced to step 2 and finally if the coil temperature falls to 0ºC the compressor is stopped. The compressor will not restart or speed up until the coil temperature reaches 7ºC. see below.
To see this in operation you need to have gauges fitted so you can read the suction temperature.
This can also be seen via a temperature probe measured on the indoor coil.
The coil temperature should be above 7ºC in normal operation

How does the fixed speed compressor start?

Once the inverter compressor has reached its maximum speed the fixed speed is called for how this happens is the inverter ramps down and stops and then the fixed speed compressor starts then the inverter will start this will take 4 mins for this operation.

Outdoor Unit fan speed operation

The condenser unit Fan speed is controlled by the outdoor unit coil thermistor, the outdoor ambient thermistor and the speed of the compressor.

In cooling operation once the system starts the outdoor fan will start at full speed (900rpm) and then after (240 Seconds) slow down to a medium speed (650 rpm).

The ambient air temperature affects the fan speed as follows

0ºC fan off
21ºC medium speed 650 rpm
46ºC high speed 900 rpm




Heating how does it work?



On compressor start up the inverter compressor starts up first and the fixed speed starts up shortly after (30 seconds) this is to build up the pressure for the reversing valve.
The compressor will ramp towards its target frequency.

At this time the indoor units fans will not running this is called pre-heat or hot start (we will talk more about this later). The refrigerant flows through the 4-way valve (energised in heating) out to the fan coil via the field pipe work. The refrigerant condenses to a liquid in the indoor fan coil and returns to the outdoor unit as a liquid the liquid passes through the electronic expansion valves where it expands into the outdoor coil (evaporator). Finally it returns to the compressor as a vapour, via the 4-way valve.
NB the solenoid valve 1 will be energised for oil return.
In heating mode All EEV’s are left open 10% to allow oil return to the compressors.












Compressor Target Speed

In normal conditions the compressor is controlled using the indoor units return air thermistor and the capacity. The indoor units measure the room temperature using the return air thermistor; this is compared with the set point temperature on the controller. The fan coils tells the condensing unit what its capacity is and what this delta t figure is. The condenser then calculates what the target compressor speed is.



It can be seen that the units all operate to 4 degrees higher than set temperature so if you set 20 degrees C on the controller the unit will continue to heat to 24 degrees C. If the room temperature is the same as or higher than the set temperature and the outdoor capacity is equal to the capacity of the fan coils then the compressor will be told to run at full speed.


When is the target speed over ridden?

Once the system starts some other parameters are measured to ensure the unit does not operate outside design conditions or operate in a condition which will cause the unit to fail.

Ambient temperature

The outdoor units return air sensor is used to protect the compressor in either high or low ambient temperatures, this will over ride the target speed of the compressor.
i.e. if the outdoor temperature is below -10ºC or above 15ºC the compressor target speed will be reduced causing the compressor to slow down.


Over heat protection

Over heat protection is the discharge temperature which is measured on the pipe sensor at the indoor coilS (due to the unit being in the reverser cycle the indoor unit becomes the condenser rejecting heat and the outdoor becomes the evaporator absorbing heat). If temperature reaches 65c the outdoor fan will begin to slow down this is to reduce the amount of heat generated by the outdoor fan until the temperature drops to 55c.
NB If the indoor coil temperature continues to rise above 65c then the compressor will stop.

De-frost how does it work?

When a unit is in heating mode a small amount of ice may form on the outdoor coil this is normal.
This will give poor heat exchange which will cause the indoor coil to drop in temperature.
NB there is a solenoid valve 2 this is to allow hot gas to enter the liquid line when the ambient temperature is below 0 degrees.
There is a defrost sensor that will measure the condensing temperature.
NB if the liquid temperature is below 15 degrees this will cause the outdoor unit to go into defrost.
NB If the unit is incorrectly charged of refrigerant ie undercharged this will cause unnecessary defrost causing little or no heat.
After defrost the unit will resume normal action starting with pre-heat.

What controls the expansion valve?

The expansion valve is controlled as a function of the speed of the compressor as the compressor speeds up then the expansion valve opens.
NB In heating mode all electronic expansion valves are open weather the indoor units are running or not this is to ensure oil return to the compressor.



Outdoor Unit fan speed operation in heating


The outdoor unit Fan speed in heating is controlled by the outdoor ambient thermistor, indoor pipe thermistor and the speed of the compressor.

In heating operation once the system starts the outdoor fan will start at full speed (900rpm) and then after (240 Seconds) slow down to a medium speed (650 rpm).

The ambient air temperature affects the fan speed as follows

-15 ºC high speed 900 rpm
5 ºC medium speed 650 rpm
25 ºC off
NB On all outdoor units that have a twin fan system one fan will switch off this will be the bottom fan and the top fan will work in the same way as above.

[Thermatech]

Just about as suspected
Basic control for a split system

1 very important piece of information is missing.
How often does the control circuit board look at the sensor data & then make any adjustment to the system operation ?
once every 30 seconds
once every min
once every 2 mins

If you have small rooms then indoor unit can easily overshoot set temp if the indoor circuit board on looks at the room temp once every 2 mins.

How many steps of speed control does the inverter actually have? 'Several' could be only 3 speeds.

Hope you dont need any low ambient cooling. Check out the cooling outdoor fan control. LG definition of low ambient control ?

At least the units have heating high temp protect function.

[back2space]

The room temp only ever goes over the setpoint by 1C then it shuts off, so I think teh control strategy has changed slightly in that there isnt a 4C difference. Its only 1C either way of setpoint that determines if its on or off. Very dissapointed it doesnt ramp down in heating mode Kind of defeats the point of having the system installed now. IN fact i think going to go back to installer and explain its not good enough.

The fan control u mention in cooling I also think is updated as when I use it in cooling as I do a lot of the time the fan remains in a very low low speed down to 0C then it remains off on the outdoor unit. I know this unit in the book says can provide cooling down to -15C so I think this extract they have sent me is a little out of date as it mentions fixed speed compressors which is what the 2008 models dont have.

[Thermatech]

I think you de activated the 4 deg dif with the dip on the indoor unit for low level unit mounting possition.

heating 4 deg dif is standard control for lots of split systems on high wall, cassette & ducted units which will have return air from high level in the room & the manufacturer considers that a good average for warmer air at high level will be about 4 deg dif.

For most systems you can deactivate this function if you use a room mounted remote sensor which is located at body height so the unit will be sensing the same temperature as you unless ofcourse you spend your time hanging from the ceiling

[back2space]

Yes I thought it was weird but its not on a 4C difference as we have deactivated that on one of the units as it was activated. Like i say there is 1C diff either side of setpoint so i think the control has been updated but it still runs at full whack on the setpoint.

[Thermatech]

Does this outdoor unit have 2 compressors ?

If it does then 1 will be inverter & 1 will be direct on line.

Do you think the direct on line comp is switching off near set point ?

You should see a large drop in current when it stops.

I suspect that the unit only looks at the data once every 2 mins or thereabouts.
If the unit can warm the room faster than 1 deg in 2 mins then the unit does not have enough time to drop out the direct on line comp & then ramp down the inverter.

If this is a twin compressor outdoor unit , I wonder how it would work if you reduce the capacity of the outdoor unit by 50% by disconnecting the direct on line compressor ?

The heating performance at the indoor units would be 50% & it would take much longer to get up to set point.
But it would reduce this constant stop start problem.

BTW
Fair play for getting some control stratagy info. Just look at how many LG experts from all around the world have come back with some further info

[back2space]

There is only one compressor inside my outdoor unit. its the new 2008 model and they did away with the constant speed compressor due to it requiring higher amps and breaker plus the high start up amps etc. This unit only has 1 compressor and when this compressor stops it takes about half a minute before the compressor has ground to a halt completly.

A bit dissapointed at how many LG experts have come back to us on this one.

TO be honest I dont think LG have a clue how their equipment works because the guy at LG was saying it should be winding down once it reaches set point. But the control strategy document says otherwise so this doesnt give me much confidence when the own company doesnt know how their equipment works! Kind of regret having ever got LG equipment, they have been useless at customer service, they dont like speaking to the end user and their product knowledge is poor also. Graham Hendra who emailed me on one occasion regarding the matter didnt really look into my problem properly and made me feel like I didnt know what I was talking about!

YOu also mention about it not having enough time to reduce the compressor speed. Well for it to overshoot by 1C were looking at about 8minutes before it goes over. FOr instance I have a setpoint of 21C when it gets to 21C the compressor speed remains the same for 8minutes till it reaches 22C then the compressor shuts down.

[Gary]

Well for it to overshoot by 1C were looking at about 8minutes before it goes over. FOr instance I have a setpoint of 21C when it gets to 21C the compressor speed remains the same for 8minutes till it reaches 22C then the compressor shuts down.

I'm confused. Please define each of the above "it"s.

[nike123]

As Gary has already pointed, you are discussing control strategy of unit with two compressors, and this one in question, is not with two compressors, therefore, this latest discussion is pretty much pointless.

[back2space]

As Gary has already pointed, you are discussing control strategy of unit with two compressors, and this one in question, is not with two compressors, therefore, this latest discussion is pretty much pointless.

Nike123 LG advised me to disregard the bit referring to the 2nd compressor as this is only used in back up on previous units when the unit needs high capacity.

The newer unit which is mine has a larger inverter compressor so they didnt require the 2nd stationary compressor.

LG say the control strategy is the same just without the 2nd compressor kicking in.

[nike123]

If the room temperature is the same as or higher than the set temperature and the outdoor capacity is equal to the capacity of the fan coils then the compressor will be told to run at full speed.

This doesn't make sense. It is wrong statemant or bad translation from original.

Why would compressor run in full speed when room temperature is same or higher than set temperature.
It looks like it is copy/paste from cooling control description.
I would not take this document for good explanation of control strategy.

Could you email me that document and I will then upload it to some server and link it here? Or you could done that at this page (you need to register first).

[back2space]

This doesn't make sense. It is wrong statemant or bad translation from original.

Why would compressor run in full speed when room temperature is same or higher than set temperature.
It looks like it is copy/paste from cooling control description.
I would not take this document for good explanation of control strategy.

Could you email me that document and I will then upload it to some server and link it here? Or you could done that at this page (you need to register first).

Nike can you message me your email address please.

Thank you.

[back2space]

I'm confused. Please define each of the above "it"s.

Gary

All of the Its Refer to the indoor unit It = Indoor unit.

[Gary]

Gary

All of the Its Refer to the indoor unit It = Indoor unit.

Exactly where and how are you getting your temperature measurements?

[Thermatech]

The equipment is sold through a distributor network to contractors who then sell & install it for endusers.

So the installation contractor should ideally be able to resolve any problem as you would expect that he has been to training at the LG Training centre.
If the contractor is unable to resolve a problem he should be able to call on the assistance of the distributor who's technical engineers should be fully trained in for product at the LG training centre.
So LG UK HQ should only really be providing technical support to the distributors not fielding a multitude of calls from endusers.
LG don't even have responsibilty for the warranty because that sell that on to the distributor as well with the equipment.

If the contractor & distributor have been unable to provide technical assistance to resolve this issue then really that is a poor reflection on them as well as a poor reflection on the LG training.

At the end of the day this a budget global product produced for domestic use in hot climates.
So you can't expect it to be an 'all singing & all dancing' product.
It may not be optamised for cooler climate heating operation, as you seem to have found.
But as you can see from the control description it is not even optamised for low ambient cooling as the cooling outdoor fan speed control is the most crude excuse for low ambient control you are ever likely to see on any cheap split system.

But then
How mainy domestic endusers would look in detail at how the unit actually operates ?

A common reply is that poor quality & performance was only a problem on last years product & that this years latest model is completely redesigned & improved & has no problems at all.
Yeh , ok, sure, we've heard all that before last year & the year before & the year before that.

There is always a street full of unsuspecting punters for tomorrow.

Perhaps one of the other 25,000 members who might from time to time install & maintain LG equipment can provide some further light on this.
Perhaps there is some really simple little thing that has been overlooked.

[back2space]

Can you explain what is wrong with the fan control in Low ambient cooling?

The fan control seems fine, it seems to regulate the speed dependant on outside temp. Which is what I guessed it did? The only time it remains off is if its in defrost mode and the temp is below zero.

[Gary]

What I'm seeing here is a control strategy for a multiple compressor unit, which this unit is not. We can't tell if the system has a problem if we don't know what the system is supposed to do or how it is supposed to do it.