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  1. #1
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    LG heat pump problem



    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.
    Last edited by back2space; 15-12-2008 at 06:21 AM.



  2. #2
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    Re: How much power should it be using in heating?

    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.

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    Re: How much power should it be using in heating?

    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.

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    LG heat pump problem

    Hi a/c guru's - wonder if you can help?

    I was asked (on another, non a/c site) to help with a problem. However, heat pumps are not my forte!.

    I will cut and paste the guys query below and be very interested in your kind replies.

    Thanks in advance....

    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 you shed some light on this for me? The equipment is LG and before u say it has been great in the summer no probs at all, I know LG dont have a good reputation and all that but this is what ive got!



    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.

    Any help appreciated matey.

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    Re: How much power should it be using in heating?

    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.

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    Re: How much power should it be using in heating?

    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.

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    Re: How much power should it be using in heating?

    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.

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    Re: How much power should it be using in heating?

    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.

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    Re: How much power should it be using in heating?

    .

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

    You are paying far more for your power that way.



    .

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    Re: How much power should it be using in heating?

    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.

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    Re: LG heat pump problem

    The units use more power on heat.
    It's common for inverters to go over their rated power in heat if there is a large temp differential between room temp and set point (8-10C) and the compressor is running full speed.
    You need to get pressures, pipe temps and indoor coil temp readings to diagnose if there's a fault.

    They run best with the indoor fan set to high and if course the filters clean. Normally the more heat it can get rid off indoors, the lower the HP will be, lower the current draw.
    But it shouldn't be running high current, then cycling off, then running high current, then cycling off etc. If it's doing that, it may be cycling on excess discharge temp due to piping/airflow or refrigerant flow problem.
    Make sure it's the compressor cycling off, not just the outdoor fan though
    Last edited by paul_h; 16-12-2008 at 01:07 AM.

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    Re: LG heat pump problem

    Hi there

    I asked terminator to look into this for me.

    The outdoor fan runs constantly throughout the cycle.

    Filters are clean, fan speed is set to low but this is because the unit will cycle off even quicker due to being oversized slightly. Never have to run the fan at full speed unless the room temp has difference of 10C off set point to warm up quicker.

    Why does it have to be on high fan speed? Surely if its on low then the outdoor unit is isnt having to work as hard to get heat from the air as the heat is being put indoors slower due to lower air flow? Surely the higher the fan speed the more current the outdoor unit draws as the heat is being rejected indoors a lot quicker???

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    Re: LG heat pump problem

    Indoor unit needs to get rid of heat as efficient and as quickly as possible. Otherwise pressure goes up, compressor has to work harder, coil and pipes get too warm and safetys kick in.
    Remember the smaller indoor unit is rejecting the heat in heat mode, while the system is charged with refrigerant to maximize efficiency for rejecting the heat out of the larger outdoor unit in cooling mode in the summer. That's why a normal condensing pressure in summer cooling is about 2400kPa on r410a, while you'll find condensing pressure about 3000kPa+ in heat mode.

    Which is why there's safetys and such to manage the system while in heat mode becuase the indoor coil is actually undersized for the system. Anything to help it get rid of heat better (high airflow through the indoor by using high speed fan), helps it run better on heat.
    Last edited by paul_h; 16-12-2008 at 09:42 AM.

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    Re: LG heat pump problem

    But what if this high fan speed causes the unit to think its reached set point quickly by short cycling of air? When its not really reached set point? So it kicks back in 3mins later.

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    Re: LG heat pump problem

    I have to admit I've never come across that situation and don't think it's possible. The faster the indoor fan runs, the further it blows the air away from the unit, the more the ambient (not heated) air comes into contact with the room thermistor and the less likely the air thermistor will sample any of the discharge air, short cycle or think the room in down to temp etc and wind down or slow down on safetys.

    Normally short cycling is caused by low airflow, ie the air thrown out of the indoor is at low velocity (dirty filters or low fan speed) so it's not blown far away out of the unit, so ends up coming back into the units intake a lot quicker than high speed air blown out away from the unit.

    Low speed air is more likely to make the unit short cycle, and the evap over heats, the pressures are high, the compressor draws more current, the power bills are higher, the system's protections are kicked in, the outdoor ices up more etc etc.
    Try running a unit with dirty filter, see how much trouble that has with efficiency and effectiveness. Running a split on heat on low fan speed is almost as bad, does that make sense? If so then you'll agree that high speed fan is the best, and if you still have problems, then something is wrong with the equipment or install.

    Running a split in heat mode on low indoor fan is worse than running a split in cooling mode with a blocked filter. Both drop efficency, but nothing is harmed with a blocked filter is cool mode, the room just doesn't get cold. With heat mode though, everything is under stress at higher temps and pressure, which means more load, more consumption, more safetys kicking in. Increasing airflow will reduce that load because it can blow away heat further away.

    Your situation may be unique as far as a possible falt in the equipment or installation though.
    But if a lot more air was being blown through the indoor coil, the indoor coil would be cooler, the pressure would be lower, the compressor woudn't have to work so hard, the temps would be lower so the protections wouldn't have to work so hard etc etc.

    edit: It's like saying: What would happen if you put your outdoor unit in your sealed up garage? On a hot day while running on cool mode, eventually your garage is going to get hotter and hotter until the unit can't reject heat anymore and breaks down. The lack of cooler outside fresh air coming into the condenser means the system won't work.
    Not only is your indoor unit smaller than the outdoor unit, but it also has to work in similar closed up enviroments that we would never expect the outdoor unit to work in. That's why heaeting draws more power, needs safetys, and why it benefits from the largest supply of ambient air (high fan) that you can possible give it.
    Last edited by paul_h; 16-12-2008 at 06:58 PM.

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    Re: LG heat pump problem

    i will have to look into it tmrw when i'm home as it seems that high fan speed heats the room quicker as then its running design capacity. If i have been out all day i put the unit on high fan speed as it takes ages to bring the room temp up from very cold on low. Then once its reached set point i switch on to low for the evening the unit then maintains that. I assume it would be the same.

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    Re: LG heat pump problem



    Back2Space , as you have now started this thread again by getting Terminator to cut and paste your original post
    ( http://www.refrigeration-engineer.co...ad.php?t=16465 ) would you like me to delete the original or are you trying to get maximum coverage for one question ?

    It some circles this would be classified as a spam attack which is not something that this forum approves of.



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    Re: LG heat pump problem

    The MV indoor unit is floor mounted ?

    So is the return air at floor level 3 deg C colder than at higher level in the room ?

    The consitant overshoot of 3 deg C looks like a typical heating diff for high wall & cassett type indoor units which assume higher temp at high level in the room in heating mode.

    BTW
    Can any one find in the service or data manuals for this equipment any description of the safely devices or safety fuctions.

    For instance the outdoor unit looks like it does have a low pressure switch but no HP switch

    For most good quality heatpump systems some form of heating mode indoor high temp protect safety function would be normal.

    But can the description of this or any other heating safety fuction be found in the LG manuals ?

    If there can be found no description of any heating safety function then one has to wonder if the system is equiped with any such safety function.

    From experiance I would advise caution as budget equipment like this offen have limited or no safety fuctions at all.

    It starts to become difficult to trouble shoot a system for correct operation if the service manual does not fully describe what it should be doing or what it is programmed to do.

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    Re: LG heat pump problem

    Brian im sorry the post is duplicated. But i started the original post in the air conditioning forum. I had asked terminator for help on another forum not knowing he was also registered on here. It was only when he told me that he had posted on here did I know?

    Is it possible for you to merge the two posts into one so it keeps them both together?

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    Re: LG heat pump problem

    [quote=Thermatech;129027]The MV indoor unit is floor mounted ?

    So is the return air at floor level 3 deg C colder than at higher level in the room ?

    The consitant overshoot of 3 deg C looks like a typical heating diff for high wall & cassett type indoor units which assume higher temp at high level in the room in heating mode.
    quote]

    The indoor units are both installed in bedroom and lounge. At floor level about 1.5ft off the floor. The return air at floor level is usually about 1C different to what it is at head height (if the auto louvre up & down is turned on) otherwise there can be a difference of perhaps 3 degrees at head height and floor level. However this is not evident when the louvre is moving up and down as it seems to mix the air really well.

    THere isnt an overshoot of 3C though as I always have the louvre operating so measuring with a digital thermometer at the air intake once set point of 20C is reached the unit carries on heating until it reaches 21C and then thermostat off happens. It will then kick back in again when the thermometer reads 19C.

    Outside temps today have been at the manual test conditions 7C outside and 20C inside but it has still been running higher than you would expect it to. Or is the test conditions what give the rated wattage in the combination tables? So this could be why its not running at 880w when only 1 indoor running and maintaining set point? In what conditions would you expect it to use 880w???

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    Re: LG heat pump problem

    Quote Originally Posted by back2space View Post
    Brian im sorry the post is duplicated. But i started the original post in the air conditioning forum. I had asked terminator for help on another forum not knowing he was also registered on here. It was only when he told me that he had posted on here did I know?

    Is it possible for you to merge the two posts into one so it keeps them both together?
    OK, thanks, done now.
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    Re: LG heat pump problem

    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.

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    Re: LG heat pump problem

    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?

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    Re: LG heat pump problem

    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.

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    Re: LG heat pump problem

    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.

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    Re: LG heat pump problem

    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

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    Re: LG heat pump problem

    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?

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    Re: LG heat pump problem

    Quote Originally Posted by back2space View Post
    Surely if its on low then the outdoor unit is isnt having to work as hard to get heat from the air as the heat is being put indoors slower due to lower air flow? Surely the higher the fan speed the more current the outdoor unit draws as the heat is being rejected indoors a lot quicker???
    The opposite is in fact true. In heat mode, the lower the indoor fan speed, the harder the outdoor unit has to work and the more power it requires.

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    Re: LG heat pump problem

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

    HIgh fan speed too noisy!

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    Re: LG heat pump problem

    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.

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    Re: LG heat pump problem

    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?

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    Re: LG heat pump problem

    Quote Originally Posted by Thermatech View Post
    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.
    Last edited by Gary; 17-12-2008 at 12:27 AM.

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    Re: LG heat pump problem

    Quote Originally Posted by back2space View Post
    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.
    Last edited by Gary; 17-12-2008 at 12:29 AM.

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    Re: LG heat pump problem

    Sorry for all the questions? Its so confusing!

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    Re: LG heat pump problem

    Quote Originally Posted by Thermatech View Post
    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.
    Last edited by Gary; 17-12-2008 at 05:38 AM.

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    Re: LG heat pump problem

    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?

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    Re: LG heat pump problem

    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 ?

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    Re: LG heat pump problem

    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!

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    Re: LG heat pump problem

    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.

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    Re: LG heat pump problem

    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.

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    Re: LG heat pump problem

    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.
    Last edited by back2space; 19-12-2008 at 10:43 AM.

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    Re: LG heat pump problem

    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!

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    Re: LG heat pump problem

    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.

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    Re: LG heat pump problem

    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!

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    Re: LG heat pump problem

    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?

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    Re: LG heat pump problem

    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.

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    Re: LG heat pump problem

    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.

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    Re: LG heat pump problem

    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.

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    Re: LG heat pump problem

    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.

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    Re: LG heat pump problem

    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

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