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back2space
15-12-2008, 06:17 AM
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 (http://mylg.co.uk/data%20for%20site/multi%20f%202008%20outdoor.pdf)

Any help appreciated as always guys.

Thermatech
15-12-2008, 09:39 AM
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
15-12-2008, 05:50 PM
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.

terminator
15-12-2008, 07:59 PM
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.

Thermatech
15-12-2008, 08:31 PM
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
15-12-2008, 09:09 PM
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
15-12-2008, 10:58 PM
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
15-12-2008, 11:07 PM
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
15-12-2008, 11:15 PM
.

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

You are paying far more for your power that way.



.

back2space
15-12-2008, 11:17 PM
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.

paul_h
16-12-2008, 01:04 AM
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

back2space
16-12-2008, 06:08 AM
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???

paul_h
16-12-2008, 09:40 AM
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.

back2space
16-12-2008, 05:12 PM
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.

paul_h
16-12-2008, 06:32 PM
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.

back2space
16-12-2008, 06:56 PM
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.

Brian_UK
16-12-2008, 07:59 PM
:off topic:

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

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

:off topic:

Thermatech
16-12-2008, 08:18 PM
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 :confused:

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.

back2space
16-12-2008, 08:24 PM
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?

back2space
16-12-2008, 08:32 PM
[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???

Brian_UK
16-12-2008, 08:52 PM
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.;)

Thermatech
16-12-2008, 08:55 PM
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
16-12-2008, 09:09 PM
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
16-12-2008, 09:37 PM
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
16-12-2008, 10:11 PM
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
16-12-2008, 10:55 PM
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
16-12-2008, 11:06 PM
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?

Gary
16-12-2008, 11:14 PM
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.

back2space
16-12-2008, 11:19 PM
Gary... just shows how you learn something new every day!

HIgh fan speed too noisy!

Thermatech
16-12-2008, 11:27 PM
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.

back2space
16-12-2008, 11:36 PM
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
17-12-2008, 12:17 AM
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
17-12-2008, 12:23 AM
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
17-12-2008, 12:49 AM
Sorry for all the questions? Its so confusing!

Gary
17-12-2008, 01:14 AM
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
19-12-2008, 07:46 AM
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
19-12-2008, 09:27 AM
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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back2space
19-12-2008, 10:09 AM
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
19-12-2008, 10:26 AM
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
19-12-2008, 10:28 AM
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
19-12-2008, 10:30 AM
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
19-12-2008, 11:49 AM
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
19-12-2008, 11:57 PM
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
20-12-2008, 12:20 AM
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
20-12-2008, 04:45 PM
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
20-12-2008, 05:09 PM
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
24-12-2008, 12:22 AM
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
24-12-2008, 05:42 PM
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
24-12-2008, 05:53 PM
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
24-12-2008, 06:04 PM
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 :D

back2space
24-12-2008, 06:10 PM
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
24-12-2008, 07:05 PM
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
24-12-2008, 08:44 PM
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.

Thermatech
24-12-2008, 11:06 PM
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
25-12-2008, 12:01 AM
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
25-12-2008, 03:47 AM
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.

Gary
25-12-2008, 03:55 AM
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
25-12-2008, 07:12 AM
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
25-12-2008, 07:39 AM
I'm confused. Please define each of the above "it"s.

Gary

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

back2space
25-12-2008, 07:42 AM
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
25-12-2008, 08:13 AM
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 (http://www.mediafire.com)(you need to register first).

Gary
25-12-2008, 03:31 PM
Gary

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

Exactly where and how are you getting your temperature measurements?

Gary
25-12-2008, 04:02 PM
Trying to piece the puzzle together:

According to the control strategy, the unit is designed to overshoot temp by 4C in heating mode. According to Thermatech, this function has been overridden by a dip switch on the indoor unit. The unit now overshoots by 1C.

Is this a problem or is this normal?

If the compressor is running 100% in heating mode with on/off as opposed to modulating control, then some minimum overshoot is needed in order to avoid short cycling.

If the compressor runs 100%, then we cannot expect ramped down wattage... so is the wattage a problem or is this also normal?

Does this system have a problem or does it not have a problem?

back2space
25-12-2008, 09:00 PM
The 1C overshoot is not a problem for me as I guess this is to avoid short cycling. They (LG) told me the unit has a 1C buffer zone either side, when the unit reaches its set point of 21C then the unit should ramp down even further to maintain that, however if the temp continues to rise for instance overshooting to 22C the compressor is then told to switch off.

The issue I have is why is it not ramping down when it is approaching set point. The time it takes to overshoot 1C is approx 10minutes so plenty of time for it to ramp down but it still runs as if it is trying to achieve the set point.

back2space
25-12-2008, 09:01 PM
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 (http://www.mediafire.com)(you need to register first).


Nike can you message me your email address please.

Thank you.

nike123
25-12-2008, 09:40 PM
Nike can you message me your email address please.

Thank you.

Download my Vcard (http://www.refrigeration-engineer.com/forums/member.php?do=vcard&u=13885)! It is there.

back2space
26-12-2008, 12:10 AM
Ok bud

You have mail!! :)

nike123
26-12-2008, 02:03 AM
Here it is!
http://www.mediafire.com/?tkwggjj4njy

momo
26-12-2008, 02:04 AM
I recently installed a non sale LG switched unit at home (a solution to its occupying storeroom shelf space) To get it to behave in any reasonable manner -- for heating -- I had to place the ambient sensor outside the casing of the unit, since then it follows room temperature quite adequately. It is not the first time that I have done this.... in the case of heating I suspect that the sensors can get "poisoned" by radiant heat from the coils and the units do not cycle/ramp at the correct temperatures. Incidentally the programming of the unit is weird (it allows short cycles and other oddities - part of the reason I think the switched units were removed from catalog and were quite expensive because of the decoration).

back2space
26-12-2008, 02:11 AM
Momo, the installer tried to have the sensor pointing outside the unit as u r correct the sensor was being affected by the temperature inside the unit. However this resolved problems of the temp not being monitored.

We are having remote sensors installed to fully resolve the problems of temp control, However putting the sensor outside the unit has not allowed the unit to ramp down either.

nike123
26-12-2008, 08:02 AM
http://farm4.static.flickr.com/3024/3137001397_eb38ec28f4_o_d.jpg

Here on diagram should be written below picture:
Delta T = Set temperature - return air temperature

Also this description should have one word changed:

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 lower 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.
From what I see in diagram, control strategy is OK and it is executed in 4 capacity steps. Dip switch you moved should be back to its original position and sensor positioned as I firstly said long before.


Then, your target temperature will be maintained as set temperature +- 1K and maximum speed of compressor will be when return temperature is 20°C and compresor will stop at 24°C or more. That is control band of 4K and should not be changed.

Also, stop looking at temperature display (cover it with duct tape);) and set temperature higher or lower according to your feeling of comfort. Be sure to not stand in air path.

You should experience lowest power consumption only when space heat loss is small and compressor then need to lower his output to last step. That is when return air temperature is between 23°C and 24°C (sensed at sensor as that value).
When return air temperature is 21°-22°C you should have power consumption one step lower than max. And when return air temperature is 20°C or lower your power step is max.
That strategy is OK by me, only what is lacking is some fuzzy logic.

Return your dip switch to position before intervention and then coll your flat to 16°C. Then switch on your AC and record return air temperature, time of changes, and power consumption, to establish is this AC works as it should be.

back2space
26-12-2008, 12:03 PM
Hi Nike

As I have 2 units I have switched the dip switch over on one unit. My installer told me that this was the high ceiling mode, as he first had to come back out after installnig as one of the units was setup in this mode by default despite them being mounted at radiator level. This unit that was in this mode seemed to keep heating until it reached 24C no matter what if the set point was 21 it would keep on going to 25C but the unit would achieve the 25C too with no sign of slowing down... cooling in this mode works fine.

SO are you saying I have to put the unit in high ceiling mode and perhaps set the set point at 20C to perhaps happily maintain about 22C?

Where should the sensor be positioned, currently it is poking out the front of the grille as inside the unit it didnt sense temp properly. Remote sensors are coming in January.

The data sheet above mentions nothing abut this control strategy only working in hi ceiling mode.

So what is the position of the dip switch for that I am using at the moment that either switches on or off the compressor should the setpoint be + or - 1C

nike123
26-12-2008, 01:17 PM
[quote=back2space;129833]Hi Nike

As I have 2 units I have switched the dip switch over on one unit. My installer told me that this was the high ceiling mode, as he first had to come back out after installnig as one of the units was setup in this mode by default despite them being mounted at radiator level. This unit that was in this mode seemed to keep heating until it reached 24C no matter what if the set point was 21 it would keep on going to 25C but the unit would achieve the 25C too with no sign of slowing down... cooling in this mode works fine.

SO are you saying I have to put the unit in high ceiling mode and perhaps set the set point at 20C to perhaps happily maintain about 22C?


We don't know for fact (without instalation sheet or service manual) that that particular switch is for correction of set temperature for ceiling or floor use of indoor unit. Therefore I advise to move it back to original position and then measure and record behavior of indoor and outdoor unit.
For this purpose (checking control sequence), I would leave set point to 20°C.


Where should the sensor be positioned, currently it is poking out the front of the grille as inside the unit it didnt sense temp properly. Remote sensors are coming in January.For now, leave it there and make your measurements of temperature of return air on exactly same place.




The data sheet above mentions nothing abut this control strategy only working in hi ceiling mode.From what I know from Fujitsu, control strategy remains same only what switch make is that sensor compesate his reading by 2 or 3°C.


So what is the position of the dip switch for that I am using at the moment that either switches on or off the compressor should the setpoint be + or - 1CI don't know. You could check your room temperatures in both positions after unit has worked some time (2 hours or more) to establish what position gives value that is closer to your set value.

Please, make check of control strategy as I asked in my previous post and do not change set points or anything during that check until compressor turns of or stay turned on one power step for more than half hour.

back2space
26-12-2008, 01:50 PM
the switch is deffo the hi ceiling mode activation switch as I am looking in the installation manual for the indoor unit and it shows a diagram pointing to this switch that says it is the hi ceiling mode button.

The position that keeps it closer to the setpoint temperature is the one that is not for high ceiling where the unit goes 1C over set point and compressor goes off.

I cannot find a copy of the installation manual online to show you. But this switch is deffo the high ceiling button. And as per the book it says that in high ceiling the temperature offset is 4C in heating mode.

nike123
26-12-2008, 02:07 PM
Ok, then leave it in that position.

back2space
26-12-2008, 03:49 PM
But this control thing in the data sheet is not doing as it should?? What would you do?

nike123
26-12-2008, 04:39 PM
I would not say that it is not doing as supposed, according to what you say here:




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.




Minimum compressor speed and min power consumption is only when result of equation "set temperature - return air temperature" is -3°C on both indoor units and not when both indoor units maintain temperature and got return air temperature 19°C (100 hz or full power) or 20°C (80 hz or one step below full power), and this is where it should be according to control logic. Nowhere in documents I saw that is said that it should be at minimum power consumption when unit maintain set point.

Compressor should stop only when result of equation " set temperature - return air temperature" is -4°C or more for both indoor unit together(-5,-6 etc.... which indicates to much generated power, ergo over dimensioned indoor units for space heat loss).

Minimum power consumption you should expect only when outdoor temperature is high (probably more than 10°C, or even 15°C) and then you could experience set point overshoots of 3°C because of space low heat load.

If I remember correctly, I think that is what was happening to you earlier, when outdoor temperatures are high and you wrote about that in your first post about your problematic unit.


If a temp of 22c is selected on the controller, the unit will sometimes continue until room temp reaches 3 or 4 degrees above this limit, meaning the temperature is very high and uncomfortable, and when the unit needs to kick back in it doesnt come back on quick enough meaning large differences in room temperature.

From data you presented here, I would not say that this unit is technically faulty in any way. It just do what it is programed and constructed to do.

If you cannot live with such rough control, you should sell this unit to someone who can, and buy more advanced units with fuzzy logic and more linear power control from Daikin, Fujitsu, Mitsubishi, Toshiba.

Good luck!

Gary
26-12-2008, 06:48 PM
http://farm4.static.flickr.com/3024/3137001397_eb38ec28f4_o_d.jpg


If I am reading the chart correctly, it is saying that the compressor ramps down to zero when the return air (average of both indoor units) temp is 4C above the setpoint. Since each unit only runs until the return is 1C above setpoint, we would expect the compressor to only ramp down to 80% at best... and that's only if both indoor units are 1C above setpoint.

I still see no indication of a problem.

Gary
26-12-2008, 07:04 PM
You seem overly concerned with the wattage used by your system. In fact this is not important at all. What matters is how much heating you are getting for the amount of power used. Or as we say on this side of the pond, how much bang for the buck. Its not about the bang and its not about the buck. Its about the bang for the buck.

back2space
26-12-2008, 10:13 PM
Ok Nike and Gary.

Ok I think im starting to understand now you are explaining it in a way I can relate to...

I was going by the figures on the LG databooks as and the figures I was quoting were from the page 218 of http://mylg.co.uk/data%20for%20site/multi%20f%202008%20outdoor.pdf

If you can look at that and look at the figures for 1 unit operation which is usually the case, I only have 1 unit switched on.

Now look at the right side of the table the "input" colums, it shows MIN, RATED & MAX,

For rated it shows 1200w... now look at the bottom of that page it shows a note.

This gives the heating capacity based on an indoor temp of 20C and outdoor temp of 7C... Is this to get the figures in the rated column of 1200?

The figures above under the RATED column for input are these the ones that are based on the outdoor temp of 7C.

So basically if its high ambient outside of perhaps 15C you might get the figure in the min column and the colder it is below 7C the more its going to be in the max column?

Nike you mention my first post about the problems with temp control.. this is down to the postining of the return sensor as the temperutres recorded at the sensor were diff to what they were at the other part of the room. Remote sensors have rectified this issue. So temp of comp on or off is 1C above or below set point.

Thermatech
26-12-2008, 10:43 PM
So if the performance data is based on 230v a/c power supply & the customer has 245v a/c power supply that would make a slight difference to the compressor speed & amps drawn but would also result in slightly better heating performance.

But the problem is not flat out performance in this case.

The basic problem that the customer has noticed is that the compressor does not ramp down & reduce power input at low load conditions.

What is the point of having an inverter system which should save energy by ramping down the compressor at low load conditions if it actually only works to the same control stratagy of a fixed speed compressor ?

Gary
26-12-2008, 10:50 PM
For rated it shows 1200w... now look at the bottom of that page it shows a note.

This gives the heating capacity based on an indoor temp of 20C and outdoor temp of 7C... Is this to get the figures in the rated column of 1200?

The figures above under the RATED column for input are these the ones that are based on the outdoor temp of 7C.


Yes... A/C systems are rated in a laboratory under tightly controlled conditions. The primary variables are the temperature, humidity and volume of the air flowing through both the indoor and outdoor coils.

And as they say in the automotive industry... Your mileage may vary.

Gary
26-12-2008, 10:56 PM
So if the performance data is based on 230v a/c power supply & the customer has 245v a/c power supply that would make a slight difference to the compressor speed & amps drawn but would also result in slightly better heating performance.

But the problem is not flat out performance in this case.

The basic problem that the customer has noticed is that the compressor does not ramp down & reduce power input at low load conditions.

What is the point of having an inverter system which should save energy by ramping down the compressor at low load conditions if it actually only works to the same control stratagy of a fixed speed compressor ?

Nonetheless, this seems to be the case with this system in the heating mode.

back2space
26-12-2008, 11:17 PM
yes exactly what is the point! It seems it ramps down one step when goes over the set point but when it hits 1c exactly over compressor goes off. Why does the document mention it ramps down as it goes over by 4c one step for each degree but to max of 4c then cut off. But in reality were only gettin one step. This should be ramped down as it approaches set point. Never mind after.

SteinarN
26-12-2008, 11:46 PM
The control logic document mentiones the EEV stays 100% open in heating active indor units and 10% open in OFF inndor units.

Such a control logic mimics a capilary tube system and has very poor performance in part load/reduced compressor speed operation as well as in low ambients below nominal (+7C) operating conditions. If the compressor was to operate at, say 40% speed in heat the result would be liquid flodback to the compressor and very poor performance.

Here in Norway air to air inverter heat pumps started to be installed in great numbers some 5 years ago. All Panasonic heat pumps had capillary tube system for several years. These systems is run in heat for maybe 6.000 hours a year, a lot of the time in part load and the rest of the time in low ambients well below nominal operating conditions. This means the compressor is running constantly in a liquid floodback condition.

It now seems like these compressors starts to wear out, loosing its pumping performance and requiring replacement in great numbers after having been in operation for 4 to 6 years.

Luckily I didnt install any heat pumps with capillary systems.

Thermatech
26-12-2008, 11:48 PM
Perhaps that data is just for the outdoor unit.
Each indoor unit fan motor will be about 100w to 150w.

Are you measuring the total watts input for just the outdoor unit or the complete system including the indoor units.

A cunning 'slight of hand ' deployed by manufacturers can be to only give power input for the outdoor unit in the performance chart.
You then need to add the power input for the indoor units but they dont tell you that in the data book.

However if you read the sales brochure you would expect the compressor to ramp down as it approaches set temp & run at min compressor speed at set temp.

Two weeks ago I spent a day monitoring the performance of 3 split systems from Japan.
They spent all day operating at min compressor speed & within 1 deg C of set point.
From time to time they got to set point & switched off & then after a while the room temp droped 1 deg C & the compressor started again & ran again at min compressor speed.

But then those units have much more advanced control stratagy.
The LG units are crude by comparison.

Thermatech
27-12-2008, 12:07 AM
The data in the performance charts are for 7m interconnecting refrigeration pipe.

If you have longer pipe length the power input will be slightly higher.

But no correction factor quoted for longer interconnecting pipe lenght ?

So there are a number of small adjustments which could be estimated for indoor unit fans, longer pipe lenght & higher than rated power supply voltage

but

none of that explains why the compressor does not ramp down to minimum speed.

The possibilities are
1/ The system has a fault which is causing incorrect operation.
2/ The system is doing exactly what the control stratagy is requesting.
In which case the low load heating control stratagy is very crude.

In view of the cooling low ambient control stratagy which is about as much use as a choclate tee pot then you have to suspect that the low load heating control stratagy is also very crude.

I still think that the system is slow to respond due to the system only making one adjustment every 2 or 3 mins.

But LG would not want to admit to that, would they.

Brian_UK
27-12-2008, 12:15 AM
Just a thought and I know this goes someway back to the starting point of your queries b2s but what happens if you reset the control differential from 1°C back to the high wall of 4°C ?

I am just wondering whether the system could ramp down properly with a 4° band but with only 1° there isn't enough control logic space left (if that makes any sense). By this I mean that it could step down over 4° expecting a reasonable time for that to happen but with only 1° it has to do things four times as fast to achieve the same result; but it appears that the control cannot respond that quickly.

back2space
27-12-2008, 01:14 AM
Brian, I will try this on one unit next week but that then asks a question why there is no control strategy for the low wall applications such as mine. One of the units was left in high ceiling mode when it was installed by accident when it was first installed in June, the outdoor unit ran at full pelt at a set point of 20C until it reached 24C i didnt connect the energy meter at this time but you could tell by the loudness of the compressor how fast it was going. So the high ceiling switch just offsets the temperature to make up for lower temps at floor level and higher temps at ceiling level. All that happens is that the unit wants to achieve 24C instead of the set point of 20C so will go at 100% till it reaches this, then it should wind down like any other system.

Thermatech, thanks for your comments, but how to tell if the system has a fault.

One thing I can advise you is if I set the remote controller to 30C the outdoor unit current drawn is about 500watts higher than if it was maintaining the setpoint. I have just tried this now. So the compressor is not running 100% but it doesnt ramp down any more.

nike123
27-12-2008, 08:48 AM
This gives the heating capacity based on an indoor temp of 20C and outdoor temp of 7C... Is this to get the figures in the rated column of 1200?

The figures above under the RATED column for input are these the ones that are based on the outdoor temp of 7C.

No, all 3 columns are based at outdoor temperature 7°CDB and indoor temperature 20°CDB. What is going to be depends on what is set temperature.


So basically if its high ambient outside of perhaps 15C you might get the figure in the min column and the colder it is below 7C the more its going to be in the max column?No, what is going to be, minimum or maximum or somewhere in between depends on diference between set temperature and air return (indoor) temperature of both units and result of internal equation who consider both indoor units power needs.



Nike you mention my first post about the problems with temp control.. this is down to the postining of the return sensor as the temperutres recorded at the sensor were diff to what they were at the other part of the room. Remote sensors have rectified this issue. So temp of comp on or off is 1C above or below set point.I would carefully check that compressor speed and temperature readings of that sensor correlate in that matter. Turn off second indoor unit and then make measurments as I earlier asked and post here measured data and not conclusions.

Coll your flat to 16°C. Then switch on your AC, set temperature at 20°C and record return air temperature (at place when indoor unit sensor is now placed) and power consumption in regular intervals (say, every minute) for period of 30-60 min, then we will together establish is this AC works as it should be.

nike123
27-12-2008, 09:10 AM
Just a thought and I know this goes someway back to the starting point of your queries b2s but what happens if you reset the control differential from 1°C back to the high wall of 4°C ?

I am just wondering whether the system could ramp down properly with a 4° band but with only 1° there isn't enough control logic space left (if that makes any sense). By this I mean that it could step down over 4° expecting a reasonable time for that to happen but with only 1° it has to do things four times as fast to achieve the same result; but it appears that the control cannot respond that quickly.

From what I know about ceiling/floor universal units, you don't changing differential of unit with deep switches, you only offsetting probe reading for 2K, maybe 3K or even maybe 4 K, but differential stays same.

But we cannot tell that here for sure, without service documentation.

nike123
27-12-2008, 12:13 PM
T


but

none of that explains why the compressor does not ramp down to minimum speed.

Because it is not suppose to do that if heat load of conditioned space is not low. It supose to maintain set temperature within tolerance dead band of 1°C by switching between 105 hz and 80 hz (according to graph) or, if outdoor ambient is high, restricted to 60 hz when return temperature in relation to set temperature is overdrawn less than 2°C and therefore acting similar like simple on-of control of capacity.


The possibilities are
1/ The system has a fault which is causing incorrect operation.I still don't see any evidence to conclude that.


2/ The system is doing exactly what the control stratagy is requesting.
In which case the low load heating control stratagy is very crude.
I bet on this option.;)



I still think that the system is slow to respond due to the system only making one adjustment every 2 or 3 mins.I could not find any data which confirm that. In fact, we are very low on amount of data who could lead to that conclusion. If you could point me to where did you draw that information from B2S posts, I would appreciate.


But LG would not want to admit to that, would they.None of manufactures do that admission. They all say that new unit has/will have better strategy, but admission is non existent.

I know only that small inverter multi split systems doesn't have enough sensors and complex control in comparison to older brothers from VRV/VRF range (price would be probable excuse) and therefore, comfort is reduced. Small multi split systems are compromise, and as such, their performance is also compromise.

nike123
27-12-2008, 12:56 PM
All that happens is that the unit wants to achieve 24C instead of the set point of 20C so will go at 100% till it reaches this, then it should wind down like any other system.

And that is exactly how it should behave according to control strategy, and if the dip switch mean that air return sensor is offset by 4K.




Thermatech, thanks for your comments, but how to tell if the system has a fault.By measuring and recording compressor frequency, return air temperature, time of changes and set point setting in some time while indoor temperature changes from 16°C (or 18°C, depending on lowest possible set temperature) to set temperature + 4K on both indoor units. For that to happen, you need to simulate low and high heat load conditions by forcing some amount of indoors units discharge air to short cycle.


One thing I can advise you is if I set the remote controller to 30C the outdoor unit current drawn is about 500watts higher than if it was maintaining the setpoint. I have just tried this now. So the compressor is not running 100% but it doesnt ramp down any more.Once again, it cannot ramp down if air return temperature is not higher than it is needed to switch to lower capacity step (and that must be for sum of capacities for both indoor units).:eek:

If change in one capacity step is enough to maintain set temperature within 1K than there is no need to ramp down any more. Only if that capacity change doesn't establish 1K temperature control, outdoor unit switch to lower capacity step and etc...

Please, read that text above carefully few times because, that is foundation for understanding of function of control logic. And, it seems, that part is most confusing to you, according to your questions.;)

P.S. Sorry, if I something misunderstood, because of language.

back2space
27-12-2008, 02:30 PM
Quote:
Originally Posted by back2space http://www.refrigeration-engineer.com/forums/images/VA_RE/buttons/viewpost.gif (http://www.refrigeration-engineer.com/forums/showthread.php?p=129872#post129872)
All that happens is that the unit wants to achieve 24C instead of the set point of 20C so will go at 100% till it reaches this, then it should wind down like any other system.

And that is exactly how it should behave according to control strategy, and if the dip switch mean that air return sensor is offset by 4K.


I am referring to the dip switch being activated in high ceiling mode. The system doesnt aim for 4C higher when not in high ceiling mode it only has a 1C above setpoint.

nike123
27-12-2008, 02:36 PM
Quote:
I am referring to the dip switch being activated in high ceiling mode. The system doesnt aim for 4C higher when not in high ceiling mode it only has a 1C above setpoint.

Exactly as it should be!

back2space
27-12-2008, 02:43 PM
I mean if the control strategy sheet was right it says once it has reached setpoint of 20C it will continue to heat to 24C ramping down a step every 1C.

In high ceiling mode the unit does not do this, once it has reached 20C it will continue at 100% tilll reached 24C. Are you sayign that if high ceiling mode is activated after it has reached 24C it will then start to ramp down and if another 4C increase is sensed it will stop?

How complicated that sheet is!

Thermatech
27-12-2008, 02:58 PM
niki 123

I was working one day last year with an engineer who had an old LG training power point presentation for the first generation R410a split systems.

I had a quick scan though it & I seem to recall that the inverter had about 6 steps of control & the system made any required change to compressor speed & electronic expansion valve opening once every 2 mins.
I remember commenting at the time that was very poor control in comparison to other split systems

nike123
27-12-2008, 03:00 PM
I mean if the control strategy sheet was right it says once it has reached setpoint of 20C it will continue to heat to 24C ramping down a step every 1C.

In high ceiling mode the unit does not do this, once it has reached 20C it will continue at 100% tilll reached 24C. Are you sayign that if high ceiling mode is activated after it has reached 24C it will then start to ramp down and if another 4C increase is sensed it will stop?

How complicated that sheet is!

You are forgetting that, for control logic, if switch is in high ceiling mode, it senses that 20°C return air is in fact interpreted as 16°C. That way, control logic remains same as for floor mode and only difference is that is compensated for difference in placement of air sensor.

back2space
27-12-2008, 03:09 PM
So where does this 4C control strategy come into play then as its not doing that.

I do feel that it is working better today though its 2C outside and the unit is only cycling off once every hour (twice max) as apposed to every 10minutes.

The unit does seem to be stepping down perhaps only a couple of steps but its certainly not running at 100% when its maintaining the setpoint. As when I turned it on last night the room temp was 18C, set point was 22 and the unit was drawing a lot more when it was maintaining this.

So its deffo working so perhaps the fact its drawing a little more wattage is due to the lower than rated temp outside.

nike123
27-12-2008, 03:09 PM
niki 123

I was working one day last year with an engineer who had an old LG training power point presentation for the first generation R410a split systems.

I had a quick scan though it & I seem to recall that the inverter had about 6 steps of control & the system made any required change to compressor speed & electronic expansion valve opening once every 2 mins.
I remember commenting at the time that was very poor control in comparison to other split systems


Could be also the case here, but we cannot tell that for a fact.
Also, 2 minutes sampling rate and 1K dead band is not that bad in comparison to 6 min (10 compressor starts per hour) and 2K dead band, normally found in non-inverter systems, and peoples are still not complaining that much with old on-off systems.;)

back2space
27-12-2008, 03:10 PM
When the compressor ramps down does the EEV valve also close down a few steps also???

Thermatech
27-12-2008, 03:19 PM
For the last year or two LG have been providing training for air conditioning engineers in the UK at a new training centre.
Some engineers have been & then posted comments on this forum about it.

So here we are 99 posts on this thread & not one single post from any a/c engineer who is prepaired to try & defend the product.

Yet we know that some of the 25000 members have been to LG training.
We know that some who post on this forum carry out installation & service of LG split systems.

Listen to the sound of silence
it tells a story.

nike123
27-12-2008, 03:20 PM
When the compressor ramps down does the EEV valve also close down a few steps also???

Jes! .......


The expansion valve is controlled as a function of the speed of the compressor as the compressor speeds up then the expansion valve opens.

back2space
27-12-2008, 03:22 PM
I hope you guys are not getting fed up with me. Its a shame that the guys who install this kit are not speaking? Either they dont know how it works properly or as you say Thermatech, the sound of silence paints a picture!

nike123
27-12-2008, 03:32 PM
I do feel that it is working better today though its 2C outside and the unit is only cycling off once every hour (twice max) as apposed to every 10minutes.



As I already said here (http://www.refrigeration-engineer.com/forums/showpost.php?p=122478&postcount=18), that is probably because this units are to big for your heat loss.

back2space
27-12-2008, 03:38 PM
So I think its going to cost me less to run it when its cold as its going to stay on for longer but ramped down as it should. Whereas when it cycles back on again and theres a 1c difference it runs at full pelt to get to the setpoint.

nike123
27-12-2008, 03:42 PM
I hope you guys are not getting fed up with me.
Not at all, for me. In fact, what could service engineer could do when is not on work, except talk about work or beer or girls. Since there is not much active girls here, and Frank keeps his beer wisdom for himself, only what is left is to talk about work.:D

Its a shame that the guys who install this kit are not speaking? Either they dont know how it works properly or as you say Thermatech, the sound of silence paints a picture!
You are maybe expecting to much from installers. They dont need to know all details to be able to install AC-s.
Details are only required for service engineers and technical support personnel.

back2space
27-12-2008, 03:48 PM
What do they teach you on the LG training though? The operation of the system or just how to install it?

back2space
27-12-2008, 03:48 PM
Were just deciding what to do tonight... thinking were going to have a party tonight so we will end up having it in cooling mode!

nike123
27-12-2008, 04:18 PM
So I think its going to cost me less to run it when its cold as its going to stay on for longer but ramped down as it should. Whereas when it cycles back on again and theres a 1c difference it runs at full pelt to get to the setpoint.

Nope.
If it is cold, then your space heat loss is higher and that mean that totally produced heat (for keeping indoor temperature at set point) from AC is going to be higher and therefore costs will be also higher.
It is not your AC who consumes energy, it is your space who do that and AC could produce that energy with higher or lower efficiency.
Highest power consumption is when outdoor temperature is lowest (low COP) and AC still produces enough heat to maintain set point. Lowest consumption is when outdoor temperature is high enough that COP is highest and heat loss of space is lowest.

You could compare that with barrel of water with opening of x cm at bottom, filled with buckets of water
Water leaks constantly and you need to fill it with certain tempo to replenish spilled water. If you have too big bucket you will need to fill it rarely. If you have small bucket you will need to fill it more often or without pauses at all. If opening is big enough you cannot replenish water even with big bucket.
But amount of replenished water will be always same as leaked water as long as you could keep up with leaks.
Now imagine that level of water is set temperature and
fluctuations of level of water between two bucket pouring are your variations in return temperature.
Also imagine that bottom opening is heat loss of space.
Now play little in your head with variating these tings in analogy with your AC and you should have pretty plastic picture what is happening there.

If you replace bucket (as on-of compressor analogy) with hose from water supply with valve with 4 flow rates and closed position you are now have analogy for your inverter compressor.

back2space
27-12-2008, 04:22 PM
Yes I understand that analogy. Surely though that when the ac isnt cycling and is happy maintainging setpoint at lower compressor Hertz the energy meter shows lower power consumption. But when its constantly cycling and starting up at 100% this is usnign more energy. I was told by installer that inverter ramping down avoids the cycling issues cos it operates slower thus stopping it having to operate at 100% to regain the temp.

I understand the heat loss, but Ive also found leeaving the system on all night but at a lower temp means it works less harder to regain the setpoint when i increase it again.

nike123
27-12-2008, 04:37 PM
What do they teach you on the LG training though? The operation of the system or just how to install it?

I suppose that installers learns how to install properly, and service engineers learns how units works and how to diagnose and service them.

That is why on larger systems, after instalation work is done, startup usually makes service engineer to establish that everything works as it should be.

Thermatech
27-12-2008, 05:40 PM
B2S

I would encourage you to look at the Eurovent web site & check the energy rating for the system combination you have.

There is listed an FM25AH UE1 with 2 MS12AH N50 indoor units.
Not exactly the same as your combination but look at the ratings.

Heating COP = D rating
Cooling EER = B rating

This tells us that the system is better at cooling efficiency than heating.
But also tells us that its not very good efficiency in heating or cooling as the best rating is AA & some other more expensive cost manufactures have AA ratings for most multi split combinations.

The system would seem to be optimized for cooling performance not heating performance.

The standard test conditions for Eurovent is for max load & even at that the system performance is not so good.
The performance at low load is not tested & so if the system is not optimized for low load performance by factory design engineers then that does not affect the energy rating.

back2space
27-12-2008, 05:48 PM
OK thermatech Have you a link to these statistics, i will make my way over.

Thermatech
27-12-2008, 05:54 PM
The system performance evaluation procedure which you are carrying out on this system does confirm some things which some of us have come to expect from experiance of trouble shooting split / multi split / VRF systems.

1/ Just because it has the word INVERTER on the box does not mean that the system has excellent efficiency. That all depends on the control stratagy & how well the manufacturer has optamised the system control stratagy for high & low load operating conditions.

2/ Just because the outdoor unit has an energy lable on it that does not mean that the system will be energy efficient in all operating conditions.

3/ You get what you pay for.
The premium brands cost more but have much better control stratagy programed into the more expensive chips on the more expensive circuit boards which take much more R&D to develop.

back2space
27-12-2008, 05:56 PM
I guess I know for next time dont I know. Either way ive got a better system than a standard on off compressor. Plus im getting a lot more better value heating and more for my money than using electric fan heaters.

To be fair the A/C system with only one unit on heats the entire flat. So it has no probs outputting heat even in cold weather!

Thermatech
27-12-2008, 06:05 PM
www.eurovent-certification.com

Gary
27-12-2008, 06:12 PM
I guess my perspective is a little different than some. As a service tech it is not my job to select the equipment. It is my job to make the existing system perform to the best of its abilities.

With this in mind, I find a comparison of different brands/ratings... uninteresting.

I was hoping that someone would jump in here with a definitive description of what this system is supposed to do so we could learn something, but apparently that just isn't happening.

nike123
27-12-2008, 06:35 PM
I was hoping that someone would jump in here with a definitive description of what this system is supposed to do so we could learn something, but apparently that just isn't happening.

I think that posted document explains control strategy prety much transparently except part of how exactly looks calculation of outdoor unit capacity in relation to indoors required capacity, and how is EEV steps related to that. Rest of control process is pretty much clear.

nike123
27-12-2008, 06:38 PM
I guess I know for next time dont I know. Either way ive got a better system than a standard on off compressor.
I would not say that is generally always the case or even in your case, maybe.

back2space
27-12-2008, 06:41 PM
I would not say that is generally always a case.


Why is this?

nike123
27-12-2008, 06:58 PM
Why is this?

Because only thing what is matter is is how comfortable you are, and on what efficiency that comfort is delivered. If you don't feel any difference in comfort with on-off system and that on-off system deliver heat more efficiently, than you could say that there is not necessary inverter system better than on-off system. Especially when its poor control nulls its gain in performance on other points.

nike123
27-12-2008, 07:21 PM
But when its constantly cycling and starting up at 100% this is usnign more energy. I was told by installer that inverter ramping down avoids the cycling issues cos it operates slower thus stopping it having to operate at 100% to regain the temp.



From power consumption stand point, it doesn't matter if 2kWh are consumed in intervals or as steady or varying current draw.
It is same 2kWh of power consumed.
However, it is important at what COP is outdoor heat transfered to heated space.

Only real comparison in real life conditions could tell you if your inverter system is more efficient and comfortable than on-off system.
That real comparison is when you, in two identical places, put two different systems at identical conditions for one season and then compare total power consumption of each and feel of comfort.
I personally don't like feeling when indoor unit of inverter is at minimum.
From what I know, there is no such comparisons documented.

Gary
27-12-2008, 07:44 PM
I think that posted document explains control strategy prety much transparently except part of how exactly looks calculation of outdoor unit capacity in relation to indoors required capacity, and how is EEV steps related to that. Rest of control process is pretty much clear.

I found it fairly ambiguous and confusing.

In particular, the specs are for a dual compressor system. Having one compressor changes things.

As to the min/nominal/max ratings: No two systems are truly identical. I would assume that a number of systems were tested under tightly controlled conditions and some performed at min while others performed at max, the nominal rating being the average performance. Therefore, given the specified conditions, anywhere in that range should be considered normal... but then, this assumes a dual compressor system, for which we do not have the specs.

nike123
27-12-2008, 08:49 PM
I found it fairly ambiguous and confusing.

In particular, the specs are for a dual compressor system. Having one compressor changes things.

As to the min/nominal/max ratings: No two systems are truly identical. I would assume that a number of systems were tested under tightly controlled conditions and some performed at min while others performed at max, the nominal rating being the average performance. Therefore, given the specified conditions, anywhere in that range should be considered normal... but then, this assumes a dual compressor system, for which we do not have the specs.


I would say that spec are for that particular AC, as you could see from model# on header of specifications.
Also, I would say that description of control logic is maybe not for this particular model and I would love to see this model service manual for that reason.

Regarding min/nominal/max ratings: Maximum rating is when compressor speed is highest at that particular temperatures of return air and outdoor air, and that is usually "120-130%" of nominal capacity. That speed compressor could hold only relatively short time period, when there is need for capacity high, like after power up.
Then, min rating is when compressor is on his last power step before shut down (and at same return and outdoor temperature as above) , and that is usually around 30-40% of nominal capacity.


Nominal capacity is "100%" capacity.

back2space
28-12-2008, 01:24 PM
I found it fairly ambiguous and confusing.

In particular, the specs are for a dual compressor system. Having one compressor changes things.

As to the min/nominal/max ratings: No two systems are truly identical. I would assume that a number of systems were tested under tightly controlled conditions and some performed at min while others performed at max, the nominal rating being the average performance. Therefore, given the specified conditions, anywhere in that range should be considered normal... but then, this assumes a dual compressor system, for which we do not have the specs.

Gary page 210 of http://mylg.co.uk/data%20for%20site/multi%20f%202008%20outdoor.pdf shows that the FM25AH UE3 has just the inverter compressor. My model is the UE1 version, which also has just the inverter compressor. Mine is the European Model however the specs book doesnt show the UE1 so I have been told to go by the UE3 specs which is the same as mine apart from a few cosmetic changes.

So gary the specs on page 218 are indeed for one inverter compressor. Can you eleborate on this now?

back2space
28-12-2008, 01:31 PM
Regarding min/nominal/max ratings: Maximum rating is when compressor speed is highest at that particular temperatures of return air and outdoor air, and that is usually "120-130%" of nominal capacity. That speed compressor could hold only relatively short time period, when there is need for capacity high, like after power up.
Then, min rating is when compressor is on his last power step before shut down (and at same return and outdoor temperature as above) , and that is usually around 30-40% of nominal capacity.


Nominal capacity is "100%" capacity.

Ok so its never reaching the last step down it prefers to shut off totally so I thought that it wasnt reaching this because the outoor ambient wasnt high enough. I thought that the min, rated & max were based on a max for the highest comp output in very cold weather and the rated is what the indoor and outdoor temps were based on

back2space
30-12-2008, 07:20 PM
Right guys, despite the problems and confusion above the outdoor temp ambient has been hovering at 0.2 and is now -0.5 now. I got in the flat at 3pm and the indoor temp was 10C!!! It was cold!

back2space
28-01-2009, 11:28 PM
UPDATE:

Remote sensors arrived today, what a mess around trying to fit them as the plugs on the end that connects to the board are designed for cassette/ducted unit. SO had to take the plugs off and fit to the existing return air plug.

Have mounted them at 1.5mtr from the floor on a wall where warm air flow from the unit will not affect it.

Couple of things: The lounge sensor had to move several times as it appeared that the sensor was being affected by the temperature of the outside wall which is very cold to the touch, this was making the outdoor unit run at full speed However moving it so it wasnt touching an outside wall means that temperature control in this room is no longer an issue.

2nd point is on the bedroom unit... now seems to be the problem unit. Have mounted it on a non external wall however (but fitted on wall opposite the external wall) temperature control in this room is even worse now. Before warm air was cycling back to the unit and shutting off too soon but now the temperature is way overshooting the set point temperature. For instance set point of 19C the room temp reaches 22C before shutting off. If I try to compensate by putting down to 18C doesnt make any difference unit still seems to be a couple of degrees over. Tried connecting the old temp sensor to the end of the new long cable and same results. COuld the wire be damaged or something? I have measured temps with an accurate digital thermometer right next to the remote sensor, is it still sensing wall temperature despite not being on an external wall? I dont understand as the digital thermometer is small yet manages to pick up the air temp being 22C when 19C is wanted. I appreciate a 1C differential either side of set point but not 3C.

MODS: Any chance of moving this to the Main Air Con forum and out of Heat pumps as I feel will get more attention and if possible could post be renamed to LG Air Con Problem as I did not start the original post someone did it for me.

Thanking you all.

Brian_UK
29-01-2009, 12:23 AM
I think that it has been receiving enough attention not to need moving and as it is about a heat pump seems to be in the right place.

back2space
01-02-2009, 11:25 PM
Sensors arrived,

After being quoted £40 by several distributers for each sensor I ended up dealing with LG comfort cooling who have been helpful from the start to finish they quoted £18 per sensor... much more reasonable!

After receiving these and arranging for them to be fitted, they didnt fit, wasnt just simple unplug existing sensor! had to remove the plug at the end and mess around with existing plug to get it fitted as the plug was too big on sensor. But then this didnt work so have had to just extend the existing sensor using the cable provided with the remote sensor. So I have paid for a posh box and cable for nothing really.

nike123
02-02-2009, 12:18 AM
Sensors arrived,

After being quoted £40 by several distributers for each sensor I ended up dealing with LG comfort cooling who have been helpful from the start to finish they quoted £18 per sensor... much more reasonable!

After receiving these and arranging for them to be fitted, they didnt fit, wasnt just simple unplug existing sensor! had to remove the plug at the end and mess around with existing plug to get it fitted as the plug was too big on sensor. But then this didnt work so have had to just extend the existing sensor using the cable provided with the remote sensor. So I have paid for a posh box and cable for nothing really.




If you listened my advice than you will be now richer for that 36 pounds and you will be having hot home from day one of your posting! Don't forget, this is first response on your problem.;)
http://www.refrigeration-engineer.com/forums/showpost.php?p=122451&postcount=2

Sorry, but I just cannot resit to tell you "I told you so!". :D:D

back2space
02-02-2009, 12:23 AM
Yes nike but I paid £18 per sensor from LG comfort cooling not the quoted £40 from other installers.

So I have done ok. An electrician would have charged same ammount. Plus electrician would have had to mess with the control board to get it wired in.

Sensors now put 1.5metres above floor level.