is 38C air off at -0.3C ambient...

[back2space]

Is this good enough on my system.

My multi unit is supposed to be good down to -15C I know you get performance loss the colder it gets.

This is with just one unit running, if one of the unit comes on and demands heat the air off increases to about 43C.

What do you think?

[VRVIII]

Is this good enough on my system.

My multi unit is supposed to be good down to -15C I know you get performance loss the colder it gets.

This is with just one unit running, if one of the unit comes on and demands heat the air off increases to about 43C.

What do you think?

Hi,
What type of multi system? Vrv/vrf/multi split/inverter/non inverter

The air off temp has no relevance unless you know the air on temp to calculate the delta t. However you also need to consider the indoor fan speed, connection ratio, frost/ice on outdoor heat exchanger etc. These will also effect indoor heating capacity.

Switching off an indoor will increase the head pressure/Tc as you are reducing the size of the condenser. Most inverter systems have a target Tc of around 46 C in heating mode and will modulate the compressor frequency accordingly, if the compressor is operating at 100% but unable to meet target conditions switching off an indoor would then allow the Tc to increase.

[back2space]

Hi,
What type of multi system? Vrv/vrf/multi split/inverter/non inverter

The air off temp has no relevance unless you know the air on temp to calculate the delta t. However you also need to consider the indoor fan speed, frost/ice on outdoor heat exchanger etc.

Switching off an indoor will increase the head pressure/Tc as you are reducing the size of the condenser. Most inverter systems have a target Tc of around 46 C in heating mode and will modulate the compressor frequency accordingly.



Thanks for coming back so quick.

Set point is 22C air on temp is 21C. It is an LG Multisplit. FM25AH is the model number.

On high fan speed air off is 38.5C and on low it is 40.8C

This was 5 minutes after a defrost so outdoor coil is clear

[VRVIII]

Thanks for coming back so quick.

Set point is 22C air on temp is 21C. It is an LG Multisplit. FM25AH is the model number.

On high fan speed air off is 38.5C and on low it is 40.8C

This was 5 minutes after a defrost so outdoor coil is clear

I’m not familiar with LG splits, but a delta T of 18~20 C @ 0 C ambient sounds good to me. But if I was checking the air on/off delta T, I would also increase the set point 4 or 5 C higher than the room temp.
The control software on most modern inverter systems also looks at the delta T between set point and actual room temp, this can reduce the Tc when the indoor is close to set point (reducing indoor capacity). The control strategy is trying not to over shoot the set point and keep the compressor operating.

[back2space]

I’m not familiar with LG splits, but a delta T of 18~20 C @ 0 C ambient sounds good to me. But if I was checking the air on/off delta T, I would also increase the set point 4 or 5 C higher than the room temp.
The control software on most modern inverter systems also looks at the delta T between set point and actual room temp, this can reduce the Tc when the indoor is close to set point (reducing indoor capacity). The control strategy is trying not to over shoot the set point and keep the compressor operating.

Yes I understand... when turning one of the units on the air off temp increases because the compressor starts to work harder, but as soon as one of the units is satisfied and if only one unit demanding heat then air off temp drops. Its now at 32C air off on high fan speed and controller set to 30C and room temp starts to drop.

If I turn off one of the other units then air off increases to 41C and set point is achieved.

If I turn them all off air off rises to 44C. Air on temps are 20C in the lounge so the compressor should be ramped up to achieve the set point.

The only way to seem to be able to get it to ramp us to turn one of the other units set point up so that 2 units are demanding heat rather than one.

Does the unit perform better if its got at least 2 units demanding heat?

It seems that on the units that are satisfied the fan comes on to clear heat from the coil and stays on, this extra refrigerant that is being sent to them would be better off sent to the units that are still demanding heat. I understand the oil return and 10% open EEVs on units that are off, but on units that are thermo off do the EEVs close down to 10% or do they stay at the same position they were when the unit was heating?

This may explain why the fan stays on.

[VRVIII]

Yes I understand... when turning one of the units on the air off temp increases because the compressor starts to work harder, but as soon as one of the units is satisfied and if only one unit demanding heat then air off temp drops. Its now at 32C air off on high fan speed and controller set to 30C and room temp starts to drop.

If I turn off one of the other units then air off increases to 41C and set point is achieved.

If I turn them all off air off rises to 44C. Air on temps are 20C in the lounge so the compressor should be ramped up to achieve the set point.

The only way to seem to be able to get it to ramp us to turn one of the other units set point up so that 2 units are demanding heat rather than one.

Does the unit perform better if its got at least 2 units demanding heat?


As I said I'm not familiar with LG control strategy but inv compressor freq/speed is normally controller by target Tc. The number of operating indoor units does not usually have effect on the target Tc.
Also remember when switching indoors on/off the system will take time to make operation adjustments and stabilize.
.


It seems that on the units that are satisfied the fan comes on to clear heat from the coil and stays on, this extra refrigerant that is being sent to them would be better off sent to the units that are still demanding heat. I understand the oil return and 10% open EEVs on units that are off, but on units that are thermo off do the EEVs close down to 10% or do they stay at the same position they were when the unit was heating?

This may explain why the fan stays on.


Most multi splits have the EEV's installed in the outdoor unit and do not require the valves to be held open 10%. Does your LG system have EEV's installed in idoor unit? )This sounds more like VRV/VRF control)

Are you sure this is not due to the type of thermostat control used, this could be thermo on @ setpoint -1 /off set point +1 (set point +/- 1 EEV closes to reduce capacity).

[back2space]

As I said I'm not familiar with LG control strategy but inv compressor freq/speed is normally controller by target Tc. The number of operating indoor units does not usually have effect on the target Tc.
Also remember when switching indoors on/off the system will take time to make operation adjustments and stabilize.
.


Most multi splits have the EEV's installed in the outdoor unit and do not require the valves to be held open 10%. Does your LG system have EEV's installed in idoor unit? )This sounds more like VRV/VRF control)

Are you sure this is not due to the type of thermostat control used, this could be thermo on @ setpoint -1 /off set point +1 (set point +/- 1 EEV closes to reduce capacity).

LG confirmed that the EEVS are in the outdoor unit and that they remain open on units that are turned off 10% to allow oil return.

I dont know if they remain open further on units that are turned on but thermo off. Perhaps they stay open the same ammount they were when they were last heating meaning more refrigerant can leak into the unit.