VRV oil return issue

[Lc_shi]

dear sirs

If the evapoator is much lower than compressor(I've read the distance can be more than 50m), how VRV system deal with the oil return issue? adding the U bend every 10m height or other ways?


regards
LC

[taz24]

dear sirs

If the evapoator is much lower than compressor(I've read the distance can be more than 50m), how VRV system deal with the oil return issue? adding the U bend every 10m height or other ways?


regards
LC


No they do not trap pipes.

The runs are sized to allow the correct flow and there are regular gas flushes to push the oil back.

Cheers taz.


.

[Lc_shi]

Hi taz

You mean that the proper gas velocity can bring back the oil to compressor. Is it necessary to apply oil separator at the discharge ?

thx & regards
LC

[Thermatech]

VRV & VRF systems have oil seperators which are very efficient & return most discharge oil straight back to the compressor so only a very very small volume of oil gets to circulate through the system.
but
The outdoor unit has to be able to cope with low load / slow compressor speed for long periods of time.
Different manufacturers have different control stratagy to cope with is operating condition.

VRV systems for many years had fixed oil recovery mode after a fixed number of operating hours. Later models have operating conditions compensated time period for oil return mode.
The oil return mode ensures that any small volume of oil which gets through the oil seperator will be returned to the compressor at the latest by the oil return mode.
The operation & compressor speed is dictated by the oil return control stratagy during oil return mode to ensure refrigerant velocity is high enough to force oil to return to outdoor unit & compressor.

For many VRV / VRF systems oil traps on risers not required due to this control stratagy provided the correct pipe sizes have been installed.

Cheap copies of the Japan VRV / VRF systems have been noted to take short cuts to make equipment cheaper but this is one area where short cuts are not a good idea.

[Peter_1]

What I heard Lc is that they open on a regular base all the EEV's at once with a low SH so that max speed is achieved in the lines.
Low SH to flush out the oil. The liquid separator prevents eventual liquid slugging.
We do it also this way on packs with long lines.
If you look once to AC lines, they're always calculated with high to very high speed.
I suppose they select rather on a 1K pressure drop over the line then on a certain speed.

[RANGER1]

What is a VRV VRF , is it some type of variable speed drive ?

Sorry off the subject .

[Peter_1]

http://www.refrigeration-engineer.com/forums/showthread.php?t=16670&highlight=daikin+patented