Hot gas bypass settings on Carrier screw chiller

[Teto]

Hi All,
I have a Carrier 23XL, water cooled screw chiller with a glycol/water mix and a setpoint of 35 degrees leaving chilled water. It has digital controls (LID). My question pertains to the settings on the hot gas bypass. Add to that, the screw loads and unloads. I have experience with other hot gas bypass equipment and understand that there is a setpoint where the hot gas valve will open and close to keep the brine at a certain temperature range. What I want to know is: Anyone out there familiar with the hot gas bypass algorithm on this machine? Can you please explain it? I have the manual and from what I understand, this feature is to prevent displacement of oil. The manual does not devote much to the details. What exactly will happen to the oil if the entering and leaving temperatures get close? Is temperature control in any of this? The local rep has been of little use and the factory points me back to him.
Thanks,
Teto

 

[wzal]

Hi, the screw compressor relies on minimum gas velocity to take the oil in the evaporator back to the compressor. If the compressor is running unloaded for extended period of time. The oil will accumulate in the evaporator. There will be not enough oil back to the compressor.

wzal