solution for oil return problem

[naifmbo]

hi everybody,
Is it practical to avoid the oil escape from compressor (due to the low load) by reducing the interval of unloading time,i mean to specife a restart setpoint temperature higher than the water setpoint by 2 degree , we start loading compressor quickly until we reach the setpoint then the compressor will de-energize then we will wait the water temperature to reach the restart sepoiont to re-energize it again , and so on.
(No unloadign ,restart then stop,restart then stop whith the limitation of number of start per hour )

thanks.

 

[imok2]

If this is a reciprocating compressor and has unloaders and it's too big for the load you can remove a suction valve on the head that loads last so you derate the compressor to better balance the load, this will keep the compressor on for longer periods of time. However, if it,s belt driven all you need to do is change one of the pullies. If the load is a result of extreme load changes that are seasonally then you might look into an oil seperator in the discharge line. In order to get a better handle on this problem more information may be needed

 

[sterl]

The efficiency decrease and potentially reliability decay that would accompany your control strategy depends on the weight of water in your circuit and the extent to which you let its temperature rise.

Lots of systems run a cooling compressor in an on-off mode of control. Ready example is an brine cooled ice rink; but consider, each cycle involves the removal of some 60,000 BTU from the Brine and something like 250,000 BTU from the concrete around the tubes...for only a 2-deg. change in brine temperature. You apply 20 TR to that mass, it takes about 75 min. to go through the dead band, and thats if the mass was well insulated. Its a flywheel, so identify its extent and you will have a pretty good idea whether this is a good control strategy for your purposes or not.

How fast it warms back up is the flip side of the topic; for the rink, that's steady state load and by the sound of it, your equipment's capacity is considerably higher than the steady load. If you are leaving oil around due to low evaporator flow and Low Suction Pressure, and this is a system whose load jumps up and down rapidly, you might consider Hot Gas Bypass to the inlet of the evaporator.