lana
26-02-2011, 06:15 AM
Dear Experts,
I would like to open this discussion and know different ideas about compressor capacity control.
As all know, capacity control is a way to match evaporator load with the compressor load. The main benefits are:
1- Energy saving
2- Relatively constant suction pressure
3- Precise fluid outlet temperature
4- Less compressor cycling
Now the set backs are :
1- Oil return problems at part loads
2- Power consumption reduction at part load is not exactly equal the capacity reduction (where screws are the worst)
3- TEV is selected for full load capacity. At part load TEV is oversized
My main concern here is the oil return problem at part load.
Now lets consider a different approach which is to use multiple circuits (separate systems) for a given capacity. For example, for a total cooling capacity of 100kW instead of using one compressor with capacity control, use 4 x 25kW compressors with 4 individual cycles.
In this case we will have 4 step control with the same percentage of power reduction.
There will be no oil return problem at part load and also, TEV for each circuit will operate as designed.
Nowadays we see huge chillers with 4 or 6 individual circuits for the very reasons.
Another scenario is where we need precise fluid outlet temperature which requires compressor capacity control. In this case we have to sacrifice some technical issues to get the job done. No argue in this case.
I have seen a few people and companies who used capacity control methods just to show off "technology", but they encountered very serious problems, especially with oil return.
My question is this : Does it really worth to complicate the system with some real technical problems to gain a little bit in power savings? Of course where other alternatives are available.
Really appreciate your comments and ideas.
Thanks a lot
Cheers
LANA
I would like to open this discussion and know different ideas about compressor capacity control.
As all know, capacity control is a way to match evaporator load with the compressor load. The main benefits are:
1- Energy saving
2- Relatively constant suction pressure
3- Precise fluid outlet temperature
4- Less compressor cycling
Now the set backs are :
1- Oil return problems at part loads
2- Power consumption reduction at part load is not exactly equal the capacity reduction (where screws are the worst)
3- TEV is selected for full load capacity. At part load TEV is oversized
My main concern here is the oil return problem at part load.
Now lets consider a different approach which is to use multiple circuits (separate systems) for a given capacity. For example, for a total cooling capacity of 100kW instead of using one compressor with capacity control, use 4 x 25kW compressors with 4 individual cycles.
In this case we will have 4 step control with the same percentage of power reduction.
There will be no oil return problem at part load and also, TEV for each circuit will operate as designed.
Nowadays we see huge chillers with 4 or 6 individual circuits for the very reasons.
Another scenario is where we need precise fluid outlet temperature which requires compressor capacity control. In this case we have to sacrifice some technical issues to get the job done. No argue in this case.
I have seen a few people and companies who used capacity control methods just to show off "technology", but they encountered very serious problems, especially with oil return.
My question is this : Does it really worth to complicate the system with some real technical problems to gain a little bit in power savings? Of course where other alternatives are available.
Really appreciate your comments and ideas.
Thanks a lot
Cheers
LANA