The company that I am working for has one of the world's largest installed base of compressors. We have tried many systems from many vendors. From experience the best ones, in terms of performance and reliability, are from CCC (Compressor Controls Corpn.)
If you want to control just one compressor, the best one is series 3++ from CCC. For series/parallel network of compressors Seires 5 is the best one.
You should look for a control system that can be tailored to your changing loads. That is one that can control the pressure by loading and unloading the compressors you have running. They should be able to keep the largest compressors fully loaded and use a smaller one as the trim machine. If you have several compressors running at part load you have a poor control system. The system should be able to know the point to bring more compressor on line or shed a running compressor. These steps should be able to happen at varying speeds depending on load shifts out in the plant.
Couple other things to look for are how much can the operator fine tune the system after the control vendor leaves. Can you change what compressors are running? Also, how easy is it to add compressors in the future? Can the control vendor make online changes or do they have to make constly site visits? Do they offer variable speed drive control, and do they control the drive correctly? (which is keep the Slide Valve loaded and have the drive trim to 50% before unloading.)
Many vendors say they are the best. I have found many of them won't do anything custom. Do some research on the web under "Refrigeration Control" and "Compressor Control" and that should give you some good ideas.
l know this problem was putted many years ago, but with time goes by , the answer may change. At this time, i may say there is alreay more intelligentized system of compressor, so if you are still in demand ,you can further learn about from the dealer.
