Hi everyone,

I'm brand new to the forum and I'm hoping I can get some help. I've been hired by an Electrical Contractor to redesign a control panel for a chiller system for an ice rink. At first it didn't sound like a big deal but the more I read about chillers I'm realizing there is more to it than meets the eye. The last thing I want to do is destroy some equipment. I've designed many electrical systems in the past (not for chillers or refrigeration equipment) so I don't need help with the electrical end, more with the theory of operation and terminology regarding chillers.

The existing system has three 50Hp compressors but one hasn't worked for several years. They want to eliminate this from the system and only use two compressors. The compressors have a water ciculation pump and each compressor has a water solenoid associated with it. There is a condensor with a 2-speed, 10Hp fan and a 1.5Hp water cooling pump. The system also has a 20Hp Brine pump. There is a set-back timer (stand-alone) and a thermostat.

In this existing system it appears the Brine pump starts (from the setback clock and thermostat) and then compressor #1 starts after a time delay then compressor #2 starts after a time delay and then compressor #3 starts after a time delay. The compressor water pump runs whenever any compressor is running. The condenser fan runs when an RAHP switch activates it and the condenser water pump runs when an RAHP switch activates it.

The RFQ (which isn't very detailed) asks the new system to have a VFD on the Condenser fan. It also asks to use a Honeywell 4-stage rink thermostat with set-back clock.

So here we go, time for me to show my ignorance. Please be gentle with me! What is meant by 4-stage? Is each compressor a stage? So instead of having timers activate the compressors would the 1st stage be to have compressor #1 turn on then if temperature isn't met then 2nd stage (2nd compressor) turns on? If so, then this is really a 2-stage system isn't it? Is the brine pump considered a stage? We've selected a Honeywell T775P controller which can have up to 12 stages. When used as a 4-stage the manual says you can dedicate the last stage as a pump output that would turn on when any stage 1 to 3 is on. Would I use this for the brine pump, or possibly the condensor water pump?

I appreciate any feedback. Thanks.