Chiller setup

[Matt]

This forum is the best!
I'm sitting here with my dogs thinking of times in the recent past when I questioned my judgement on a job. What better place to let my thoughts fly, wether I get an "ataboy" or a " you screwed up".
The facts: A 20 ton Contenentel chiller, process cooling at 45 df, two scroll compressors, low ambient options.
The question: What should the cut-in and cut-out pressures be on the two fans per ckt. when I have headmasters trying to maintain 170#.The microprocessor can be set for whatever you want.I get confused when I see two methods of head pressure control used at the same time. Am I correct in setting the fans higher than the headmaster. So as to keep a solid column of liquid to the valve without the headmaster going crazy trying to offset the fans if I were to set them lower?
Thanks in advance!

[clydemule]

You post a couple of months ago so I don't know if a reply is useful.

You might check and see if your chiller has a VFD, fan cycle control, or dedicted outputs from the controller to the fan(s) contactor. Also see if there is a place where you acutally read head pressure in the controller.

It may be that there is a headmaster in the system, and that even though you can set the head pressure it may not really mean anything. It could be that the program is generic and they supply chillers with condenser flooding OR fan cycling/speed modulation. The problem is that even if there is no fan speed control, it still looks like there is.

This is done so if the chiller is changed from one method to the other later, to don't have to get a new reprogrammed controller. It is sloppy programming practice though. There should be a setting in the controller that is password protected that lets you set whether or not you have fans speed control. If not, it hides any place where you would set the head pressure.

By the way, my first foray into using headmaster's I made the mistake of using a combination approach. Fan cycle and a headmaster on a dual circuit 25 ton process chiller. The fans cycled way too much. I was using the concept of the fans took care of the warmer low ambient, and the headmaster the colder low ambient. The problem was is the headmaster setting was custom from Alco (long lead time) and when it was really cold (Chicago area) the head pressure was just too dang low. I built 3 this way. Cost my company a lot of money to get it fixed.

By the way alco actually advises against fan cycle and headmaster combinations. The funny thing was I had a lot of converstions with their engineers about the above mentioned chillers and they though it was okey dokey.

Good Luck.

Clyde