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andyh
12-13-2005, 06:42 PM
I have a MUA on a condo building, used for hallway pressurization. New install. They decided to put A/C on unit after the original installation. The A/C installed is 2 stage(2 compressors), both with hot gas bypass. The Mua is Eng A, with a DJM and C-TRAC board. Does anyone know of a way to properly control both stages of A/C. (The C-Trac board is only designed for 1 stage of cooling)
jogas
12-13-2005, 07:59 PM
When dealing with 100% OA DX cooling, you must remember temperature drop verses OA temperature.
We did a Pharmacuetical clean room with a system like this. Between 60 to 80 degree OA, we'd enable stage #1 with a Staefa HGBPV to keep discharge temp setpoint. Above 80 degree OA we brought on stage #2 and let stage #1 with HGBPV trim to wanted discharge temperature.
We also sized the stage #1 HGBP to the same tonnage as stage #1's capacity.
Worked perfectly. Problem is, those Staefa HGBPV's are expensive, but VERY good.
Jogas
filterbuoy
12-13-2005, 11:04 PM
Each of these units is factory built to customer requirements,what version of c-trac do you have?As far as i know c-trac-2 and 3 both have 5 stages of mech cooling.Is it operating strictly as discharge temp or is there space reset?
filterbuoy
12-13-2005, 11:13 PM
Oops,i just reread that cooling was added after.
Carnak
12-13-2005, 11:40 PM
The Ctrac can stage multiple compressors.

http://hvac-talk.com/vbb/showthread.php?threadid=87988
andyh
12-13-2005, 11:42 PM
We would have put a room reset in one of the hallways, but did not know it would be used for cooling at the time the building was built(building has cement floors/walls). Running the stages off outdoor temp should work though, I never thought of that. Whats the difference between Staefa HGBPV's, and just normal HGBPV's that work off pressure? I don't remember what version the C-Trac was.
Carnak
12-13-2005, 11:43 PM
The link will lead you to EngA's top technical guy.
andyh
12-13-2005, 11:54 PM
Sorry, my mistake. There is only a DJM board in this unit. I haven't been there for a few months and forgot. I was looking at the C-Trac manual on the EngA website, wondering why I didn't notice the 5 stage capabilities, while I was on the job. There is a smaller circuit board hooked up to the DJM board, its just a temp setpoint for cooling though.