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hem057
02-04-2007, 12:16 PM
interested in your comments
have 3 hussman racks, we are installing new cpc E2 controllers, what would you suggest as parameters or set points for the operation of the system,
1. ambient to switch to half condensers
and at what point to cycle condesnsers fans on/off
2. suction point to cycle compressors (404a), (one rack as 5 compressors, 10 and 7.5 hp med temp, other 2 racks have 4 -7.5 hp low temp compressors
3. sensor point to terminate defrost on the defrost sensor (reverse hot gas defrost, so sensor is on the liquid line before the check valve<!-- / message --><!-- controls -->

750 Valve
03-04-2007, 09:56 AM
1. Don't really switch much on ambient down here, guess we don't get that much ambient fluctuations here, normally only split for h/reclaim. HP setpoint will depend on txv/eev selection, what nominal PD did you select txv for, check out ratings and see what the affect is on the valve with a lower PD (less capacity), if you're splitting on ambient then overcondensing is not likely going to be an issue. With EEV's we run down to about 13 bar HP on a MT/HT rack (507/404a). The lower the better for energy.
2. Higher SST's will draw less power, is it LT or MT? Rack setpoint will depend on case design sst's, find the lowest, allow for suction PD (shouldn't be much should there!) and set for that. We run LT racks at 1.0 to 1.3 bar on 404a/507, MT's to 3.2 to 4.0 bar and HT's anywhere up to 4.5 bar, but these really depend on the requirements of the cases. Refer mfg data for sst's - they have done the r&d, good for a starting point or if you don't have much commissioning time.
3. Do not use this type of defrost so sorry no good to you (would you not be better off with the sensor on the coil and terminate at say 10 to 15C coil temp) We terminate MT cases with off cycle defrost at 10C discharge air but this only after working on 10,000,000,000 of the same setup to KNOW its gonna work, if it doesn't then you got other issues. If in doubt, run a defrost with a good frost load and find coldest part of coil, stick probe there and watch how long it takes (add safety factor for misuse/abuse)

junior
15-04-2007, 05:03 PM
Hey Hem057

I work alot with cpc old and new, I'll see if I can give you some help.

1. amb split could be between 55 & 65f depending on your location & your sys.

2. Leave your 1st set of fans on all the and then use the basic setup that comes in the E2, As far as the cond set point us pt chart and set at 90f if it is a standard rack.

3.For your suction setpoints you can use the float option, wich will change your set point between your preset high and low based on the sys temp of your coldest case on that rack. ie.fresh meat for med temp or ice cream for low temp.If you don't have temp sensors then you can use the design temp, typically -25 for I/C, -20 for froz food,
+15 for med temp with fresh meat and +20 without. The E2 will learn the demand and then cycle the compressors as per the need.

4.The defrost sensors should be on the check valve on the dump line(the bypass for the tx valve) and on offtime defrost in the supply air preferably in the honeycombs.

Hope this helps if there is anymore Q's
you can post, PM me or Email me anytime. I also know of acouple good cpc tech's I can give you there #'s


Jamie