g.mccormick
13-09-2022, 04:11 PM
I am looking at one of our systems mainly from a controls aspect. This system is on an environmental chamber designed to drive a vehicle into. The system has two high stage DX coils, a DX brazed plate hx, and 2 low stage DX coils. The high stage is 404A and low stage is 508.
The system has 2 air handlers, each housing 1 high stage and 1 low stage evap. There are liquid line solenoids that allow the use of high stage DX evaps, or low stage DX evap and high stage cascade hx. The compressors are:
HS:
Bitzer 6FE-50Y-2NU
404A
11.5TR @ -20F SST / 105F SCT
LS:
Bitzer 6B6462PH-2NU
508B
25.9TR @ -80F SST / -10F SCT
Per the prints, the evaps/HX have:
High Side:
2 evaps each 13.8TR
1 hx 360 kBTU/Hr
Low side:
2 evaps each 15.9TR
Gas cooler for low side discharge gas not rated.
Condenser for 404A:
Base rating 282.7 kBTUhr @ 105F SCT
It seems to me that the compressors are quite undersized for 2 evaps running. I see this in running that the suction pressure is quite high. I can turn off one evaporator so that system load decreases and that brings suction pressure and temperature down. I can also decrease load by slowing down fans.
Is it better to let the system run overloaded and hopefully bring down the suction pressure or should I only run 1 evaporator at a time? I don't know if the original intent was to have 2 evaporators running or if it was done this way so that 1 evaporator could be defrosting while the other is running?
The system has 2 air handlers, each housing 1 high stage and 1 low stage evap. There are liquid line solenoids that allow the use of high stage DX evaps, or low stage DX evap and high stage cascade hx. The compressors are:
HS:
Bitzer 6FE-50Y-2NU
404A
11.5TR @ -20F SST / 105F SCT
LS:
Bitzer 6B6462PH-2NU
508B
25.9TR @ -80F SST / -10F SCT
Per the prints, the evaps/HX have:
High Side:
2 evaps each 13.8TR
1 hx 360 kBTU/Hr
Low side:
2 evaps each 15.9TR
Gas cooler for low side discharge gas not rated.
Condenser for 404A:
Base rating 282.7 kBTUhr @ 105F SCT
It seems to me that the compressors are quite undersized for 2 evaps running. I see this in running that the suction pressure is quite high. I can turn off one evaporator so that system load decreases and that brings suction pressure and temperature down. I can also decrease load by slowing down fans.
Is it better to let the system run overloaded and hopefully bring down the suction pressure or should I only run 1 evaporator at a time? I don't know if the original intent was to have 2 evaporators running or if it was done this way so that 1 evaporator could be defrosting while the other is running?