Carrier 17/19EX - Page 158

Calculate Minimum Load
To calculate minimum load conditions, estimate the temperature difference that the cooler
will have at 20% load, then estimate what the suction and condensing temperatures will be at
this point. Use the proper saturated pressure and temperature for the particular refrigerant
used.
Suction Temperature:
43 F (6.1 C) = 38 psig (262 kPa) saturated refrigerant pressure (HFC-134a)
Condensing Temperature:
70 F (21.1 C) = 71 psig (490 kPa) saturated refrigerant pressure (HFC-134a)
Minimum Load ∆T1 (at 20% Load):
2° F (1.1° C)
Minimum Load ∆P1:
71 – 38 = 33 psid (490 – 262 = 228 kPad)
Again, to avoid unnecessary surge prevention, add 20 psid (140 kPad) at ∆P1 from these
conditions:
∆T1 = 2° F (1.1° C)
∆P1 = 53 psid (368 kPad)