Thermo Pride MODEL OPA - Manual (Page 74)

All installations and services must be performed by qualified service personnel.
73
Now, the degree of superheat can be calculated.
48
°F (Suction line temperature at outlet of evaporator)
- 40 °F (Saturation temperature for R22 at 68 PSIG)
-----------------------
8
°F = Degree of evaporator superheat.
Example 4:
Problem: Additional refrigerant measurements are made on the cooling system
of our typical GPA installation. The liquid line pressure, measured at the
condenser unit, liquid line, charging port, is 210 PSIG. The temperature of the
refrigerant (R22) at the evaporator liquid line connection is measured as 95
°F.
What is the degree of subcooling for this system?
Solution: Calculate the pressure of the refrigerant at the evaporator liquid line
connection. With the estimated refrigerant pressure and measured temperature
at the same point, tabulated data on R22 from the refrigerant manufacturer, or
ASHRAE, can be used to evaluate the degree of subcooling.
210 PSIG (Liquid line pressure measured at condenser)
+ 0 PSIG (Added for pressure drop of liquid line)
------------------
210 PSIG = Estimated pressure of refrigerant at evaporator inlet
From the R22 pressure/temperature chart, at 210 PSIG (224.7 PSIA), the
saturation temperature is approximately 105
°F
Now, the degree of subcooling can be calculated.
105 °F (Saturation temperature for R22 at 210 PSIG)
- 95 °F (Suction line temperature at outlet of evaporator)
------------------
10
°F = Degree of evaporator subcooling