Question

Operating pressures of the refrigerants at the evaporator in the ascending order for any application are
1. R11, R12, R717, R22
2. R22, R717, R12, R11
3. R11, R12, R22, R717
4. R717, R22, R11, R12

Answer 1

Correct Answer - Option 1 : R11, R12, R717, R22

Explanation:

Evaporator and Condenser pressure:

• Both the evaporating (low side) and condensing (high side) pressure should be positive (i.e. above atmospheric) and it should be as near to the atmospheric pressure as possible.
• Positive pressure is necessary in order to prevent leakage of air and moisture into the refrigerating system. It also permits easier detection of leaks.
• Too high evaporating and condensing pressure (above atmospheric) would require stronger refrigerating equipment (i.e. compressor, evaporator and condenser) resulting in the higher initial cost.

The following table shows the evaporating and condensing pressure, and compression ratio for various refrigerants when operating on the standard cycle of -15°C evaporator temperature and 30°C condenser temperature.

Refrigerant	Evaporator pressure (At -15°C, in bar)	Condensor pressure (At -15°C, in bar)
R-11	0.2021	1.2607
R-12	1.8262	7.4510
R-21	0.3618	2.1540
R-22	2.9670	12.034
R-30	0.0807	0.7310
R-40	1.4586	6.5310
R-113	0.0676	0.5421
R-114	0.4650	2.5161
R-123	0.0163	0.1095
R-134a	1.6397	7.7008
R-717	2.3634	11.670
R-744	22.90	71.930
R-764	0.8145	4.5830

Based on the above data, we can conclude that R-11 < R-12 < R-717 < R-22 as per evaporator pressure.