Horsepower and condenser duty for specific refrigerants

Example. A 50 ton two-stage propane refrigeration system has a 40°F evaporator temperature and a 120°F refrigerant condensing temperature. Find the gas horse-pow er requirement and condenser duty. 

If equations are desired, the cur -es can be fitted accurately using polynomials. Here are the equations for the single-stage propane horsepower graphs, for example. 

Equations were generated using FLEXCURV V.2, Gulf 

Hydrocarbon Refrigerants series, parts 1, 2, 3, and 4, Chemical Engineering, December 18, 1978, January 15, 1979, February 12, 1979, and March 26, 1979. 

Using the two-stage propane graphs at 40°F evaporator temperature and 120°F condensing temperature, the gas horsepower requirement is lOOhp/lO BTU/hr. A 50 ton unit is equivalent to 50 x 12,000 = 600,000 BTU/hr, so the gas horsepower is 100 x 0.6 = 60. The condenser duty read from the companion two-stage propane graph is 1.25 X 0.6 = 0.75MMBTU/hr. 

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