Evaporative Condenser Calculator
Determine Total Heat of Rejection (THR), nominal model selection rating, water spray recirculation flow (GPM), and airflow CFM for ammonia (R-717) and halocarbon condensers.
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Evaporative Condenser Heat Rejection Mechanics
Evaporative condensers combine a water cooling tower and a refrigerant condenser into a single unit. Hot high-pressure refrigerant gas discharges through serpentined steel coils continuously wetted by spray water and swept by high-volume airflow. Because heat is rejected directly through latent evaporation at the coil surface, condensing temperatures can run 10°F to 15°F cooler than air-cooled condensers, significantly reducing compressor horsepower.
Total Heat of Rejection (THR) Formulations
- THR Equation:
THR = Evaporator Capacity (Tons) × 12,000 BTU/hr × Heat Rejection Factor (HRF) - Heat Rejection Factor:
Accounts for the compressor's mechanical work of compression (BHP). For screw compressors:
At +20°F SST:HRF ≈ 1.25 to 1.30
At -20°F SST:HRF ≈ 1.45 to 1.55(colder suction requires more compressor work per ton). - Rated Model Selection:
Manufacturers rate condensers at 96.3°F condensing and 78°F wet bulb. Deviations in design SCT or wet bulb require correction factors.
Frequently Asked Questions
What is Total Heat of Rejection (THR)?
Total Heat of Rejection (THR) is the sum of the refrigeration cooling capacity (evaporator load) plus the electrical heat equivalent of the compressor work of compression.
Why does an evaporative condenser operate more efficiently than an air-cooled condenser?
Evaporative condensers reject heat against the ambient wet-bulb temperature (typically 15°F to 25°F lower than the dry-bulb temperature), allowing much lower condensing pressures and saving substantial compressor energy.
Why does low-temperature refrigeration (-20°F SST) require a larger condenser per ton?
At lower suction temperatures, the compressor must work significantly harder across a higher compression ratio, converting more electrical kilowatts into heat that must be rejected by the condenser.