In testing the efficiency of a water-cooled condenser, the refrigerant condensing temperature should be no more than approximately how many degrees higher than the leaving water temperature?

• A. 5°F
• B. 15°F
• C. 10°F
• D. 20°F

Answer: (C)

In a water-cooled condenser, heat transfer efficiency depends on how close the refrigerant’s condensing temperature is to the water leaving temperature—the smaller the approach, the more efficiently heat is rejected. The refrigerant must reach its condensation temperature while the cooling water picks up that heat and exits warmer. If the condensing temperature is much higher than the leaving water temperature, heat transfer becomes less efficient, condenser duty increases, and overall system efficiency drops.

Practically, keeping the condensing temperature within about 10°F of the leaving water temperature provides a good balance: enough driving force for heat transfer without wasting energy on a large temperature lift. That’s why 10°F is the commonly used guideline. Larger differentials, like 15°F or 20°F, reduce efficiency, while a much smaller differential (around 5°F) is more stringent than typically needed in many applications.