In determining head pressure for air-cooled condensers, the added degree value used with 35°F is

In determining head pressure for air-cooled condensers, the added degree value used with 35°F is

• A. 30
• B. 10
• C. 50
• D. 5

Answer: (A)

Head pressure for an air-cooled condenser is estimated from the condensing temperature, which rises with outdoor temperature and the condenser’s heat-transfer ability. A common quick rule is to add about 30°F to the outdoor air temperature to approximate the condensing temperature. In problems using a 35°F reference, adding 30°F gives about 65°F, and you’d then use a refrigerant pressure–temperature chart to convert that condensing temperature to the head pressure (psig). The 30°F offset reflects the typical temperature rise between the ambient air and the refrigerant as heat is rejected in an air-cooled condenser under normal conditions. The other values don’t fit this standard rule of thumb. A smaller offset would underestimate head pressure, while a much larger offset would overestimate it for everyday operating conditions.

Head pressure for an air-cooled condenser is estimated from the condensing temperature, which rises with outdoor temperature and the condenser’s heat-transfer ability. A common quick rule is to add about 30°F to the outdoor air temperature to approximate the condensing temperature. In problems using a 35°F reference, adding 30°F gives about 65°F, and you’d then use a refrigerant pressure–temperature chart to convert that condensing temperature to the head pressure (psig). The 30°F offset reflects the typical temperature rise between the ambient air and the refrigerant as heat is rejected in an air-cooled condenser under normal conditions.

The other values don’t fit this standard rule of thumb. A smaller offset would underestimate head pressure, while a much larger offset would overestimate it for everyday operating conditions.