Chapter 3, Problem 3.53P

An interior zone of a large building is designed to have a supply air-flow rate of 5000 cfm (2.4 m³/s). The cooling load is constant at 10 tons (35 kW) with a SHF of 0.8 year-round. Indoor conditions are 75 F (24 C) db and 50 percent relative humidity (RH). (a) What is the maximum air dry bulb temperature and humidity ratio that would satisfy the load condition using all outdoor air? (b) Consider a different time when the outdoor air has a temperature of 40 F (4 C) db and 20 percent relative humidity. Return air and outdoor air may be mixed to cool the space. but humidification ill be required. Assume that saturated water vapor at 14.7 psia (101 kPa) is used to humidify the mixed air, and compute the amounts of outdoor and return air in cfm (m³/s). (c) At another time, outdoor air is at 65 F (18 C) db with a relative humidity of 90 percent. The cooling coil is estimated to have a minimum apparatus dew point of 45 F (7.2 C). What amount of outdoor and return air should be mixed before entering the coil to satisfy the given load condition? (d) What is the refrigeration load for the coil of part (c) above?