Return air from a house enters an air-conditioning unit at 72oC, 70% relative humidity with a volumetric flow rate of 1800 ft3 /min where it is mixed with 900 ft3 /min of outside air at 90oF, 80% relative humidity. Refrigerant-22 enters the evaporator coil with a quality of 22% at 90 lbf/in.2 and exits at 90 lbf/in.2 , 50oF. Condensate is drained away at 48oF, and the moist air stream exiting the evaporator coil is saturated at 50oF. The air leaving the heating section is at 66oF. The flow through the duct is at 14.7 lbf/in.2 Determine, for steady state operation with no significant kinetic or potential energy effects, (a) the mass flow rate of refrigerant, in lb/min, (b) the rate of heat transfer in the heating section, in Btu/h, and (c) the relative humidity of the supply air.