Industrial buildings have fresh air requirements depending on the occupancy level and its function. Assume 15,000 cfm of moist air from the outdoors, which is at 32°F and a relative humidity of 80%, is heated to 70°F in order to provide a supply of fresh air to the inside of an office building.
a. What is the energy rate (Btu/min) for heating the air?
b. What is the relative humidity of the air after heating? If water vapor was added to the 70°F air to increase its relative humidity to 50%, what is the mass flow rate (Ibm/min) of water vapor required?
c. What is the daily cost of heating this building by using natural gas if the gas cost is $0.5 per therm where a therm is 100,000 Btu's?