Question

A manufacturing building is being ventilated to maintain air temperature, air moisture levels and air quality. The following is known about the situation: • The desired inside conditions are 68°F db with a maximum of 60% RH. • The average outside conditions are 42°F db and 35°F wb. • The building has an overall heat loss factor of 454 BTU/(h·ºF) with a total volume of 76,000 ft3. • Inside the building, people and equipment generate sensible heat at a rate of 46,500 BTU/h. • Inside the building, people and equipment generate moisture at a rate of 14.2 lb H2O/h. • There is no significant amount of water evaporation. • Air quality is provided at a minimum of 1.4 air exchanges per hour. • The ventilation fans exhausts from the building (fan inlet is at the inside conditions). 1. What ventilation rate (in cfm) is needed to maintain the desired inside air temperature? 2. What ventilation rate (in cfm) is needed to maintain the desired maximum relative humidity at the desired inside air temperature? 3. What ventilation rate (in cfm) is needed to maintain air quality? 4. What ventilation rate (in cfm) should be used? 5. Is supplemental heat necessary when the building is ventilated at the rate in #4? If so, how much (in BTU/h)?

Answer 1

1. We are provided with the Air change rate = 1.4 /h

Volume of room = 76000 cu ft

So, Ventilation rate (cu ft/h) = Air change rate X Room Volume (cu ft)

= 1.4 X 76000 = 106400 cu ft/h