Chapter 8.2, Problem 60P

A small auditorium that can accommodate 30 people allows smoking. The design engineers of the auditorium assume that the smokers each are responsible for an average of 50 micrograms per minute of tobacco smoke being added to the auditorium space. The volumetric flow rate of recirculated room air is 200 cfm. Outdoor air is also supplied, and is mixed with the recirculated room air. The system has a ventilation effectiveness of 80%. In an effort to maintain the level of particulate matter from the tobacco smoke in the auditorium to no more than 5.5 micrograms per cubic foot, filters with an effective efficiency of 90% are added to the ventilation system downstream of the point in the system where outdoor air and recirculated room air are mixed. a) What is the necessary volumetric flow rate (in cfm) for the supply outdoor air? Assume the outdoor air is clean. b) The outdoor air taken into the system becomes contaminated with tobacco smoke due to a leak in an adjacent building’s…

room to be maintained with a dry-bulb temperature of 72ºF and 30% relative humidity. The room has a sensible heat factor of 0.8 and a total hourly heating load of 200,000 Btu. A flow rate of 1000 cfm of outdoor air (at 20% relative humidity and a dry-bulb temperature of 40ºF) is used. In order to maintain adequate comfort, the supply air to the room is set to a dry-bulb temperature of 120ºF. To humidify the air, steam with a specific enthalpy of 1150 Btu per pound is utilized.Determine the wet bulb temperature, specific enthalpy, and volumetric flow rate of the supply air to the room. Evaluate the increase in dry-bulb temperature as the air is sensibly heated, and the mass flow rate (in lb/hr) of steam required during the latent heating of the air. Calculate the heat added to the room during sensible heating (i.e., excluding humidification).

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