The heating system of a building is being retrofitted with a humidifier so that
ID: 516929 • Letter: T
Question
The heating system of a building is being retrofitted with a humidifier so that the relative humidity of the 76°F-air released into the building is at a comfortable 30%. The process starts with outside air at 41.5°F and 60% relative humidity. The air enters the first heater, where the temperature of the air is raised to 63°F. At this point, the air enters a humidifier where vaporized water is added. The temperature of the incoming water is at the wet bulb temperature of the air stream entering the humidifier, such that the specific enthalpy of the air and water streams are the same. The humid air exiting the humidifier enters a second heater and exits at 76°F and 30% relative humidity.
Air V1 17.9 ft /min rh1 60% Heater 1 T2 63°F Humidifier Heater 2 rh4 water m3 T5 376°F rhs 30%Explanation / Answer
a) Relative humidity = 0.60,
For humid volume we have,
Humid Volume = 22.41/273 * T (in K) [ 1/29 +H/18 ]
= 1.548 m3/kg = 24.8ft3/lbm
c) Applying energy balance, T4 = 41.6 degree F
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