Question

4.1A clothed or unclothed person feels comfortable when the skin temperature is about 33oC. Consider an average man wearing summer clothes whose thermal resistance is 0.109 m2 ? oC/W. The man feels very comfortable while standing in a room maintained at 20oC. If this man were to stand in that room unclothed, determine the temperature at which the room must be maintained for him to feel thermally comfortable. Assume the latent heat loss from the person to remain the same. (12) NB: At low air velocities, the convection heat transfer coefficient for a standing man is 4.0 W/m2 ? oC and the radiation heat transfer coefficient at typical indoor conditions is 4.7 W/m2 ? oC. The surface area of an average man is 1.8 m2 2Consider a large classroom with 150 students on a hot summer day. All the lights with 4.0 kW of rated power are kept on. The room has no external walls, and thus heat gain through the walls and the roof is negligible. Chilled air is available at 15oC, and the temperature of the return air is not to exceed 25oC. 4.2.1 Draw diagram to represent the situation described above. (5) 4.2.2 Determine the required flow rate of air, in kg/s, that needs to be supplied to the room. NB: Properties of air: The specific heat capacity of air at room temperature is 1000 J/kg? oC. The average rate of metabolic heat generation by a person sitting or doing light work is 115 W (70 W sensible heat and 45 W latent heat).

Answer 1