3. Under conditions for which the same room temperature is maintained by a heating or cooling system, it is not uncommon for a person to feel chilled in the winter but comfortable in the summer. Provide a plausible explanation for this situation (with supporting calculations) by considering a room whose air temperature is maintained at 20 C throughout the year, while the walls of the room are nominally at 27 °C and 14 °C in the summer and winter, respectively. The exposed surface of a person in the room may be assumed to be at a temperature of 32 °C throughout the year and to have an emissivity of 0.90. The coefficient associated with heat transfer by natural convection between the person and the room air is approximately 2 W/m²K.

3. Under conditions for which the same room temperature is maintained by a heating or cooling system, it is not uncommon for a person to feel chilled in the winter but comfortable in the summer. Provide a plausible explanation for this situation (with supporting calculations) by considering a room whose air temperature is maintained at 20 C throughout the year, while the walls of the room are nominally at 27 °C and 14 °C in the summer and winter, respectively. The exposed surface of a person in the room may be assumed to be at a temperature of 32 °C throughout the year and to have an emissivity of 0.90. The coefficient associated with heat transfer by natural convection between the person and the room air is approximately 2 W/m²K.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter6: Forced Convection Over Exterior Surfaces

Section: Chapter Questions

Problem 6.29P

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Under conditions for which the same room temperature is maintained by a heating or cooling system, it is not uncommon for a person to feel chilled in the winter but comfortable in the summer.Consider a room whose air temperature is maintained at 18ºC throughout the year, while the walls of the room are nominally at 24°C and 14°C in the summer and winter, respectively. The exposed surface of a person in the room may be assumed to be at a temperature of 32°C throughout the year and to have an emissivity of 0.90. The coefficient associated with heat transfer by natural convection between the person and the room air is approximately 2 W/m2·K. Calculate the following. a. heat flux due to convection in W / m^2 b. Heat flux due to radiation in the summer in W / m^2 c. Heat flux due to radiation in the winter in W / m^2
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