Radiative Heat Transfer Coefficient of a Human Calculator

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Radiative Heat Transfer Coefficient of a Human Calculator

Heat Transfer Engineering
Thermodynamics
Physics

The linearized radiative heat transfer coefficient can be calculated by

Eq. 1
h_r = 4 ε σ ( A_r / A_D ) ( 459.7 + ( t_cl + t_r ) / 2 )³

where

h_r = radiative heat transfer coefficient, Btu/h·ft²·°F
ε = average emissivity of clothing or body surface, dimensionless
σ = Stefan-Boltzmann constant, 0.1712 x 10^-8 Btu/h·ft²·°R⁴
t_cl = temperature of clothed body or clothing °F
t_r = mean radiant temperature °F
A_r = effective radiation area of body, ft²
A_D = Activity metabolic rates Btu/h·ft² (met), typical metabolic rates for an average adult
( A_D = 19.6 ft² ) for activities performed continuously. see: Metabolic Rate Thermal Energy Created by the Human Body

The ratio A_r/A_D is 0.70 for a sitting person and 0.73 for a standing person (Fanger 1967). Emissivity ε is close to unity (typically 0.95), unless special reflective materials are used or high-temperature sources are involved. It is not always possible to solve Equation 1 explicitly for h_r, because t_cl may also be unknown. Some form of iteration may be necessary if a precise solution is required. Fortunately, h_r is nearly constant for typical indoor temperatures, and a value of 0.83 Btu/h·ft²·°F suffices for most calculations. If emissivity is significantly less than unity, adjust the value by

h_r = 0.83 ε

where ε represents the area-weighted average emissivity for the clothing/body surface.

Conversions

1 met = 18.4 Btu/h· ft² = 50 kcal/h ·m².

Source

2016 ASHRAE Handbook - HVAC Systems and Equipment, ASHRAE: 2016.