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### Radiative Heat Transfer Coefficient of a Human Calculator

Radiative Heat Transfer Coefficient of a Human Calculator

The linearized radiative heat transfer coefficient can be calculated by

Eq. 1
hr = 4 ε σ ( Ar / AD ) ( 459.7 + ( tcl + tr ) / 2 )3

where

hr = 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
tcl = temperature of clothed body or clothing °F
tr = mean radiant temperature °F
Ar = effective radiation area of body, ft2
AD = Activity metabolic rates Btu/h·ft2 (met), typical metabolic rates for an average adult
( AD = 19.6 ft2 ) for activities performed continuously. see: Metabolic Rate Thermal Energy Created by the Human Body

The ratio Ar/AD 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 hr, because tcl may also be unknown. Some form of iteration may be necessary if a precise solution is required. Fortunately, hr 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

hr = 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.

Related

Source

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