Sol-Air Values

Sol-air temperature is the outdoor air temperature that, in the absence of all radiation changes, gives the same rate of heat entry into the surface as would the combination of incident solar radiation, radiant energy exchange with the sky and other outdoor surroundings, and convective heat exchange with outdoor air.

The heat balance at a sunlit surface gives the heat flux into the surface q/A as

(28)

where

= absorptance of surface for solar radiation

= total solar radiation incident on surface, Btu/h·ft²

= coefficient of heat transfer by long-wave radiation and convection at outer surface, Btu/h·ft²·°F

= outdoor air temperature, °F

= surface temperature, °F

= hemispherical emittance of surface

= difference between long-wave radiation incident on surface from sky and surroundings and radiation emitted by blackbody at outdoor air temperature, Btu/h·ft²

Assuming the rate of heat transfer can be expressed in terms of the sol-air temperature te,

(29)

and from Equations (28) and (29),

(30)