Masonry Magazine October 1981 Page. 14
A simplified method for determining the appropriate correction factor is offered in Fig. 1. The maximum exterior surface temperature for a vented wall is given in Fig. 1 for the appropriate value of maximum exterior surface temperature for an unvented wall as determined by using Equation 1.
Tmax = (α/0.98) × Cg × Co × 160°F (1)
where: Tmax = Maximum exterior surface temperature, in °F.
α = Absorptivity of the brick masonry.
Cg = Glass transmittance correction factor,
single glass = 1.212
double glass = 1.000
triple glass = 0.825
Co = Orientation correction factor.
For a 127°F maximum exterior surface temperature of an unvented brown brick thermal storage wall, the maximum exterior surface temperature of a similar wall with vents would be about 114°F.
Minimum. The minimum exterior surface temperature is dependent on the operation of the vents. The vents, top or bottom, should be closed when the circulating air is cooler than the interior ambient temperature. If only the top or bottom vents are closed, the minimum exterior surface temperature may be taken as equal to the interior design temperature. If both top and bottom vents are closed, the minimum exterior surface temperature may be approximated in the same way as the minimum exterior surface temperature of the unvented thermal storage wall is calculated using Equations 2 and 3.
Rt = f。 + Rg + fa + Rr + R。 + fi (2)
where: Rt = Total resistance of the thermal storage wall system, in (°F. ft² hr)/Btu.
f。 = Thermal resistance of the exterior air film, in (°F. ft² hr)/Btu.
Rg = Thermal resistance of the glazing material, in (°F. ft² hr)/Btu.
fa = Thermal resistance of the airspace between the glazing material and the brick thermal storage wall, in (°F. ft² hr)/Btu usually taken as 0.97 (°F. ft² hr)/Btu if the airspace is between ¾ in. and 4 in.
R, = Thermal resistance of any night insulation which might be used, in (°F. ft² hr)/Btu.
R。 = Thermal resistance of the brick thermal storage wall, in (°F. ft². hr)/Btu.
fi = Thermal resistance of the interior air film, in (°F. ft² hr)/Btu, usually taken as 0.68 (°F ft² hr)/Btu.
Tmin = T; - [[(fi/Rt) + (Rb/Rt)] × (T; - T。)] (3)
where: Tmin = Minimum exterior surface temperature of the brick thermal storage wall, in °F.
T; = Interior design temperature, in °F.
T。 = Exterior design temperature, in °F.
For various thicknesses of brick vented thermal storage walls, the minimum exterior surface temperature when both the top and bottom vents are closed would be the same as for the unvented walls discussed in Technical Notes 43E, i.e.:
8-in. wall, Tmin = 54°F
12-in. wall, Tmin = 51°F
16-in. wall, Tmin = 48°F
24-in. wall, Tmin = 41°F