Heat gain through fenestrations
Total heat gain = (Solar heat gain)
+ (Conduction heat gain)
Conduction heat gain = U (T0 — Tj)
Define:
Solar heat gain factor: SHGF Transmitted solar heat gain factor: TSHGF Absorbed solar heat gain factor: ASHGF
SHGF = TSHGF + ASHGF
• For double-strength sheet glass (DSA):
TSHGF = Gd ‘Ed + Gd xti
With
J—0
And
J—0
Where 0 = incident angle
Tj = values in TTable 6-2 or ATable 23
ASHGF = Gd ocd + Gd 0Cd
With
5
AD =EaJ(COS0)J
J—0
And
Ad=2^aj/(j + 2)
J—o
Where aj = values in T Table 6-2 or A Table 23.
• For non-DSA materials:
Transmitted heat gain, TSHG:
TSHG = (SC) (TSHGF)
And absorbed heat gain, ASHG:
ASHG = (SC) (ASHGF) (N,)
Where SC = shading coefficients in T Tables 6-3 to 6-6 or A Tables 24 to 27.
Ni = inward flowing fraction of absorbed heat gain.
N; = hi / (hi + h0)
Continue from Example 7-4. Assume the window uses a 2.4 mm single-glass with light Venetian blinds. Find the solar heat gain under a clear sky with an outside wind speed of 3.35 m/s and an inside convective heat transfer coefficient of 4.0 W/m K.
Solution
From T Table 6-4 or A Table, SC = 0.67
Td=22tj/G + 2)=0.8
J—o
Ad=2^a,/(j + 2)=0.54
J—o
Ni = hi / (hi + h0) = 4.0/(4.0 + 23.0) = 0.148
Transmitted solar heat gain:
TSHGF = Gd Id + Gd xti = 0 + (Gde + Grb) id = 0 + (49 + 94) x 0.8 = 114 W/m2
TSHG = (SC) (TSHGF)
= 0.67 x 114 = 76 W/m2
Absorbed solar heat gain:
ASHGF = Gd ocd + Gd 0Cd = 0 + (Gde + Grb) ad
= 0 + (49 + 94) x 0.54 = 77 W/m2
ASHG = (SC) (ASHGF) (H) = 0.67x77x0.148
= 8 W/m2
Total solar heat gain:
SHG = TSHG + ASHG = 77 + 8 = 85 W/m2
Posted in Fundamentals of Heating. Ventilating, and Air-Conditioning