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

=Ztj(COS6)J

J—0

And

=2X^/0 + 2)

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)

Example 7-5

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