Table 2: Material properties, resistance, UA, and capacitance for each roof layer

U

(1/R)

W/m2-

с

25

F01 Outer Surface Resistance

F13 Build-Up Roofing

4 cm Roofing Insulation

10 cm Concrete

R5 Combined

10 cm Steel Joints

10 cm Airspace

20 mm Plaster Ceiling

F03 Inside Horizontal Surface

Resistance

Total

R

R1

R2

R3

L k

mm

9.5 0.16

28

W/m-

с

40

rho Cp R

C-

kg/m³

kJ/kg-

с

m²/W

0.04

0.06 16.84

0.75

1,120

0.03 43

1.46

1.21

0.84

R4

R5

R5a 100 45.4 7,800 0.5

R5b 100 0.0251 1.2

R6

20

0.16 800

R7

100 0.53 1,280

1.004

1.05

1.33

0.19 5.30

0.18

5.56

0.12 8.33

0.18

5.56

0.13 8.00

0.16 6.25

XXX XXX

с

(tho*cp*L)

kJ/m2-C

15.53

2.08

107.52

11.82

390.00

0.12

16.80

a. Determine the overall conductance of the roof.

b. Use the thermal network approach to represent the transient response. Assume that all of the

thermal storage is in the concrete and that the other roof elements have only a thermal

resistance. Verify that the capacitance of the steel joists is negligible.

c.

Determine and plot the heat gain as a function of time over the course of the day

d. Discuss how the HVAC system design is affected by energy storage in the concrete.