Civil Engineering Reference
In-Depth Information
Table 8.4
Heat losses from a composite wall (reference Fig.
8.2
)
Heat losses Q
Energy saving
Thickness of insulation (d
2
)
Overall thermal resistance
ft
2
10
-3
rn
2
W/m
2
Btu/h
ft
2
W/m
2
ft
2
kg
oil
/h
m
2
mm
ft
K/W
h
°F/Btu
Btu/h
0.0
0.190
1.079
167
0
0
0
526
0.000
10
32.8
0.372
2.112
269
85
257
82
0.026
20
65.6
0.554
3.144
181
57
346
110
0.035
30
98.4
0.735
4.177
136
43
390
124
0.039
40
131.2
0.917
5.209
109
35
417
132
0.042
1.099
6.242
91
29
435
138
0.044
50
164.0
60
196.9
1.281
7.274
78
25
448
142
0.045
70
229.7
1.463
8.307
68
22
458
145
0.046
466
148
0.047
80
262.5
1.645
9.340
61
19
472
149
0.048
90
295.3
1.826
10.372
55
17
2.008
11.405
50
16
477
151
0.048
100
328.1
INPUT DATA
wall conductivity k
1
2.500 W/m
K
1.444 Btu/h
ft
°F
BASIC FORMULA
fiberglass conductivity k
2
0.055 W/m
K
0.032 Btu/h
ft
°F
t
i
−
t
o
R
th
wall thickness d
1
0.100 m
0.328 ft
Q
=
A
20 W/m
2
ft
2
heat-transfer coefficient h
i
K
3.522 Btu/h
°F
10 W/m
2
K
ft
2
heat-transfer coefficient h
o
1.761 Btu/h
°F
R
th
=
h
i
+
+
h
o
d
1
k
1
+
d
2
k
2
t
i
-t
o
100°C = 100 K
180°F
ANNUAL ENERGY SAVING
70 mm insulation
5,000 h/year
100 m
2
surface
23 TOE/year
saving in
kg
oil
h
m
2
=
W
3,600
η
41,860
10
3
m
2
η
combustion assumed 0.85 (LHV as reference)
LHV of oil 41,860 kJ/kg
