Cork insulation; a complete illustrated textbook on cork insulation ...

STRUCTURAL SUGGESTIONS 181
T» = 50° F. average temperature outside wall.
Tm=r90° F.
t = cold room temperature, degrees F., as assigned,
(t—tp) = 10° F.
K = 2.0 surface transmission coefficient.
A = $1.00 per ton.
P z= $4.35 per square foot.
I' = 6 per cent.
Y' = 8 years.
R' = 3 per cent.
S = 0.
U = 0.303.
the economical thickness, X, of <strong>insulation</strong> was readily obtained
for a range of cold room temperatures, t, and curve B of Fig.
53 was platted.
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I I
FIG. 53.—WALL INSULATION—ECONOMIC THICKNESS AGAINST
TEMPERATURE.
With the same set of conditions and a cold room temperature
of 20° F., the true yearly cost, per square foot, based on
various thicknesses of <strong>insulation</strong>, were computed and curve B
of Fig. 54 was platted.
According to the definition, the economic thickness of
<strong>insulation</strong> occurs when the yearly cost is a minimum, which
thickness is (3.99— 1.06) 2.93 inches on the curve in Fig. 54;
and the shape of the curve shows that the refrigeration cost
per square foot increases at a more rapid rate with a given de-
crease below the economic thickness than it does for a similar
increase. It will also be noted that such curve is compara-
tively flat on each side of the economic thickness, indicating