Page 95 - Low Temperature Energy Systems with Applications of Renewable Energy

84 Low-Temperature Energy Systems with Applications of Renewable Energy

Next, let us consider the inverse problem. The area of the site should not exceed
2
100 m ; it is necessary to determine the number of loops.
n 1
A ¼ 100 ¼ 215 0:75
n
Hence,

1
¼ n ¼ 2:63
100
1
215$0:75
2
Since the area of the site should not exceed 100 m , we round off n on smaller side,
i.f., n ¼ 2. Then the real area of the section will be
2 1 2 2
A ¼ 215 0:75 ¼ 81 m 100 m
2

Vertical collector
The specific heat flux from the soil to the pipes of the vertical collector, using Eq.
(2.7) and k ¼ 1.2 is

q 0 ¼ 1:2½ð1:4 3:56Þ 0:5ފ½ð0:4 þ 1ފð8 0Þ¼ 60:26 W=m

The length of vertical manifold pipes is

15100 3:5 1
L ¼ ¼ 179:0m.
60:26 3:5
We accept the design of two well collectors, each with a depth of 90 m.
Case B. This example follows the specifications for Case A except that the soil is
3
sand: r ¼ 1400 kg/m , humidity is 5%. Determine the length of the ground collector
for the heat pump.
Solution.
Horizontal collector
The specific heat flux from the ground to the horizontal pipe is

q 0 ¼½ð1:4 1:57Þ 0:5Šð0:4 þ 1Þð8 0Þ¼ 19:0W=m

The thermal collector capacity is Q 0 ¼ Q hp W ec , where Q hp is HP power and, W ec
is electric power of the compressor.