Exampl e

Suppose that a collector system supplies heat to an industrial process. The collector inlet temperature (process return temperature) varies as shown in Table 11.9 but, for a certain hour, is constant during the month. The calculation is done for the month of April, where Kt = 0.63. The system is located at 35°N latitude and the collector characteristics are FRUL = 5.92 W/m2-°C, Fr(to>)„ = 0.82, tilted at 40°, and the incidence angle modifier constant bo = 0.1. The weather conditions are also given in the table. Calculate the energy output of the collector.

Table 11.9 Collector Inlet Temperature and

Weather Conditions for Example 11.11

Table 11.9 Collector Inlet Temperature and

Weather Conditions for Example 11.11

Hour

T (°C)

Ta (°C)

It (MJ/m2)

8-9

25

9

1.52

9-10

25

11

2.36

10-11

30

13

3.11

11-12

30

15

3.85

12-13

30

18

3.90

13-14

45

16

3.05

14-15

45

13

2.42

15-16

45

9

First, the incidence angle is calculated, from which the incidence angle modifier is estimated. The estimations are done on the half hour; for the hour 8-9, the hour angle is 52.5°. From Eq. (2.20), cos(9) = sin(L - |3)sin(6) + cos(L - |3)cos(6)cos(h)

= sin(35 - 40)sin(9.41) + cos(35 - 40)cos(9.41)cos(52.5) = 0.584 or 9 = 54.3°.

The dimensionless critical radiation level, Xc, is given by Eq. (11.40):

0.294

From Table 2.5, Ho = 35.8 MJ/m2. From the input data and Eq. (2.82),

To avoid repeating the same calculations as in previous examples, some values are given directly. Therefore, hss = 96.7°, a = 0.709, and f3 = 0.376. From Eq. (2.84a),

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Getting Started With Solar

Getting Started With Solar

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