Page 213 - Handbook of Energy Engineering Calculations

4. Compute the airflow produced by the windows
The two windows can be used to ventilate the engine room. One window will

serve as the air inlet; the other, as the air outlet. The area of the air outlet
must at least equal the air-inlet area. Airflow will be produced by the stack
effect resulting from the temperature difference between the inlet and outlet
air.
0.5
3
The airflow C ft /min resulting from the stack effect is C = 9.4 A(hΔ t ) ,
a
2
where A = free air of the air inlet, ft ; h = height from the middle of the air-
inlet opening to the middle of the air-outlet opening, ft;Δ t = difference
a
between the average indoor air temperature at point H and the temperature of
the incoming air,°F. In this plant, the maximum permissible air temperature
rise is 15°F (8.3°C), from step 2. With a 100°F (37.8°C) outdoor temperature,
the maximum indoor temperature would be 100 + 15 = 115°F (46.1°C).
Assume that the difference between the temperature of the incoming and
0.5
3
outgoing air is 15°F (8.3°C). Then C = 9.4(30)(5 × 15) = 2445 ft /min
3
(69.2 m /min).

5. Compute the cooling airflow required
This 60-kW internal-combustion engine generating set radiates 2625 Btu/min
(12.8 W), step 3. Compute the cooling airflow required from C = HK/Δ t ,
a
3
where C = cooling airflow required, ft /min; H = heat radiated by the engine,
Btu/min; K = constant from Table 6; other symbols as before, Thus, for this
engine with a fan discharge temperature of 111 to 120°F (43.9 to 48.9°C),

Table 6, K = 60;Δ t = 15°F (8.3°C) from step 4. Then C = (2625)(60)/15 =
a