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  Hastings Industries Inc. Vari-Cool Evaporative Vari-Cool Evaporative - Page 7
SELECTION
EXAMPLE
PSYCHROMETRIC PROCESS
| Step# 1 - |
Supply air quantity= 24,000 CFM Supply air
temperature= 60°F |
| Step #2 - |
Design Condition = 99° DB & 68°WB |
| Step #3 - |
Trial selection. Two I/D-65 units in parallel
on common base 12,000 CFM per package (24,000 CFM total). Efficiency indirect unit= 60%
Efficiency direct unit= 90% |
| step #4 - |
Indirect unit performance:
99° - (99° - 68°) (.60) = 80.41Lvg. D B (61.6°WB)
Direct unit performance:
80.4° - (80.4°- 61.6-) (.90) = 63.5° DB, S.A. temp. |
| Step #5 - |
Calculating booster refrigeration capacity to
drop the
supply air temperature from 63.5" to the required 60'
supply air temperature.
Coil located ahead of direct unit:
(60) (27.7 - 25.6) (24,000 CFM) = 21 9,770 Btuh (1 8.3 tons
13.76
Coil located in the leaving air of direct unit:
(60) (27.7 - 25.6) (24,000 CFM) = 225,000 Btuh (1 8.8 tons)
13.44 |
From the above calculations, depending on the location of
the booster cooling coil, the conventional booster refrigeration capacity is determined
and the cooling coil selection can be made.
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