Rapid 4044 - SECTION 16: Cooling Specifications; Evaporative Cooling; Table 21: Formulas; Table 22: Abbreviations

4000-SERIES INSTALLATION, OPERATION AND SERVICE MANUAL
68 of 154
SECTION 16: COOLING SPECIFICATIONS
16.1 Evaporative Cooling
Table 21: Formulas
* Bleed-off and recirculation rates will vary with
locale, water quality and chemical treatment
program. These values are only for approximation.
NOTE: Refer to saturation efficiency table below.
Table 22: Abbreviations
Table 23: Evaporation Rate
• Heat of vaporization = 1043 BTU/lb
• Weight of water = 8.34 lb./Gallon
• GPH = CFM x WBD x SE x 1.08/1043/8.34 = CFM x WBD x SE/8050
Table 24: Suggested Air Changes Per Hour (Air
Change Method)
* For existing buildings: Average amount indoor
temperature exceeds ambient outdoor temperature
when evaporative cooling is not in use.
** Experience has shown that significant benefit can
be achieved with 10-15 Air Changes per Hour (AC/
Hr) through the lowest 12' of the facility. For a 24'
high building, this would mean 5-6 Air Changes per
Hour (AC/Hr) for the entire volume. This will v
ary by
application.
Table 25: Saturation Efficiency at Stated Media
Depth
Table 26: Static Pressure Drop (in wc) at Stated
Media Depth
NOTE: Moisture limiter pressure drop is added for
face velocities greater than 600 Feet per Minute
(FPM). Rapid Engineering LLC's standard media
thickness equals 12".
Formulas
1 Leaving Dry Bulb = ODB – [SE* x (ODB - OWB)]
2
Leaving Wet Bulb = Entering Wet Bulb (actually, it’s slightly less
than the entering wet bulb, but is normally considered equal.)
3Wet Bulb Depression = ODB – OWB
4Evaporation Rate (GPH) = CFM x WBD x SE/8050
5 Bleed-off Rate = approximately 20% of evaporation rate*
6Recirculation Rate = approximately 3 times evaporation rate*
Abbreviations
CFM Cubic Feet Per Minute
GPH Gallons Per Hour
IDB Indoor (Design) Dry Bulb Temperature
LDB Leaving Dry Bulb Temperature
LWB Leaving Wet Bulb Temperature
ODB Outdoor (Design) Dry Bulb Temperature
OWB Outdoor (Design) Wet Bulb Temperature
SE Saturation Efficiency of the Evaporative Media
WBD Wet Bulb Depression
Wet Bulb
Depression (°F)
Gallons per Hour (GPH) Per 1,000 Cubic Feet per Minute (CFM) at Stated Saturation Efficiency
0.800.820.840.860.88 0.90 0.92 0.94 0.96 0.98
5 0.50 0.51 0.52 0.53 0.55 0.56 0.57 0.58 0.60 0.61
10 0 . 9 9 1. 0 2 1. 0 4 1. 0 7 1. 0 9 1. 1 2 1. 1 4 1. 1 7 1. 1 9 1. 2 2
15 1. 4 9 1. 5 3 1. 5 6 1. 6 0 1. 6 4 1. 6 8 1. 7 1 1. 7 5 1. 7 9 1. 8 3
20 1.99 2.04 2.09 2.14 2.19 2.23 2.28 2.33 2.38 2.43
25 2.48 2.55 2.61 2.67 2.73 2.79 2.86 2.92 2.98 3.04
30 2.98 3.05 3.13 3.20 3.28 3.35 3.43 3.50 3.58 3.65
35 3.48 3.56 3.65 3.74 3.82 3.91 4.00 4.08 4.17 4.26
40 3.97 4.07 4.17 4.27 4.37 4.47 4.57 4.67 4.77 4.87
45 4.47 4.58 4.69 4.80 4.92 5.03 5.14 5.25 5.36 5.48
Leaving Air
Temperature
(°F DB)
Indoor Air
Temperature Above
Ambient (°F)*
Air Changes/Hour**
78° 20° 30 - 60
76° - 78° 15° - 20° 20 - 40
74° - 76° 10° - 15° 15 - 30
72° - 74° 5° - 15° 12 - 20
< 72° < 10° 10 - 15
Airflow
Feet per
Minute (FPM)
6" 8"12"18" 24"
400 0.71 0.81 0.90 0.98 0.99
500 0.68 0.79 0.89 0.98 0.99
600 0.66 0.77 0.88 0.97 0.99
700 0.64 0.75 0.87 0.97 0.98
Airflow
Feet per
Minute (FPM)
6" 8"12"18" 24"
400 0.06 0.09 0.14 0.19 0.24
500 0.09 0.14 0.21 0.30 0.39
600 0.13 0.20 0.30 0.42 0.55
700 0.23 0.31 0.44 0.62 0.80