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3
SELECTION PROCEDURE
Table 4 shows the performance specifications for
Liebert drycoolers using a 40% by volume ethylene
glycol solution at an average fluid temperature of
115°F with flow rates from 1.5 to 3 GPM/circuit and
at standard air (.075 lbs/ft
3
). Figure 2 and Figure 3
offer correction factors to Table 4 for average fluid
temperatures and glycol percentages other than
115°F and 40%. Table 3 correction factors may be
used for performance at altitudes above sea level.
For cooling applications other than shown, contact
the Liebert Heat Transfer Division.
To select a drycooler from the tables in this
bulletin, the following information must be known:
1. Fluid Flow Rate (GPM).
2. % Ethylene Glycol (% EG).
3. Design Air Temperature at the Drycooler (EAT).
4. Entering and Leaving Fluid Temperatures (EFT,
LFT) or Total Heat Rejection (BTU/HR) and one
of the Fluid Temperatures.
5. ITD (Initial Temperature Difference) = EFT -
EAT
From the known data, calculate the following:
• Average Fluid Temperature (AFT) = (EFT +
LFT)/2.
• Heat Rejection (BTUH) = Fluid Temp. Diff. x
GPM x BTU/GPM Factor (Table 2).
(Leaving Air Temperature should be lower than
145°F for proper motor operation.)
Using Table 4 to select a drycooler
Calculate required MBH/ITD with corrections for
glycol % and average fluid temperature.
2. Locate Model No. in Table 4 having a GPM
range within the required flow rate and an MBH
equal to or greater than required. This gives an
approximate size.
3. Divide the given GPM by the “No. of circuits” of
the drycooler selected. The result is “GPM/CIR”
and should be in the range of 1-1/2 to 3.
4. In Table 4, look up the model selected above and
under “GPM/CIR” find the actual MBH. You may
interpolate between columns.
The MBH found should be equal to or greater than
the “required MBH /ITD.”
If the MBH is less than required, repeat from Step 2
with a larger model. You may wish to repeat from
Step 2 with a smaller model for the most economical
selection meeting the required MBH/ITD.
Pressure Drop - After selecting a model, look up
the unit pressure drop following Step 3 and 4 above.
Multiply the pressure drop found by the Figure 3
correction factor. If the product is higher than your
system design, go back to Step 2 and select a model
with more circuits. This may be the same, or larger,
unit.
Example
Cool 40 GPM 20% ethylene glycol and water solution
from 125(F) to 115(F). Design EAT = 95(F).
Calculate:
BTUH = (125 - 115) x (40 GPM) x (480 BTU/
GPM)
BTUH = 192,000
AFT = (125 + 115)/2 = 120(F)
From Figure 2, corr. factor for 120 AFT and
20% EG = 1.04
2. Locate model in Table 4. Models 092 through
139 fall into the GPM range but do not have the
MBH capacity. Model 174 with 16 circuits is the
smallest model meeting both the GPM range and
MBH requirements.
3. GPM/CIR = 40 GPM/16 CIR = 2.5 GPM/CIR.
4. In Table 4, Model 174 with 16 circuits at the 2.5
GPM/CIR column provides 6.9 MBH/ITD, which
exceeds the required MBH/ ITD of 6.15.
Pressure Drop = 10.5 ft. (from Table 4) x 0.93 (from
Figure 3) = 9.8 ft. H
2
O.
• Leaving Fluid Temperature =
EFT - BTUH
(GPM) (BTU/GPM)
• Other useful information:
Leaving Air Temp. = EAT +
Drycooler BTUH
(1.08) (Drycooler CFM)
1. Required MBH/ITD =
BTUH
(EFT - EAT) (1000) (Fig. 1 Factor)
Table 2 Determining actual BTUH and MBH
% Glycol
Solution
0% 10% 20% 30% 40% 50%
BTUH/GPM 500 490 480 470 450 433
Table 3 Altitude correction
Alt. (Ft.) 0 1000 2000 5000 8000 12000 15000
Corr. Fact. 1 .979 .96 .9 .841 .762 .703
1. Required MBH/ITD =
192,000 BTUH
(125-95) (1000) (1.04)