AIR COOLED CHILLERS
12
DESIGN REQUIREMENTS
The followingdesign requirementsmust be known to select a proper packagechiller.
1. Required cooling capacity in kilowatt (kW)
2. Leaving chilled water temperature in
0
C (LCWT)
3. Chilled water flow rate in LPS
4. Chilled water cooling range in
0
C (water in temp. _ water out temp.)
5. Design ambient temperature
6. Minimum ambient temperature
7. Altitude
8. Electrical power supply
SAMPLE SELECTION
Select an Air Cooled Packagedchiller for the followingconditions:
Required system capacity is 300 kW at 12
0
C enteringchilled water
and 6
0
C leaving water. Design ambient temperature is 35
0
C.
Altitude is 600 meter above sea level.
Water cooler fouling factor is 0.000018. Power supply: 380V-3Ph-60Hz.
STEP-1:
UNIT SELECTION
Entering the capacity performance data at given LCWT and ambient temperature.
OALC100 chiller unit at sea level will produce346.3 kW and 111.8 kW compressor
power input at 6
0
C leaving chilled water temperature with 6
0
C water temperature
difference and 35
0
C ambient temperature.
For the conditions required, the unit actual cooling capacity when corrected for
altitude (0.99) and fouling factor (1.0).
Capacity = 346.3x0.99X1.0 = 342.84 kW, which then exceeds the requirements.
So the selection is correct.
STEP-2:
CHILLED WATER FLOW (LPM):
Water LPS =
Required capacity (kW) x 0.239
=
300 x 0.239
= 12 LPS
Cooling Range, DT
6
0
C
ELEVATION ABOVE
SEA LEVEL (Meter)
CAPACITY
CORRECTION
FACTOR
0
600
1200
1800
1.00
0.99
0.98
0.97
TABLE- 1
Referring to pressure drop chart, pressure drop at 12 LPS with pressure drop of 27.5 kPa of water for selected model.
STEP-3:
ELECTRICAL
Refer to electrical data at 380V-3Ph-60Hz, the main power wire size for OALC100 is to be sized for a minimum
circuit ampacity (MCA) of 325.4 Amps and maximum over current protection (MOCP) of 450 Amps.
STEP-4:
CHILLED WATER PUMP SELECTION
For chilled water pump selection, add all pressure drop in the closed chilled water loop piping to the pressure drop
calculated in step 2.
STEP-5:
LCWT CORRECTION
When a corrected LCWT is used, cooler pressure drop must also be corrected for new LCWT.
Refer to table-3. Add correction factor to design leaving chilled water temperature (LCWT) when chilled water tempera-
ture range is above 6
0
C and subtract correction from design leaving chilled water temperature (LCWT) when water
temperature range is below 6
0
C.
EXAMPLE:
If LCWT rise is 7.4
0
C, enter correction curve at 7.4
0
C and read the correction factor of 0.11. The corrected LCWT is
6
0
C+0.11 = 6.11
0
C.
NOTE: 1. When the chilled water temperature rise is less than 3
0
C, the high water flow rate will result to excessive
pressure drop. In such cases, contact factory for special selection of a cooler with wider baffle spacing.
2.Please refer to water pressure drop curves.
TABLE- 2
EVAPORA TOR FOULING
FACTOR (M
2
-
0
C/W)
0.000018
0.000044
0.000088
0.000132
0.000176
CAPACITY
CORRECTION
FACTOR
1.000
0.992
0.978
0.965
0.951
POWER
INPUT
FACTOR
1.000
0.997
0.990
0.984
0.978
ARI
STANDARDS
ARI-550/590-98
ARI-590-86
ARI-590-81
TABLE- 3
-0.22
-0.11
0
+0.11
+0.22
+0.33
4
5 6 7
8 9
10
COOLER WAT ER TEMPERATURE RISE ( C)
CORR
ECTION
F
ACT
OR
(C
)
SELECTION PROCEDURE
(Metric units)
