AIR COOLED CHILLERS
SELECTION PROCEDURE
(English units)
11
DESIGN REQUIREMENTS
The followingdesign requirementsmust be known to select a packagechiller.
1. Required cooling capacity in tons
2. Leaving chilled water temperature in
0
F (LCWT)
3. Chilled water flow rate in PM
4. Chilled water cooling range in
0
F (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 Packaged chiller for the following conditions:
Required system capacity is 90 tons at 54
0
F entering chilled water
and 44
0
F leaving water. Design ambient temperature is 95
0
F.
Altitude is 2000 feet above sea level.
Water cooler fouling factor is 0.00010. 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 produce100.3 tons and 113.5kW compressor
power input at 44
0
F leaving chilled water temperature with 10
0
F water temperature
difference and 95
0
F ambient temperature.
For the conditions required, the unit actual cooling capacity when corrected for
altitude (0.99) and fouling factor (1.0).
Capacity = 100.3x0.99x1.0 = 99.2 Tons, which then exceeds the requirements.
So the selection is correct.
STEP-2:
CHILLED WATER FLOW ( PM):
Water
PM =
Required capacity (Tons) x 24
=
90 x 24
= 216 PM
Cooling Range, DT
10
0
F
ELEV ATION ABOVE
SEA LEVEL (FT .)
CAPACITY
CORRECTION
FACTOR
0
2000
4000
6000
1.00
0.99
0.98
0.97
TABLE- 1
TABLE- 3
TABLE- 2
EVAPORATOR FOULING
FACTOR (HR-FT
2
-
0
F/BTU)
0.00010
0.00025
0.00050
0.00075
0.00100
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
Referring to pressure drop chart, pressure drop at 216 PM = 11.5 ft. 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 10
0
F and subtract correction from design leaving chilled water temperature (LCWT) when water
temperature range is below 10
0
F.
EXAMPLE:
If LCWT rise is 12.5
0
F, enter correction curve at 12.5
0
F and read the correction factor of 0.2. The corrected LCWT is
44+0.2 = 44.2
0
F.
NOTE: 1. When the chilled water temperature rise is less than 5
0
F, 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.
-0.4
-0.2
0
+0.2
+0.4
+0.6
5
10
1
5
2
0
COOLER WATER TEMPERATURE RISE ( F)
CORR
ECTION
F
ACT
OR
(
F)
