Selection Procedure
The chiller capacity tables presented in the “Performance Data” section cover the most frequently encountered leaving water temperatures.The tables reflect a 10°F temperature drop through the evaporator. For temperature drops other than 10°F, fouling factors other than 0.0001 (in accordance with ARI Standard
To select aTrane
1
Design system load (in tons of refrigeration).
2
Design leaving chilled water temperature.
3
Design chilled water temperature drop.
4
Design ambient temperature.
5
Evaporator fouling factor.
Evaporator chilled water flow rate can be determined by using the following formula:
Tons x 24
GPM = Temperature Drop (Degrees F)
NOTE: Flow rate must fall within the limits specified in the “General Data” section of this catalog.
SELECTION EXAMPLE
Given:
Required System Load = 53 tons
Leaving ChilledWaterTemperature (LCWT) = 45°F
ChilledWaterTemperature Drop = 10°F
Design AmbientTemperature = 95°F
Evaporator Fouling Factor = 0.0001
1
To calculate the required chilled waterflow rate we use the formula:
GPM = Tons x 24
∆T
From the 60 ton unit table in the “Performance Data” section of this catalog, a
GPM = 56.8 Tons x 24 = 137.5
10°F
2
To determine the evaporator water pressure drop we use the flow rate (gpm) and the evaporator water pressure drop curves found in the “Performance Adjustment Factors” section of this catalog. Entering the curve at 137.5 gpm, the pressure drop for a nominal 60 ton evaporator is 16.5 feet.
3
For selection of chilled brine units or applications where the altitude is significantly greater than sea level or the temperature drop is different than 10°F, the performance adjustment factors should be applied at this point.
For example:
Corrected Capacity = Capacity
(unadjusted) x Appropriate Adjustment
Factor
Corrected Flow Rate = Flow Rate
(unadjusted) x Appropriate Adjustment
Factor
Corrected KW Input = KW Input
(unadjusted) x Appropriate Adjustment
Factor
4
Verify that the selection is within design guidelines.The final unit selection is:
Quantity (1)
Cooling Capacity = 57.3Tons
Entering/Leaving ChilledWater
Temperatures = 55/45°F
ChilledWaterflow Rate (GPM) = 137.5
EvaporatorWater Pressure Drop = 16.5 ft.
System Power Input = 70.2 KW
Unit EER = 9.8
MINIMUM LEAVING CHILLEDWATER TEMPERATURE SET POINTS
The minimum leaving chilled water temperature set point for water is listed in the following table:
Table
Evaporator | Minimum Leaving Chilled Water | |
Temperature | Temperature Set point (°F) | |
Difference | CGAF- | CGAF- |
(Degrees F) | C20,C25,C30 | C40,C50,C60 |
6 | 40 | 39 |
8 | 41 | 39 |
10 | 42 | 40 |
12 | 43 | 40 |
14 | 44 | 41 |
16 | 45 | 41 |
18 | 46 | 42 |
1These are for units without HGBP, for units with HGBP, add 2°F to each minimum temperature in the table.
For those applications requiring lower set points, a glycol solution must be used. The minimum leaving chilled water set point for a glycol solution can be calculated using the following equation:
LCWS (Minimum) = GFT + 5 + ∆T (Evap)
# of stages of capacity.
LCWS = | Leaving ChilledWater | |
|
| Set point (F) |
GFT | = | Glycol Freezing |
∆T |
| Temperature (F) |
= | DeltaT (the difference |
between the temperature of the water entering and leaving the evaporator)
Solution freezing point temperatures can be found in the Performance Data section and the number of stages of capacity in the General Data section. For selection assistance, refer to the CGA Chiller Selection program.
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