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RLC-PRC016-EN
Selection
Procedure
The chiller capacity tables, P-1 through
P-12, cover the most frequently
encountered leaving water
temperatures. The tables reflect a 10°F
(6°C) temperature drop through the
evaporator. For temperature drops other
than 10°F (6°C), refer to Table F-1, and
apply the appropriate Performance Data
Adjustment Factors. For chilled brine
selections, refer to Figures F-2 and 3 for
Ethylene and Propylene Glycol
Adjustment Factors.
To select a Trane air-cooled Series R
™
chiller, the following information is
required:
1. Design load in tons of refrigeration
2. Design chilled water temperature drop
3. Design leaving chilled water
temperature
4. Design ambient temperature
Evaporator flow rates can be determined
by using the following formulas:
GPM =
Tons x 24
Temperature Drop (Degrees F)
OR L/S =
kW (Capacity) x .239
Temperature Drop (Degrees C)
NOTE: Flow rates must fall within the
limits specified in Table G-1 (for GPM or
for l/s).
Selection Example
Given:
Required System Load = 115 Tons
Leaving Chilled Water Temperature
(LCWT) = 44°F Chilled Water
Temperature Drop = 10°F Design
Ambient Temperature = 95°F
Evaporator Fouling Factor = 0.0001
1. To calculate the required chilled water
flow rate we use the formula given
below:
GPM =
115 Tons x 24 = 276 GPM
10°F
2. From Table P-6 (RTAA Performance
Data), an RTAA 125 at the given
conditions will produce 120.1 tons
with a compressor power input of
136.3 kW and a unit EER of 9.8.
3. To determine the evaporator pressure
drop we use the flow rate (GPM) and
the evaporator water pressure drop
curves, Figure F-1. Entering the curve
at 276 GPM, the pressure drop for a
nominal 125 ton evaporator is 18 feet.
4. 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 from Tables F-1, F-2, and/or F-3
should be applied at this point.
For example:
Corrected Capacity = Capacity
(unadjusted) x Glycol Flow Rate
Adjustment Factor
5. The final unit selection is:
• QTY (1) RTAA 125
• Cooling Capacity = 120.1 tons
• Entering/Leaving Chilled Water
Temperatures = 54/44°F
• Chilled Water Flow Rate = 276 GPM
• Evaporator Water Pressure Drop = 18
feet
• Compressor Power Input = 136.3 kW
• Unit EER = 9.8
Minimum Leaving Chilled Water
Temperature Setpoint
The minimum leaving chilled water
temperature setpoint for water is 40°F.
For those applications requiring lower
setpoints, a glycol solution must be used.
Contact the local Trane sales engineer for
additional information.