Trane CG-PRC007-EN - Manual (Page 14)

CG-PRC007-EN 14
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
550/590-98) and for units operating at
altitudes that are significantly greater
than sea level, refer to the “Performance
Adjustment Factors” section and apply
the appropriate adjustment factors. For
chilled brine selections, refer to the
“Performance Adjustment Factors”
section for ethylene glycol adjustment
factors.
To select a Trane air-cooled chiller, the
following information is required:
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 Chilled Water Temperature
(LCWT) = 45°F
Chilled Water Temperature Drop = 10°F
Design Ambient Temperature = 95°F
Evaporator Fouling Factor = 0.0001
System Power Input = 70.2 KW
Unit EER = 9.8
MINIMUM LEAVING CHILLED WATER
TEMPERATURE SET POINTS
The minimum leaving chilled water
temperature set point for water is listed
in the following table:
Table SP-1 — Minimum Leaving Chilled
Water Temperature Set points for Water
1
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
1 These 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 Chilled Water
Set point (F)
GFT = Glycol Freezing
Temperature (F)
∆ T
= Delta T (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.
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 CGAF-C60 at the given
conditions will produce 57.3 tons with a
system power input of 70.2 kw and a unit
EER of 9.8
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) CGAF-C60
Cooling Capacity = 57.3 Tons
Entering/Leaving Chilled Water
Temperatures = 55/45°F
Chilled Waterflow Rate (GPM) = 137.5
Evaporator Water Pressure Drop = 16.5
ft.