Trane CCRC20, Manual

Page: 13 / 101

Selection
Procedure
PKG-PRC002-EN 13
Refer to Table PD-1 on page 31 to obtain
the capacity correction factors for +6% of
nominal cfm:
Cooling capacity multiplier = 1.009
Sensible capacity multiplier = 1.027
Multiply the capacities by the correction
factors:
419 MBh x 1.009 = 422.8 MBh
309 MBh x 1.027 = 317.3 MBh
The SCWF 35 meets the total and
sensible design requirements.
Multiply the delta T of 9.7 F, by the cooling
capacity correction factor of 1.009 to
obtain new delta T of 9.79 and add this to
the entering water temperature to obtain
the actual leaving water temperature of
94.79 F.
Determine static air pressure drops
through the accessories at the design cfm
from Chart PD-3 on page 22:
4-row waterside economizer = 0.37 in.
Medium velocity filters = 0.28 in.
add this to the 2.5 inch duct static
pressure for a total external static
pressure of 3.15 inches.
Refer to the fan curve with inlet guide
vanes, Chart PD-38 on page 43, to
determine approximate brake
horsepower and fan rpm:
Fan brake horsepower = 16 bhp
Fan rpm = 1020 rpm
Determine net capacities by subtracting
fan motor heat from gross capacities:
2.8 x 16 bhp = 44.8 MBh
Net total capacity = 422.8 MBh -
44.8 MBh = 378.0 MBh
Net sensible capacity = 317.3 MBh -
44.8 MBh = 272.5 MBh
Determine waterside economizer
capacity by referring to Table PD-17 on
page 42. Use entering air of 80/67 and
entering water temperature of 55 deg F
at 105 gpm. The table provides a gross
total capacity of 282.1 MBh and gross
sensible capacity of 277.2 MBh and
60.4 deg F leaving water temperature at
nominal cfm.
Determine gross capacities at design cfm
by applying the cfm correction factors
from waterside economizer from Table
PD-1 on page 31. Use the following
correction factors:
282.1 MBh x 1.009 = 284.6 MBh
277.2 MBh x 1.027 = 284.7 MBh
Apply the cooling correction factor to
water delta T to determine new delta T of
5.45 F.
Determine net capacities by subtracting
fan motor heat for net total capacity of
239.8 MBh and net sensible capacities of
239.9 MBh.
Self-Contained
Selection Example
Design Conditions
Total gross capacity required =
420 MBh = 35.2 Tons
Total sensible capacity required =
315 MBh
Entering air temperature = 80/67
Entering water temperature = 85
Water flowrate = 105 gpm
Airflow = 14840 cfm at 2.5-inch
duct static pressure
Unit includes:
Inlet guide vanes
Waterside economizer
Medium velocity throwaway filters
Unit Selection
Tentatively select a 35 ton unit
Model SCWF 35.
Refer to Table PD-19 on page 43 to obtain
gross total and sensible unit capacities,
and gpm at the design conditions:
Total capacity = 419.0 MBh
Sensible capacity = 309.0 MBh
Leaving water temperature = 94.7 F
Since the design cfm is greater than the
nominal cfm, adjust the capacities and
condenser water delta T to reflect the
higher cfm:
design cfm 14840 = +6% of nom. cfm
nominal 14000
cfm