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11RT-PRC001-EN
Selection
Procedures
Cooling Capacity
Step 1 — Calculate the building’s total
and sensible cooling loads at design
conditions. Use the Trane calculation form
or any other standard accepted method.
Example: The following are the building
requirements:
a. Electrical Characteristics: 460/60/3
b. Summer Design Conditions: Entering
Evaporator Coil: 80° DB/ 67° WB
Outdoor Ambient: 95° DB
c. Total Cooling Load: 220 MBh
d. Sensible Cooling Load: 140 MBh
e. Airflow: 8000 cfm External Static
Pressure: 0.450 in wg
f. downflow configuration
g. economizer
Step 2 — As a starting point, a rough
determination must be made of the size
of the unit. The final selection will be
made after examining the performance
at the given conditions. Divide the total
cooling load by the nominal BTUH per ton
(12 MBh per ton); then round up to the
nearest unit size.
220 MBh / 12 MBh = 18.333 (approx 20
tons).
Step 3 — Examine gross capacity: Table
PD-4 shows that a YC*240B3 has a gross
cooling capacity of 246 MBh and 176
MBh sensible capacity at 95 DB ambient
and 8000 cfm with 80 DB/ 67 WB air
entering the evaporator.
To Find Capacity at Intermiediate
Conditions Not in the Table
When the design conditions are between
two numbers that are in the capacity
table, interpolation is required to
approximate the capacity.
Note: Extrapolation outside of the table
conditions is not recommended.
Step 4— Verify the unit will have enough
capacity to meet the building
requirements by determining the net
capacity, which includes heat generated
by the fan. In order to select the correct
unit, the fan motor heat must be
deducted from the gross coolingcapacity.
The amount of heat that the fan motor
generates is dependent on the effort by
the motor - cfm and static pressure.
To determine the total unit static pressure
add the external static pressure to the
additional static created by the added
features:
External Static (duct system) 0.45 wg
Standard Filter 2 in. (from Table PD-36)
0.11 g
Economizer (100% Return Air from Table
PD-20) 0.05 wg
Total static pressure 0.61
Note: The Evaporator Fan Performance
Table PD-20 has already accounted for
the pressure drop for standard filters and
wet coils (see note below Table PD-20).
Therefore the actual total static pressure
is 0.61-0.11 = 0.50 wg.
With 8000 cfm and 0.50 inches external
static pressure. Table PD-20 shows 3.96
bhp for this model. At these conditions,
the note below the table gives a formula
to calculate Fan Motor Heat:
3.15 X bhp = MBh
3.15 X 3.96 = 12.47 MBh.
Subtracting the fan motor heat from the
gross cooling capacity of the unit:
Net Total Cooling Capacity =
246 MBh - 12.47 = 251.53 MBh
Net Sensible Cooling Capacity =
176 MBh - 12.47 = 163.53 MBh.
Since the Net Total Cooling Capacity
meets the cooling load requirements of
220 MBh, we are satisfied with this
selection.
Heating Capacity
Step 1 — Calculate the building heating
load using the Trane calculation form or
other standard accepted method.
Step 2 — Size the system heating
capacity to match the calculated building
heating load. The following are building
heating requirements:
a. Total heating load of 165 MBh
b. 8000 cfm
c. Fuel - Natural gas
For the YC*240B3, there are two heating
capacities available, 250 MBh and 400
MBh input models shown in Table PD-35.
The output capacities of these furnaces
are 175 MBh and 300 MBh respectively.
The low heat model with 175 MBh best
matches the building requirements,
indicating a YC*240B3 should be
selected.
Air Delivery Selection
External static pressure drop through the
air distribution system has been
calculated to be 0.50 inches of water.
Enter Table PD-20 for a YC*240B3 at 8000
cfm and 0.50 static pressure. The
standard motor at high speed will give
the desired airflow.
Accessory Selection
Select accessories needed to
accommodate the application.