9
SS-PRC003-EN
Selection
Procedure
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.
Step 2
— Size the equipment using Table
PD-1. Match the cooling loads at design
conditions.
Example: The following are the building
cooling requirements
a
Electrical Characteristics: 380-415/50/3
b
Summer Design Conditions: Entering
Evaporator Coil: 80 DB/67 WB
(27 DB/19 WB C)
Outdoor Ambient: 95° F (35° C)
c
Total Cooling Load: 75 MBh (22 kW)
d
Sensible Cooling Load: 53 MBh
(15.5 kW)
e
Airflow: 3000 cfm (5097 m
3
/h)
External Static Pressure: 0.77 in.
(192.5 Pa)
Table PD-1 shows that a TTA075A
matched with a TWE075A has a gross
cooling capacity of 86.5 MBh (25.3 kW)
and 64.4 MBh (18.8 kW) sensible
capacity at 95 DB (35° C) ambient and
3000 cfm (5097 m
3
/h) and 80 DB/67 WB
(27 DB/19 WB) air entering the
evaporator.
To find the net cooling capacities, fan
motor heat must be subtracted.
Determine the total unit static pressure:
In.
Pa
External Static
0.77 193
Standard Filter
0.10
25
Supplementary
Electric Heat
0.23
57
Total Static Pressure
1.10 275
Note: The Evaporator Fan Performance
Table has included the effect of a 1 in.
(250 Pa) filter already. Therefore, the
actual Total Static Pressure is 1.10 - 0.10 =
1.00 in. (275 - 25 = 250 Pa).
With 3000 cfm (5097 m
3
/h) and 1.00
inches (250 Pa), Table PD-29 shows a
1.17 bhp (0.8 kW).
Note: The formula below the table can
be used to calculate Fan Motor Heat,
3.5 x Bhp = MBh
3.5 x 1.17 = 4.10 MBh
(1.375 x (kW) = kW)
(1.375 x 0.8 = 1.1 kW)
Net Total Cooling Capacity =
86.5 MBh – 4.10 = 82.4 MBh
18.8 - 1.1 = 17.7 kW
Net Sensible Cooling Capacity =
64.4 MBh – 4.10 = 60.3 MBh
25.3 - 1.1 = 24.2 kW
Heating Capacity
Step 1
— Calculate the building heating
load.
Step 2
— Size the system heating
capacity to match the calculated building
heating load. The following are building
heating requirements:
a
Total Heating Load at 97.0 MBh (28.4 kW)
b
3000 cfm (5097 m
3
/h)
c
Electric Supplementary Heaters
Table PD-39, the 34.88 kW heater has a
capacity of 119,045 btu. From Table
ED-5, the 34.88 kW indicates the heater
model number is BAYHTRL435A. This
heater will adequately cover the
building’s heating requirement.
Air Delivery Selection
External static pressure drop through
the air distribution system has been
calculated to be 0.77 inches (192.5 Pa) of
water gauge. From Table PD-38 static
pressure drop through the electric
heater is 0.23 inches (57.5 Pa) of water
(0.77 + 0.23 = 1.00 in.) (192.5 + 57.5 = 250
Pa). Enter Table 39-1 for TWE075AD at
3000 cfm (5097 m
3
/h) and 1.00 static
pressure (250 Pa). The standard motor at
821 rpm will give the desired airflow.
