SSP-PRC001-EN 7
Cooling Capacity
Step 1 — Calculate the building’s total
and sensible cooling loads at design
conditions.
Step 2 — Size the equipment using
Table PD-1. Match the cooling loads at
design conditions.
Example: The following are the build-
ing cooling requirements:
a. Electrical Characteristics: 460/60/3
b. Summer Design Conditions:
Entering Evaporator Coil:
80° F DB/67° F WB
Outdoor Ambient: 95° F
Total Cooling Load: 90 MBh
d. Sensible Cooling Load: 64 MBh
e. Airflow: 3000 cfm
External Static Pressure:
0.77 inches of water gauge
Table PD-1 shows that TWA090A4
with TWE090A has a gross cooling ca-
pacity of 91.1 MBh and 65.9 MBh sen-
sible capacity at 95° F DB ambient and
3000 cfm with 80° F DB/67° F WB air
entering the evaporator.
To find the net cooling capacities, fan
motor heat must be subtracted. Deter-
mine the total unit static pressure:
External Static0.77 in.
Standard Filter 1 in.0.10 in.
Supplementary Electric Heat 0.23 in.
Total Static Pressure1.10 in.
Note: The Evaporator Fan Perfor-
mance Table has included the effect of
a 1 in. filter already. Therefore, the ac-
tual Total Static Pressure is
1.10 - 0.10 = 1.00 in. With 3000 cfm and
1.00 inches, Table PD-19 shows a 1.17
Bhp.
Note: The formula below the table can
be used to calculate Fan Motor Heat:
3.5 X Bhp = MBh
3.5 X 1.17 = 4.09 MBh
Net Total Cooling Capacity =
91.1 MBh - 4.09 = 87.01 MBh
Net Sensible Cooling Capacity =
65.9 MBh - 4.09 = 61.81 MBh
Heating Capacity
Step 1 — Calculate the building heat-
ing load using the Trane calculation
form or any other standard accepted
method.
Step 2 — Size the equipment using
Table PD-13 to match the heating
loads at design conditions. The follow-
ing are building heating requirements:
a. Total Heating Load: 95.0 MBh
b. Outdoor Ambient (Winter): 17° F DB
c. Indoor Return Temperature: 70° F
DB
d. Airflow: 3000 cfm
Table PD-13 indicates the mechanical
heating portion of the heat pump will
provide 54.8 MBh for the winter design
conditions.
Step 3 — Because 54.8 MBh is less
than the building’s required heating
capacity, a supplementary heater
must be selected. 95.0 - 54.8 = 40.2
MBh minimum heater capacity.
From Table PD-36, the 14.96 kw heater
has a capacity of 51,058 Btuh. From
Table ED-5, the 14.96 kw heater at
460V indicates the heater model num-
ber is BAYHTRL415A. This heater will
be adequate to cover the residual heat
capacity needed for the application.
Air Delivery Selection
External static pressure drop through
the air distribution system has been
calculated to be 0.77 inches of water
gauge. From Table PD-35 static pres-
sure drop through the electric heater is
0.12 inches of water (0.77 + 0.12 = .89
in.) Enter Table PD-19 for TWE090A4 at
3000 cfm and .90 static pressure. The
standard motor at 790 RPM will give
the desired airflow.
Selection
Procedure
