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8 SSP-PRC001-EN
Cooling Capacity
Step 1.
Calculate the building’s total and
sensible cooling loads at design
conditions.
Step 2.
Size the equipment using Table 3.
Match the cooling loads at design
conditions.
Example: The following are the
building 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
c. Sensible Cooling Load: 64
MBh
d. Airflow: 3000 cfm
External Static Pressure:
0.77 inches of water gauge
Table 3 shows that TWA090A4 with
TWE090A has a gross cooling
capacity of 91.1 MBh and 65.9 MBh
sensible 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.
Determine the total unit static
pressure:
External Static Duct System 0.77 in.
Standard Filter 1 in. 0.10 in.
Supplementary Electric Heat 0.23 in.
Total Static Pressure 1.10 in.
Note: The Evaporator Fan
Performance Table has
included the effect of a 1 in.
filter already. Therefore, the
actual Total Static Pressure is
1.10 - 0.10 = 1.00 in. With
3000 cfm and 1.00 in.,
Table 17 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 heating load
using the Trane calculation form or
any other standard accepted
method.
Step 2.
Size the equipment using Table 11 to
match the heating loads at design
conditions. The following 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 11 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 32, the 14.96 kW heater
has a capacity of 51,058 Btu/h.
From Table 37, the 14.96 kW heater
at 460V indicates the heater model
number 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 in. of
water gauge.
From Table 31 static pressure drop
through the electric heater is 0.12 in.
of water (0.77 + 0.12 = .89 in.)
Enter Table 17 for TWE090A4 at 3000
cfm and .90 static pressure. The
standard motor at 790 RPM will give
the desired airflow.
Selection Procedure