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35
SELECTION PROCEDURE (with 558F048 example)
I DETERMINE COOLING AND HEATING REQUIRE-
MENTS AT DESIGN CONDITIONS:
Given:
Cooling Capacity Required . . . . . . . . . . . . . . 44,000 Btuh
Sensible Heat Capacity . . . . . . . . . . . . . . . . . 32,000 Btuh
Required Heating Load . . . . . . . . . . . . . . . . . 50,000 Btuh
Condenser Entering-Air
Temperature . . . . . . . . . . . . . . . . . . .95 F Edb/78 F Ewb
Evaporator Entering-Air
Temperature . . . . . . . . . . . . . . . . . . .80 F Edb/67 F Ewb
Evaporator Air Quantity . . . . . . . . . . . . . . . . . . . .1600 cfm
External Static Pressure . . . . . . . . . . . . . . . . . 0.75 in. wg
Heating Capacity . . . . . . . . . . . . . . . . . . . . . . 50,000 Btuh
Power Supply (V-Ph-Hz) . . . . . . . . . . . . . . . . . . . 230-3-60
Edb — Entering dry bulb
Ewb — Entering wet bulb
II SELECT UNIT BASED ON REQUIRED COOLING
CAPACITY.
Enter cooling capacity table for 558F048 on page 36 at
condenser entering dry bulb temperature 95 F, air entering
evaporator at 1600 cfm, 80 F edb and 67 F ewb. The
558F048 unit will provide a total cooling capacity
of 50,500 Btuh, and a sensible heating capacity of
35,600 Btuh. For evaporator-air temperatures other than
80 F edb, calculate sensible heat capacity correction as
required using the formula in the notes following the Cool-
ing Capacities tables.
NOTE:
Unit ratings are gross capacities and do not
include the effect of evaporator-fan motor heat. To calcu-
late net capacities, see Step V.
III SELECT ELECTRIC HEAT.
Heating load required is 50,000 Btuh.
Enter the Electric Heating Capacities table on page 64 for
the 558F048 at 230-3-60. The 16.0 kW electric heater
most closely satisfies the heat required.
To calculate kW at 230 v, use the multiplication factors
table on page 64.
16.0 x .918 = 14.7 kW
16.0 x .918 x 3.413 = 50,115 Btuh gross capacity
IV DETERMINE FAN SPEED AND MOTOR HORSEPOWER
REQUIREMENTS AT DESIGN CONDITIONS.
Enter Accessory/FIOP Static Pressure table on page 61 at
selected unit size and heater kW.
Find that at given air quantity (1600 cfm), pressure loss is
0.09 in. wg.
Before entering the Fan Performance tables, calculate the
total static pressure required based on unit components.
From the given find:
External static pressure 0.75 in. wg
16 kW Heater static pressure 0.09 in. wg
Total static pressure 0.84 in. wg
Enter Fan Performance table for the alternate motor verti-
cal discharge unit 558F048 on page 41. At 1600 cfm and
0.84 in. wg external static pressure, the fan speed is
1038 rpm and the watts are 877. (Interpolation is neces-
sary.) The alternate motor and drive is suitable.
V DETERMINE NET COOLING CAPACITY.
Cooling capacities are gross capacities and do not include
indoor (evaporator) fan motor (IFM) heat. Use the watts
input power to the motor calculated in “Section IV” above.
IFM watts = 877
Determine net cooling capacity using the following
formula:
Net sensible capacity = 35,600 Btuh – 2992 Btuh
= 32,608 Btuh
As demonstrated above, the 558F048 with the 16.0 kW
electric heater and an alternate motor meets the cooling
capacity, sensible heating capacity, and heating capacity
requirements.
50,000 Btuh
= 14,654 Watts of heat required
3.412 Btu/W
= 14.7 kW
Net capacity = Gross capacity – IFM heat
= 50,500 Btuh – 877 Watts (3.413
Btuh
)
Watt
= 50,500 Btuh – 2992 Btuh
= 47,508 Btuh
0TFQ004-012
558F036-150