Bryant 579F - Manual (Page 21)

SELECTION PROCEDURE (with 579F180270 example)
I DETERMINE COOLING AND HEATING REQUIRE-
MENTS AT DESIGN CONDITIONS:
Given:
Total Cooling Capacity Required . . . . . . . . 173,000 Btuh
Sensible Heat Capacity . . . . . . . . . . . . . . . . 114,000 Btuh
Required Heating Capacity . . . . . . . . . . . . . 200,000 Btuh
Condenser Entering Air Temperature . . . . . . . . . . . . 95 F
Evaporator Entering Air Temperature . . . . . . . . 80 F Edb/
67 F Ewb
Evaporator Air Quantity . . . . . . . . . . . . . . . . . . . 4500 cfm
External Static Pressure . . . . . . . . . . . . . . . . . . 0.8 in. wg
Power Supply (V-Ph-Hz) . . . . . . . . . . . . . . . . . . 460-3-60
edb — Entering dry bulb
ewb — Entering wet bulb
II DETERMINE UNIT SIZE:
Select unit based on cooling requirements.
Enter Gross Cooling Capacities tables on pages 22-29 at
condenser entering temperature of 95 F, evaporator air en-
tering at 4500 cfm and 80 F db and 67 F wb. The 579F180
unit will provide a gross cooling capacity of 180,200 Btuh
and a sensible heat capacity of 120,000 Btuh. For evapo-
rator air temperatures other than 80 F, calculate sensible
heat capacity correction, using the formula found in Note 3
following the Gross Cooling Capacities tables.
NOTE: Unit ratings are gross capacities and do not include
the effect of evaporator-fan motor heat. To calculate net
capacities, see Step V.
III SELECT HEATING CAPACITY OF UNIT TO PROVIDE
DESIGN CONDITION REQUIREMENTS:
In the Heating Capacities table on page 5, note that unit
579F180270 will provide output capacity of 216,000 Btuh,
which is adequate for the given application.
IV DETERMINE FAN SPEED AND POWER REQUIRE-
MENTS AT DESIGN CONDITIONS:
Before entering the Air Delivery tables on pages 30-48,
calculate the total static pressure required based on unit
components. From the given and the Pressure Drop table
on page 50, find:
External static pressure 0.80 in. wg
Economizer 0.04 in. wg
Total Static Pressure 0.84 in. wg
Enter the Air Delivery table on page 46 for standard
579F180 460-v unit at 4,500 cfm and 0.84 in. wg external
static pressure. By interpolation, find that the rpm is 1080
and the bhp is 1.75. The factory-installed standard motor
will suffice.
V DETERMINE NET COOLING CAPACITY:
Cooling capacities are gross capacities and do not include
indoor (evaporator) fan motor (IFM) heat. Use the watts in-
put power to the motor from the Air Delivery table.
IFM Watts = 1554
Determine net capacity using the following formula:
Net capacity = gross capacity – IFM heat
Btuh
= 180,200 Btuh – 1554 Watts (3.412 )
Watt
= 180,200 Btuh – 5302 Btuh
Net capacity = 174,898 Btuh
Net sensible capacity = 120,000 – 5302 Btuh
Net sensible capacity = 114,698 Btuh
The 579F180270 is the correct selection for the given
conditions.
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