Bryant 581C - Manual (Page 182)

182
SELECTION PROCEDURE (With 579F180 Example)
I DETERMINE COOLING AND HEATING REQUIRE-
MENTS AT DESIGN CONDITIONS.
Given:
Required Cooling Capacity . . . . . . . . . . . . . . 170,000 Btuh
Sensible Heat Capacity . . . . . . . . . . . . . . . . 111,000 Btuh
Required Heating Capacity. . . . . . . . . . . . . . 200,000 Btuh
Condenser Entering Air Temp. . . . . . . . . . .95 F (Summer)
Evaporator Entering Air Temp. . . . . . . . . . . . . . . 80 F edb,
67 F ewb
Evaporator Air Quantity . . . . . . . . . . . . . . . . . . . 4,500 cfm
External Static Pressure . . . . . . . . . . . . . . . . . . . 0.6 in. wg
Electrical Characteristics (V-Ph-Hz) . . . . . . . . . . 460-3-60
Vertical discharge unit with optional EconoMi$er IV
required.
edb — Entering dry-bulb
ewb — Entering wet-bulb
II SELECT UNIT BASED ON REQUIRED COOLING
CAPACITY.
Enter Cooling Capacities table for 579F180300 (page 152)
at condenser entering temperature 95 F, evaporator air
entering at 4,500 cfm and 67 F wb. The 579F180300 unit
will provide a total cooling capacity of 179,000 Btuh and a
sensible heating capacity of 117,000 Btuh. For air entering
evaporator at temperatures other than 80 F edb, calculate
sensible heat capacity correction as required using the for-
mula in the notes following the Cooling 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 HEATING CAPACITY OF UNIT TO PROVIDE
DESIGN CONDITION REQUIREMENTS.
In the ARI Heating Capacities and Efficiencies table
(page 12) note that the 579F180300 will provide an
output capacity of 243,000 Btuh, which is adequate for the
given application.
IV DETERMINE FAN SPEED AND POWER REQUIRE-
MENTS AT DESIGN CONDITIONS.
Before entering the Fan Performance tables, calculate the
total static pressure required based on unit components.
From the given and the Accessory/FIOP Static Pressure
table on page 164 find:
Enter the Fan Performance table 579F180300 (page 161)
at 4,500 cfm and 0.64 in. wg external static pressure. By
interpolation, find that the rpm is 1017 and the watts are
1743.
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 = 1743
Determine net cooling capacity using the following
formula:
Net capacity = Gross capacity – IFM heat
= 179,000 Btuh – 1743 Watts
= 179,000 Btuh – 5947 Btuh
= 173,053 Btuh
Net sensible capacity = 117,000 Btuh – 5947 Btuh
= 111,053 Btuh
The calculations show that a 579F180300 unit with the
standard motor and standard low-medium static drive is
the correct selection for the given conditions.
External static pressure 0.60 in. wg
EconoMi$er IV static pressure 0.04 in. wg
Total static pressure 0.64 in. wg
(3.412
Btuh
)
Watts