Bryant 580D - Manual (Page 25)

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 . . . . . . . . . . . . . . . 114,000 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 economizer
required.
edb — Entering dry-bulb
ewb — Entering wet-bulb
II SELECT UNIT BASED ON REQUIRED COOLING
CAPACITY.
Enter Cooling Capacities table for 579F180 (page 29) at
condenser entering temperature 95 F, evaporator air en-
tering at 4,500 cfm and 67 F wb. The 579F180
unit will provide a total cooling capacity of 180,000 Btuh
and a sensible heating capacity of 120,000 Btuh. For air
entering evaporator at temperatures other than 80 F edb,
calculate sensible heat capacity correction as required us-
ing the formula in the notes following the Cooling Capaci-
ties 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 and Efficiencies table (page 7)
note that the 579F180 300 will provide an output capac-
ity 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, cal-
culate the total static pressure required based on unit com-
ponents. From the given and the Accessory/FIOP Static
Pressure table on page 52 find:
External static pressure 0.60 in. wg
Economizer static pressure 0.04 in. wg
Total static pressure 0.64 in. wg
Enter the Fan Performance table 579F180 (page 47) at
4,500 cfm and 0.64 in. wg external static pressure. By in-
terpolation, find that the rpm is 988 and the watts are 1334.
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 calculated in Section IV above.
IFM Watts = 1334
Determine net cooling capacity using the following
formula:
Net capacity = Gross capacity – IFM heat
= 180,000 Btuh – 1334 Watts
Btuh
(3.412 )
Watts
= 180,000 Btuh – 4552 Btuh
= 175,448 Btuh
Net sensible capacity = 120,000 Btuh – 4552 Btuh
= 115,448 Btuh
The calculations show that a 579F180 unit with the stand-
ard motor and standard low-medium static drive is the cor-
rect selection for the given conditions.
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