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238
SELECTION PROCEDURE
I DETERMINE COOLING AND HEATING REQUIRE-
MENTS AT DESIGN CONDITIONS.
Given:
Required Gross Cooling
Capacity (TC) . . . . . . . . . . . . . . . . . . . . . . 168,000 Btuh
Gross Sensible Heat
Capacity (SHC). . . . . . . . . . . . . . . . . . . . . 121,000 Btuh
Required Heating Capacity. . . . . . . . . . . . . . 190,000 Btuh
Condenser Entering Air
Temperature . . . . . . . . . . . . . . . . . . . . . . .95 F Summer
Indoor Air Temperature. . . . . . . . . . . . 80 F edb, 67 F ewb
Evaporator Air Quantity . . . . . . . . . . . . . . . . . . .6,000 cfm
External Static Pressure . . . . . . . . . . . . . . . . . . 1.40 in. wg
Electrical Characteristics (V-Ph-Hz) . . . . . . . . . . 230-3-60
II SELECT UNIT BASED ON REQUIRED COOLING
CAPACITY.
Enter Cooling Capacities table for 581A180 at condenser
entering temperature of 95 F, evaporator air quantity of
6,000 cfm, and indoor air temperature of 67 F. The
581A180 unit will provide a total cooling capacity of
190,000 Btuh and a SHC of 136,000 Btuh. For evaporator
air temperatures other than 80 F, calculate SHC correction
using formula in notes under cooling capacity tables.
Unit meets design conditions for TC and SHC.
NOTE: Unit ratings are gross capacities and do not
include the effect of indoor fan motor heat. To calculate net
capacities, see Step V.
III SELECT HEATING CAPACITY OF UNIT TO PROVIDE
DESIGN CONDITION REQUIREMENT.
In Heating Capacities and Efficiencies table, note that
581A180275 unit will provide 223,000 Btuh with an input
of 275,000 Btuh.
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.
Tabulated fan performance includes filters and wet evapo-
rator coil. Refer to Accessory/FIOP Static Pressure table
for added pressure drops.
Calculate pressure drop:
Design External Static Pressure 1.40
EconoMi$er IV 0.07
1.47 in. wg (ESP)
Enter Fan Performance tables for 581A180 (low heat
units) at 6,000 cfm and 1.47 in. wg. The rpm is 1228 and
the Bhp is 4.73. The factory-installed 5 hp motor and alter-
nate high-static drive are sufficient for this operation.
V DETERMINE NET COOLING CAPACITIES.
Cooling capacities are gross capacities and do not include
indoor (evaporator) fan motor (IFM) heat. To determine
input power to the motor, enter the Fan Performance
tables for 581A180 (low heat units) at 6,000 cfm and
1.47 in. wg. Input watts to the motor are 4035.
Determine net cooling capacity and net sensible cooling
capacity using the following formulas:
IFM Heat = Input Watts x 3.412 Btuh/Watt
= 4035 x 3.412
= 13,767 Btuh
Net Capacity = Gross Capacity – IFM Heat
= 190,000 – 13,767
= 176,233 Btuh
Net Sensible Cap. = Gross Sensible Cap. – IFM Heat
= 136,000 – 13,767
= 122,233 Btuh
The calculations show that a 581A180275 unit is the cor-
rect selection for the given conditions.
VI SELECT THE UNIT THAT CORRESPONDS TO POWER
SOURCE AVAILABLE.
The electrical data table shows that the 230-3-60 unit is
available.