Bryant 551A, User Manual

Page: 118 / 170

118
SELECTION PROCEDURE (with 559F180 example)
I DETERMINE COOLING REQUIREMENTS AT DESIGN
CONDITIONS.
Given:
Required Cooling Capacity . . . . . . . . . . . . . . 170,000 Btuh
Sensible Heat Capacity . . . . . . . . . . . . . . . . 111,000 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 559F180 (page 119) at
condenser entering temperature 95 F, evaporator air enter-
ing at 4,500 cfm and 67 F wb. The 559F180 unit will pro-
vide a total cooling capacity of 178,000 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 IV.
III 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 125 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 559F180 (page 123) at
4,500 cfm and 0.64 in. wg external static pressure. By
interpolation, find that the rpm is 905 and the watts are
1503.
IV 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 III above.
IFM Watts = 1503
Determine net cooling capacity using the following
formula:
Net capacity = Gross capacity – IFM heat
= 178,000 Btuh – 1503 Watts
= 178,000 Btuh – 5128 Btuh
= 172,872 Btuh
Net sensible capacity = 117,000 Btuh – 5128 Btuh
= 111,872 Btuh
The calculations show that a 559F180 unit with the
standard motor and standard low-medium static drive is
the correct selection for the given conditions.
(3.412
Btuh
)
Watts
0
T
F
Q
0
04
-0
12
55
9F1
80-
30
0