Bryant Single Package Rooftop Electric Heating/Electric Cooling Unit 558D - Manual (Page 15)

d. After installation is complete, calculate the mini-
mum airflow across the economizer. To calculate the
minimum airflow, the following data is needed:
total cfm (cfm
3
), temperature of the total cfm (T
3
),
temperature of the return air (T
2
), and tempera-
ture of the entering outside air (T
1
). Cfm
1
is the
outside air cfm, which will be the minimum airflow.
Insert the data into the following equations:
T
1
(cfm
1
) + T
2
(cfm
2
)
= T
3
cfm
3
cfm
2
= (cfm
3
− cfm
1
)
Therefore:
T
1
(cfm
1
) + T
2
(cfm
3
− cfm
1
)
= T
3
cfm
3
Use this equation to determine cfm
1
, which is the
minimum airflow across the economizer.
(T
3
−T
2
) cfm
3 cfm
1
=
(T
1
− T
2
)
If cfm
1
does not match the desired minimum air-
flow from Step 1, readjust the minimum position
setting screw.
6. Determine the enthalpy changeover set point from
Fig. 28. The enthalpy changeover set point should be
set to return the outdoor air damper to the minimum
position when enthalpy rises above the set point. The
settings are A, B, C, and D. Set the enthalpy changeover
per the setting in Fig. 29.
7. Replace outdoor-air opening panel using screws from
Step 2. Replace filter access panel. Ensure the filter
access panel slides along the tracks and is securely en-
gaged. See Fig. 30.
8. Fasten hood top and side plate assembly (Fig. 31) to
outdoor-air opening panel with screws provided.
9. Slide outdoor-air inlet screen into screen track on hood
side plate. While holding screen in place, fasten screen
retainer to hood using screws provided. See Fig. 32.
NOTE: Refer to Fig. 33 for PARABLADE economizer baro-
metric relief damper characteristics.
MINIMUM POSITION
OPEN
3 1
T P
P1 T1 4 2 5
S S
O
D
C TR
B
REV
. B
198818A
% H U M I D I T Y 90 70 60 30 10 D
C
B
A
60
65
70
75
55
50
85
80
DAMPER
DAMPER CLOSED
OPEN OUTDOOR TEMP
.
° F
REV. 97-3672
CW–SETPOINTS–CCW
CONT
A
CTS SHO
WN IN HIGH ENTHALPY
RUSH A
T 24V
AC
3 mA
MIN.
A T 1 1 VDC
CONT
ACT RA
TINGS: 1.5A
RUN, 3.5A
IN
OR UNPOWERED ST
AT
E
1
2
3
TR
TR1
24V
AC
ENTHALPY
CONTROL
Fig. 25 — Outdoor-Air Thermostat/
Enthalpy Control Installation
OAT — Outdoor-Air Thermostat
NOTE: See unit wiring diagram for details.
Fig. 26 — Wiring Connections for Outdoor-Air Thermostat
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00 100 200 300 400 500 600 700 800
CFM
PRESSURE DROP
(in. wg)
Fig. 27 — Durablade Economizer Barometric Relief
Damper Characteristics
—15—