Installation manual
035-16682-000-E-0303
78 Unitary Products Group
16. Power Exhaust Option with Modulating Dampers: The
power exhaust controls are powered through relay MR
(supply air motor relay) with a call for the supply fan.
Once powered, null pressure switch SSP1 (Switch, Static
Pressure - Building) provides floating point control of the
exhaust dampers. A contact closure is provided (COM to
HI) whenever the building pressure exceeds the building
pressure setpoint of SSP1, which applies a 24 VAC sig-
nal to wire 4 of the power exhaust damper actuator
(ACT2, OPEN damper). A contact closure is provided
(COM to LO) whenever the building pressure falls below
the building pressure setpoint minus the null span adjust-
ment of SSP1, which powers wire 3 of ACT2 (Close
Damper). As long as the building pressure floats within
the null range, neither contact is closed and ACT2 holds
the damper in position. When ACT2 opens more than 5°
an internal end switch (ACT2-1) closes to power the 10M
starter and engage the power exhaust fan motor. When
the power exhaust is disabled, ACT2’s spring return
closes the exhaust dampers and 10M opens to shut
down the exhaust fans.
17. Non-Modulating Power Exhaust Option:
The power
exhaust controls are powered through with a call for the
supply fan. Switch SSP1 (Switch Static Pressure - Build-
ing) closes whenever the building pressure exceeds set-
point. If the exhaust motor has been off for a minimum of
5 minutes, TDR (Time Delay Relay -5 minutes Anti-
Short-Cycle Timer) power is applied to the 10M starter to
engage the power exhaust fan motor. The outlet pres-
sure of the power exhaust fan forces the barometric
relief dampers open. Exhaust fan operation is continued
until the building static pressure falls below the SSP1
setpoint or until the supply fan call is satisfied. Gravity
closes the barometric relief dampers when the exhaust
fans are off.
18. Power Exhaust Option with Variable Frequency Drive
(VFD). The power exhaust controls are powered through
relay MR (supply air Motor Relay) with a call for the sup-
ply fan. The variable frequency drive is controlled by the
Building-Static-Pressure sensor (BSP) and the Power
exhaust Relay (PR).
Where the unit has a standard relay control, the VFD,
BSP, and PR are located in the exhaust blower section.
The BSP sensor translates the building pressure signal
to a VDC signal, which is the speed signal for the VFD.
Fine tuning is accomplished by setting parameters in the
VFD [ref: separate instruction]. Relay PR is pulled in by
power to MR, giving permission for the VFD to run.
On a unit with the Synthesys control, the BSP is located
in the electrical box. Its signal goes to the Synthesys
control, which sends a 2-10VDC speed signal to the
VFD. The Synthesys adjusts its output based on the
input from the BSP and the control setting entered in
Setpoints.
Both controls:
Pressure-tap tubing must be run from an appropriate
location in the building to the "high" port, and from a cus-
tomer-supplied wind proof outdoor pressure box to the
pressure sensor "low" port. Dampers on the VFD power
exhaust are gravity-closed and are not modulated.
The BSP signal is proportional with the difference
between outside ambient pressure and building pres-
sure. The VFD is set for a minimum speed of 33% and a
maximum of 100%. For the units with standard relay con-
trols, fine tuning of motor speed to building pressure can
be made by adjusting VFD parameters or the zero and
span settings in the pressure sensor. For Synthesys™
units, set the value in the Setpoints using the Palm Pilot.
The VFD parameters are factory set, specific for each
control system, and are detailed on a sticker by the drive.
The drive manual is shipped with the unit.
For smoke purge, etc., special connections: for standard
controls, consult a controls specialist familiar with your
local codes. On Synthesys control, your separately
installed network can call for overrides.
HEAD PRESSURE CONTROL
DESCRIPTION
The head pressure control option controls the speed of con-
denser fan #1 for low ambient mechanical cooling operation
of systems #1 and #2. System #3 on a 30 ton and system #3
and #4 on a 40 ton are locked out below 45°F ambient.
The option includes tow pressure transducers, a proportional
integral sequence controller and a one horsepower variable
frequency drive.
The pressure transducers are connected to the discharge line
of system #1 and #2. Each pressure transducer is equipped
with a switching diode on the white signal wire to eliminate
feedback through the transducer.
TABLE 42: SYSTEM MOISTURE INDICATOR
INDICATOR
COLOR
75° 100° 125°
Green (Dry) Below 30 Below 45 Below 60
Chartreuse 30 - 90 45 - 130 60 - 180
Yellow (Wet) Above 90 Above 130 Above 180