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Economizer Enthalpy Control
The economizer can be ordered with the optional differential
enthalpy control. With this option a solid-state humidity and
temperature sensing device is located in the return and
outdoor airstreams. These devices are labeled RAE and OAE
respectively. When the outdoor enthalpy is lower than the
return air enthalpy, the economizer operation will be initiated.
If the outdoor air enthalpy is higher than the return air, the
outdoor air damper position will be at the minimum setpoint.
See
OM 1141
for further information on the economizer
operation .
External Time Clock
You can use an external time clock as an alternative to (or in
addition to) the MicroTech III controller's internal scheduling
function. The external timing mechanism is set up to open and
close the circuit between field terminals 101 and 102 on Rebel
units 3 to 15 ton on larger Rebel units 16 to 28 ton they are
terminals 200 & 201. When the circuit is open, power is not
supplied to binary input DI3. This is the normal condition where
the controller follows the programmable internal schedule.
When the circuit is closed, power is fed to DI3. The MicroTech
III controller responds by placing the unit in the occupied mode,
overriding any set internal schedule.
Exhaust Fan Option
Economizer units may include exhaust fan options. For units
with CAV applications, the exhaust fans can be ordered as
staged control or they may be ordered with building pressure
control. The building pressure control option has an inverter
that runs the exhaust fan motors and is controlled by the static
pressure sensor number 2 (SPS2). The units are only available
with building pressure control on VAV units.
The exhaust fan motors are permanently lubricated and do not
require any additional periodic lubrication.
Proof-of-Airflow and Dirty Filter Switch
Proof of air flow is accomplished through Modbus
communications with the ECM motor/VFD for proof of air flow.
The Dirty filter switch senses the pressure difference across
the filter; from the entering air side of the filter to the leaving air
side of the filters. The switch is factory set at 1.0". When the
pressure difference across the filters is sensed at this value,
the dirty filter alarm will appear on the DDC controller. Typically
the dirty filter switch and the Duct High limit (DHL) are tied
together with Polly tubing to direct the proper static pressures
to the proper ports.
(Figure
WC. When this differential pressure is sensed the normally
closed contacts will open on the switch giving the DHL alarm at
the unit controller.
The DHL is factory set at 3.5". When this differential pressure
is sensed the normally closed contacts will open on the switch
giving the DHL alarm at the unit controller.
IM-1125-13 • REBEL ROOFTOPS
93). The DHL is Factory set at 3.5"
Figure 93: Pressure Tubing Diagram
Duct High Pressure Limit
The duct high pressure limit control (DHL) is provided on all
VAV units. The DHL protects the duct work, terminal boxes,
and the unit from over pressurization, which could be caused
by, for example, tripped fire dampers or control failure.
The DHL control opens when the discharge plenum pressure
rises to 3.5" wc (872 Pa). This setting should be correct for
most applications and should not be adjusted.
If the DHL switch opens, digital input ID9 on the Unit Control
Board will be de-energized. The MicroTech III controller then
shuts down the unit and enters the Off-Alarm state. The alarm
must be manually cleared before the unit can start again.
Refer to the operation manual supplied with your unit for more
information on clearing alarms (refer to
92
Unit Options
Unit Options
OM
1141).
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Troubleshooting
