AAON RM-030 - Manual (Page 20)

20
II. VAV (Variable Air Volume) SYSTEMS
NOTE: VAV BOXES AND CONTROLS ARE
SUPPLIED BY OTHERS FOR FIELD INSTALLATION.
When a call for cooling is received, the controller board
stages on compressors to maintain a field set supply air
temperature. As different zones become satisfied their
VAV boxes will close. This in turn causes the supply duct
pressure to rise. The VAV controller board senses this
increase in pressure and modulates the supply fan speed
to maintain the required field set supply air pressure
setpoint.
Normally VAV units are cooling only units. There are
certain applications where electric or gas heat is used to
provide morning warmup. When gas or electric heat is
used for morning warmup the airflow will not be allowed
to vary. The fan speed control will be disabled until a call
for cooling is received, then the heating system will be
locked out and VAV will be enabled.
III. POWER EXHAUST OPTIONS
When space over pressurization occurs, due to econo-
mizer operation, a power exhaust will be utilized to
provide relief.
A. When three position economizer is called for, an
On/Off power exhaust will be used.
POWER EXHAUST w/ 3 POSITION ECON.
In the unit "OFF" or in the minimum economizer
position, the power exhaust fan is off. When the unit
goes to 100% outside air operation, the power
exhaust fan motor starts and operates until the unit
is shut off or the economizer goes back to minimum
position.
The end switch located on the economizer outside air
damper section, is field adjustable to allow for differences
in building design. The switch engages and disengages
the power exhaust motor(s) through a contactor. The end
switch is included in the 24 VAC circuit.
B. Full modulating economizer, a full modulating power
exhaust will control the amount of actual exhausted
air by means of a building sensing pressure control
which opens or closes according to desired pressure
in the space.
POWER EXHAUST w/ FULL MODULATING ECON.
In the unit "OFF" or in the minimum economizer
position, the power exhaust is off. As the economizer
begins to modulate open, an end switch (adjustable)
closes which starts the power exhaust fan motor.
The power exhaust operates until the economizer
modulates below the end switch setting or the unit is
shut off.
POWER EXHAUST w/ FULL MODULATING ECON.
WITH BUILDING PRESSURE CONTROL
In the unit "OFF" or in the minimum economizer position
the power exhaust is off. As the economizer begins to
modulate open, an end switch (adjustable) closes which
starts the power exhaust fan motor. The amount of
exhaust air is controlled by a set of dampers in response
to the unit mounted building static pressure controller.
The power exhaust operates until the economizer modu-
lates below the end switch setting or the unit is shut off.
(NOTE: Static pressure sensing tubing is field supplied
and installed).
SEQUENCE OF OPERATIONS Continued