AAON RK-60 - Manual (Page 14)

14
II. VAV (Variable Air Volume) SYSTEMS
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. (Boxes and controls are supplied
and installed by others). 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 pres-
sure 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. Two types of power exhaust control are
available.
A. Three position economizer, an On/Off power ex-
haust will be utilized to exhaust when economizer is
called for.
The end switch located on the economizer O. A. 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 in the 24 VAC circuit.
B. Full modulating economizer, a full modulating
power exhaust will control the amount of actual ex-
hausted air by means of a building sensing pressure
control which opens or closes according to desired pres-
sure in the space.
POWER EXHAUST w/ 3 POSITION ECON.
In the unit "OFF" or in the minimum economizer posi-
tion, 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.
POWER EXHAUST w/ FULL MODULATING ECON.
In the unit "OFF" or in the minimum economizer posi-
tion, 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