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Variable air volume controllers
General Description
In Variable Air Volume (VAV) systems, supply of cool air
increases as the cooling load increases, and the air supply
decreases as the load decreases.
VAV systems are the most modern, energy efficient all air
systems available for comfort air conditioning. VAV sys-
tems require less fan capacity than a comparable constant
volume system because with VAV only the required air is
used. Typically a VAV system fan volume is 60% of a CAV
system.
Control of air flow in a VAV system is accomplished
through an electronic device, which regulate the amount
of supply air to the space in response to a proportional
room/space temperature controller.
Pressure Independent
Systemair VAV units are pressure independent The ac-
curate volume control achieved by pressure independent
VAV units results in substantial energy savings as well
as increased comfort to the occupant. Conditioned air
volume is precisely regulated according to demand. A
maximum air volume setting avoids drafty air distribution;
a minimum air volume setting avoids cold air dumping and
stuffiness.
Minimum and Maximum air flow requirements are set to
suit the space application. “Pressure independent units
have controls consisting of an inlet duct sensor, damper,
controller/actuator and room temperature controller”. The
VAV device controls the air supply volume through the
inlet duct velocity pressure sensor to maintain air flow, as
the air-conditioning load in the space changes the ther-
mostat signal will reset the VAV controller to change the
supply air volume to suit the space requirements. At any
given setting, the controller will maintain the required air
volume regardless of inlet static pressure changing. This
mode of operation is called “Pressure Independent”.
Variable Air Volume units allow the design to take full ad-
vantage of shifting loads from lights, occupancy, solar and
equipment diversity, which typically leads up to a 40%
saving in the total air volume required. Consequently, the
central plant and ducting would cost less, thus compen-
sating for the additional cost of VAV terminal units and fan
speed controls.
Systemair offers complete range of VAV’s factory tested
and calibrated. The VAV range offered are as following:
1. Round single skin VAV units (Optima-R), used in instal-
lations for return or supply air in low pressure systems
as single-zone control
2. Round double skin VAV units (Optima-R-I), used in
installations for return or supply air in medium to high
pressure systems as single-zone control
3. Round to rectangular single skin insulated VAV units
(Optima-R-S), used in installations for return or supply
air in medium to high pressure systems as multi-zone
control
Benefits
The VAV system offers some advantage and benefits over
conventional systems as given below
y
y
Fan energy savings from longhour usage at reduced
volumes, also installed fan horsepower reductions.
y
y
Greater flexibility in respect to varying loads, which
are easier zoned, resulting in occupancy controlled
comfort and energy saving.
y
y
Reduced installation and set-up cost.
y
y
Reduced system energy consumption cost.
y
y
Single unit for easy mounting.
y
y
Integrated high efficiency sound attenuator.
y
y
Suited for mounting of all controls according to cus-
tomer specification.
y
y
Accurate air volume control with centre averaging
multi-point airflow differential cross velocity pressure
sensor.
