Application Principle
Variable Air Volume or VAV systems have some kind of sysetm to
control the air volume. The simplest control is On-Off control
of fans but the damper control is more common and variable speed
control of fans is the most economic method to control the air
volume. The system is usually designed to maintain constant
static pressure in the supply duct. |
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Variable air volume system with variable speed
control fans |
The positive building static pressure is kept by regulating the
airflow of both the supply and return fans. Terminal devices or
VAV boxes supply the conditioned space with a variable flow of constant
temperature airflow. Plant maintenance is centralised. The system
may be designed so that cooling by outside air can be obtained without
operating the refrigeration plant. Room temperature can be
achieved by:
- Air volume control
- Bypass damper control
- Control of refrigeration capacity
Detailed Description
This variable air volume system brings outside air and return air to
the Air Handling Unit (AHU) (3). where the incoming air (8.) temperature
and humidity can be controlled. The main AHU components are supply
fan (2.) heating coil (5.) cooling coil (6.), filter (7.), and humidity
control equipment (not in above). The three way valves for heating
and cooling are remotely operated. The temperature in the
individual rooms is measure by thermostats (11.), which directly control
the dampers in each room. The supply air fan is speed controlled
by an AC drive (4.) and it delivers the air to individual rooms
throughout the building by supply air ducts. The AC drive controls
the air volume by keeping the air pressure constant. The pressure
is measured by the sensor (13.). The return air fan (1.) delivers the
exhaust air (9.) out of the building or part of the air (10.) is
returned back to the AHU. The fan is controlled by an AC drive
(14.) which keeps the room pressure measured by sensor (12.) constant.
Performance in Creating comfort zone
Constant volume - variable temperature system have been
dominating the HVAC applications in the past for obvious reasons.
the implementation of variable volume control has been done with
dampers or other mechanical control methods.
The advantages of variable air volume system implemented with
variable speed control are:
- Fast control to keep the comfort zone limits
- Low consumption of electrical energy
- Lower consumption of heating and cooling energy than in
constant air volume systems
- Simpler to keep noise level down
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Air conditioning unit with electrical switchboard |
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