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Low Rise Offices |
VAV Terminal with Packaged Equipment |
VAV Terminals |
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Variable Air Volume (VAV) Terminals
Variable air volume (VAV) devices are duct-mounted
terminal units which modulate the amount of conditioned air that
enters the space. A damper located in the supply airstream modulates
the amount of conditioned air that enters the space in response
to space thermostat requirements.
VAV boxes may be broadly classified into two types:
pressure independent and pressure-dependent. Both pressure-independent
and pressure-dependent VAV boxes modulate the amount of air delivered
to the space based on requirements from the space thermostat.
By allowing the airflow quantity to vary, in proportion to the
cooling load in the space, large savings in fan energy can be
realized since most systems rarely operate at their maximum capacity
for more than a few hours each year.
A pressure-independent box delivers a constant amount
of air regardless of pressure fluctuations inside the ductwork.
On the other hand, airflow quantity fluctuates along with duct
pressure for a pressure-dependent VAV box. Hence, the higher
the duct pressure, the higher the airflow quantity for a pressure-dependent
VAV box. Pressure-dependent VAV boxes do not control to a specific
air volume quantity, instead they modulate a primary air damper
inside the VAV box in response to the amount of cooling or heating
required in the space. Pressure-dependent boxes are generally
less expensive than pressure-independent boxes and should not
be used on systems with widely varying duct pressures.
VAV boxes usually have an adjustable minimum position
damper to allow the minimum acceptable airflow quantity to be
defined while some boxes "shut-off" completely.
Various types of control systems are available and
range from pneumatic or electric and may be either system-powered
(from duct pressure) or from an external electric power source.
In order to modulate the quantity of air delivered from the central
station air handler, special fan controls are required including
inlet guide vanes, variable speed drives, variable frequency drives,
fan discharge dampers and variable pitch controls. Sophisticated
direct digital (DDC) controls available today allow the actual
airflow quantity to be controlled at each VAV box. This information
can then be used to monitor and record space operating conditions
such as total airflow rate, ventilation rate, temperature and
relative humidity.
The 35D single duct variable air volume (VAV) unit
provides cooling only or cooling with reheat to meet all your
application needs. The 35D is offered in 11 sizes covering an
air delivery range from 45 to 4000 cfm.
Carrier's 37HS Moduline terminals offer: heating
and cooling distribution from the same terminal with automatic
changeover and control, a full range of system (duct pressure)
powered controls which offer both volume and temperature control
without separate energy control supply. Integral linear slot
diffusers available with one-way and 2-way direction, multiple
slots, and heating/cooling options.
37HC Moduline VAV Terminals with Product Integrated Control (PIC)
Carrier's 37HC Moduline terminals offer: heating and cooling distribution from the same terminal with direct digital (DDC), automatic changeover control, a full range of system (duct pressure) powered controls which offer both volume and temperature control with a direct digital communication link to the central station air handler. Integral linear slot diffusers available with one-way and 2-way direction, multiple slots, and heating/cooling options.
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