VLT
®
6000 HVAC
19MG.60.B1.02 - VLT is a registered Danfoss trademark
Introduction to
HVAC
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■ Constant Air Volume
CAV, or Constant Air Volume systems are central
ventilation systems usually used to supply large
common zones with the minimum amounts of fresh
tempered air. They preceded VAV systems and
therefore are found in older multi-zoned commercial
buildings as well. These systems preheat amounts of
fresh air utilizing Air Handling Units (AHUs) with a
heating coil, and many are also used to air condition
buildings and have a cooling coil. Fan coil units are
frequently used to assist in the heating and cooling
requirements in the individual zones.
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■ The new standard
With a VLT frequency converter, significant energy
savings can be obtained while maintaining decent
control of the building. Temperature sensors or CO2
sensors can be used as feedback signals to VLT
frequency converters. Whether controlling
temperature, air quality, or both, a CAV system can be
controlled to operate based on actual building
conditions. As the number of people in the controlled
area decreases, the need for fresh air decreases. The
CO2 sensor detects lower levels and decreases the
supply fans speed. The return fan modulates to
maintain a static pressure setpoint or fixed difference
between the supply and return air flows.
Several features of Danfoss HVAC dedicated VLT
frequency converter, the VLT 6000 HVAC can be
utilized to improve the performance of your CAV
system. One concern of controlling a ventilation
system is poor air quality. The programmable
minimum frequency can be set to maintain a minimum
amount of supply air regardless of the feedback or
reference signal. The VLT frequency converter also
includes a two zone, 2 setpoint PID controller which
allows monitoring both temperature and air quality.
Even if the temperature requirement is satisfied, the
drive will maintain enough supply air to satisfy the air
quality sensor. The controller is capable of monitoring
and comparing two feedback signals to control the
return fan by maintaining a fixed differential air flow
between the supply and return ducts as well.
With temperature control, especially used in air
conditioning systems, as the outside temperature
varies as well as the number of people in the
controlled zone changes, different cooling require-
ments exist. As the temperature decreases below the
setpoint, the supply fan can decrease its speed. The
return fan modulates to maintain a static pressure
setpoint. By decreasing the air flow, energy used to
heat or cool the fresh air is also reduced, adding
further savings.
Pressure
signal
Cooling coil
Heating coil
D1
D2
D3
Filter
Pressure
transmitter
Supply fan
Return fan
Temperature
signal
Temperature
transmitter
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