GE AF-600 FP Series, Руководство по конструкции

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2.7.15 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.
2.7.16 The AF-600 FP Solution
With a frequency converter, significant energy savings can be obtained while maintaining decent control of the building. Temperature sensors or CO
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sensors
can be used as feedback signals to 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 CO
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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.
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 requirements exist. As the temperature decreases below the set-point, the supply fan can decrease its speed. The return fan modulates
to maintain a static pressure set-point. By decreasing the air flow, energy used to heat or cool the fresh air is also reduced, adding further savings.
Several features of the GE dedicated frequency converter 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 frequency converter also includes a 3-zone, 3 setpoint PID controller which allows monitoring both temperature and air quality. Even if the temperature
requirement is satisfied, the frequency converter 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.
Pressure
signal
Cooling coil
Heating coil
D1
D2
D3
Filter
Pressure
transmitter
Supply fan
Return fan
Temperature
signal
Temperature
transmitter
AF-600 FP Design Guide
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