What is VAV? What are the benefits?
Variable Air Volume (VAV) is a type of HVAC system that maintains a constant temperature while varying the airflow in order to heat or cool buildings. This is in contrast to Constant Air Volume (CAV) systems, that supply a constant airflow while varying the temperature of that air.
To better understand a VAV system, let’s use an example of how such an implementation works. An air handling unit pushes air into the HVAC duct system at a consistent temperature, let’s say 13°C. This air temperature is constantly maintained throughout the HVAC system, moving through the ductwork to each zone of the building. As the air goes to each zone, it passes through a VAV box or terminal, which allows different amounts of airflow into the zone depending on the thermostat setting of that area. In addition to a damper that adjusts to regulate airflow, many VAV boxes also contain a heating element for warming the air as needed.
Each VAV terminal modulates according to the needs of the specific zone it is serving. This allows the HVAC system to more efficiently provide various temperatures and fan speeds throughout the system to accommodate the needs of the individual zones. The added control of VAVs provides several important benefits:
- More precise temperature control: unlike a CAV system that operates the fan and compressor at full capacity in an on/off cycle, a VAV system continually varies the fan speed to maintain a constant air temperature.
- Reduced compressor wear: as a VAV system modulates the control of the compressor, it reduces its wear over the long term.
- Lower energy consumption by system fans: VAV fan control, especially with electronic variable speed drives, reduces the energy consumed by fans which is a substantial part of the total cooling energy costs of a building.
- Less fan noise: CAV systems operate fans at full speed and constantly turn them on/off resulting in greater noise compared to a VAV system that runs a more consistent, lower speed fan at a reduced decibel level that more easily blends into the background.
- Increased dehumidification: a VAV system exposes air to cooling coils for a longer time than CAV systems, with more moisture condensing on the coils and thus dehumidifying the air.
Figure 1 – HVAC Implementation with VAV Terminals
The Role of Differential Pressure Sensors in VAV
As VAV systems maintain a consistent temperature and vary the airflow to achieve the desired conditions, differential pressure sensors play a vital role in their operation. Specifically, the sensors measure the volume of air across two points and provides feedback to the control system to open or close dampers to maintain the appropriate temperature in each of its zones.
Figure 2 – VAV Airflow Test
While differential pressure sensors are a critical component of VAV systems, they are subject to external factors that can impact performance. For example, fans and blowers generate noise and vibrations that can impact the accuracy of the sensor. Filtering out that noise before it reaches the sensing element will greatly improve accuracy.
A more important consideration in deploying sensors in a complex system is the need to maintain long-term stability as replacing sensors or VAV units is costly and time consuming, especially in larger HVAC implementations. Finally, as the various zones of the ‘air network’ may have different requirements (e.g., an interior lab or server room vs a window facing conference room), the ability to have one differential pressure sensor that can support all the different pressure requirements will simplify system design and VAV device inventory management.
Superior Sensor’s Technology Advantages in VAV
Superior Sensors’ proprietary NimbleSenseTM architecture is the industry’s first System-in-a-Sensor integrated platform. Incorporating a highly differentiated advanced pressure sensing system with the ability to integrate optional building blocks enables us to combine the highest accuracy and reliability with application exclusive features. With unique technology deployed in our HV Series of differential pressure sensors, Superior’s products offer many advantages for VAV terminals.
Excellent Long-Term Stability
Long-term stability is defined by the maximum change in zero signal and output span signal of a pressure sensor under reference conditions within one year. This value is of greater importance in low pressure ranges as the effect on the signal is stronger. Factors such as temperature and mechanical stress can have negative effects on the long-term stability. Based on Superior Sensor’s implementation, the HV Series has market leading long-term stability measured typically within 0.15% of FSS per year.
Highest Levels of Accuracy
Sensor accuracy is important in measuring the responsiveness of HVAC systems. Superior’s HV Series of differential pressure sensors have the industry’s leading accuracy typically within 0.05% of the selected range and total error band (TEB) typically within 0.15% of FSS.
Lowest Noise Floor
External noise from blowers, fans and other sources can have a negative impact on the accuracy and long-term stability of differential pressure sensing systems. Utilizing our integrated advanced digital filtering technology, Superior’s pressure sensors eliminate the noise created by these factors prior to their reaching the sensor sub-system. By eliminating the noise before it becomes an error signal, we can offer the industry’s lower noise floor.
Multi-Range technology allows one sensor to replace several different sensors. On the HV Series, Multi-Range can support up to 8 different pressure ranges in one device with each pressure range factory calibrated and optimized to ensure no degradation in total error band, accuracy or long-term stability regardless of the range selected. Figure 3 shows the difference between a typical differential pressure sensor and Superior Sensor’s HV Series.
Figure 3 – HV Series Multi-Range Technology Comparison
With Multi-Range, manufacturers can offer one VAV terminal with up to 8 pressure range options that can be set with a single software command. This allows a building to implement the same box throughout the HVAC network and simply configure each box at installation. No need to worry about buying different VAV terminals for different zones, as the same terminal can be used throughout. The larger the HVAC system, the more benefit you get from Multi-Range technology.
HVAC systems greatly benefit when they implement VAV systems as they are more accurate and energy efficient. A key element of VAV boxes is differential pressure sensors that constantly measure airflow and direct the control system to make adjustments as needed.
Superior Sensor’s unique differential pressure sensor technology, based on our proprietary NimbleSense architecture, provides many benefits for VAV systems including excellent long-term stability, higher accuracy and the ability to utilize the same VAV box throughout your network and configure each during implementation. For more detailed information about our solutions, please visit our HV Series product page or contact us.