The following are commonly used terms known within the critical airflow control industry and specific terms used by Phoenix Controls.
Pressure independence is the characteristic of an airflow control device to maintain constant airflow control regardless of the system static pressure delivered to the device. While flow measurement based devices claim pressure independence, they rely on controller’s ability to accurately measure the airflow and compensate for static pressure changes by adjusting the control element, typically a damper blade. Phoenix’s pressure independence does not rely on airflow measurement. We use a mechanical regulator integral to the flow control element (a cone assembly within the venturi) to instantaneously compensate for system static pressure changes. As shown in the diagrams below as the system static fluctuates, the movement of a spring-loaded cone assembly along the center shaft provides the correct orifice opening at a wide range of static pressures.
Flow metering is the technology of using the predefined characteristic of position versus airflow control for accurate flow control. In the case of Phoenix’s Accel II valve, the position of the valve is measured using the voltage produce by potentiometer connected to the shaft and cone assembly’s drive train. The corresponding airflow measurements are collected at our factory using precision instruments under controlled conditions. The resulting table of voltage versus airflow is programmed in to a variety of controllers we offer thereby providing an airflow control device factory characterized to produce the desired airflow without the associated issues of field flow measurement. A typical characterization curve is shown in the photograph of our factory characterization station.
To control space pressurization, differential pressure sensors are often used to control airflow devices and maintain directional airflow. This is a very challenging method when doors are often left open. Phoenix Controls developed a unique approach to maintaining directional airflow. This simple concept is called the “Volumetric Offset” approach. The theory is that if you are able to accurately exhaust more air from a space then what is being brought in, additional air would infiltrate the space to make up the difference: Exhaust volume = Supply volume + Offset.
In fume hood laboratories where the door(s) are opening and closing often, the volumetric offset approach was, and still is the best solution. This same approach also works well in many other applications or industries. In facilities where animal research takes place, or Vivariums are used to house animals, proper pressurization is critical. In places where biological research is conducted, (BSL) there are often multiple levels of pressurization from the corridor outside to the space within. Phoenix Controls has used this Volumetric Offset approach in these settings as well as other research facilities and in healthcare facilities around the world.
Phoenix Controls’ equipment is not measuring flow. Because of the inherent nature of the venturi design and the pressure compensating mechanism, our products are inlet and exit insensitive. These products can be installed in the duct in any configuration upstream or downstream of the valve without any impact on the accuracy, repeatability or stability of the flow control.
Typically two valves, a supply and tracking exhaust. For temperature control applications where consistent directional airflow in or out of the space is critical. In these flow tracking applications, the Traccel®
controller maintains an offset between the volume of air supplied into and exhausted from a space to maintain positive or negative space static pressure. For example: when room temperature rises, the supply valve opens and the exhaust valve tracks. All control for both valves is being done by one main valve - see diagram below.
Usage Based Controls (UBC)
Modulates hood flows based on the presence or absence of a fume hood operator. UBC can be used in both two-state and variable air volume applications.
UBC has been designed to significantly reduce the risk in downsizing the building’s mechanical equipment. UBC senses the actual presence at the fume hood of an operator, not just sash position alone. Even though an operator may leave a sash fully open all day, the amount of time the hood is occupied is typically less than one hour. Thus, the fume hood would operate in the standby mode of 60 fpm most of the day instead of 100 fpm, resulting in a 40% reduction in airflow. Furthermore, if sashes are closed, up to 80% reduction in airflow is realized.
Progressive Offset Control (POC)
Phoenix Controls developed the progressive offset control function which layers a pressure control loop over top of the conventional Celeris volumetric offset control. A base offset establishes a positive or negative space then the volumetric control function responds to dynamic flow changes within the lab. The pressure control loop then makes finite adjustments to the offset in order to achieve the precision of control and responsiveness required for Biocontainment and Pharmaceutical Cleanroom spaces. The subtle tuning by the pressurization control function provides superior performance in terms of closeness of control, responsiveness to changes airflow, and recovery from a door opening or closing.