Variable-Geometry Supply Diffusers

Variable-geometry supply diffusers can be used to ensure adequate air movement when the supply volume is low. These contain a mechanism which varies the size of the outlet aperture in response to the volume of air delivered. For low volumes the aperture is throttled so that the air velocity leaving the diffuser is maintained at a sufficient level to ensure good air distribution.

Air movement

For air-based cooling systems to be effective, it is important that the air is distributed evenly within the occupied space. Air diffusers are used to supply air to a space as they provide control of airflow and direction. The system designer will select the most appropriate type(s) of diffuser for the space, taking into account the following points.

  • Use of space and required aesthetics of diffuser
  • Constraints imposed by layout and structure
  • Partitioning of space
  • Volume flow rate of air
  • Maximum noise levels
  • Length and type of throw required.


What are the benefits of using variable-geometry supply diffusers in air-based cooling systems?
Variable-geometry supply diffusers offer several benefits, including improved air distribution, increased flexibility, and enhanced system efficiency. By adjusting the outlet aperture to match the supply volume, these diffusers ensure consistent air velocity, which leads to better air distribution and more effective cooling. Additionally, they can accommodate changes in system demand, making them ideal for applications with varying occupancy or load patterns.
How do variable-geometry supply diffusers maintain adequate air movement at low supply volumes?

When the supply volume is low, the variable-geometry mechanism throttles the outlet aperture, increasing the air velocity leaving the diffuser. This ensures that the air is distributed effectively, even at reduced flow rates. By maintaining a sufficient air velocity, these diffusers prevent stagnation and promote good air circulation, which is essential for effective cooling and indoor air quality.

What are the common applications of variable-geometry supply diffusers?

Variable-geometry supply diffusers are commonly used in air-based cooling systems, particularly in applications where air distribution is critical, such as in offices, hospitals, and laboratories. They are also suitable for use in variable air volume (VAV) systems, where the supply volume varies in response to changing occupancy or load patterns. Additionally, they can be used in retrofit projects to improve the performance of existing air distribution systems.

How do variable-geometry supply diffusers compare to fixed-geometry diffusers in terms of performance?

Variable-geometry supply diffusers outperform fixed-geometry diffusers in terms of air distribution and system efficiency, especially at low supply volumes. Fixed-geometry diffusers can lead to poor air distribution and reduced system efficiency when the supply volume is low, as the air velocity leaving the diffuser may be insufficient. In contrast, variable-geometry diffusers adapt to changing supply volumes, ensuring consistent air distribution and optimal system performance.

What are the key design considerations for specifying variable-geometry supply diffusers?

When specifying variable-geometry supply diffusers, designers should consider factors such as the desired air velocity, supply volume, and pressure drop. They should also ensure that the diffuser is compatible with the system’s ductwork and that the control mechanism is integrated with the building management system (BMS). Additionally, designers should consider the diffuser’s noise level, aesthetic appeal, and maintenance requirements.

Can variable-geometry supply diffusers be used in conjunction with other air distribution devices, such as grilles and registers?

Yes, variable-geometry supply diffusers can be used in conjunction with other air distribution devices, such as grilles and registers. In fact, combining these devices can enhance the overall air distribution performance of the system. For example, using a variable-geometry diffuser in conjunction with a grille can provide more precise control over air direction and velocity, leading to improved air distribution and system efficiency.