Taking a Closer Look at Air Distribution in Critical Environments
Creating high-performing, well-ventilated spaces is essential in critical environments such as hospital operating rooms, patient rooms and other medical spaces. Indoor air quality directly affects occupants’ well-being and productivity and, in the case of pharmaceutical compounding, for instance, can have a profound impact on processes that occur in the space.
Recognizing this, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) established ANSI/ASHRAE/ASHE Standard 170, Ventilation of Health Care Facilities to provide a guideline for air distribution in healthcare environments. One crucial aspect of optimizing air distribution in healthcare applications is implementing the appropriate diffusers.
Diffuser Classification
Diffusers play a vital role in HVAC systems, facilitating the distribution and diffusion of conditioned air into occupied spaces. Within the 2017 ASHRAE Handbook – Fundamentals, ASHRAE has classified diffusers into groups based on their performance characteristics, allowing engineers and architects to select the most suitable options for their specific applications:
- Group A: Mounted in or near the ceiling, projecting air horizontally (e.g., Square Plaque Diffuser)
- Group B: Mounted in or near the floor, projecting air vertically in a linear jet (e.g., floor-mounted Linear Bar Grille)
- Group C: Mounted in or near the floor, projecting air vertically in a spreading jet (e.g., Modular Floor Diffuser with a twist pattern)
- Group D: Mounted in or near the floor, projecting air horizontally (e.g., Displacement Flow Diffuser)
- Group E: Mounted in or near the ceiling, projecting air vertically downward (e.g., Linear Slot Diffuser)
The table below from ASHRAE Standard 170 indicates the type of supply air outlets that should be selected in a variety of healthcare applications.
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| Diffuser requirement table from ANSI/ASHRAE/ASHE Standard 170, Ventilation of Health Care Facilities |
Diffuser-Integrated Filtration
Another important consideration when selecting diffusers for critical environments is whether they are equipped with air filtration. Filtered diffusers offer additional benefits for maintaining indoor air quality by capturing and removing airborne particulates before the air is distributed to the occupied space.
In critical environments, where maintaining low particulate levels is vital, diffusers that incorporate high-efficiency particulate air (HEPA) or ultralow particulate air (ULPA) filters or other specialized filtration media are often the preferred choice – and are even required in some applications.
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| Price’s Radial Flow Diffuser with a drop face and integrated HEPA filter |
Diffuser Selection in Critical Environments
When selecting diffusers for critical environments, consider the ASHRAE diffuser classification groups and whether integrated filtration is required for the application. Specialized critical environments diffusers combine the necessary air distribution features to provide solutions that are tailored to applications that demand exceptional air quality.
Laminar-Flow Diffusers
Laminar-flow diffusers are classified as ASHRAE Group E nonaspirating diffusers. These diffusers provide a uniform, nonturbulent airflow with a vertical down projection and low initial face velocity. Typically, laminar-flow diffusers are positioned directly over a desired “clean zone,” and the column-like airflow displaces airborne particulates down and away from that clean zone with minimal entrainment of room air. Laminar-flow diffusers are widely used in operating rooms, cleanrooms, pharmacies and laboratories, where the mixing of room air is undesirable.
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| Price’s Laminar Flow Diffuser |
Radial-Flow Diffusers
Radial-flow diffusers handle large volumes of air with short throws to minimize velocity in the occupied zone while providing a high level of dilution. Radial-flow diffusers can be described as a combination of ASHRAE Group A and Group E diffusers, distributing air in a radial pattern.
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| Drop-face (left) and flush-face (right) radial-flow diffusers with a radial airflow pattern | |
These diffusers are designed to minimize entrainment of room air while displacing particulates down and away from the occupied zone. Radial-flow diffusers are available in a variety of styles to suit the architectural and air distribution needs of the space.
The drop-face style extends below the ceiling plane to provide exceptional performance through the increased surface area of the face. A flush-face design prevents interference with sprinkler heads and other ceiling-mounted equipment and maintains architectural appeal while providing a radial airflow pattern. Radial-flow diffusers are commonly used in laboratories and airborne infection isolation rooms, where a high level of dilution is required while maintaining occupant comfort.
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| Price’s Radial Flow Diffuser with a drop face and integrated HEPA filter in a pharmacy application |
When designing air distribution systems, it is crucial to consider the needs of the space and the occupants. By incorporating specialized critical environments diffusers, design teams can create well-ventilated spaces that promote occupant well-being and comfort while meeting strict air quality standards.
For more information on how to select diffusers for your next healthcare project, reach out to the Critical Environments team at criticalenvironments@priceindustries.com.
