Below is one part of a series of white papers based on our Conversation Series: New Perspectives on Health and Well-Being where we discussed a range of mitigation strategies with our community of engineers, architects, specialists, and industry professionals. We break down all the latest and greatest (and not so great) methods of disease control through engineering, design, and building maintenance strategies by their effectiveness and considerations for sustainability.
Prior to changing existing spaces pressurization, building existing conditions will need to be verified and a feasibility study is essential. Industries that can benefit from the most impact from pressurization include healthcare facilities like hospitals, clinics, assisted living homes, laboratories, pharmaceutical manufacturing, and commercial buildings. In addition to mitigating the spread of airborne contaminants like COVID-19, positive air pressure can keep out outside air temperature, contaminants (chemical vapors, solvents, etc.), odors, particulate matter (dust and pollen), infiltration air, and diseases (CDC Infection Control Guidelines) out of the building. It also protects the indoor environment by maintaining cleanliness (ISO Class). Areas like corridors are not occupied consistently, therefore the air quality may contain fewer particles at any given moment. Occupancy and program should be factored into the decision process of pressurizing rooms or spaces.
Pulling Air into Occupied Spaces
This diagram in Figure 1 is a visualization of a “cascade”. Stacked black boxes represent the patient’s bed. A long open box with cross-hatch represents supply air. Open boxes with single, diagonal slashes represent air exhaust registers. Arrows indicate the direction of airflow. The conditioned air is supplied from the supply duct via terminal unit (can be constant volume or variable volume) and supply air diffusers into space. The amount of air being exhausted from the room is larger than the amount of air being supplied into the room. Thus, the room is negatively pressurized. Airflow cascades from the corridor (neutral) into this room (negative). The adjacent bathroom is negative-pressurized compared to the room, airflow continues to cascade from the room (negative) into the bathroom (double negative).
In healthcare, this is used for isolation rooms in order to contain the disease and protect others that are in passing. The CDC suggests this method for the treatment or procedure rooms, bronchoscopy rooms, and autopsy rooms in the healthcare industry. This strategy could potentially be used in classroom settings upon returning for in-person classes. If occupants were required to wear masks while in the corridor, the air quality would remain rather clean considering there is no permanent occupancy load and droplets are contained within the mask. It is also recommended that building air handling units (AHUs) should be equipped with a MERV-13 or MERV-15 filter (see Air Filtration) in order to better filter out contaminants/particles inside the return air before redistributing throughout the building.
Pushing Air Out of Occupied Space
The diagram in Figure 2 is intended to illustrate an anteroom or airlock were, in healthcare, a high-risk patient’s room is positively pressurized to create a protective environment, called “Bubble”, Airlock/Ante Room. Stacked black boxes represent the patient’s bed. A long open box with cross-hatch represents supply air. Open boxes with single, diagonal slashes represent air exhaust registers. Arrows indicate directions of airflow.
In healthcare facilities, PE’s are used for sealed rooms with positive air pressure, ≥ 12 ACH, in conjunction with HEPA filters (see Air Filtration). Doors leading to and from these rooms require a self-closing door to assure consistent air pressure. It is unlikely and not feasible to try and convert every office space into a PE. Possible uses include immunocompromised patient rooms (e.g., hematopoietic stem cell transplant or solid organ transplant procedure rooms) and orthopedic operating rooms.
Environmental impacts of mitigation efforts
When considering pressurization as a mitigation technique upon returning back to places of work and school, recommissioning and correcting the existing systems is likely the first order of business to determine feasibility and options. HVAC systems vary from building to building. Integrating pressurization with air filtration, air monitoring, and fresh air can provide a building with a highly efficient operating cost and energy use in the long run. Making calculated decisions about system upgrades and controls can be beneficial health effects for little infrastructural changes. Taking extreme measures, like increasing the air velocity in an office with socially distanced desks can still cause droplets to be blown off a person and onto another. “Efficiency of the filtration system is dependent on the density of the filters, which can create a drop in pressure unless compensated by stronger and more efficient fans, thus maintaining airflow.” In most cases, pressurization should not cause energy to hit too significantly compared to without pressurization.
* Social distancing, wearing a mask, frequent hand washing, avoiding touching your face and other orifices, and cleaning high contact surfaces as outlined by the CDC are the primary modes of prevention from contracting COVID-19. All previously mentioned strategies and mechanical techniques are secondary or tertiary measures intended to guide the conversation between AEC industry professionals and building owners when considering options for indoor health, safety, and sustainability.
All rooms are not pressurized equal
Controlling “dirty” air movement that contains particulate matter (PM) through pressurization can help contain aerosolized droplet PM contaminated with COVID-19. The length of time a large group of people spends in one space correlates directly with the perceived “dirtiness” of the air. The direction of airflow can directly affect the spread of COVID-19 or any airborne disease for that matter. By controlling air pressure from room to room, facility managers and engineers can work together to control where air flows to and from. By controlling the air movement via mechanical methods, it can avoid unwanted air infiltration through wall openings such as doors and windows, contaminants, odor, particles, and disease. Pressurized rooms are more often found in healthcare facilities, laboratories, pharmaceutical manufacturing, and commercial buildings.
Pressurization can be achieved by volumetric differentials such as constant volume and variable volume. The airflow created by pressure gradients. Airflow cascades from higher pressure to lower pressure.
Air Change per Hour (ACH) is a measure of the air volume added to or removed from a space divided by the volume of the space per hour.
Bubble Airlock is a method where the inside airlock has a higher pressure than the outside, pushing air from the airlock into the adjacent rooms or spaces.
Sink Airlock is a method where the inside airlock has a lower pressure than the outsides, pulling air from the adjacent rooms or spaces into the airlock
Pharmaceutical Cascade is a method where air cascades from a higher grade to a lower grade.
Figure 2: Example of a bubble, a positive-pressure room control for protection from airborne environmental microbes (PE) (Source: https://www.cdc.gov/infectioncontrol/guidelines/environmental/background/air.html#figure2)
Figure 3: This chart identifies strategies, calls out sustainability factors and ranks the efficacy of COVID-19 / SARS-CoV2 mitigation and keys in a color and abbreviation linking to the larger, compiled strategy chart.
Figure 4: This image is a key, specifying the location of each solution on the compiled strategies chart.
Air Innovations (Knowledge Base)
Negative and Positive Pressure Rooms 101 | Hospital Infection Control