KEY CONCEPTS

Program-Specific Pressurization

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.