HVAC and COVID-19: Designing Buildings with Proper Ventilation for Indoor Spaces in a Pandemic

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An April 2020 study published by the Centers for Disease Control and Prevention (CDC) found that strong airflow from an air conditioner could have helped spread SARS-CoV-2, the virus which causes COVID-19, at a restaurant in Guangzhou. It’s still unclear to what extent aerosolized particles spread the disease, but pandemic conditions have many rethinking the role that HVAC can play in mitigating transmission both now and in the future.

“HVAC design teams for any new or existing build will consider going beyond the minimum required design standard,” says Jason Killinger, assistant professor of HVAC Technology at Pennsylvania College of Technology. “We understand how infectious aerosols can be disseminated through a building, but we must look at the building-usage plan and determine best practices to reduce risk of transmission through the HVAC system. Information regarding this pandemic is still very fluid, and more information is required before solidifying new design standards. ”

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has released guidance on managing the spread of COVID-19 with respect to the operation and maintenance of HVAC systems in buildings. It asserts that the ventilation and filtration of HVAC systems can reduce the airborne concentration of SARS-CoV-2, and thus the risk of transmission through the air. Unconditioned spaces, on the other hand, can cause thermal stress that may be directly life-threatening to people and may lower resistance to infection.

ASHRAE also launched an Epidemic Task Force to address the challenges of the current pandemic and future epidemics as they relate to the effects of HVAC systems on disease transmission. The task force includes not only HVAC specialists but also leading experts in medicine and public health, who serve as consultants.

ASHRAE’s work so far, which is aligned with the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), has been pivotal in helping hospitals and clinics cope with the increasing volume of COVID-19 cases. It’s also helping people ensure the safety of their own homes and offices.

“The industry will need to investigate HVAC design strategies and develop minimal design requirements beyond medical-treatment facilities,” Killinger says. “These new strategies will help reduce the spread of airborne infectious diseases. Risk assessment protocol for HVAC design strategies would help HVAC design teams ensure key items were covered and help reduce airborne spread. We must understand that it is not practical for every building, but should be considered to help reduce risk and still maintain human comfort.”

Maintaining HVAC Systems in a Pandemic

In the case of residential buildings, ASHRAE recommends maintaining normal thermal comfort conditions, increasing the ventilation rate, operating restroom fans when facilities are in use, and utilizing air purifiers.

Homes with forced-air systems, which recirculate air throughout the home through ducts, should install high-efficiency media filters, operate the HVAC system continuously, and consider the use of Ultraviolet Germicidal Irradiation (UVGI). Multi-family homes should take extra care in making sure water is in the plumbing traps, pressurization is maintained, and chases and bypasses are sealed.

When creating an isolation zone within a home (for when a household member is known to be infected, for example), additional precautions are suggested. The isolation space should be on a high floor during the heating season and a low floor during the cooling season. A separate HVAC system is recommended for the isolation zone, and air barriers and separate exhaust ventilation should be provided as well.

For those conducting HVAC maintenance and replacing filters that are potentially contaminated with the virus, ASHRAE suggests appropriate personal protective equipment (PPE), including a properly fitted respirator (N95 or higher), eye protection (safety glasses, goggles, or face shield), and disposable gloves. They also advise potentially letting a filter load up further than usual, in order to reduce the frequency of filter changes. When possible, filters can be disinfected with a 10 percent bleach solution or another appropriate disinfectant, approved for use against SARS-CoV-2, before removal.

Three HVAC Technologies That Can Mitigate Disease Transmission

ASHRAE has further identified three main technologies that can be effective in mitigating disease transmission: mechanical air filters, electronic air filters, and ultraviolet energy (UV-C) systems.

Mechanical Air Filters

In the case of mechanical air filters, ASHRAE recommends a Minimum Efficiency Reporting Value (MERV) of 13 for efficient capture of airborne viruses, with a MERV of 14 preferred for hospital inpatient care settings.

High-Efficiency Particulate Air (HEPA) filters are even more efficient than the highest MERV rated filters. The overall effectiveness of reducing particle concentrations depends on factors such as filter efficiency, airflow rate through the filter, the size of the particles, and the location of the filter in the HVAC system.

Electronic Air Filters

ASHRAE recommends including a wide variety of electronically-connected air-cleaning devices that are designed to remove particles from airstreams. Removal of particles generally occurs by electronically charging particles with corona wires, generating ions (e.g., pin ionizers), and collecting particles on oppositely charged plates. The overall effectiveness depends upon removal efficiency, the airflow rate through the filter, the size and number of particles, the location of the filter within an HVAC system or air cleaner, and the proper maintenance and cleanliness of electronic filter components.

Ultraviolet Energy (UV-C) Systems

Ultraviolet energy inactivates viral, bacterial, and fungal organisms so that they are unable to replicate and potentially cause disease. While the entire spectrum of UV can inactivate microorganisms, UV-C with wavelengths of 100 to 280 nm provides the most germicidal effect, with 265 nm being optimal. Most modern UVGI lamps produce roughly 95 percent of their energy at the near-optimal wavelength of 253.7 nm.

The use of UV-C requires special PPE to prevent damage to the eyes and skin from overexposure. UV-C has applications on in-duct air disinfection, upper-air disinfection, duct surface disinfection, and portable room decontamination. Further guidance and frequently asked questions specific to its applications towards COVID-19 are available from the Illuminating Engineering Society (IES) Photobiology Committee.

HVAC Systems in a Post-Pandemic World

The safe operation of HVAC systems is a critical component of reopening buildings that have been closed or operating at low-capacity since the start of the pandemic. High-touch areas of an HVAC system need to be disinfected. System maintenance and filter replacement are required. Above all, a strategic plan must be in place that includes measures to make occupants feel safer, to ensure a supply chain for critical items such as filters, and to promote communication plans with occupants for further building support. Additional guidance is available on the ASHRAE website.

Looking forward, more buildings are going to be viewing HVAC systems that take pandemic conditions into consideration. Buildings will need to perform assessments on the current performance of their HVAC systems to determine their readiness as it relates to occupant safety and mental wellbeing. A rise in the installation of advanced building automation systems is possible, where HVAC performance can be measured effectively and optimized against cost and use.

But simply adding the highest quality filters available is not necessarily the preferable option: high-efficiency filters may have a high initial pressure drop, and/or load up with dust and particles very quickly, which would require frequent filter changes.

In residential or light commercial cases, an HVAC system’s fan may not run very often, and the efficiency of the filter is not as important as it otherwise could be. Each building must take into consideration its own context, and these assessments will need to be ongoing as more information becomes available.

“Future installation, maintenance, and operation of HVAC systems will remain the same with a few added advanced features,” Killinger says. “I see systems being designed with more zones to eliminate the risk of airborne disease spread from room-to-room, and more outside air being introduced to help air quality and humidity control.”

It’s unlikely that the current pandemic will completely transform the way HVAC is installed, maintained, and operated. But it will provide opportunities for optimization and improvement.

Matt Zbrog

Matt Zbrog is a writer and researcher from Southern California. He's been living abroad since 2016. Long spells in Eastern Europe, Southeast Asia, and Latin America have made the global mindset a core tenet of his perspective. From conceptual art in Los Angeles, to NGO work on the front lines of Eastern Ukraine, to counterculture protests in the Southern Caucasus, Matt's writing subjects are all over the map, and so is he.

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