The COVID-19 pandemic has forced pharmaceutical companies and other life sciences organizations to be extra vigilant in the sanitization of their facilities, specifically, in mitigating the transmission of COVID-19 and other respiratory illnesses in interior spaces — research laboratories, production facilities, office spaces, and more.

A vital aspect of this mitigation is the building heating, ventilation, and air conditioning (HVAC) system. Proper air circulation, particulate filtration, and humidity control all contribute to a cleaner, safer environment for employees and prevent sterile surfaces and materials in the building from being compromised.

This article examines how existing HVAC systems can be retrofitted – or new systems designed – to mitigate the airborne transmission of COVID-19 and other pathogens.

The Four Commandments Of Pharmaceutical HVAC

While some elements of HVAC (e.g., filtration) may seem well understood, others are easily overlooked. Here, we examine each of these elements, as well as how they complement one another to form a reliable, effective system.

First, humidity control should be provided within all occupied spaces to maintain the environment between 40 percent and 60 percent relative humidity (RH). This range has been considered an optimal range, reinforced by research on the topic, for 50+ years.¹

Adequate humidity in the air prevents the water in virulent particles — generated when coughing or sneezing — from evaporating before the particles can settle on the ground. Without the additional weight of the water, small particles containing the virus could potentially stay airborne indefinitely. Conversely, control of excessive humidity prevents the growth of molds and other pathogens while also reducing contaminants’ active life on surfaces. Humidity control can also provide increased product quality and consistency in products with stringent weight requirements or utilizing dry ingredients.

In many facilities, unless it is deemed process-critical, humidification is not viewed as a necessity and subsequently is not included in the design of the HVAC system (i.e., RH is likely to drop below 40 percent during the winter in the majority of the United States). Depending on where the facility is located, humidity could drop as low as 10 percent in the winter months, potentially increasing the time a virus or contagious material can hang in the air. Are you regularly getting shocked when you touch a cubicle, desk, or doorknob? That could be indicative of low humidity inside the building.

Next, in new or existing facilities, ultraviolet germicidal irradiation (UVGI) should be considered as an option within the air handling system. Exposing wet surfaces within the unit to UV light prevents organic growth on cooling coils and within drain pans that could otherwise be transported through the HVAC system. Secondary benefits of UVGI systems include increased intervals between unit cleaning and limiting the pressure drop in the system, as they prevent biological coil fouling. These benefits help to reduce the maintenance activities during a facility shutdown and reduce the electrical load of the fans.

UV light has been known for 100+ years to cause damage at the cellular level, but in the 1990s, the technology saw a resurgence in response to the discovery of drug-resistant bacteria in hospitals.^{2, 3} In certain systems, such as units located in humid climates or large make-up units, UVGI has proven its value because of the primary and secondary benefits listed above. However, in most installations, UVGI is viewed as an HVAC system option, versus a must-have.

Still, UVGI is beginning to gain traction in the pharmaceutical industry, due to its various benefits combined with the relative ease of retrofitting it into existing systems (picture installing a fluorescent tube in the air handling unit). The principal consideration when utilizing this system is ensuring personnel safety. To prevent UV exposure to personnel, viewing windows for inspection must be UV shielded and the access door to the unit must be wired to the UV lights, shutting them off automatically when the door is opened.

Moving to air filtration, in new HVAC systems it has been recommended that filters with a minimum rating of MERV 13 are considered for any process spaces or any densely populated spaces to mitigate the spread of airborne disease.⁴ These more robust filters capture a minimum of 90 percent of airborne particles, versus 30 percent of particles offered by a typical MERV 8 filter seen in most commercial units — which is why states like New York are investigating implementing a requirement for these filters in malls and other indoor areas where large groups of people gather. Additionally, the filtration ratings of any existing HVAC system should be investigated and, if viable, the system should be updated with new MERV 13 or greater filters.

The two biggest inhibitors in upgrading the filters in existing systems are the filters’ physical dimensions and the added filter pressure drop. A MERV 8 filter is pleated and comes in various sizes up to four inches deep, while a typical MERV 13 filter starts at 12 inches deep to account for the additional filtration media required. To compound matters, utilizing a single high-efficiency filter is not recommended, as larger particles, such as pollen, will quickly clog the filter. Instead, it is standard practice to install a MERV 8 filter or equivalent upstream of the higher efficiency filter to extend the latter’s useful life. All of these considerations, however, require additional space in the HVAC unit. Thus,  the need for additional filtration should be evaluated during the initial system design, as it may be difficult to retrofit in the future.

The second item to consider when upgrading the filters within the unit is the limitations of the fan within the unit. The addition of increased filtration will require the fans to discharge air at a higher pressure, and so great care should be given to confirming the existing fan’s performance. In systems where the existing fan can not handle the increased pressure motor upgrades, more frequent filter changes, reduced system airflow, or some combination of these items should be investigated.

Where modifications to existing HVAC systems are not possible due to physical or capacity limitations, consider adding local units (terminal HEPA filters) to decrease the time it takes to turn over the volume of air in a space (typically referred to as the air change rate). The additional airflow will decrease the time a potential threat will remain airborne and provide additional filter media to capture any undesirable particulate.

For example, consider a pharmaceutical facility with an existing HVAC system that provides adequate cooling, but not enough air movement in high-traffic areas (airlocks, changing rooms, corridors, etc.). In such a situation, a terminal HEPA filter — basically a fan in the ceiling that pulls air from the space, pushes it through a HEPA filter, and recirculates the air within the room — could be installed to provide additional filtration. At the same time, the existing building system continues to control the temperature in the space. The same approach could be extended to an office setting or any other area deemed to be at high risk for transmission.

Finally, to maximize the effectiveness of the HVAC system in mitigating the spread of airborne diseases, the condition of each air handling unit’s air-side economizer should be inspected. The air-side economizer operates by comparing interior building conditions to the outside air conditions and, when more energy efficient to do so, introduces additional fresh air from outside into the building (the system equivalent to opening a window). When operational, this system reduces the amount of recirculating air within the building and subsequently reduces the overall viral load within the space. Energy codes and building codes currently compel many facilities to use economizers, but that’s no guarantee the economizers are operating properly.

Because the economizer is a dynamic system that actively compares the temperature, and often the humidity, of two airstreams, its various sensors require periodic maintenance and recalibration to operate properly. Without this recalibration, the system may begin to operate less frequently, increasing the amount of recirculated air in the building along with energy usage.

The use of an economizer in a pharmaceutical environment comes with an additional set of concerns. In many production suites, the required differential pressure across a door can be as low as 0.03 in. W.C. (0.001 psig) to meet the regulatory requirements. These demands are typically met by actively controlling and/or monitoring the position of the dampers in the unit’s economizer. However, if the system is not regularly serviced or is not properly commissioned, the subsequent pressure swings can cause problems between rooms and, if severe enough, will require a product variance or recleaning of the space. In these situations, the economizer is sometimes disabled without a full understanding of the impact on system performance.

Conclusions

Measures that minimize the amount of time an infectious particle generated by a person remains in the air — or capture, deactivate, exhaust, or otherwise reduce the viral load in a building — have been proven effective at minimizing the spread of infectious diseases and bacteria. As facilities begin to reopen, implementation of these measures will be important in reducing the risk to clients, employees, and businesses moving forward.

Recommendations herein are based on industry standards and previously studied viruses and infectious diseases.⁵ Scientific consensus (as of the writing of this article) is that person-to-person (i.e., aerosol spray) infection represents the most common transmission of the COVID-19 virus, and space-to-space transmission continues to be researched.⁶

About The Author

Louis Bruno is a Senior Mechanical Engineer at IPS-Integrated Project Services, LLC (IPS) with 10 years of experience in the pharmaceutical sector. During that time, he has been actively involved in the design and implementation of high-performance HVAC and utility systems in various biotherapeutic and active pharmaceutical ingredient production facilities, as well as pilot laboratories. His technical background includes the specification and design of chiller, boiler, and air-handling unit systems to meet the often-stringent control tolerances required within the pharmaceutical industry. 

Resources

1. Noti, John D et al. “High humidity leads to loss of infectious influenza virus from simulated coughs.” PloS one vol. 8,2 (2013): e57485. doi:10.1371/journal.pone.0057485 -- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3583861/
2. “The Nobel Prize in Physiology or Medicine 1903.” NobelPrize.org. Nobel Media AB 2020. 22 Jun 2020. https://www.nobelprize.org/prizes/medicine/1903/summary/
3. “UV-C Lamps - A Short(Wave) History.” UV Resources. Mon. 22 Jun 2020. www.uvresources.com/blog/uv-c-lamps-a-short-wave-history/
4. Minimum Efficiency Reporting Value (MERV) is testing standard developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to rate filter performance based upon worst-case conditions. Values range from 1 to 16, with the higher values corresponding to a greater percentage of captured particles.
5. Marr, Linsey C et al. “Mechanistic insights into the effect of humidity on airborne influenza virus survival, transmission and incidence.” Journal of the Royal Society, Interface vol. 16,150 (2019): 20180298. doi:10.1098/rsif.2018.0298. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6364647/
6. Turpin, Joanna R. “Can HVAC Systems Spread COVID-19?” ACHR News, 31 May 2020. https://www.achrnews.com/articles/143255-can-hvac-systems-spread-the-covid-19-virus  
7. ASHRAE Journal. May 2020

This article originally appeared on CellandGene.com.