By Bo Petersson, PE, mechanical engineer, EFI Global
There is a great deal of uncertainty regarding the ways in which buildings can contribute or prevent the spread of COVID-19.
Engineering professionals and other experts have indicated the transmission of COVID-19 can be reduced with changes to building operations. Similarly, federal agencies have advised that the best way to reduce the potential for recirculated or ongoing COVID-19 in indoor environments is to provide an increase in fresh air ventilation and increased filtration of return air whenever available, but without compromising the existing HVAC system.
Businesses today should be familiar with the concerns and pitfalls that may be encountered when altering heating, ventilation and air conditioning (HVAC) systems. Operators and managers of any facility should carefully consider their options before altering an HVAC systems given the complexities associated with such operational adjustments.
Air quality considerations
Air changes vs. ventilation – When people discuss “air changes,” they typically refer to the number of air changes per hour provided by the ventilation system. For most ventilation systems, the supply air that comes from an air handling unit (AHU) is a mix of return air (RA) and outside air (OA). Newer systems often consist of in-room recirculation devices, such as chilled beams (CBs) or fan coil units (FCUs), combined with dedicated outside air systems (DOAS). As a result, the ACH rate is based on a mix of OA and RA, or only OA depending on the air handling system configuration.
Filtration – A typical AHU for school and office applications is designed to use filters with MERV 8 ratings. The higher the MERV rating, the higher the filter effectiveness. Some professional organizations have recommended increasing the filtration to MERV 13-rated filters to improve building readiness. Any changes to the filtration should include an evaluation of the associated fans since increasing filtration efficiency generally requires additional fan power and space for filters.
Local HEPA filtration units – Another option is the use of local standalone high efficiency particulate air (HEPA) filter units that can be plugged into a wall outlet. These units are equipped with replaceable HEPA filters that recirculate room air. Even with correctly functioning HVAC systems, many buildings may experience poor mixing, end of branch isolation or poorly ventilated areas that may require local filtration. It is also important to consider areas that house at-risk building occupants or visitors. These locations may consider additional local filtration for added safety.
Increase ventilation – HVAC systems are designed for a certain mixture of outside air and return air with varying tolerances from those concentrations. This means that if the operator increases the amount of outside air, they may overwhelm the existing heating coil and increase the risk for freezing the coil and causing widespread damages. To avoid extensive damages, equipment failure or reduction of equipment life-expectancy, an engineering evaluation is recommended before altering the operation of a system.
Scheduling and maintenance – If an HVAC system is operating on a schedule, the operators may opt to increase the operating hours to achieve a “flush out” of the building before and after occupancy. The operators should also review the condition of the ventilation equipment. Debris on intake screens, coils and heat recovery components can reduce the airflow significantly. Increasing the operational time of the equipment will increase the need and required frequency of filter changes and system maintenance and cleaning.
Local units – Many spaces are equipped with smaller local units that either work alone or together with other building HVAC systems such as fan coil units or chilled beams. These units do not bring in any outside air and simply recirculate the room air. Local units with low performing filters are not intended to be used with high performing filters. While certain local units do bring in outside air, they are very similar to FCUs and are relatively common in school classrooms. UVs are designed to bring in small volumes of outdoor air to be mixed with room return air. These units are typically equipped with a heating coil, filters, and sometimes a cooling coil. Like larger AHUs, these units are not intended to bring in 100% outdoor air during colder temperatures. Altering them can result in frozen coils and resultant water damage.
System assessments
HVAC system assessment – Over a period of years, the operation and performance of a commercial HVAC system can vary considerably from its originally intended design characteristics. If an owner has concerns about the operation of its HVAC systems or is considering alterations, they should contact a firm with specialized expertise in the evaluation of existing systems and environments before proceeding with alterations. The consulting firm should investigate the condition and operation of the existing systems and evaluate their original designs to determine which enhancements might be implemented to increase outdoor air delivery or increase filtration capabilities. Its professionals should be adept in identifying deficiencies in existing HVAC systems that can be corrected and and what adjustments can be made to increase system performance.
Environmental assessment – As part of a complete assessment of an environment to further evaluate the indoor air quality, as reputable industrial hygiene consulting firm should be utilized. In addition to viral hazards, a qualified team of air quality scientists can further evaluate mold, dust and other pathogens and contaminants in the air.
Solutions moving forward
EFI Global employs air quality experts who work seamlessly with our engineering experts and our client buildings’ teams to provide real-time data with direct-read instrumentation and fast track reporting. EFI’s multidisciplinary team of experts has extensive experience and a proven track record performing these critical ventilation assessments. They are equipped to provide documentation that HVAC systems are operating properly and that air quality guidelines are met for the health and safety of building occupants.
To learn more, visit https://www.efiglobal.com/ or you can always reach out to us for further support.
Additional contributors:
– Jay Kramarczyk, MS, PE AVP and senior principal engineer, EFI Global
– Keith Pokorny, Mechanical engineer vice president, EFI Global
– Jennifer Archacki, Environmental service principal, EFI Global
– Peter von Au, Senior industrial hygienist, EFI Global
– Joseph Whitlock, PhD, CIH Industrial hygienist, EFI Global