By Brian Baker, P.E. and John McCarthy, Sc.D., C.I.H.
With the 2019-2020 school year cut dramatically short by the COVID-19 pandemic, public and private school systems and higher education institutions across the nation are exploring strategies today to prepare their buildings for a safe return to school this fall. Appropriately operating and maintained HVAC systems will play a critical role in creating a safe environment—and in building trust from staff and parents as these buildings are reoccupied.
As the Philadelphia Federation of Teachers recently learned from a 13,000-member survey, teachers are adamant that they will not return to school until facilities are in adequate condition. Schools that do not have a plan in place for a safe reopening will be hard-pressed to bring faculty and students back to the classroom. This plan should also address occupant perceptions of an unsafe building that may become conflated with COVID-19.
While there are abundant recommendations for reopening schools, it will be important that each school address their specific mechanical needs based on available resources, school demographics and specific building characteristics to create an effective approach to achieve their safe reopening and re-occupancy. Further, schools should periodically reassess their plans as communities move into different phases of reopening and deeper knowledge of response to COVID-19 becomes available.
A varied response
Across the board, schools are being advised to create layered control strategies, focusing on de-densifying classrooms, increasing physical spacing, improving ventilation, upgrading filtration, and considering supplemental air cleaning. Increased ventilation of spaces using clean air has proven to be an important and effective tool in helping prevent the spread of COVID-19 as it dilutes the concentrations of the virus in the air. Although Centers for Disease Control and Prevention (CDC) recommendations focus largely on disinfection and social distancing protocols, it offers brief guidance on school mechanical systems:
“Ensure ventilation systems operate properly and increase circulation of outdoor air as much as possible, for example by opening windows and doors. Do not open windows and doors if doing so poses a safety or health risk (e.g., risk of falling, triggering asthma symptoms) to children using the facility.”
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) provides more robust guidance to help schools identify specific opportunities for increasing ventilation. However, it’s important to note this guidance is being updated on an ongoing basis on the ASHRAE website, www.ashrae.org, as research around SARS-CoV-2 evolves.
The challenge, of course, with this broad advice is that there are a wide variety of natural, mechanical (both local and central) and hybrid mechanical systems operating in schools across the country. Moreover, many older schools, particularly public K-8th grade facilities, may be challenged in achieving adequate air distribution in the classrooms due to the age and limitations of their HVAC systems. Many of these systems may struggle to meet pre-COVID code requirements or ASHRAE recommended ventilation rates, as highlighted in a June 2020 Government Accountability Office report. This report concluded that more than 40 percent of the nation’s school districts need to update or replace systems, including HVAC and plumbing, in at least half of their schools. That amounts to approximately 36,000 schools beginning their COVID-19 response plan at a disadvantage.
However, this report also offers a starting place. Schools must begin by examining their own ventilation systems for maintenance needs and opportunities to increase ventilation. HVAC and other routine maintenance will become absolutely critical in creating a safe environment.
Must-do maintenance for HVAC equipment
Today, school facility managers have an incredibly strong and very valid case for growing their maintenance budget, so this is no time to hold back on inspections and identifying needed corrections or delaying preventive maintenance.
The first step is to begin with a review of existing systems to ensure they’re performing as intended. That includes examining air handling systems to make sure dampers are connected, fan belts are in good condition and appropriately tensioned, cooling and heating coils are functional and working appropriately, filters are being maintained, etc. This also includes ensuring general cleanliness of units, condensate drain pans, and related components. Further, knowing the actual flowrates for both outdoor air and recirculated air for each space that is intended for reoccupancy is essential in helping decide upon allowable class sizes.
Now is also the time to review common historic complaints about indoor air quality to identify patterns or problem areas. Any existing maintenance concerns must be addressed because they can give the impression of poor indoor air quality and erode faculty and parent trust in the building’s safety.
Today’s maintenance activities should also include putting a plan in place for managing both routine preventive maintenance as well as the actions that may be needed to address potential system trade-offs that may be associated with increasing ventilation rates. The most significant of these is likely be to thermal comfort. By increasing outdoor air ventilation beyond design limitations, you risk sacrificing comfortable temperature and indoor humidity levels. More than uncomfortable, this could heighten occupant concerns about the overall health and safety of the building.
In addition, there is the potential that increasing outside air ventilation without accompanying dehumidification can increase the likelihood of condensation on interior building components such as piping and ductwork. This can lead to the deterioration of building materials and the potential for future mold problems. Working with your HVAC engineer can help maintenance teams prepare for possible implications of increasing outdoor air ventilation through building air handling systems.
It’s also critical that facilities staff work closely with school administrators to keep abreast of the potential for reduced occupancy loads. Many school systems are evaluating partially digital schedules to reduce the number of students in a facility at a given time, thereby increasing the ability to keep adequate social distance between people. This reduced occupancy will improve the effectiveness of ventilation given that reduced occupancy means less potential contaminant or viral sources within the space as well as essentially increasing outdoor air ventilation rates per person, based on the lower number of occupants in the space.
Address shutdown-specific risks
CDC recommends specific actions be implemented by facilities staff if the building or systems were shut down, or usage was dramatically curtailed, for prolonged periods of time prior to re-occupying. Unless there was a program in place during the shutdown to regularly “flush” water systems, potential Legionella contamination, must be addressed now. Stagnant water can result in ideal conditions for bacteria like Legionella to grow. While Legionnaire’s disease poses its own risks, it’s important to note that it presents symptoms similar to those seen in COVID-19-infected patients and similarly affects vulnerable populations. Addressing Legionella is a critical safety step and will also reduce the risk of another school closure.
The CDC outlines several steps to take to minimize the risk of Legionella prior to reopening a school facility. The first step should be to create a water management plan that identifies high risk areas for water to stagnate, such as dead legs or unused taps or showers, and outlines steps to correct each problem.
Next, flush the building’s water systems with all terminal devices on a branch opened at the same time for a minimum of five minutes. Ensure hot water systems reach the maximum heat available. If these systems have not been flushed throughout the shutdown, there is a risk of inviting residual bacteria into the area where the test is being performed. In this case, be sure to work in a well-ventilated area and wear appropriate personal protective equipment, including a properly fitted N95 respirator.
Finally, perform cleaning in all areas where stagnant water is possible. This includes clearing running drains to eliminate standing water, cleaning gym and dormitory showers and checking cooling towers for proper operation and chemical treatment for scale, corrosion and biocide. For buildings or populations at highest risk, consider proactive sampling for Legionella.
Options for filtration and air cleaning
While maintenance will play a critical role in supporting higher levels of ventilation, schools are also looking to invest in other products to strengthen their infection control response.
ASHRAE advises increasing filtration at the air handling unit to limit the spread of viral particles recirculated through the return air system. The association’s guidance suggests MERV 13 filters as preferable as these filters are able to capture particles as small as 0.3-1.0 microns with reasonable efficiency. However, few of the older school HVAC systems will be able to accommodate the recommended minimum MERV 13 filters. Higher efficiency filters add a restriction to the airflow and without compensating for this restriction, result in a decrease in airflow. To make up for this, schools are looking to utilize portable air filters with HEPA filtration for each classroom. If this is an option your school is considering, it’s best to act now. Obtaining HEPA filters and portable purifiers could become more challenging in the fall as demand increases.
In addition, some schools are exploring UV-C and ionization solutions as a potential avenue for limiting the spread of viral particles. ASHRAE provides guidance on the use of UV-C for in-duct air disinfection and surface disinfection and although there are specific applications where this technology is effective in degrading viruses, the products are not considered plug-and-play solutions. To be effective, a UV-C system must be appropriately designed into the existing HVAC system(s) and its output matched with the system’s airflow. Consult an experienced design professional if considering the use of UV-C. Regarding ionization, there is limited information about the effectiveness of this technology in commercial HVAC systems and this should be considered when evaluating its use and installation costs.
Budget for critical improvements
While recommended maintenance activities may stretch school budgets, these activities are critical to ensure student and staff safety. For many schools, it will be a matter of bringing mechanical systems up to current code performance and catching up on too long deferred maintenance. For others, it may mean investing in the staff to perform routine maintenance or forging relationships with HVAC contractors or consultants to supplement the in-house team.
Schools are also likely to see an uptick in operational costs. Among other recommendations ASHRAE advises extending HVAC system operating hours compared to typical occupied hours to provide an increased ventilation rate prior to and after occupants leave the building. This increased energy use can drive up energy bills.
However, this is but one more reason why it is critical to outline today the steps necessary to safely reopen and identify the potential impacts of each step. Preparing early gives schools time to brace for budget impacts. It also gives facilities managers time to help project where investments are most needed and how to minimize the overall impact on the building. By preparing today, schools can minimize the impact of COVID-19 on their budgets and their communities and create a building environment that is both welcoming and safe for its occupants.