A large portion of commercial, educational, and healthcare facilities have been either partially occupied or unoccupied for several weeks, even months. With extended periods of unoccupancy, building systems can become stagnant, potentially resulting in adverse effects on air systems, domestic water systems and building materials. Most of us know the smell of dust burning off the heating coil on the first cold day of autumn. To some people, it signals the coming winter, to others, it is just another allergen causing red eyes and an itchy nose. Returning to a stagnant building can have the same effect, including mold, mechanical failures and potentially harmful bacteria in domestic water systems that would not be immediately evident when you re-occupy your facility. With a little planning, these issues may be mitigated.
Temperate conditions in the northeast in the past few weeks have helped buildings that have been unoccupied maintain relative low temperatures and moderate relative humidity levels inside the building. However, this should not be an invitation to turn everything back on an hour before people start to return to the office. Stagnation in an HVAC system can lead to mold growth on filters, duct liner and other materials where the surface relative humidity exceeds 90%. Leaking dampers and/or poor insulation can allow cool night-time air to lower interior surfaces to the point where moisture in the air condenses. Moisture, combined with a food source for mold spores like cardboard or accumulated dust can lead to widespread air quality issues. A brief visual inspection now can save headaches for you and your staff in the future.
Performing some standard maintenance prior to re-occupying a facility can yield benefits beyond reducing the chance of developing an adverse environment. Remember that many of the building occupants have spent most of their recent time in their own homes. Any odd or different odors or poor temperature/humidity control will be far more noticeable to occupants returning from an extended hiatus. Recommendations to curtail some of these potential issues include the following, depending on system type and size:
- Change pre- and final-filters on all air systems.
- Lubricate fan and pump bearings.
- Exercise actuating dampers, and valves that may have been in a single position for extended period.
- Replace UV lamps in air systems that have been in place longer than 12 months.
- Verify charge on solar-powered control devices, batteries and fixtures that may have discharged due to weeks of no lighting or use.
- Clean heating and cooling coils.
- Clean condensate drain pans.
- Fill cooling condensate traps that may have dried out.
- Check outside air intakes, clean intake screens, and make sure ventilation is being provided during system operation.
- Check all belts and replace as needed and inspect sheaves for excessive wear during this process.
- Fill plumbing traps that may have dried out, allowing sewage gases to enter the space.
Once you think your HVAC system is in good operational condition, you should begin running the system as if people were present several days to a week prior to re-occupying the space. If the facility has small unitary equipment, you may want to run only a few of the units at first, while utilizing fans and open doors to circulate air. The goal of this method is to slowly bring all the surfaces in the space to a normal occupied temperature, and more importantly, humidity level. There is research appearing to show that viruses are less likely to thrive with relative humidity ranges between 40% and 60%. Furthermore, mold is less likely to propagate when air is maintained below 60% relative humidity. During a period of stagnation, some building materials, such as drywall, carpeting, wood and acoustical ceilings act as sponges, absorbing moisture from the air in the building. This condition progresses over time, so it will also take time to reverse the process and return the environment to equilibrium.
Large buildings with partial occupancy face similar issues as smaller buildings that have had little to no occupancy. These larger buildings have more complex HVAC systems and generally have variable airflow systems that have been operating at a minimum rate for the same time-period. When people return en masse, systems suddenly increase airflow rates, stirring up particulate that has settled during the low usage period. Strategies to bring the system back online include:
- Force air-handling units into economizer mode for several hours to flush the spaces. When outdoor air conditions are suitable.
- Set system to “occupied mode” for several days before anticipated occupancy.
- Turn on local exhaust systems periodically.
- Open interior doors to allow effective transfer air between rooms where practical or allowed by usage.
Once the building is occupied and the systems are functioning correctly, you may want to revisit your preventative maintenance schedule for the equipment. If you have recently upgraded your air filtration level, you will need to determine a revised filter replacement schedule. Ideally, the filtration upgrade included manometers (pressure gauges) or pressure switches to notify you when the filter is loaded to the manufacturer-recommended pressure drop. If you have installed UV lamps, it is very important to schedule a replacement according to the lamp manufacturer’s recommendation. Just because the lamp is on, doesn’t mean it is performing its job. The UVC output deteriorates over time, and most lamps are just pretty blue lights after 8,000 hours of operation.
Finally, there is the question of what to do to when people, and presumably the novel coronavirus, return to our facilities. Is my HVAC system supposed to clean the air of viruses, giving occupants a sense of security? Should my housekeeping staff sanitize hourly, daily? Should I install UV lighting in all air systems and spaces? Will UV lighting kill all viruses?
There is no one-size-fits-all solution to operating a building’s HVAC system, and there’s certainly no magic wand to keep all building occupants safe from viruses and other contagions. While you could install HEPA filtration at significant cost and operational expense, the average air system only changes the air out of a space every 20-30 minutes. During that time, the virus carriers (people), have taken 12 to 20 breaths per minute, according to the Cleveland Clinic. That’s 720 to 1,200 exhales of potentially infected air per person, in classroom, that could be 36,000 breaths per hour! In this light, it seems clear that the HVAC system is fighting a losing battle. However, implementing a multi-faceted approach addressing occupants, physical spaces, and building operation can help mitigate current and future risks.
It is also important to pay careful attention to plumbing systems before re-occupying a building. Many buildings have been closed for weeks, leaving them vacant. Others are operating with few essential personnel and while the facilities have been open to these employees, the use and circulation of water in the plumbing system is much less than typical.
The water in building piping systems, water heaters, expansion tanks, pumps, etc., has been aging several weeks and residual levels of active disinfectant, if there are any, are likely below what is required. Bacteria are present in every water system, including potable water, fountains and cooling towers, and they can rapidly multiply and colonize when water is stagnant.
Furthermore, water heaters may be a breeding ground for bacteria as Legionellae flourish in hot water systems operated at temperatures below 125 degrees. Because adequate amounts of fresh water have not been introduced for many weeks, and system flow rates have likely been too low to scour the internal walls of the domestic water piping, it should be assumed that water systems need to be drained, flushed and disinfected prior to re-occupancy.
There are two sources from The American Society of Heating Refrigerating and Air Conditioning Engineers (ASHRAE) for guidelines in the safe operation and use of plumbing systems: ASHRAE Standard 188-2018 – Legionellosis: Risk Management for Building Water Systems, (and associated Addenda) and ASHRAE Guideline 12-2020 – Managing the Risk of Legionellosis Associated with Building Water Systems. Legionella pneumophila (the bacterium that causes the disease Legionellosis or Legionnaire’s Disease) is not the only waterborne pathogen known to be present in a plumbing system. Following these standards and guidelines may also reduce the risk posed by other bacteria as well. (ASHRAE publications are available for purchase from their website: ASHRAE Standards and Guidelines). Please keep in mind that while draining, flushing and disinfecting your plumbing system is necessary prior to occupying a building, active mitigation of Legionella bacteria and other pathogens over the long term is necessary, even when buildings are fully occupied.
During our research and development of Preparing for the New Normal?, our initiative to provide resources for building owners and operators during the COVID-19 pandemic, we learned that a respected plumbing industry columnist and lecturer, Ron George, CPD, recently published an article available to the public that provides a step-by-step procedure for flushing your building water system.
Everyone is assuming some level of risk whenever they leave their house, from driving a car, to eating fast food, and yes, exposure to a potentially lethal virus or bacteria. As a facility owner, you shouldn’t be expected to provide a completely sanitary environment, but you also can’t neglect the facility. Owners and operators need to make educated decisions based on expert guidance, employ best practices, and make reasonable accommodations to provide an acceptable level of risk for their workers and building occupants. That may include higher levels air filtration, UV lighting, hand sanitizing stations, foot-pulls or auto-openers for doors, increased ventilation, among a myriad of other options.
If you have any questions, please do not hesitate to contact Stephen E. Oskin, PE, LEED AP at (814) 880-6070 or firstname.lastname@example.org or Jonathan B. Slagel, PE, LEED AP HFDP, at (717)-817-2277 or email@example.com.