By Michael Frank, Vice President, Engineering and Design
Many people are wondering what it will look like when we all return to work in buildings that have been mostly vacant for weeks, and in some cases months. There are a lot of conversations happening and articles being written about occupant density, and I imagine seating layouts will never look quite the same.
How about the HVAC and plumbing systems that have been put into a holiday schedule or turned off for this same time period? How do we get them ready so our employees can return with confidence? Once they are ready, and employees start returning in a staged occupancy, how should we operate them and what should we be thinking about? There is a lot of research and reporting being done on the role of an HVAC system in keeping us safe, or potentially spreading the novel coronavirus.
HVAC systems are made up of many smaller sub-systems and there is a lot of choice in how these parts are engineered and assembled; unfortunately, not all are created equal. Heating and cooling (local or central), ventilation (DOAS or integrated), filtration (to capture dust, smoke, pollen, viruses and bacteria), humidification (steam, atomization, direct evaporation), diffuser type and placement, zoning (choosing which spaces are grouped together on common systems) – the list goes on and on and each choice impacts how well our buildings perform.
In an ideal world, all our buildings would deliver ventilation via dedicated outdoor air system (DOAS), with distributed terminal heating and cooling devices, and humidification systems to maintain space relative humidity between 40-60%. This article is meant to offer practical guidance to building owners and operators for the systems they do have. I have broken it down by things I believe are “Must Do” and “Additional Recommendations” for consideration.
- Perform a physical inspection of your filters for loading, damage and air gaps where air can bypass. Seal any air gaps.
- Change all filters.
- In systems that recirculate air, consider replacing with higher MERV-rated filters as these can do a better job at capturing smaller particle sizes. Be aware that these come with added air resistance. The fans in HVAC systems are designed to deliver a certain amount of air to overcome a certain pressure (your filters and distribution ductwork); if you increase the pressure, you get less air as there is only so much power in your fan motor. To mitigate this, consider if your total system airflow can be reduced. Building occupancy will ramp up slowly and initially no buildings will be at full capacity so there is no need to have total system airflow at full capacity. Alternatively, will certain spaces simply not be used as they were designed? I can’t imagine we will be rushing back to sit in densely packed conference rooms anytime soon and these zones may be able to be dialed back.
- If you must keep high occupancy spaces operational (cafeterias in schools, restaurants, critical conference rooms or meeting spaces, etc.) consider localized filtration and ensure the system is sized appropriately for the space it is serving.
- Ultraviolet germicidal irradiation (UVGI) is another technology to consider for critical spaces and the air handlers serving them.
- If your ventilation system has been off for an extended period, posture your HVAC system to perform a building air flush with clean filters in place.
- Once your system is up and running, don’t turn your ventilation system off. A lot of building control systems are set to shut outdoor air dampers outside of normal working hours to conserve energy. To ensure any virus-laden particles have the maximum chance of being exhausted out of the building, keep your ventilation system running 24×7 (at lower ventilation rates during unoccupied times).
- Understand the amount of outdoor air your system can deliver under all operating conditions and compare that with your return to work occupancy strategy, as certain zones will likely have fewer people than originally designed. Assess your system, perform code-driven ventilation calculations, and make modifications as needed to increase the amount of ventilation air being delivered (or modify your occupancy strategy if this is not possible – see limitations in additional recommendations below).
- Temporarily disable demand-controlled ventilation systems.
- When possible, increase the amount of outdoor air being brought into a facility. There are heating and cooling limitations (as well as energy) of the systems in your building and they were all designed and sized with certain assumptions. An HVAC engineer can help you determine how much “wiggle room” your system has and provide guidance on increasing the percentage of outdoor air. Don’t drive your system to a point where it can’t maintain indoor comfort as this will lead to occupants turning systems off and we want to keep air moving.
GENERAL HVAC SYSTEM COMPONENTS
- Perform a physical inspection of all aspects of your HVAC system to ensure everything is working as intended (control dampers are operational, fire dampers and fire-smoke dampers are in their normal operating position, etc. to allow you to posture your system as described in the Ventilation section above) and fix anything that is preventing your ventilation system from being able to function properly.
- Make sure any occupant changes to the HVAC systems have been mitigated (blocked floor vents in underfloor air distribution systems, closed off ceiling or wall diffusers due to comfort concerns) as you want to avoid any stagnant spaces.
- Re-balance airflows to ensure ventilation is getting to the zones it is intended to get to.
- If you are in the process of designing a new building, consider a DOAS for occupant health and energy savings. This type of ventilation system has many inherent health and efficiency benefits.
- If you are in the process of designing a new building, consider installing a humidification system to maintain relative humidity in the 40%-60% range as this is known to negatively impact virus viability as well as improve the human body’s natural ability to filter the air we breathe.
In addition to posturing HVAC systems to ensure safety as we return to the workplace, occupants will need to change their behaviors. One way to train and inform people on required behavior changes is to use some sort of dashboard. Facilities often have operating dashboards that report energy and water usage in buildings along with information on environmental impact such as the amount of CO2 emissions avoided. Adding information about safety protocols will be critical in getting occupants to do their part in keeping our buildings safe and their occupants healthy.
This is new territory for many of us and just like we have shown so far, we will get through this together.
McKinstry delivers the assurance needed for your building occupants to return with confidence. Learn more.