Excepting hospitals or labs, coils are rarely sized for 100% outside air throughout all seasons of the year. Room temperature set points will not be met because the temperature and moisture condition of the supply air is no longer under reliable control. Zones and VAV boxes may “see” enough airflow (unless operations doubled down with the HEPA filters mandate above). Much like the loss of airflow from a forced-HEPA retrofit, interior zones with heavy use of glazing (windows) and loads (people, computers, equipment) will find the resulting supply air cannot maintain the interior conditions and “runaway” uncontrolled conditions are likely. Building zones will continue to not meet set points, and all systems, fans, and pumps will respond by requesting up to 100% of their design airflow per zone and position command.
The situation is not over yet. For first cost and energy efficiency purposes, systems are not sized to allow every zone to achieve 100% airflow at the same time. Rather, the designer will have assumed a diversity factor. A good example of this is sizing a system for offices with an adjacent event space served by the same equipment. The assumption from the designer was if everyone is in the event space, they are not in the offices, and the cooling load can balance out accordingly. Alternatively, if they are in their offices, the event space is empty and not loaded. Due to the leadership mandates, this diversity factor balancing act is now thrown out the window. Buildings will begin to pressurize, and doors will suck closed or hold open. If they are no longer fully able to close and lock behind occupants, this may jeopardize site security and evacuation door strength requirements. System controls will continue to attempt to achieve 100% airflow balanced across all zones with operations paying for every minute of that electricity and disappointment.
Noise will become a problem too. It is most likely the interior zone controls (i.e., VAV boxes). Assume the supply air temperature condition in the ductwork is achieved at the plant/equipment level. All zone controllers will request up to maximum airflow, “thinking” it is cold or warm enough to impact change, but they will wait in vain. Some systems measure supply air temperature at a zone level and may outsmart this, but this is the exception not the rule. The occupant experience will get noticeably noisy due to maximum flow possible pushed to air outlets. These outlets are selected by a design engineer for a couple of key things beyond just looks: a certain “throw” pattern of the air into the space (think: how effective it will be spreading air in the room), noise criteria (at a selected assumed air flow), and first cost. The key point is these criteria are all usually met at the design assumed flow rates of the outlets. Outlets were sized for a maximum design condition; however, occupants are not used to hearing them all at that condition at the same time. To assess outcomes, we ask a few questions: How good was your design acoustician? Did your basis of design include noise criteria for your space types? If you have not heard of this terminology, your experience may be on the worse end.
In addition to noise, in warmer months, the runaway zone airflow conditions will continue to hold from late morning onward as the sun rises into the sky waiting for the sweet release of the cool evening air. If nights are typically warm, operations may have the added cost of systems never achieving their set back temperatures and, therefore, running through the night. Significant energy implications will result from this, driven by more hours of operation in a high energy use configuration.
All hope is not lost. There are alternative approaches to these mandates. Operational adjustments with minimal upfront costs exist. In the climate of 2020/2021 (pandemic, global, workplace, or otherwise), we are starting to see more trust in the work-from-home model. This change is still too recent and temporary to modify the approach to HVAC design methods or immediate updates to building or energy codes. We see most companies taking an approach of wait and see for a vaccine solution instead of undertaking major retrofits for existing systems. Several large tech companies are taking this approach. Overall, the authors feel this will result in more widespread likelihood of “quick fixes” (our examples herein) instead of an engineered design evaluation and capital project upgrade. Who has the money for that?
A staggered occupancy is a good first step instead of system overrides. By staggering occupancy, facility operations is increasing relative airflow per occupant. This works even with demand control ventilation systems (CO2 responding) because the “code minimum” outside air balanced during construction assumed more people in the building. If a system adjustment is required to appease leadership, one approach is to replace filter rack segments with a physically wider retrofit segment to permit a bag-style or V-shaped filter install for better filtration rating. This will maintain reduced pressure drop (due to increased flow area) and avoid the aforementioned force-fit HEPA replacement outcomes. Require your vendor or design engineer to model your specific air-handling units both before and after the retrofit and review those observations with them prior to issuing any purchase orders.
An alternative to the solution-to-pollution-is-dilution concern is to fight with light. A photocatalytic treatment system can be retrofit as a segment into existing supply air ductwork to aid in the deactivation of airborne biologicals. Photocatalysts are proven to deactivate viruses, mold, mildew, and volatile organic compounds (VOCs) as well as improve odor removal, as evidenced from many years of successful application in hospitals (reduction of infectious disease spread) and casinos (reduction of smoke gas phase contamination). This will allow a system to function with the original filtration system (no HEPA upgrade) in normal design parameters with minimal added pressure drop, only 120-V power for the treatment light and no other control overrides.
We now present a final recommendation applicable to all scenarios for how to approach pandemic-induced system mandates: Create a written system adjustment plan containing several important sections with the goal of formalizing and documenting changes.
The first section is a written charter from leadership for requested system directives. The charter should include wording specifically acknowledging energy use implications and performance impacts to occupants may result, including noise, comfort, and airflow. If leadership is reluctant to provide this, operations may author one for their review and agreement.
The next section should attempt to define the criteria to roll back these changes. This is important to define upfront. Addressing this topic later may result in heavy political pushback around this topic (“You don’t care about our occupants?”) resulting in leadership stuck between increased cost and perception of safety. Help company leaders define this the best they can and make sure they know the system adjustment plan is a living document.
The third section should include a commitment to meet and revisit the plan and resulting energy outcomes quarterly to discuss energy use, performance issues, and changing pandemic immunization conditions. Commit to preparation for the next unknown pandemic. For example, consider designing a control button on your BMS that could be pushed to place the system in a “pandemic response” configuration. Attach the three trailing years of energy bills to this document as a comparison for future energy use. In these meetings, provide a healthy amount of pushback for semi-permanent adjustments to engineered systems and instead considering alternative approaches, including operational adjustments (such as staggered occupancy).
The fourth and final section in the adjustment plan should be a detailed log recording all direct changes made to the system. It should be organized by equipment identification tag, and specific set points should be adjusted. This is the time to be very specific and to note the original set point prior to changing it (for future use). If physical changes are made, mark them with paint and take photos to revert. The original set points were put in place using calibrated measurement equipment and should not be changed lightly.
In closing, consider these questions: If you were pressured into making changes your system was not designed for, can you realistically undo them? What will be the criteria for reverting? Is it measurable? What is your appetite for significant increases in recurring energy and materials costs, including possible tiered-rate structure or account adjustments by your utility? As ongoing climate change results in exaggerated seasonal peak conditions, such as heat, fires, and storms, will your systems from five, 10, or 15 years ago keep up with the increased load? This will not be the last test of the built environment responding to societal change and biological spread. The best move we can make together is to commit to collaboration with leadership, educate them on existing system limitations, and document modification every step of the way.