Well-meaning reactions to high-level mandates will result in waking the sleeping giants of the pandemic: wasted energy, materials, and effort. Owners who reactively implement system changes without regard for secondary consequences will inherit long-lasting cost and performance impacts. This has the potential to reverse decades of progress in energy efficiency programs and policy. These outcomes can be minimized or avoided with better conversation, leadership understanding, and alternate approaches.
The situation is most ripe for directed reactionary behavior in facilities with a higher employee count and dedicated facility staff. Employees returning to work after an extended period of working off-site will likely pressure leadership, who may in turn issue operational mandates. These mandates will likely come in the form of high-level stakeholder requests to a facility manager. Our examples for discussion are the following: A COO says,
“I want HEPA filters for our buildings like my air purifier at home. We treat our employees like family, so they should get the same.”
Or, a senior vice president who says,
“We need to bring in outside air to mix with indoor air. I want all the outside air you can provide. The solution to pollution is dilution.”
When leadership walks out of the room, what happens next? How does a facility manager push back on leadership when appropriate? With occupant health at stake (including that of our faithful facility manager), fatigue from behavioral restrictions, and sensitivity to biological spread, these mandates will likely result in compliance and implementation. What does this compliance look like? We will assume air filters are replaced with HEPA filters of approximately the same dimensions, and, to maximize outside air, adjustments are made to linkages or set points. We assume operator modifications only, not re-engineering systems or sequences of operation (overall re-engineering would yield a better outcome).
For a small or mid-size company, facility engineering may be outsourced. Large companies can be assumed to have an on-site facility engineering office and staff supporting multiple buildings. An on-site facility engineering group may act as directed but will have the ability to better reconfigure equipment, to some degree. An outsourced facility management provider is expected to implement changes as requested with minimal pushback; the customer is always right.
Let us compare which energy and performance outcomes will likely occur. With some assumptions of the average built environment and system types, ages, and approaches to maintenance, we can predict performance and energy outcomes. Energy impacts are not restricted to the specific units themselves but rather multiplied by other systems in the facility, including subsequent reactionary behavior from occupants. Other impacted systems may include the loading of hot and chilled water systems, increased pump energy, occupant plug loads, set point control ineffectiveness, trim-and-respond turning into just respond, and other considerations.
To begin comparison, we need to make some assumptions. Published air-handling unit service life, in most cases, is assumed as 15 years (ASHRAE 2011), and, for discussion, we will assume an approximate age of eight years (generous) with conditions and deferred maintenance we typically observe from clients. We assume basic maintenance is accomplished, meaning the filters are changed on a schedule, major service is only performed if there is an indication of failure, and a supervisory control system is in use (if applicable to system size, see below). We also assume a seasonal climate where temperatures can be over 100°F or near freezing. Outside air economizers and mixed air dampers are commonly found. Based on this, our cautionary outcomes are further amplified for more extreme climates or less efficient/older equipment than these assumptions.
We propose three example systems to offer relevance to the reader:
1. Small packaged units (2,000 cfm, 5 ton, 0.6-inch external static pressure [ESP]) — These are typically installed in multiples, are not very adjustable, and offer a lower first cost. We will assume they are simple unitary, with everything onboard, and no building automation system (BAS). They would likely have a single-zone, seven-day programmable thermostat. The outside air damper or economizer is a basic linkage, and let’s assume the unit utilizes a single filter rack.
2. Large packaged units (44,000 cfm, 150 ton, 2-inches ESP) — These are for larger facilities, typically selected with options, and installed in one piece. We assume they include an onboard refrigerant cooling coil and gas furnace or a hot water heating coil. A simple automation system provides zone control with maybe three zones per unit. They typically include large metal fans, dampers, and adjustable economizers. We also assume they include a dual filter rack.
3. Large custom units (80,000 cfm, hydronic, 3-inches ESP) — These are the apex predators of air handling and are typically for large facilities, labs, and campuses. We assume these are served by a chilled and hot water plant and contain several water coils as well as multiple fans and filter racks. We assume they are configurable by an on-site facilities team with BAS integration.
"Put HEPA filters in our buildings."
Walking out of a meeting with this leadership mandate, we assume HEPA filters either fit in the existing filter rack or can be “made to fit.” We can expect the immediate energy use and performance outcomes as simulated in Table 1. These outcomes represent initial/clean pressure drops for our three aforementioned hypothetical pieces of equipment. What is not represented is the subsequent filter-loading and resultant impact on cfm, ESP, brake horsepower (BHP), and fan heat. Small packaged units are engineered with razor-thin margins of operation to reduce first cost. Once an additional pressure drop is introduced, such as a HEPA filter, this small margin of durability becomes its undoing, for both fan power and heating/cooling abilities.
Filters are measured by their minimum efficiency reporting value (MERV) rating — the higher the number, the finer the filtration. The typical commercial built environment will have MERV-8 or -10 filters, with MERV 13 in newer buildings (read: LEED rated). The MERV rating is given based on efficiency class at a particulate size range. For example, a MERV-8 filter is 84.9% efficient at removing particles 3-10 microns in size while a MERV-14 filter is 84% efficient at removing particles 0.3-1 micron in size (smaller/better capture). HEPA, a well-known and effective air filter, is rated for 99.97 to 99.99% efficient capture at removing particles 0.3 microns in size. This filter starts to become attractive when viruses, such as COVID-19, range from 0.06-0.14 microns in size, a size that HEPA is theoretically capable of capturing; however, at a lower efficiency. The higher the MERV rating, the better the efficiency at removing smaller particulates but also the greater the air pressure drop (effective resistance to flow).
In addition to immediate equipment impacts, we need to consider the connected systems and subsequent human behaviors from perceived performance (all well-meaning, of course). The first thing occupants will notice is that some rooms are too hot, too cold, or stuffy. This Goldilocks-type problem is due to less airflow serving the most remote zones down the ductwork, leading to a loss of control in some zones or rooms but curiously not in others (those closer to the air-handling unit). Buildings with a high level of glazing will experience noticeable daily temperature fluctuation resulting from solar gain changing angle throughout the day with lower system durability to adapt and respond. Rooms will feel stuffy for occupants since outlet throw and air speed will be reduced at the equipment location before it even has a chance to reach the end of the ductwork.
In the summer months, if the building has operable windows, occupants may open them if they feel airflow is inadequate, resulting in further temperature fluctuation and global coil command open percentage (100% open). In a more modern building with an automation system, supervisory control will also begin to lower the set point of the chilled water loop (making an electric chiller work harder), since the zones appear to not be “satisfied” at set point, even though this problem is experienced due to less airflow and occupant reactions and not the coil’s designed ability to satisfy a set point. In winter months, it is possible warm supply air may not reach all spaces as effectively as before, resulting in the unwelcome addition of personal heaters (think increased plug energy, potential safety concern). Once occupants build the human habit of using their own heater, it will be hard for them to stop in the future.
In a humid climate, a facility will experience more humidity indoors compared to previous years. This will be sensed by the occupants, especially if they’re congregating inside a busy conference room, and result in discomfort (reference ASHRAE 55) and degradation risk to the facility, since such an environment is conducive to mold or rot. In the past, the building operator relied on a supply of cooled (and, therefore, dried) air delivered to the space to absorb the latent load from sweat, cooking, etc. This clammy feeling may result in humidity uncontrolled further when occupants prop windows and doors open to help “get more airflow,” making the problem worse.
The cost of filter media and subsequent environmental waste should be considered too. Adding HEPA filtration to a facility previously operating at a lower level of filtration will cause the filters to load quickly after installation. This will result in a greater pressure drop than the clean filter value shown in Table 1 in only a short period of time. This is important because many facilities are in the habit of changing filters on a schedule, so this loaded pressure drop will remain in effect until the next planned maintenance. HEPA filtration segment dimensions are also less varied than lower MERV-rated filters and increase steeply in price for custom sizing. This means operations may not find an assortment that fits existing filter rack lengths and widths without either spending extra or providing some in-house modifications. The depth of the filters will cause issues for physical fitment, especially in units with close coil proximity. These cascading operational reactions will result in additional cost and effort and less airflow to confined spaces, contrary to health guidance — the comfort and safety outcomes are not assured while the energy and material cost outcome is guaranteed.
"Get more outside air in here, I want all outside air starting now.”
This follows the logic of “the solution to pollution is dilution.” Walking out of a meeting with this leadership mandate, we assume outside air ratios are overridden to the maximum possible extent. In the architecture and design phase of a building, the air-handling fans, coils, air duct sizing, pipe diameters, etc., are carefully designed for a selected range of expected operating conditions and parameters based on construction type and occupancy loads. These parameters are meant to balance system performance, energy use, fresh air percentage, and reliability of control. Indoors, the engineer will size systems based on a combination of “loads,” such as the heat and moisture of human bodies and kitchens, the dry heat of computers and lights, and the radiant and convective impacts of windows and architecture. Outdoors, the regional ASHRAE design conditions are based on previous climate trends. The limits of what a system is designed to accommodate are codified.
When operations proceed with the adjustments, the method will vary by the equipment type. The small, packaged unit may simply require a linkage adjustment or pinning a damper open. The greatest risk with this is that it’s not remotely monitored or revokable and remains permanent until someone thinks to undue the change. Hopefully, it is not forgotten. Our large packaged unit will allow an electronic controller adjustment, possibly at the unit itself (centralized automation is better for monitoring if available). While still somewhat permanent, the electronic controller is more flexible than resetting linkages. The large custom unit will most assuredly be adjusted by software set point at the building automation front-end computer in an operations office. This is the most reversible of the options since operators typically leave notes of changes made and will have software data trends of system performance. (For a quick comparison of our test unit sizes and the impacts of the outside air leadership mandate, see Table 2.) The tables featured in this article paint a grim picture of three hypothetical situations, which result in an 8°-13° leaving dry bulb temperature increase.
Unfortunately, much of the built environment is not as closely monitored or controlled as large facilities can afford. Most reactionary changes will have the risk of remaining semi-permanent. We ask the reader to consider: What happens six months or a year from now? When the current pandemic starts to wind down, who will know to get up on the roof and readjust the linkages in the multiple small, packaged units back to their original positions? What was that original position? Are set points on the large packaged unit documented? What buttons did they push to program it? Sometimes the devil is in the details.
Regular energy costs reflect operating at design conditions only a small portion of the year by regional design. Those extremes sometimes last just a few hours. Each year, these design conditions occasionally occur and systems aren’t able to keep up, but, thankfully, it’s not for long. When it occurs, it’s usually only noticed by computer trends with the occupants remaining blissfully unaware. Almost all air-handling systems will recirculate some of the air from the space back into the supply to mix with outside air before the heating and cooling coils. This is to buffer the capacity and efficiency of the system. Now, by manually overriding the outside air intake amount, that recirculation buffer effect is lost, and the amount of time spent closer to "design conditions" increases significantly throughout the year. This will result in more heating and cooling energy use since seasonal conditions will be directly passed to the coils and exceed the intended unit capacity more often. Another risk to consider is frozen water coils. If adjustments are made to systems in freezing climates, the units’ prior freeze protection programming may not properly activate, and coils will burst with ice overnight only to leak when they thaw.
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.