ASHRAE Part 2: Optimizing Indoor Spaces in the COVID Era

Hysteria around the COVID-19 pandemic provided the perfect cover for many enterprising companies to peddle all sorts of products of varying antiviral utility. While I may have the most experience with the opportunistic hand sanitizer industry, the markets for masks, sanitizing chemicals, COVID tests, infrared thermometers, plexiglass barriers, air purifiers, UV disinfection lamps, and bug-out bags all exploded since early 2020. A steady hand through all of this was ASHRAE – though I knew them for their useful weather datasets, the HVAC experts that make up this trade organization have been putting out clear, concise, scientifically-motivated resources since the pandemic began.

As a respiratory virus, the defining challenge in pinpointing SARS-CoV-2 transmission risk was determining the extent of airborne/aerosol transmission versus droplet/surface transmission. ASHRAE released their first guidance in April 2020 to clarify this question early, acknowledging that the primary risk was from droplets but that aerosol spread couldn’t be ruled out. This codified the 6-foot social distancing in indoor spaces, allowing businesses like restaurants to reopen on an interim, wait-and-see basis. From there, ASHRAE set an ambitious research schedule, leading to a series of detailed and informative white papers to guide HVAC professionals…and that’s about it. A downside to leaving such an important task to a trade organization is that the adoption of guidelines feels optional, completely unenforceable in all but a few jurisdictions.

To me, it’s logical that indoor air management should be the primary focus to prevent the spread of a respiratory virus, especially with the emergence of more highly contagious variants like Omicron. This goes beyond a simple air purifier, a common scam item that ASHRAE played an active role in screening/warning against – strategies include directing airflow patterns downward and toward local exhaust registers, modulating pressure to isolate high-risk rooms, adding UV treatment and HEPA filtration to recycled air, and boosting outside air intake and exhaust flow rates. New requirements for hospital air filtration/ventilation are in the works, with the goal of mitigating the spread from contagious patients. Likewise, the next edition of the International Mechanical Code will possibly include airflow design requirements specifically aimed at curbing viral spread in high-occupancy indoor spaces.

The science is settled: we have the expertise to greatly reduce airborne transmission within new construction for very little added cost. While it’s unlikely that existing buildings are forced to upgrade their HVAC anytime soon, I do hope that the appropriate regulatory pathways (building codes, OSHA, etc.) begin to require a consideration of viral spread in ventilation design. Our society as a whole may not be prepared for the next pandemic, but thanks to subject matter experts at ASHRAE working in conjunction with public health professionals, at least we may be able to breathe a little easier going forward.

ASHRAE Part 1: Weather at Work

Over the course of renovating an industrial facility to meet code, I have encountered several aspects where meteorological/climatological factors play a role in guiding design. Resistance to natural disasters might be the first aspect that comes to mind, as many coastal locations mandate hurricane clips and other structural reinforcement techniques in new construction. Rainfall management is also important, as the outdoor surfaces must be engineered to ensure adequate runoff and spill containments must be sized to also include a maximum daily rainfall (11 inches in our south Texas location). Monthly temperature and humidity averages designate the climatic zone for building code purposes, which determines the required R-value of insulation and whether a vapor barrier should be placed on the inside or outside of walls. Other design implements, like high-albedo coatings or shades to protect against insolation, may not stem from a specific code requirement but can be critical to the functionality of a facility throughout the seasons.

Lately, I have been tasked with redesigning the heating and cooling systems for our facility. To meet the requirements of the International Energy Conservation Code (IECC), HVAC systems must be sized with consideration to the location’s expected weather conditions throughout the year. The American Society of Heating, Refrigerating and Air-Conditioning Engineers, or ASHRAE, has developed a compendium of resources to estimate HVAC loads based on climatic averages and assess risk for extreme weather events. It’s meteorology data processed in a way that is most useful for understanding how your building will interact with the elements. I included a sample of the data for nearby Victoria, Texas, embedded below for your perusal; it’s a lot of information but it’s pretty digestible, even for non-experts:

Victoria, Texas – ASHRAE 2009 PDFDownload

From this extensive tabulation of data, I was mainly concerned with the extreme temperatures (dry-bulb for winter and wet-bulb for summer) to establish edge cases for facility HVAC sizing. The summer extreme was straightforward: a design temperature/humidity difference is easy to pinpoint when the dew point maximum is a fixed value and there’s only about a few degrees difference between the yearly average dry-bulb temperature and the 50-year extreme. The winter extreme had some nuance, however: with twice the standard deviation for yearly dry-bulb minima, some winters barely freeze whereas last winter brought an extended winter blast of single-digit temperatures. While code requires that the roof deck of our building be heated to 40 °F to prevent wet-pipe sprinklers from freezing, there is some room for engineering judgment in deciding what minimum temperature becomes central to the design. I considered the 10-year value a reasonable design target, back-calculating to ensure that even last year’s all-time extreme case would keep the roof deck above 32 °F.

To put a ribbon on this meteorology-aided design, I incorporated some analytical techniques from previous work on local heat island modeling. I recycled some Delaunay triangulation code to establish two other data vertices at San Marcos and College Station then perform a weighted average calculation to interpolate the necessary data values for Hallettsville. Despite other stations being closer as the crow flies, this triangulation technique filtered out noisy results and provided a directionally balanced estimate of the climatic conditions at the exact location of our facility. A relatively simple way to add specificity and cross-check the data – I firmly believe that more local-level data is always a good thing.

With ASHRAE weather data in my toolbox, I feel better prepared to model generalized conditions for normal and extreme weather across the United States. It was fun to explore the intersection between engineering design and meteorology, even though the owners may decide not to build any of this according to my design – as it stands, we have an unprotected sprinkler system but no budgetary approval for further safety or weatherization installations. Meanwhile, I will continue using my fascination with weather to analyze 10-day forecasts in the hopes that our pipes don’t freeze and our building doesn’t flood.