Optimizing indoor air quality strategy and energy efficiency are important, but often competing, goals for energy and facility professionals.
When it comes to ventilation in air handling systems there are two possible extremes in how outdoor air can be controlled: (1) maximization of outdoor air and (2) minimization of outdoor air. Maximizing outdoor air during most times of the year, depending on location, often leads to poorer energy performance due to the conditioning requirements of the outdoor air which may be very hot, very humid, very cold, and/or very dry. Conversely, minimizing outdoor air tends to improve energy performance for the same reasons, but the minimum amount must be maintained by code and to protect health of occupants. Since around 1970, commercial buildings have dropped their HVAC energy consumption by 60%, but what were the potential indoor air quality costs to occupant health and wellbeing? (see chart below)
This article will highlight potential extremes on indoor air quality strategies and their impact on energy use — and what could be done to address these challenges.
Maximization Extreme: what happens if the air inside is of profoundly poor quality or contains biologically unsafe substances?
Many traditional indoor air quality initiatives in HVAC systems focus on maximizing, within reason, the amount of ventilation from outdoor air so as to purge spaces of potential contaminants. This is the reason why laboratory environments and other critical spaces that may contain dangerous substances require 100% outdoor air at all times. Additionally, this principle was strongly emphasized early during the COVID-19 pandemic where the U.S. Environmental Protection Agency and other organizations recommended increasing outdoor air ventilation to help reduce viral load1, though the guidance has changed significantly since the onset of the pandemic. The inevitable outcome of this is that during times of the year when airside economizing cannot be used, energy usage will increase compared to a baseline because the outdoor air must be conditioned to the requirements of the space. For example, during hot, humid times of the year, more energy must be used to cool and dehumidify the air. Conversely, during cold, dry times of the year, more energy must be used to heat and humidify the air depending on how the spaces are utilized.
Minimization Extreme: what happens if the air outdoor is of poorer quality than the air inside?
On September 29, 2024, a fire broke out at a chemical supply company in Conyers, Georgia. According to media reports, a sprinkler malfunction caused water to come into contact with a water-reactive chemical, triggering off-gassing of chlorine and chlorine compounds, in addition to bromine2. While the cause of the fire and subsequent air quality issues remains unknown, what is known is the plume of strong-smelling gas that permeated in the air for days after the incident. In fact, the author of this article had to return home while taking his children to school because of how strong the odor of chlorine was and its visibility in the air as a yellow/brown fog. Additionally, schools in the area were canceled that day as a result of the chemical plume 3. According to the Centers of Disease Control (CDC), “chlorine gas is highly corrosive when it contacts moist tissues such as the eyes, skin, and upper respiratory tract”4. The priority of all local governments was the safety and health of the citizens, and this led to businesses shutting their doors in addition to the schools. This had obvious health and economic impacts to the local area. The author of this article is reminded of the similarity between this incident and the wildfires that are becoming more common in California and other western states as well as Canada5.
Interestingly, even if a state is not prone to wildfires, the impact of the drift of wildfire smoke can have an impact far away. A 2023 study by scientists at Standford, Cambridge, University of British Columbia and UC San Diego estimated that a majority of wildfire smoke comes from sources outside the local jurisdictions, with 60% coming from fires in other states6.
In seeking to minimize inside air contaminants in a space to a healthy low, the assumption is made that the air outdoor is better than the air inside. The example discussed above is a situation becoming more common where this is not necessarily the case. It is arguable in this situation that outdoor air should be shut off completely, which is allowable in certain situations in building codes based on ASHRAE 62.1. Obviously in this case, energy savings are not the priority.
Addressing These (Rare?) Extremes
The data presented above begs the following questions:
· How can building systems simultaneously conserve energy and ensure indoor air quality?
· What benefits would occur if there was a way to ventilate a space appropriately with precise control while driving energy savings and ensuring the indoor environmental quality is satisfactory?
In the real world, the extremes used to be rare outside of certain building types (e.g., laboratories) but, unfortunately, extremes are becoming more common. The ideal control methodology would be properly equipped with sensors and sequences of operation to account for these extremes, potentially leveraging AI-driven optimization that can dynamically respond to these extremes. Imagine a scenario where the difference between indoor and outdoor air quality is continually evaluated and the outdoor air damper controls automatically prevent ventilation when outdoor air is very poor. Further, AI-driven optimization would provide the correct supply temperature and static pressure setpoints to a VAV system knowing that ventilation condition is occurring, automatically learning the behavior of the system based on real-time feedback.
This type of optimization would also be based on an equivalent “clean” air per person ventilation terminology which is emerging within ASHRAE 62.1 through the indoor air quality procedure (IAQP) and ASHRAE 241, which allows for additive performance-based layers of air cleaning and source control to supplement the general reliance on outdoor air ventilation to drive cleanliness.
An overall package should also incorporate properly-sized filtration with strong consideration of ionization, ultraviolet, and other disinfecting and purifying technologies. Perhaps most importantly, a strategy must incorporate digitally enhanced technologies that measure and track performance of indoor air quality to ensure safe and efficient operation at all times with the ability to quickly remediate issues through work orders.
The benefits to any organization are confidence that the building is operating as safely and efficiently as possible in any scenario with maximized energy savings while prioritizing health and safety above all else. Perhaps, finally, indoor air quality and energy savings can be mutually enhanced in buildings simultaneously – finding the perfect balance for buildings.
Click below for more about what Siemens is doing on this topic: https://www.siemens.com/us/en/products/buildingtechnologies/energy/energy-efficiency/energy-services.html https://www.siemens.com/us/en/products/buildingtechnologies/services/mechanical/smart-air-quality.html 1 https://www.epa.gov/indoor-air-quality-iaq/ventilation-and-coronavirus-covid-19 2 https://www.ajc.com/news/crime/conyers-chemical-plant-fire-what-to-know/ZECJVWIRDNCR5P2DZJFSAXUQ2A/#:~:text=What%20chemicals%%20released%3F,Management%20and%20Homeland%20Security%20Agency 3 https://www.wsbtv.com/news/local/newton-county/rockdale-county-chemical20were-fire-newton-co-schools-closed-monday-due-potential-biolab-impact/RJCCRV6MN5HPFHW3AV4JB3V24Y/ 4 https://wwwn.cdc.gov/TSP/MMG/MMGDetails.aspx?mmgid=198&toxid=36 5 https://oehha.ca.gov/climate-change/epic-2022/impacts-vegetation-and-wildlife/wildfires#:~:text=Over%20the%20last%2020%20years,natural%20part%20of%20California’s%20landscape 6 https://pubmed.ncbi.nlm.nih.gov/38085772/
Feature Image Courtesy of: Siemens
