Decarbonization and Indoor Air Quality Improvements
Are They Compatible?
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The COVID-19 pandemic has heightened awareness among the general population about the importance of indoor air quality in unprecedented ways. While this acute, disaster-borne focus is clearly something that most would have preferred to avoid, there is growing momentum to position our industry to better respond to future pandemics in the wake of this global tragedy.
As described in an AIHA report published in 2020 (PDF), multiple studies have shown that better IAQ can result in higher worker productivity, better cognitive performance, increased job satisfaction, reduced absenteeism, and less reported job stress. Specific interventions associated with these types of improvements include higher ventilation rates, lower indoor pollutant emissions, more efficient air filtration, improved temperature and humidity control, and reduced dampness and mold in buildings. For the most part, however, building owners, operators, and managers have not recognized or appreciated the potential financial benefits of good IAQ, instead focusing on energy costs. This predilection persists even though the value of increased productivity among employees is more than 150 times greater than the associated energy costs for enhanced ventilation, according to a 2015 paper published in the International Journal of Environmental Research and Public Health.
As described in the journal Atmosphere, for the most part, the efficiency of ventilation systems has been prioritized over effectiveness at controlling and minimizing contaminants, so it should come as no surprise that many ventilation systems commonly found in buildings are not designed to—and are quite ineffective at—controlling airborne transmission of such agents. Concerns over ventilation and COVID-19 reached a boiling point in 2021, when hundreds of healthcare workers, scientists, engineers, and industrial and occupational hygienists signed open letters calling on government officials in the United States, the United Kingdom, Canada, Australia, and elsewhere to address substandard IAQ and take steps to reduce airborne transmission of SARS-CoV-2.
Traditionally, mechanical ventilation has been used primarily to provide thermal comfort by ensuring that temperatures throughout a building do not vary widely. Controlling relative humidity levels in buildings has typically been achieved as an ancillary consideration. A secondary aim of mechanical ventilation is to reduce the buildup of indoor air contaminants, and thereby mitigate potential adverse health effects, by mixing “fresh” outdoor air with the indoor air. While such dilution ventilation is generally acceptable for controlling low-toxicity gaseous contaminants such as carbon dioxide, it is much less effective at preventing the transmission of highly infectious viruses or other microorganisms.
In response to the COVID-19 pandemic, various agencies and professional associations have recommended upgrading, to the extent possible, filtration on heating, ventilation, and air-conditioning (HVAC) systems and increasing the amount of outdoor air brought into buildings. However, the impact of these types of interventions on energy usage is often a major consideration for companies and institutions that are looking to reduce their carbon footprint. The Journal of Building Engineering recently published a study that simulated ventilation rates and filtration methods across 13 U.S. cities and reported that, on average, the annual energy consumed by an improved filtration system was 31 percent lower than the energy consumed by 100 percent outdoor air ventilation. A similar study published in Energy and Buildings found that increasing outdoor air ventilation from 7 liters per second per person (l/s/person) to 21 l/s/person tripled HVAC energy consumption. The same increase in outdoor air, combined with sensible heat recovery, resulted in a more modest 40 percent increase in energy usage.
VENTILATION AND IAQ The recommended minimum ventilation rate, as prescribed by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), varies depending on the building type and space usage. The current ASHRAE recommended minimum ventilation rate for office spaces is 5 cfm per occupant, plus 0.06 cfm per square foot of floor area. Using default values from Table 6-1 of ASHRAE standard 62.1-2019, Ventilation for Acceptable Indoor Air Quality, this results in a net of approximately 17 cfm (8 l/s) per occupant.
The practice of recycling a majority of air (for example, 90 percent or more, in some constant-volume systems) in mechanically ventilated buildings, in order to conserve energy, has long been recognized as a likely contributor to complaints about “sick building syndrome” and reported adverse health effects. Energy conservation in the 1970s and 1980s was largely driven by the oil embargo in 1973–1974 and the ensuing spike in oil prices. Some energy conservation measures, undertaken to reduce the operational costs of HVAC systems, resulted in insufficient amounts of outdoor air or inadequately conditioned air being supplied to the occupied space. Today, however, energy conservation efforts are increasingly motivated by concerns about climate change, a primary driver of which are greenhouse gases released when fossil fuels are burned to produce energy. A corresponding push for decarbonization of buildings and the U.S. energy system has established a goal of net-zero carbon emissions by 2050.
AIR CLEANERS AND FILTRATION HVAC filters are designed to remove particles from the air before supplying it to the occupied spaces in a building. Particles are either physically trapped by the fibers of the filter media or become stuck to the media due to an electrostatic charge. Filter performance depends on many variables, including airflow rate and velocity, filter media thickness and composition, particle size and mass, amount of dust on the filter, and amount of air leakage bypassing the filter.
Caution, and informed professional judgment, are advised when deciding upon the use of portable air cleaners.
ASHRAE standard 52.2 describes a method of testing that results in a Minimum Efficiency Reporting Value (MERV), which serves to standardize and simplify air filter efficiency ratings for consumers. The MERV rating on an air filter describes its efficiency as a means of reducing the level of 0.3–10 micron-sized particles in air that pass through the filter. A higher MERV means a higher proportion of particles are removed from the air. MERV ratings for filters range from a low of one (for example, a low-cost disposable fiberglass furnace filter) up to 16 (for high-efficiency filters commonly used in certain healthcare applications). According to EPA, the removal efficiency for smaller particles varies substantially by MERV and can even vary within different makes and models of filters with the same MERV rating (PDF).
In the wake of COVID-19, recommendations for increasing the amount of outdoor air introduced into buildings have included either reducing or eliminating air recirculation and targeting 4 to 6 air changes per hour (ACH) in occupied spaces. ASHRAE and others have also recommended that HVAC systems be fitted with MERV 13 filters, or better, to help mitigate the transmission of infectious aerosols. In many instances, building owners and occupants have turned to portable air purifiers to address airborne contaminants, including viruses and other bioaerosols, as well as other gaseous contaminants such as volatile organic compounds (VOCs). Depending on building configuration, such units can be more energy efficient than introducing large volumes of outside air through a central HVAC.
The amount of filtered, recirculated air from an air purifier is often referred to as the clean air delivery rate (CADR), which is expressed in units of cubic feet per minute (CFM) or cubic meters per hour (m3/h). The CADR was developed by the Association of Home Appliance Manufacturers in 1989 as a standardized testing and reporting method (ANSI/AHAM AC-1, Portable Electric Room Air Cleaners) for the efficacy of air cleaners in removing airborne particles. As described in a report from ACGIH, the CADR indicates the volume of filtered air that an air cleaner delivers, with separate scores for cigarette smoke (0.09–1.0 µm diameter), Arizona road dust (0.5–3.0 µm diameter), and paper mulberry pollen (5–11 µm diameter). The higher the CADR number for each particle type, the faster the unit filters the air.
In March 2022, AHAM published a standard test method (AHAM AC-5) to measure the ability of room air cleaners to remove aerosolized mold spores (Aspergillus brasiliensis), bacteria (gram-positive, gram-negative, and endospores), and viruses (MS2 bacteriophage) from indoor air, referred to as m-CADR. Currently, AHAM is developing a standard test method (AHAM AC-4) to measure the efficacy of air cleaners to remove gas-phase chemical compounds, including formaldehyde, toluene, and d-limonene, commonly found in indoor environments.
Caution, and informed professional judgment, are advised when deciding upon the use of portable air cleaners, particularly those that rely on emerging technology. A review performed by a major HVAC equipment manufacturer identified many limitations and uncertainties associated with use of these technologies in real-world situations, which are always more complicated than laboratory test conditions. Additionally, multiple studies have found that many of these technologies have the potential to generate various unintended intermediates and byproducts, such as ozone, organic acids, oxidation VOCs, and ultrafine particles, into the indoor environment.
VENTILATION, HEATING, COOLING, AND ENERGY USAGE The fans and equipment necessary to provide conditioned ventilated air are often a significant portion of a building’s overall energy demand and carbon emissions. This is particularly true for older buildings that have less efficient HVAC equipment. Many commercial buildings use rooftop HVAC package units for their supply and makeup air. Hotels and multi-unit residential buildings regularly incorporate natural gas-fired supply/make-up air units to provide corridor ventilation and pressurization. Often, these units deliver a constant air volume at a set temperature. Meanwhile, bathroom exhausts in guest rooms or residential units usually run constantly, pulling out conditioned air that then needs to be replaced.
According to a 2015 report from the U.S. Department of Energy, over 76 percent of all electricity in the U.S., and more than 40 percent of all energy in the U.S. (along with the associated greenhouse gas emissions) was used to “provide comfortable, well-lit residential and commercial buildings,” and for conditioning and lighting industrial buildings (PDF). Nearly 35 percent of all the energy used in residential and commercial buildings was for heating, cooling, and ventilation. Around the world, nearly 20 percent of the total electricity used in buildings is for air conditioning and electric fans to keep occupants cool, as revealed in a 2018 report by the International Energy Agency. If left unchecked, that number could more than triple by 2050.
A paper in the April 2022 issue of Joule calculated that air conditioning is responsible for the equivalent of 1,950 million tons of CO2 released annually, or approximately 3.94 percent of all global greenhouse gas emissions. Of that number, 599 million tons (31 percent) comes from removing humidity, 531 million tons (27 percent) from temperature control, and 720 million tons (37 percent) from refrigerant loss. According to the authors, managing indoor humidity levels with air conditioning contributes more to climate change than controlling temperature alone, and the problem is expected to worsen as consumers in other countries install mechanical cooling systems in spaces that previously were unconditioned.
In the U.S., most homes are heated using either furnaces or boilers. Furnaces heat air and then distribute it via ducts. Boilers heat up water and then provide either hot water or steam for heating. Hot water is typically distributed via baseboard radiators or radiant floor systems, or is piped to an air-handling unit where it then warms the air by means of heating coils. Steam is distributed through pipes to steam radiators. Because steam boilers operate at temperatures much higher than needed to condition a space, they tend to be less energy efficient than hot water systems.
In the buildings of the future, combining ventilation, filtration, and air cleaning will be the key to lowering energy usage and improving IAQ.
Efficiency for residential and small commercial furnaces or boilers is commonly measured by annual fuel utilization efficiency (AFUE), which is the ratio of the furnace’s or boiler’s annual heat output compared to its total annual fossil fuel energy consumed. An AFUE of 80 percent indicates that 80 percent of the energy in the fuel becomes heat for the home, while the other 20 percent is exhausted outdoors via the chimney and lost elsewhere. AFUE does not include heat losses from the piping or duct system. According to a 2012 guide on green building practices, these losses can be as much as 35 percent of the energy for output of a furnace when ducts are uninsulated and located in unconditioned or partially conditioned spaces, such as attics, crawlspaces, or garages.
NEWER ENERGY-EFFICIENT TECHNOLOGIES Heat recovery ventilators (HRV) and energy recovery ventilation (ERV) systems provide controlled ventilation while minimizing energy loss from directly exhausting conditioned air outdoors. Unlike HRV systems, ERVs transfer both heat and humidity, and thereby affect both the temperature and the moisture of the supply air. In the winter, ERVs capture heat from the indoor air being exhausted and transfer it to the outdoor supply air being brought into the building. In the summer, the opposite occurs: the indoor air being exhausted helps to pre-cool the incoming outdoor supply air. ERCs therefore reduce the costs of both heating and cooling air and can be anywhere from 50 to 98 percent efficient in recovering the energy that would otherwise be exhausted outdoors.
Air source heat pumps work by transferring heat absorbed from the outside air to an indoor space. Certain heat pumps can also work as cooling systems in the summer months by transferring heat from the indoors to the outside air. Air-to-air heat pumps can deliver up to three times more heat energy than electrical energy consumed. Enhanced, high-performance air-to-water heat pumps can provide 350 percent greater energy efficiency than typical gas boilers in heating mode. The International Energy Agency estimates that heat pumps could satisfy 90 percent of global space and water heating needs; yet in 2020, heat pumps accounted for only 7 percent of residential heat demand, while fossil fuel-based technologies made up nearly half of heating equipment sales globally. As focus on decarbonization and electrification of buildings grows, heat pumps are poised to become much more prevalent.
According to the National Renewable Energy Laboratory (NREL), existing technology to cool and dehumidify buildings using refrigerants and cooling coils is reaching practical and theoretical limits (PDF). Typically, to control indoor humidity levels, supply air is over-cooled to below the dew-point temperature and then reheated to an appropriate temperature, wasting energy in the process. Newer technologies that divide cooling and humidity control into two separate processes show potential to improve efficiency by 40 percent or more. One such technology is liquid desiccant-based cooling. Desiccant liquids are often high-concentration salt-water solutions that can absorb water directly from air and reduce the need for mechanical dehumidification. Thermal energy is then used to dry the desiccant solution after water has been absorbed. NREL researchers note that liquid desiccants fundamentally change the way humidity is controlled and have a theoretical efficiency limit 10 times higher than technology based on an electrically driven vapor compression cycle (for example, heat pumps, chillers, and direct expansion units). In addition, liquid desiccants can be implemented to shift latent loads to times when energy is cheaper, either because energy demand is low or when renewable energy is abundant.
IAQ AND ENERGY CHALLENGES GOING FORWARD The COVID-19 pandemic has clearly shown that current ventilation standards and practices for acceptable IAQ in non-healthcare settings are inadequate when dealing with infectious agents. History teaches us that pandemics eventually run their course or transition to endemic issues, similar to influenza or seasonal colds. While this outcome will be welcomed, concerns regarding ventilation and IAQ, climate change, energy savings, and decarbonization will persist. Ventilation and IAQ need to become resilient and adaptable to the future we face—not only with respect to airborne infectious diseases, but also to disasters such as wildfires, extreme heat, and pollution-driven air quality concerns.
New technologies for heating, cooling, and ventilation do more than deliver large gains in efficiency. They can also improve the way building HVAC systems meet occupant needs—improving comfort, productivity, and health. IAQ sensors that measure specific contaminants will become ubiquitous, enabling demand-control ventilation and IAQ efforts that are targeted, efficient, and continuously optimized. Improved ventilation, filtration, and air cleaning, plus sensing and controls, will make buildings more resilient because they can be adapted to whatever situation is at hand. In the buildings of the future, combining ventilation, filtration, and air cleaning will be the key to lowering energy usage and improving IAQ. The use of combined natural and mechanical (hybrid) ventilation, air-to-air and air-to-water heat recovery (where possible), more and better demand-control sensors, economizers, dedicated outdoor air supplies, and better air delivery can make IAQ improvements achievable, while also decarbonizing buildings.
JOHN P. “JACK” SPRINGSTON, CIH, CSP, FAIHA, is the industrial hygiene services manager for Atlas Technical Consultants in New York City and Bethpage, New York.
WANE A. BAKER, PE, CIH (ret.), is a senior technical instructor in The Graduate Training Program with Trane, located in La Crosse, Wisconsin, and is a past chair of AIHA’s Indoor Environmental Quality Committee.
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ACGIH: “Engineering Controls for Bioaerosols in Non-Industrial/Non-Healthcare Settings” (2021).
AIHA: “The Value of IAQ: A Review of the Scientific Evidence Supporting the Benefits of Investing in Better Indoor Air Quality” (PDF, May 2020).
ASHRAE: “Filtration and Disinfection FAQ.”
ASHRAE: Standard 52.2-2017, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size (2017).
ASHRAE: Standard 62.1-2019, Ventilation for Acceptable Indoor Air Quality (2019).
A.S.H.V.E. Transactions: “Ventilation Requirements” (1936).
Association of Home Appliance Manufacturers: ANSI/AHAM AC-1-2020, Method for Measuring the Performance of Portable Household Electric Room Air Cleaners (2020).
Association of Home Appliance Manufacturers: AHAM AC-5-2022, Method for Assessing the Reduction Rate of Key Bioaerosols by Portable Air Cleaners Using an Aerobiology Test Chamber (2022).
Association of Home Appliance Manufacturers: “White Paper for Studies on Air Cleaners & Microbial Decontamination of Indoor Air to Support AHAM AC-5” (March 2022).
Atmosphere: “The Dichotomy Between Indoor Air Quality and Energy Efficiency in Light of the Onset of the COVID-19 Pandemic” (June 2021).
Aviation Clean Air: “SARS-CoV-2 Neutralization by Needlepoint Bipolar Ionization, Powered by GPS” (PDF, 2020).
British Medical Journal (Clinical Research Edition): “The Sick Building Syndrome: Prevalence Studies” (December 1984).
California Air Resources Board: “Evaluation of Pollutant Emissions from Portable Air Cleaners” (PDF, December 2014).
Canada Mortgage and Housing Corporation: “A Guide to Residential Wood Heating” (2008).
Delmar Cengage Learning: Green Building: Principles and Practices in Residential Construction (2013).
Energy and Buildings: “The Design of Safe Classrooms of Educational Buildings for Facing Contagions and Transmission of Diseases: A Novel Approach Combining Audits, Calibrated Energy Models, Building Performance (BPS) and Computational Fluid Dynamic (CFD) Simulations” (January 2021).
Environmental Science & Technology Letters: “Formation of Oxidized Gases and Secondary Organic Aerosol from a Commercial Oxidant-Generating Electronic Air Cleaner” (July 2014).
EPA: “Indoor Air Facts No.4 (revised) - Sick Building Syndrome” (PDF, February 1991).
EPA: “Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2020” (April 2022).
EPA: “Residential Air Cleaners: A Technical Summary,” 3rd edition (PDF, July 2018).
Health and Safety Executive: “Sick Building Syndrome: A Review of the Evidence on Causes and Solutions” (PDF, 1992).
HPAC Engineering: “Interpreting Filter Performance: The Meaning Behind the Terminology of ASHRAE Standards 52.1 and 52.2” (February 2006).
Indoor Air: “Perceptions in the U.S. Building Industry of the Benefits and Costs of Improving Indoor Air Quality” (April 2016).
Indoor Air: “Primary and Secondary Consequences of Indoor Air Cleaners” (February 2016).
Indoor Air: “Sick Building Syndrome and Perceived Indoor Environment in Relation to Energy Saving by Reduced Ventilation Flow During Heating Season: A 1 Year Intervention Study in Dwellings” (April 2005).
International Energy Agency: “Heat Pumps” (2021).
International Energy Agency: “The Future of Cooling: Opportunities for Energy-Efficient Air Conditioning” (2018).
International Journal of Environmental Research and Public Health: “Economic, Environmental and Health Implications of Enhanced Ventilation in Office Buildings” (November 2015).
John Wiley & Sons: “Indoor Air Quality in Nonindustrial Occupational Environments” in Patty’s Industrial Hygiene, Volume 4 (2021).
Joule: “Humidity’s Impact on Greenhouse Gas Emissions from Air Conditioning” (July 2022).
Journal of Building Engineering: “Modeling Impacts of Ventilation and Filtration Methods on Energy Use and Airborne Disease Transmission in Classrooms” (October 2022).
Journal of the American Medical Association: “Indoor Air Changes and Potential Implications for SARS-CoV-2 Transmission” (May 2021).
Journal of Occupational and Environmental Hygiene: “What Is an Effective Portable Air Cleaning Device? A Review” (March 2006).
National Academies of Sciences, Engineering, and Medicine: “Accelerating Decarbonization of the U.S. Energy System” (2021).
National Renewable Energy Laboratory: “Desiccant Enhanced Evaporative Air-Conditioning (DEVap): Evaluation of a New Concept in Ultra Efficient Air Conditioning” (PDF, January 2011).
National Renewable Energy Laboratory: “Low-Flow Liquid Desiccant Air-Conditioning: Demonstrated Performance and Cost Implications” (PDF, September 2014).
Nature: “Why Indoor Spaces Are Still Prime COVID Hotspots” (March 2021).
New York State Energy Research & Development Authority: “Building Decarbonization Insights.”
New York State Energy Research & Development Authority: “Multifamily Performance Program, Tech Tip—Boiler Efficiency” (April 2008).
Proceedings of the 12th International Symposium on Heating, Ventilation and Air Conditioning: “MERV 13 Filtration for Office Buildings During COVID-19 Pandemic” (November 2021).
Trane: “A Taxonomy of Air-Cleaning Technologies Featuring Bipolar Ionization” (PDF, January 2021).
U.S. Department of Energy: Quadrennial Technology Review – An Assessment of Energy Technologies and Research Opportunities, chapter 5, “Increasing Efficiency of Building Systems and Technologies” (PDF, September 2015).