Minimum ventilation rates are most often set by ASHRAE Standard 62. The standard considers the size of a building, its intended use, and the number of people expected to be in it. For commercial office buildings it was developed from survey feedback regarding odors or complaints about the “bioeffluents” emitted by people. Under this “conventional” system, an office with 200 square feet for each person requires at least 17 cubic feet of outdoor air per minute per person (CFM/Person).

To set the minimum rate, designers estimate the largest number of people expected to be in a space. The more people, the more contaminants will accumulate. If the number of people is stable contaminants reach a limit or “steady state” level. Removing pollutants and contaminants are addressed more in our filtration discussion but the effect can be tracked in real time by measuring carbon dioxide (CO₂) levels. The CO₂ level indicates whether the ventilation rate is keeping up with the people present. For a given number of people and size of space, all else being equal, a ventilation rate can be associated with a steady state amount of CO₂.

Our “enhanced” systems suggest higher than conventional ventilation rates to bring in more clean outdoor air and dilute pollutants. This results in more CFM/Person of outdoor air and a lower CO₂ steady state. Some systems are performance based, and specify a CO₂ steady state target instead of a fixed ventilation rate. The enhanced and stringent approaches often require Demand Control to save energy when fewer people show up to a space and the higher ventilation rate is not needed to “keep up” with their presence.

Researchers at Lawrence Berkeley National Lab (LBNL) found increasing the conventional ventilation rate from 17 to 22 CFM/Person across the US (i.e. shifting from the conventional to an enhanced approach) could save $12B a year in costs associated with employee performance, absenteeism, and sick building symptoms. 22CFM/Person is roughly the rate required to earn the Enhanced Ventilation credit under the LEED rating system. The same study found that further increasing the ventilation rate to 33CFM/Person would save $38B a year.¹ This is roughly what is required under the California Title 24 standard. A study of 40 buildings found that increasing ventilation to 50CFM per person reduced short term absenteeism rates by 35%² and another study found greatly reduced symptoms of sick building syndrome at this rate.³ EPA’s Building Assessment Survey and Evaluation (BASE) study found that 20-30% fewer occupants reported SBS symptoms in study spaces with ventilation rates above 20 to 25 cfm/person, compared to study spaces with lower rates between 10 to 20 cfm/person.⁴ Finally, a literature review found that increased use of economizers to bring in more fresh air related to reduced absentee costs of $0.30-$0.80 per square foot.⁵ Many of these studies accounted for the increased energy needed to provide more fresh air. They found the savings associated with increasing ventilation was an order of magnitude larger than the increased cost of moving and conditioning outdoor air to provide it.

The CogFX study tested performance on a rigorous cognitive assessment called the Strategic Management Survey under different air quality conditions. At 950ppm (less CO₂ than expected when ventilation provides 22CFM/Person outdoor air) participants performed 15% worse than at 650ppm (slightly less than the CO₂ level expected at 30CFM/Person). At 1500ppm, more CO₂ than expected at the conventional ventilation rate but still frequently found in conference and other small meeting rooms, participants fared 50% worse.⁶ A follow on field study using the same test found participants in buildings with ventilation rates of 22CFM/Person performed 26% better than those in buildings with conventional ventilation rates of 17 CFM/Person.⁷ Whether CO₂ is the direct driver of these conditions or a proxy for other conditions associated with ventilation rates is not supported by all studies,^8,9,10 but the general relation between increased ventilation and performance is less controversial.

Though not directly related to health, wellbeing and performance in commercial office buildings several studies explored the influence of classroom air quality on the performance of children in school. One study used a literature review to review other relevant studies and developed a model based on their findings. The study found students were 12% faster at certain routine tasks and psychological tests, and 2% more accurate when CO₂ was reduced from 4,100ppm to 900ppm.^11,12

Some spaces are more dynamic than others. Large, sparsely-occupied spaces like open plan or private offices will usually stay below the design target. Small, densely-occupied spaces like conference, focus and class-rooms will vary more and frequently rise above the target. When, where and how long you measure makes a big difference.

Design, build and operate ventilation systems understanding the factors that affect performance:

• The fresh air intake should be located away from loading docks and other pollution sources.
• Fresh air delivery risers, plenums and diffusers must be open and properly distributed to deliver fresh air effectively. ASHRAE rates the effectiveness of several different air distribution strategies. However, the performance of all such strategies are susceptible to impact from changes to floor plan or furniture. Ensure the system is regularly balanced and any floor modifications consider the air distribution strategy in your building.

It is important to balance the benefits of giving people more fresh air with the cost of providing it. For example, it takes energy to heat or cool fresh outdoor air to comfortable temperatures. Several strategies can mitigate or eliminate the cost of providing fresh air. Economizers make use of “free cooling” when outside temperatures are mild and heat recovery systems pull energy out of air before it is exhausted from the building during heating and cooling seasons. Heat recovery systems extract the heat or coolth of exhausted air and transfer it to incoming fresh air when conditions are too cold or too hot. Perhaps most importantly, Demand Control Ventilation (DCV) systems provide feedback to make sure that ventilation rates are slowed when spaces are not fully occupied. This makes sure ventilation energy is used efficiently to provide benefits when people are there and save energy when they are not. CA Title 24 requires use of economizers, heat recovery systems and Demand Control Ventilation.

Conventional HVAC designs usually combine the functions of maintaining air quality with maintaining thermal comfort. Often, thermal comfort conditioning takes precedence and some times fresh air flow may be compromised in a given space. DOAS decouple ventilation from conditioning. They provide ventilation consisting of 100% outdoor air at a rate that is not dependent on the heating or cooling needs of the space. The result is a more consistent amount of outdoor air and less likelihood of over-cooling or overheating. Such systems also allow individuals to set temperatures to their personal comfort without impacting the flow of fresh air to the space. DOAS do not necessarily provide more fresh air, they provide the amount of fresh air they are designed to provide and provide it more consistently than the more common VAV systems.

It is important to note that outdoor air in polluted environments may require more filtration for DOAS to truly enhance health. Our discussion on filtration goes into more detail on this subject

Natural ventilation and mixed mode systems have been shown to increase comfort and satisfaction. They are often assisted by less energy intensive personal fans, ceiling fans, etc to move air through the building during seasons or weather conditions where the air does not move sufficiently. Fans may increase satisfaction by giving people more control over their environment, providing more variability in conditions, and changing the range of conditions that feel comfortable to them. The term “adaptive comfort” derives from study of natural ventilation.

Learn more:

• Fans and circulation: How can fans improve comfort and energy efficiency?
  • Small fans can allow a 6deg shift in the temperature we find comfortable
  • Smart ceiling fans improve comfort and reduce HVAC energy by 11%
• Variability: Facility managers can create Experiential Delight for occupant
• Adaptive comfort: Occupants be empowered to promote their own comfort

Finally, buildings with natural or mixed-mode ventilation may create indoor environments with a more “natural microbiome” than buildings that rely only on mechanical ventilation.¹⁴ Tightly-sealed, mechanically-ventilated buildings tend to reduce the diversity of microorganisms overall and favor human pathogens in particular. Similarly, natural ventilation near natural features like rivers, cascades, forests, mountains or coastal surf may introduce “negative ions” which some research suggests may reduce particulates¹⁵ and ameliorate depression.¹⁶ However, these topics are not well understood and a profusion of products claiming to provide benefits related to them are based on little or no evidence. Exercise caution when designing for these benefits.

Under the Clean Air Act, U.S. outdoor air quality and pollutant levels are monitored by the EPA using a network of high-quality meters in each county across the country. The National Ambient Air Quality Standards (NAAQS) capture the pollutant levels for 6 “criteria pollutants” including PM and O₃ which require action if exceeded. NAAQS limits PM to an annual average below 12 μg/m³ and a daily average below 35 μg/m³ for PM, and it limits O2 to an 8-hour average below .07 ppm. In locations exceeding these limits, building filtration could maintain air quality within NAAQS. However, indoor air quality standards are not usually designed for this.

Indoor air quality standards are designed to protect against toxic effects of contaminants like asbestos, carbon monoxide and mold. ASHRAE’s Standard 62, referenced by many local buildings codes, requires a minimum filtration level to protect HVAC components from fouling. While these approaches do offer some protection from chronic effects, evolving building rating systems like LEED v4 and WELL v2 offer credits designed specifically to reduce them. The RESET Air for Commercial Interiors “High Performance” (RESET High) system goes further by establishing targets for indoor pollutant levels.

PM, especially ultrafine particles smaller than 2.5 microns in diameter (PM2.5), contribute to long-term chronic conditions like heart and respiratory disease, stroke, cognitive decline, and lung cancer.¹⁸ Reducing peak levels of PM can also immediately reduce acute symptoms like inflammation and irritation of airways. While the World Health Organization (WHO) says that no level of PM is risk-free it suggests a target of 10 μg/m³ over 8 hours for all regions to avoid the worst health risks. This WHO threshold is similar to the NAAQS annual level 12 μg/m³ over 8 hours.

According to the Global Burden of Disease 2010 study, PM is responsible for more than 3 million premature deaths each year. As such, the chronic effects of particulate pollution were found to be more lethal than epidemics of malaria or AIDS at the time. Most of these effects were related to pollution in the growing urban areas of Asia and Africa. However, a recent study found that reducing PM to the WHO target in the relatively cleaner conditions found in most of the developed world could save a half million lives per year.¹⁸ Moving from conventional to enhanced or stringent filtration in U.S. office buildings where local or peak conditions exceed the WHO threshold would achieve this goal.

Breathing ozone can trigger a similar variety of short term, acute health problems including chest pain, coughing, and irritation and inflammation of airways. These effects worsen chronic conditions like bronchitis, emphysema, and asthma. While the effects of O₃ are generally short-term, long-term exposure can also damage lung tissue increasing medical costs and reducing lung function over time.

Filters containing activated carbon have been shown to be effective at removing ozone.¹⁹ Carbon filtration is much less common than particulate filters and are typically added as additional pre-filters on building air intakes. Carbon filters can be normal fibrous filters with activated carbon added to them or granular beds of activated carbon. The WELL Standard v2 offers points for carbon filters.

Conventional design approaches are often prescriptive in nature and view filters as static. They provide the same level of filtration at all times regardless of actual pollutant levels. The only dynamic is that filters be cleaned or replaced as needed

Designers could base filter selection on expected levels of outdoor air pollution. Considering local air quality data, the MERV rating could be sized to ensure that indoor air levels meet NAAQS or RESET High standards under normal conditions. Further, the WELL Standard v2 suggests that the filter rack should be designed to allow space for additional filters, filters with higher MERV rating, or activated carbon filtration when such need arises. With that spare capacity, filtration can be added as needed if outdoor conditions change due to seasonal variation or other unplanned contingency like wildfires.

Indoor Environmental Quality (IEQ) sensing can be used to determine how human activities influence air quality (e.g., opening the windows). If a dense grid of appropriate sensors is deployed it could show how people use buildings, including how natural ventilation is well used or under utilized. Beyond understanding air quality through CO2, PM, CO, NOX, and VOCs, evaluating measurements of multiple IEQ factors could help to understand whether the intent of the building or building systems design is achieving the desired result. Learn more in the Human Impacts section and Buildings and Health module.

Like increasing ventilation rate, adding filtration requires more energy to move air. Creating flexibility to scale filtration to the level and type of outdoor pollution allows building operators to save energy when high levels of filtration are not needed and invest energy in protecting occupants when they are.

Increased humidity may reduce the quantity or count of particles suspended in indoor air. This is a complex phenomenon that is influenced by the size, shape and hygroscopy of the particles themselves which vary. Studies have shown conflicting results but water absorbing particles tend to spend longer in the air in dry conditions and be more easily resuspended by traffic in low RH.^22,23

Dry air degrades the eye’s tear film and mucous membranes in skin and airways making them more susceptible to inflammation^22,23,24 and infection.²⁵ Additionally, dry air has been associated with increased production of the inflammatory stress hormone cortisol in skin.²⁶ Dry air has been shown to break down precorneal tear film (PTF) in as little as an hour causing cascading inflammatory effects; the formation of dry spots also makes the eyes more susceptible to inflammatory effects of common air pollutants including particulate matter and oxidants like ozone.^24,27 Hydration from increased RH or moist inserts on glasses worn by patients with dry eyes relieved these symptoms.²⁸ Dessication of nasal mucosal membranes by cold dry air causes increased release of inflammatory mediators making particulate matter more likely to adhere to surface cells.²⁵

While the mechanisms are complex and not fully understood, cold, dry air conditions may increase the risk of transmission of certain viruses including the influenza virus in three ways.^22,29,30 First, dried airways in the nose and upper respiratory tracts are more susceptible.²⁵ Second, dry air may allow influenza virus to survive longer in the air.^29,31,32 Third, increased humidity larger droplets that may carry influenza to evaporate more slowly and remain large.³⁰ The larger particles settle out of air faster and become less likely to be later resuspended in the air by movement in the space.^22,33

Dry air contributes to dehydration through “insensate” water loss or direct transfer of water from the skin to the air; dehydration persisting several hours is common to office workers and leads to fatigue, impaired visual focus, and reduced concentration.^34,35 Additionally, chronic dehydration can lead to degradation of the immune system.³¹

Radiant heating and cooling strategies could spur energy savings by enabling a wider range of indoor air temperatures, passive humidification during heating operations,³⁶ and desiccant dehumidification during cooling operations.³⁷ Active hydration or humidification of air should be considered in locations where seasonal dry air do not allow for passive humidification especially in winter in temperate locations.

Radiant heating and cooling should be considered in the course of building design and maintenance to:

• Avoid unwanted asymmetric thermal radiation. Assess mean radiant temperature (MRT) of indoor spaces to identify hot and cold surfaces especially near the building perimeter. CMU’s CBPD identified that window quality, especially the number of panes of glass, and building insulation are strong indicators of thermal comfort.³⁸
• Evaluate the effects of perimeter cooling or heating on occupant comfort. Exposure to the flow of air from perimeter systems can lead to significant discomfort. Signs include makeshift devices installed by occupants to divert or block such airflow and occupant use of personal heaters or fans. Investments in higher-quality windows and treatments to reduce solar gain may be better solutions.
• Consider whether radiant heating and cooling may provide some or all of interior conditioning. Radiant heating and cooling combined with effective control strategies promise improved comfort at lower energy cost. The process is more efficient because energy can be moved more easily through warm or cool water in pipes than conditioned air through a network of ducts; the lower setpoint and more efficient energy transfer save energy. Additionally, use of radiant heat in winter make it easier to maintain relative humidity above 30% by allowing lower indoor air temperatures especially when combined with adiabatic humidification.³⁹

A wider range of indoor air operating temperatures within a given building could allow radiant strategies to save energy and also improve comfort for those that traditional design leave most dissatisfied. Occupants should be given the freedom to choose their workspace based on comfort or have access to personal comfort devices and greater direct control of temperature at the workspace.⁴⁰

Personal preferences, clothing choice, and physiology make it very hard to please everyone. Providing increased choice and variation in conditions may address this. Consider increasing the number of thermostats to give occupants greater control of temperature in smaller areas, and creating areas with different temperatures to allow folks to choose the workplace that best fits their preferences. UC Berkeley and Carnegie Mellon University, among others, have conducted extensive research on how to achieve greater levels of satisfaction with the work environment.

In traditional designs, temperature is controlled by thermostats which measure air temperature in a specific thermal zone and call for heating or cooling based on a target or setpoint air temperature. Thermal zones can be large, e.g., an entire floor of a building affecting many people, or small, such as individual offices or conference rooms affecting a few.

There are many strategies about how much control to give occupants including full, partial, or no control. CMU’s Center for Building Performance and Diagnostics found that smaller zone sizes and greater degree of actual control lead to higher levels of satisfaction. (They may also reduce energy use, as larger spaces often are over-conditioned when sparsely occupied.) Other studies have indicated that uncomfortable temperatures can lead to reduced work performance.⁴¹ Strategies which allow greater individual control are important to consider:

• Create small thermal zones with some degree of direct, individual control to improve occupant satisfaction and work performance.³⁸
• Provide UL-listed comfort devices like fans, foot warmers, heated chairs, etc. to provide individual microclimate control and adjust thermostat setpoints to allow a wider range and greater fluctuation of air temperatures to save energy.⁴²
• Program for some variation in conditions within buildings such as reliably warmer or cooler spaces and transitional spaces which mimic outdoor conditions more closely.

Air speed should be considered during design and building maintenance to:

• Eliminate unwanted drafts. CMU’s CBPD found that the quality of windows adjacent to a space are an important indicator of satisfaction. Drafty windows create uncomfortable air movement during both cold and hot weather.³⁸
• Evaluate the effects of perimeter cooling or heating on occupant comfort. Exposure to the flow of air from perimeter systems can lead to significant discomfort. Signs include makeshift devices installed by occupants to divert or block such airflow and occupant use of personal heaters or fans. Investments in higher-quality windows and treatments to reduce solar gain may be better solutions.
• Improve air distribution and circulation provided by ventilation systems by increasing the number of supply air diffusers across a space. CMU’s CBPD found that more diffusers, especially for supply air, related to improved occupant satisfaction with air quality and thermal comfort. Fewer diffusers increase the chances of dead spots, and localized unwanted drafts. Improved circulation will reduce concentration of contaminants that can affect work performance and long-term chronic stress.
• Consider using fans to allow individuals to modulate air movement as suggested by enhanced psychrometric strategies. The flow of cool, dry air increases comfort in higher temperatures allowing higher setpoints during the cooling season. Recent studies also indicate that increased airflow may dissipate a “personal envelope” of air created by near-body airflows during relatively sedentary office work.
  • Employ overhead fans to create room-level air flow
  • Provide personal desk-top fans to create individually-controlled air flow
• Consider natural ventilation strategies in climates and sites that support it. Under the right conditions, natural ventilation can save energy when outdoor conditions complement comfort but during hot, humid or cold weather this benefit may be negated. Opening windows can dramatically reduce buildup of CO₂ and other internally generated contaminants in small spaces like conference rooms. However, in polluted locations open windows can allow the introduction of contaminants from the outdoors. Finally, these strategies introduce air movement and the variable breezes afforded have an important biophilic benefit that can enhance comfort and satisfaction.

Distributed sensor networks could be provided in workplaces and used to prompt individuals to take restorative actions, such as micro breaks, that reduce fatigue and irritation to the human eye caused by dry air. These networks could also help building operators improve thermal comfort through more active controls over temperature and humidity.²¹ These strategies are not new but they have been narrowly applied in practice.

The prevalence of personal devices and the internet of things provide an opportunity to give feedback in personalized ways. Our devices already prompt us to be more active if we’ve been inactive. Perhaps they could prompt microbreaks to reduce eye strain and dry eyes when our computer notes we’ve been working uninterrupted for a long time and the building knows the air is dry. Perhaps when the temperature and humidity levels are high our devices could prompt us to drink water to stay hydrated and deploy a personal fan to stay cool and disperse our CO₂ Bubble if we’ve been inactive and at our seats in warm, dry air. Perhaps our temperature, sound and lighting preferences could be shared along with actual sensor measurements with a workplace reservation system so that the desk with the best set of conditions for us is suggested. All these things are coming, and gathering such data may improve our health, comfort and performance as well as our understanding of how our levers drive those things.

The majority of ventilation systems in commercial buildings do not provide 100% outdoor air. Many supply the minimum amount of fresh outdoor air required by building code. That amount of outdoor air is not enough to maintain comfortable temperatures inside the building so the outdoor air is mixed with conditioned air brought back from occupied spaces. This “return air,” or “recirculated air,” allows the system to save energy on heating and cooling outdoor air. Particulate contaminants can be removed by filters on the return air system (if there are filters) but VOCs introduced indoors must be flushed out by fresh outdoor air over time. Avoiding contamination through source control is important; increasing fresh air supply is also.

In the event of a large indoor contamination (such as a renovation or some unplanned incident) there are several tools that can be used to remove contaminants. Flushing the indoor environment with a large amount of outdoor air, temporarily placing more filtration on return air branches, and extending the hours of HVAC operation can all be effective. IAQ measurements meeting RESET Air Standards could be taken before and after this process to show whether clean air conditions have been achieved.