Global leaders assembled last week in Glasgow for COP26 and considered the impacts of climate change as imminent concerns. These impacts include more frequent and severe heatwaves and hurricanes, which lead to more heat stress, health emergencies and deaths, especially in the aftermath of disasters that bring down electrical grids for extended periods of time. In the aftermath of Hurricane Ida, more deaths in New Orleans were due to overheating than to flooding. The 2021 summer heatwave in the Pacific Northwest caused hundreds of excess deaths and thousands of emergency room visits due to heat-related illness. As a White House fact sheet on extreme weather notes, “climate-related disasters like hurricanes, wildfires, and floods produce dramatic images of devastation, extreme heat often takes place out of sight and out of the news. But heat is the nation’s leading weather-related killer.”

In North America, air conditioning (AC) is ubiquitous in areas with hot climates, and its use is increasing around the world. While the discussion of how to help people manage extreme heat is still centered around expanding access to AC, it is not affordable in many countries with hot climates, and is far from sustainable. The proliferation of air conditioning is also adding strain on electrical grids, creating high peak loads during heatwaves that lead to blackouts and rolling brownouts, which can further exacerbate heat-related health impacts to the point of being life-threatening. Still AC is not available to some of the most vulnerable populations, even in wealthier nations, and the release of refrigerants from AC systems is contributing yet more to global warming, leading to a vicious cycle.

Fans as a solution for health and resiliency

One of the most obvious alternatives to AC is the use of fans, which are found in approximately 80% of U.S. single-family homes. The benefits of fans have also been a key focus for CBE’s research team. Fans can reduce heat-related stress using a small fraction of the electrical power needed for AC. As noted in CBE’s Ceiling Fan Design Guide, the “potential HVAC savings outweighs fan energy use, typically by a factor ranging between 10 and 100 times.”

While much of CBE’s focus has been using fans for comfort and energy savings, new collaborations with Ollie Jay, a professor in heat and health at the University of Sydney, have expanded this work to include human physiology and responses to extreme heat. He notes that several U.S. cities have experimented with programs to get fans into the hands of vulnerable residents. In the early 1990s cities such as New York and Chicago had fan outreach programs, and in advance of heatwaves city workers would go to housing developments, usually poor-quality high-rise buildings, and provide fans to these at-risk populations.

An example of how ceiling fans might provide resiliency was demonstrated with an event that occurred during a CBE field study in California’s Central Valley, where summer temperatures regularly exceed 100°F (38°C). Researchers installed ceiling fans at four sites and measured the effects in terms of energy (finding a median reduction of AC energy of 21%) and also the comfort of residents. The project’s lead researcher, Paul Raftery, explains how at one site the AC failed and repairs took months. However, surveys and interviews with residents showed that the ceiling fans maintained satisfactory comfort. With the indoor temperature rising into the mid 80s°F (~29°C), the space would have been uncomfortable, and perhaps unusable, without the cooling effect of the ceiling fans. “This is one clear example where the fans provided resilience. While the conditions were not life-threatening, they could have been, and with fans people are at less risk, at least up to a certain temperature.”

This example also shows that ceiling fans offer benefits for both resiliency and regular operation. As Dr. Raftery explains, “Some solutions only provide resilience as a benefit. For example, generators may provide some resilience when power is lost, but they cost money and might spend all their time in the garage. Fans and small battery systems offer multiple benefits — energy savings, improved comfort and resilience.”

Guidelines limiting fan use are under scrutiny

While fans offer these multiple benefits, their use for resiliency and reduction of heat stress has been subject to restrictive guidelines, based on an assumption that fans do not provide a benefit once the air temperature exceeds our skin temperature. Ollie Jay explains that when the Center for Disease Control and other agencies codified the maximum temperatures for fan use, as low as 95°F (35°C), this guidance was not based on sound empirical evidence. This has led to some unfortunate consequences in practice. For example, the guidelines contributed to the termination in the 1990s of the successful urban fan outreach programs described above.

Now this standard is under scrutiny, as fans still provide cooling at higher temperatures due to the effect of sweating, and generally people are cooled more by sweating and evaporation than ‘dry heat loss’ to keep cool. Ollie Jay and his colleagues are among the first to challenge these recommendations through a series of quantitative laboratory studies spanning several years. For example, a study published in 2016 showed that male subjects benefitted from fans at temperatures of 95°F (36°C) and 108°F (42°C), and that subjects could tolerate higher levels of humidity when they have air movement. A more recent study published in 2021, used biophysical modelling to determine the combined temperature and humidity limits at which fan use would be detrimental for healthy young adults and for adults 65 and older. Using data from 108 large cities over roughly a decade ending in 2019, they found that fans would provide benefits for both groups for 29 or 30 days of a standardized 31-day ‘hot weather month.’ The researchers found that fan use could be safely recommended as an alternative to air conditioning including when temperatures exceed current limits of 95°F (35°C), the only exception being older adults, healthy or on certain medications, in extremely hot and dry conditions.

Numerous factors are relevant to this question, such as age and medication use, and this research team is now conducting additional experiments with hundreds of human subjects. Dr. Jay notes that humidity is an essential consideration, “In extreme environments, fans cool by increasing the efficiency with which sweat evaporates from the skin. In hot and dry conditions, all sweat evaporates anyway and fans just add to the dry heat load through convection. Under these conditions we know that fans worsen heat stress.”

A recently published study by Federico Tartarini, a postdoctoral scholar with the Singapore-Berkeley SinBerBEST program, with co-authors Ollie Jay and several CBE researchers, used a heat-balance model to predict physiological responses to high temperature and humidity, to better understand the benefits of fans under such conditions. The study considered the most extreme weather events for over 20 years in 115 of the world’s most populous cities. The results indicate that in 93 of these cities, the use of fans would have been beneficial. To make these findings more useful, the research team created an online tool to explore the combinations of temperature and humidity at which people should benefit from fans, and also the conditions that constitute heat stress (but where fans are still beneficial) and the maximum temperature limits for fan use. The metabolic rate and clothing levels can be input by the user (within applicable ranges) as these greatly impact the results. This tool was launched in the fall of 2021 and is incorporated in to the CBE Thermal Comfort Tool This resources adds to CBE’s growing list of free, open-source and online tools, including the CBE Fan Tool launched in 2020.

These researchers hope that this recent and ongoing research can be beneficial to disadvantaged communities and also in the commercial sector, where many workers are regularly exposed to high temperatures. Christian Taber, principal engineer for codes and standards at Big Ass Fans, explained how a customer for a large manufacturing company misinterpreted a chart, and believed that ceiling fans would not help to cool employees at high temperatures. Undoing the customer’s misunderstanding required some explaining, and ultimately the company invested millions of dollars on advanced ceiling fans for their manufacturing sites.

Christian Taber and his colleagues also created a heat index calculator using location-specific energy simulations for a heated-and-ventilated only warehouse and distribution center (based on a U.S. Department of Energy reference building). The calculator can estimate occupant heat stress throughout the year, and he notes that the addition of ceiling fans and the associated cooling effect greatly reduces the hours of dangerous heat stress for buildings of this type in many climates. This approach may be beneficial also in shipping and warehousing facilities, where a growing number of employees are being exposed to high indoor temperatures.

Advocacy and outreach

Many of the researchers cited in this article, along with scores of others, have been involved in advocacy to improve on the standards set by the CDC and other agencies that have restricted the use of air movement in the past. CBE researchers are part of a team working to address resilient cooling for buildings, as part of a program supported by the U.S. Department of Energy. Part of CBE’s task is to assess fan use policies and guidelines, and suggest improvements. Also, fans are but one of several solutions that can be used to keep cool during periods of extreme heat. Dr. Jay’s research team has studied behavioral alternatives to AC under extreme heat, for example dousing one’s body or clothing with water, and cool foot baths. They created this infographic to make the results more easily understood. To increase worldwide resilience to the inevitable increasing frequency of extreme heat, policy makers need to expand their focus beyond increasing access to AC and to consider many solutions.

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