As technology and digital solutions evolve and become more essential to our everyday interaction with the world, these tools and innovations offer the opportunity to achieve gender equality. Arup’s senior consultants Ingrid Chaires and Sara Tepfer spoke with Dr. Hui Zhang, a senior researcher and expert on thermal comfort at the Center for the Built Environment (CBE) at UC Berkeley. As an industry partner of CBE, Arup helps inform the research activities of the organization leveraging our industry perspective. The group discussed the scientific and historic factors contributing to inequity in thermal comfort and explored how we can employ a more careful approach to designing spaces that consider the differing comfort of individuals — and how this can lead to co-benefits for the planet.
Can you describe how thermal comfort in building design has historically been approached?
Sara: The historic models used for predicting thermal comfort are one driver for the very narrow definition of comfort we see in standards today. As Stefano Schiavon from UC Berkeley has noted, these are 1960s-era measures that relied heavily on the experiences of college-aged men and women from northern Europe and America. So, they are not representative of the greater population. With outdated models being so central to how designers think about thermal comfort, it’s not surprising that many groups, particularly women, more often experience thermal discomfort.
Dr. Zhang: There are large individual differences between people and between genders that are not typically accounted for in building standards.
How and why does thermal comfort differ between genders?
Dr. Zhang: There are many contributing differences between men and women from not only a physiological point of the view but also from a behavioral point of view.
Considering human physiology, thermal comfort can be thought of as the balance between heat production and loss. Because men typically have higher muscle mass on average than women, they produce more heat and are often more comfortable at lower temperatures. This difference in metabolic heat production has a big impact on people’s thermal sensation. Women in general have a higher body fat percentage, which helps to reduce their heat loss to the surrounding environment, but its combined effect with their lower heat production on thermal comfort is unclear. Women also have a higher body surface area to body mass ratio, making them more susceptible to heat loss. Another important factor is that monthly hormonal cycles in women can change their core temperature by around 0.5°C (0.9°F). That’s a huge difference and it can noticeably affect thermal comfort.
The other factor is behavioral difference. Women tend to wear clothing based on the weather or season. For example, we tend to wear light clothing in summer. But the indoor temperature design doesn't change; it is constant year-round. Therefore, women often experience overcooling discomfort.
What work is being done to address thermal comfort inequity?
Ingrid: A few years ago, Arup developed the Advanced Comfort Tool in partnership with Dr. Zhang and the CBE’s previous comfort analysis and physiological model. In the app, the user has the ability to adjust not only gender but also weight, age, amount of body fat, and other factors for the model. The platform can also compare populations of people to help better understand the breadth of thermal sensation.
One of the ideas behind developing this tool was that it is not equitable to design for a single “average person,” because that person does not exist. So, how can we better represent and design for an entire population? This ties into the greater challenge of equity in design. As design practitioners, we need to think about how we can use digital tools like the Advanced Comfort Tool to better represent the differences within a population, and then choose design options and operational parameters to better achieve comfort for all.
How can individual difference in temperature perception also impact building standards?
Dr. Zhang: Current thermal standards operate using a very narrow range for comfort classifications. My research has found that occupants cannot distinguish between subtle differences in their thermal environments, but the way we typically control buildings assumes they can, and that approach translates to expensive energy consumption. Building standards have traditionally been focused on creating a uniform, still air environment. It’s very energy intensive to heat or cool an entire space, especially if only part of it is occupied.
But that’s been changing. At CBE, we’ve been working with the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) to update standards so that buildings are controlled to heat and cool people, not the spaces they occupy. This has already been included in ASHRAE Standard 55, which widens the classification for better individual control of thermal comfort. We’ve proposed adding additional solutions including increasing air movement and implementing personal comfort controls in Standard 55 that help account for individual differences and can reduce HVAC-related energy consumption. For example, if personal control measures like heated and cooled chairs are made available to a building’s occupants per individual preference, the design is rated with higher classification.
Ingrid: It's difficult in design to push the boundaries of code. We are seeing a shift in designing to be more equitable, but we're often coming up against code. The next step is influencing building requirements to allow for more flexibility or different ways of thinking about thermal comfort.
Dr. Zhang: We are heading in that direction, and ASHRAE Standard 55 is leading the way. Engineering and consulting firms understanding this concept is really valuable. You are the ones designing the buildings and putting this into practice. That’s the value of industry partnerships and why CBE works closely with firms like Arup.
What solutions can we implement that consider the differences between individuals when managing temperatures in buildings?
Ingrid: The goal of thermal comfort is ultimately to reduce occupant complaints while minimizing energy use. When working with clients that are trying to be more energy efficient, reach zero net carbon, or just design buildings that are more suitable for their specific tenants, they are often more open to adopting more creative and individualized solutions. For example, they may set up different zones in the building that are warmer or cooler.
I am also reminded of Dr. Zhang’s research on fitness centers and gyms, which found that increased air speeds result in higher thermal comfort than simply reducing air temperature. Sometimes gyms are designed with no fans — and then fans are added in later. Designing to include fans initially can be a more elegant solution that's ultimately more comfortable for people who are doing hard exercise, with the added benefit of requiring less energy.
Dr. Zhang: When designing a building, I always recommend including faster responding equipment like fans. When there are no people in the space, you can turn off the fan. And when people are in the space, especially if they are sweating like in a gym, fans circulate the air and sweat evaporation contributes to heat loss. It's much more effective than lowering the temperature. These faster responding strategies should be considered during the preliminary design phase.
Fans are also a good personal comfort system. I always use a small desk fan in my office. They cost a few dollars and use very little power. When you walk in from lunch outdoors where it is warm, your metabolic rate may be high, and you may feel hot. So, you can turn on the fan. Another easy personal solution is a foot warmer. When feeling cold, vasoconstriction (the narrowing of blood vessels to restrict blood flow) happens in extremities such as our hand and feet, causing a cold sensation, which in turn affects the whole body’s thermal sensation. Foot warming is a good, easy way to keep warm. When designing spaces, we can provide customizable features that occupants can control. If people need it, they can use it.
Sara: Thinking about these factors at the outset of a project can also help with first cost and simplify the systems overall. There are a lot of benefits beyond the operational savings. By trying to create a uniform space and maintain a narrow temperature band, we often introduce a lot of complexities on the design side. It will require a shift in thinking to understand that introducing individual controls can easily tackle these complexities with a simpler system.
Ingrid: Personal controls also brings up the concept of smart buildings. Consider how your workspace can be personalized with your preferred desk height, a fan that you control, a heated chair — and they can all be connected and responsive to the temperature outside or the time of day. Now, I see smart buildings emerging in the US along with the trends for more human-centered and sustainable design. All of these strategies can be combined in a smart building that is focused on the individual and, at the same time, is better for the environment.
How can this research be expanded to bring about more equity in other aspects of designing and engineering spaces?
Sara: It’s not only about the research but how these concepts and ideas get translated to a wider set of people. Outside of engineers and researchers, how do we bring this information to people who could really benefit?
Ingrid: The idea of allowing occupants some control over their space also aligns with the idea of showing occupants more information about the performance of their building so that they can make informed decisions. There’s an opportunity for building owners and facility managers to be more transparent and share information such as temperature and air quality — information that will give occupants a sense of their indoor environmental quality and show confidence that the space promotes comfort, wellbeing, and productivity. This human-centered approach will lead to more equitable spaces for all.
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