“Thermal delight” — What 99 Percent Invisible didn’t say about outdoor comfort

by Ryan Danks and Ruth Shilston

In a recent episode entitled “Thermal Delight,” the design podcast 99 Percent Invisible explored how the worldwide adoption of air conditioning has radically changed how we build, where and how we live, how much energy we consume, and on and on. In the process, we’ve lost what architect Lisa Heschong calls “thermal delight”—the physical sensations and cultural meanings associated with changes in temperature.

The episode focused on homes and offices, but in our practice there’s much more to the story—the outdoors! That got us thinking about some of the issues we consider when helping clients design “delightful” outdoor spaces. 

patrons dining outside

Thermal comfort is highly subjective and context-dependent

Ryan Danks: People actively seek conditions outside that they would never tolerate inside. Think about skiing! We have to understand what people expect and create spaces that correspond to those expectations. This is why a covered stadium can be challenging. The intention may be to encourage people to feel as if they are outside, but if they are made to walk through several sets of doors and a concourse, their expectations can get skewed, because they’re not sure whether they’re inside or outside.

Ruth Shilston: The stadium experience is a complex thing to understand because it is extremely personal. Some people would say, “I’m inside a building so I expect to be comfortable.” Other people would say, “Well, I'm at a sports match, and weather is part of my enjoyment of the atmosphere.” 

Well-managed transitions improve perceived comfort

Ruth: Here the UK, we focus a lot on wind comfort at entrances. If you’re moving from indoors to outdoors, you’re adapted to calm conditions and a sudden blast of wind would be a shock. But if you were already acclimatized to breezy conditions from walking outside, you would expect wind conditions to change and perceive the change less negatively.

Ryan: We do the same for projects in the Middle East with respect to temperatures. It’s a shock to move from an air-conditioned interior at 20°C to full sun at 40°C, so we try to gradually reacclimatize people as they move to the outside.

Comfort metrics don’t capture the whole story

Ryan: A lot of what we do is provide a more nuanced understanding of standard thermal comfort metrics. For example, the Universal Thermal Climate Index (UTCI) tries to capture a lot of factors that contribute to perceived comfort, including how people adapt by what they wear. Overall the clothing model works pretty well, but it’s not always realistic about the level of clothing people would wear. Sometimes there are cultural or safety reasons that keep people from being able to fully adjust to the environment. Cultural norms may dictate the kind of clothing that is acceptable, or you may not be able to change clothes during the day (say from a dress or business suit to shorts and a t-shirt), or you may be required to wear certain work clothing, such as safety gear or a uniform.

Ruth: And in the stadium context, athletes are dressed very differently from spectators. Plus they may be expending enormous energy. So we have to use design differently and use different metrics for the field of play than we would for the spectators in the stands.

Ryan: Also, I think people miss an important point about these metrics. They don’t actually measure thermal comfort; they measure thermal discomfort. In the commonly used Predicted Mean Vote (PMV) thermal comfort index, the most positive result is “thermally neutral”; UTCI calls it “no thermal stress.” It doesn't necessarily mean you’re comfortable; it just means you’re not uncomfortable. But PMV and UTCI are straightforward metrics for engineers to compute. 

Ruth: It’s tempting to view comfort as a black and white criterion, which is sometimes appealing to clients, but ultimately comfort isn't black and white. To determine whether a space will be comfortable—or at least free from discomfort—we need to discuss how it will be used, by whom and for how long.  

Thermal issues and microclimate are key to the new city

Ruth: Globally we’re coming out of the air-conditioned era and coming back into a world that encourages walkability. We’re envisioning the end of car culture. Whereas sustainability was the only thing we talked about for the last 10 years, the whole movement toward health and wellbeing has just exploded. People will get off the bus three stops early so they can do some walking. I think cities that want to grow without cars will need to work hard to make themselves “delightful,” to create a place that people desperately want to live in. 

Ryan: It’s also a question of resilience. The 99% Invisible podcast points out that many of our buildings would be uninhabitable if we lost electricity. It’s the same with cars in cities. In a place like Dallas, if you suddenly couldn't drive, your whole world would shrink, and it would shrink even farther in summer.

Ruth: The movement for resilient cities is also going to push us to deal with urban heat islands, where the mass of a city absorbs heat over the summer. It may start out tolerable, but at the end of a heat wave, the city gets really unpleasant. Greening the city and changing the design of public spaces can prevent heat buildup and keep the city livable, even if mean temperatures are rising.

Traditional Thai building style suitable for local climate

Designing for the climate is back in style

Ruth: In the past, cities were designed for their climate, and that’s what gave them their character. People had to be clever to stay comfortable. Because of air-conditioning and uniformity, we’ve lost a lot of that. 

Ryan: We go back to what traditional builders used to do, which is to start from the climate. Where they had intuition and tradition, we’ve got a great meteorology team who can provide an extremely thorough and detailed picture of local conditions and potential future changes. We can use that data to work at any scale, from imagining a cityscape to someone sitting in a café enjoying a coffee under a cooling station.

Ruth: We use climate data to pinpoint the best thing for the client to spend money on, at each scale and at each point in the project, to improve someone’s experience of a space. It's creating spaces through designing the climate—it’s about place-making.

Clever solutions are possible at every scale

Ryan: At the city scale, when the question is cooling, the absolute first thing we look at is orientation—how can we get the prevailing winds down to grade. And you can get two benefits for one by cleverly aligning structures so they shade each other and so they promote natural ventilation both inside and outside the buildings. One great example of a locally adapted style is the traditional Middle Eastern wind tower, which catches the wind from above and drives it down to street level. They’re very effective, and we can improve on the past by using our climate data to pinpoint how these towers should be oriented, so they catch the most wind at the right times. 

Ruth: I work with microclimates, so a question I might ask is where to put a cooling pod in a café. Is it windy in that corner? If so, having a clever little thing spitting out cooled air will be a waste of money, because the wind will dilute the cooling. Now, if the corner is shady but stagnant most of the time, that’s exactly where the cooler goes. The point is to ask what will make someone truly enjoy spending time in this spot.

Ryan: In the middle, at street scale, there can be a lot of challenges but also a lot of opportunities. A good example is our work on redevelopment of the Brickell City Center in Miami—a tough climate to work in. It was an indoor-outdoor mall that did a good job of sheltering pedestrians from the sun. But it was quite stagnant, and with Miami humidity… Not good. So there were two main pieces to the solution. The first was to take exhaust air from the shops—it’s clean and already cool—and allow it to ooze out over the front wall of the shops. What we got was these “aisles” of coolness, without any extra energy use. We then suggested moving the food court (where the most people would be expected to loiter) to the lowest level, because the cooler air would settle there. 

Designing comfort means thinking beyond the building

We encourage planners, architects and urban designers to look for ways to apply these principles as you think about how people will live in and around your projects:

  • Thermal comfort is highly subjective and context-dependent
  • Well-managed transitions improve perceived comfort
  • Comfort metrics don’t capture the whole story
  • Thermal issues and microclimate are key to the new city
  • Designing for the climate is back in style
  • Clever solutions are possible at every scale.

These principles have proven themselves through our work in essentially every kind of climate on Earth, and we like to think that the daily lives of many people are more pleasant because of them. Either of us would be happy to talk though how you can make your project “delightful.”

Ruth Shilston is based in our UK office and specializes in microclimate design;
Ryan Danks is based at our headquarters in Guelph and manages thermal comfort projects worldwide.

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