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Blog Post · October 23, 2023

How to Keep Buildings Cool in California’s Warming Climate

photo - Late Summer Sunrise over Los Angeles

California is getting warmer—and that’s putting strain on residents who are struggling to stay cool. Could better architectural design help? We posed that question to Pablo La Roche, an expert in passive cooling and carbon-neutral design who’s an architecture professor at Cal Poly Pomona and sustainable design director at Arcadis.

photo - Pablo La Roche

What is passive cooling and how does it work in California?

A closed building that receives solar energy from the outside gets hotter—like a car you leave in the sun. And typically you then need to use air conditioning to cool it. In passive cooling, you design your building to become the air conditioner. A passively cooled building uses the building’s materials and design to transfer heat to heat sinks, such as the air around the building, in the same way air conditioning does—but without using electricity. This lowers the indoor temperature below the temperature outside. The simplest example is natural ventilation: opening a window when there’s cooler air outside.

One difficulty with passive systems is they are climate-specific: not all strategies work in all climates. You have to know a bit more about the appropriate strategies for your climate.

How common is this sort of design in California?

We don’t do it as much as we should. Historically we did, but in recent years, we’ve designed many buildings that don’t respond to the local climate. We’re seeing a lot of glass buildings. Glass is good for daylight and views, but too much glass allows in a lot of solar radiation and traps heat inside the building.

My favorite technology in a hot and dry climate is evaporative cooling. It’s like magic. When water evaporates, it takes energy from the air and lowers temperatures. This principle is at work in southern Spain, where many courtyards include fountains. These spaces are cool and also beautiful: they help you connect with nature, and we don’t talk about that enough.

Is passive cooling only possible in new construction? Or can you retrofit existing buildings?

We can definitely retrofit existing buildings to improve overall performance, and we should be doing that. If you’re in an old building with no insulation, single pane glass, and unshaded windows getting lots of sun, the air conditioner is either working full time or you are exceedingly and sometimes dangerously hot. And not everyone has air conditioners—which is a problem and an equity issue. You want to reduce the heat coming into the building so that the AC doesn’t have to get as much as heat out of the building. Adding external insulation and new windows and shading the windows can really help. These retrofits will pay off over time in energy savings.

It’s more difficult if a building isn’t sited properly—you can’t just lift and rotate it. Proper siting can really improve a building’s energy performance and reduce its carbon footprint.

Tell us about carbon-neutral architectural design.

About 40% of the planet’s greenhouse gas emissions come from buildings. Electricity is generated somewhere else while you’re using the building—and that has a carbon impact. You can go to the eGrid website and type in your zip code to see how clean or dirty your electricity is.

The other part of the equation is “embodied carbon.” Building materials have energy embodied in them—for example, cement, steel, and aluminum have a lot of embodied carbon. We’re now measuring the embodied carbon in our buildings in a life-cycle assessment. Environmental product declarations (EPDs) tell you the global warming potential of different building materials.

There’s a lot of emphasis on mass timber as an alternative to steel and concrete because it actually sequesters carbon from the atmosphere. But it has to come from a sustainably harvested forest.

What policy changes might help?

Building codes are important. California has the strictest code in the US regarding energy, and in a couple of years, we’ll have to measure both operational emissions and embodied carbon.

But we need to incorporate climate-responsive strategies from the beginning. Most designers learn this in school, but it doesn’t happen as much as it should. Some of it is simple and some of it is out-of-the-box thinking. Imagine you have a radiant cooling system with an operable ceiling. At night, the ceiling opens to send heat to the roof, which radiates it to space. We’ve researched things like this, as well as roof ponds, smart ventilation and shading, radiant green roofs with embedded coils that cool the building, and even windows full of water. These technologies work really well, but we haven’t done a good job of moving this research to implementation and code.

How do these design considerations link up with keeping housing affordable?

Some will increase costs, some will not. A window in the right place costs the same as a window in the wrong place. Even if these approaches add to the construction cost, they ultimately improve a building’s performance, lowering its energy use and its carbon footprint. And that’s a win.


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