Thermal Resilience: Cooling our Buildings without Warming the Planet

by Stacy Rinella | September 6, 2023 10:55 am

[1]July 2023 was officially the hottest month on earth since we began keeping records, and climate scientists believe this was the hottest period the planet has seen in 120,000 years. A heat dome persisted over the southern U.S. for more than a month, with cities repeatedly hitting new heat records day and night. This isn’t an anomaly, as the last eight years were the warmest on record. While some isolated severe weather events, like tornados, are difficult to attribute to climate change, climate scientists can directly link extreme heat and cold events to the changing climate. In his new book, The Heat Will Kill You First: Life and Death on a Scorched Planet, Jeff Goodell points out that “our bodies are finely tuned machines that work in a very narrow temperature range,” and we are now experiencing temperatures outside the range we evolved to tolerate. For example, in July, the heat index in the Middle East reached 66.6 C (152 F), nearly the limit for human survival. In addition to threatening public health, extreme heat has economic impacts, disrupting work and increasing utility bills, as well as boosting greenhouse gas emissions, which will further increase future temperatures.

The impacts of extreme heat (and extreme cold) can be multiplied by compounding or cascading weather and climate events. For example, heatwaves may occur with drought, meaning thermal energy plants (coal, natural gas, nuclear) may shut down for lack of cooling water just as electricity demand for air conditioning is peaking. Similarly, power companies may de-energize powerlines during times of wildfire risk, which often coincide with droughts and high heat events. Additionally, urban heat causes air quality issues, such as ground-level ozone, adding respiratory stress on top of heat impacts.

Increased reliance on air conditioning is a natural reaction but it is important to remember that this is not a magic solution that makes heat disappear, but rather a mechanism that moves heat from inside buildings to outside. Several studies have confirmed that high concentrations of air conditioning in cities will increase outdoor temperatures, exacerbating the initial problem. Moreover, until electricity grids are 100 percent decarbonized, more air conditioning means more carbon emissions that will further warm the planet, a perverse feedback loop. While there is no escaping the need for air conditioning on a warming planet, we must take significant steps with our cities and individual buildings to reduce urban heat islands and limit the need for air conditioning to maintain comfortable indoor temperatures.

Making our cities and buildings more heat resilient starts outside, with well-tested methods to reduce heat islands, including:

• Avoiding unnecessary paving in new projects, and de-paving in existing developments to reduce heat absorbing surfaces.
• Planting and maintaining shade trees, especially in parking lots and adjacent to roads, can reduce ambient temperatures by as much as -12.7 C (9 F).
• As a supplement to trees, shade structures with reflective roofs (high albedo) or photovoltaic panels prevent solar radiation from striking and being absorbs by paving.
• Increasing the reflectivity of paving has significant potential but also comes with tradeoffs. Concrete is more reflective than asphalt, but also has higher embodied carbon. Caution is also required as highly reflective paving may reflect heat onto the facades of adjacent buildings.
• Installing cool roofs on buildings has a triple benefit, reducing urban heat islands, limiting the transfer of heat through the roof into the building, and reducing outside air temperatures at ventilation system intakes.

While these measures on any individual building site may have a marginal impact on the urban environment, each small effort will measurably improve the micro-climate of that site, and cumulatively, will add up to a larger benefit.

Reducing urban heat islands and creating cooler microclimates is a good start but will not give our homes and businesses the heat resilience and thermal safety needed to counter the current and future effects of climate change. Cool roofs, as noted above, are an easy and important first step along with other measures to reduce the demand for air conditioning and protect occupant health and safety even in power outages coincident with heatwaves. For example:

• Using high albedo cladding, especially on the south and west sides of buildings will reduce heat transfer through the walls.
• Overhangs and shading devices (again, especially on the south and west facades) over windows (and walls) significantly reduce heat gain during the hottest times of the day.
• Continuous insulation and elimination of thermal bridging in wall and roof assemblies keeps the heat out and better maintains comfortable indoor conditions.
• Finally, on-site renewable energy generation and energy storage offset the carbon emission impact of air conditioning and allow for back-up power to maintain some level of ventilation and cooling even in blackout conditions.

Overall, adopting passive house principles reduces the need for air conditioning and allows a building to maintain livable indoor temperatures (passive survivability) during a power outage for three days or more (in both extreme heat and cold events), while a minimally code compliant building can reach unsafe conditions within hours.

Innovative material research will add to the array of strategies outlined above. New formulations of concrete with increased reflectance and reduced carbon footprint are in development, and research on reflective coatings for paving are advancing. To cite one example, the city of Austin, Texas, is conducting a pilot project using a reflective emulsion applied over asphalt on roadways. Scientists at Purdue University recently developed a super-white acrylic paint that reflects 98.1 percent of sunlight (traditional paints reflect only 80 to 90 percent) setting a Guinness World Record for the whitest paint. The paint is expected to be commercially available soon with applications for coating existing roofs, and on metals used for new buildings and automobiles. A similar white paint formulation could be used as a base to make a range of other colors more reflective, a potential breakthrough for metal roofing and cladding.

The global heat records and persistent heat domes this past summer are a wake-up call to make urban and building level thermal resilience an imperative for new developments and retrofits to our built environments. This will improve public health and safety, support business continuity, reduce utility bills, and limit carbon emissions contributing to further climate change. We have a range of measures available to us, and each one adds a cumulative benefit for all.

Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with over 35 years of experience in sustainable building design. He is the Director of Sustainability with Intertek Building Science Solutions in Portland, OR. To learn more, follow Alan on LinkedIn at www.linkedin.com/in/alanscottfaia/.

Source URL: https://www.metalarchitecture.com/articles/columns/thermal-resilience-cooling-our-buildings-without-warming-the-planet/

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