In an era marked by climatic extremes, 2023 stands out as the hottest year on record, with global temperatures soaring to 1.18 degrees Celsius above the 20th-century average. This alarming statistic underlines the urgent need for climate-resilient buildings. The United Nations Environment Program (UNEP) emphasizes five strategies to bolster buildings against climate change. Two approaches, “building resilience to heatwaves” and “building resilience to cold,” address the need for structures to accommodate wider temperature swings and the increased energy demand accompanying these fluctuations.
At the forefront of these efforts are phase-change materials (PCMs) which offer a novel approach to managing building temperatures. These materials are thermal media that can store and release significant quantities of energy by capitalizing on a material’s phase transition, such as from a solid to a liquid or vice-versa. The building facade has long been considered a promising application for PCMs, given their potential to enhance facades’ thermal performance. PCMs help control the thermal load of building envelopes—thus reducing operational energy—and assist in achieving and maintaining optimal thermal comfort levels. There are three classifications of PCMs: organic (e.g., paraffin wax), inorganic (e.g., salt hydrates), and eutectic (e.g., sodium chloride and water).
The challenge, however, lies in their application. As PCMs transition to liquid, they risk leakage. Encapsulation can be achieved at the macro level using tubes, channels, or other components—or at the micro level in tiny plastic-coated spheres. However, each scale has its drawbacks.“Microencapsulation has a negative effect on the strength and durability of construction materials,” explains Mirian Velay-Lizancos, assistant professor of civil engineering at Purdue University. “Macroencapsulation limits the shape and production method of construction materials.”
Velay-Lizancos proposes an innovative solution to incorporate PCMs into prefabricated building modules without these limitations using liquid immersion and a vacuum. This treatment enhances standard mineral-based products like bricks, pavers, concrete masonry units, and drywall. The immersion bath approach concentrates PCMs near the surface of the building units, which is where these materials are most effective against temperature swings. Velay-Lizancos’ experiment with mortars of various water-to-cement ratios revealed a 24% increase in thermal inertia, with only 7% of the volume composed of immersed PCM. The modified mortars also exhibited a 22% increase in compressive strength. Furthermore, no leakage occurs because the PCMs infuse the capillary pores of the building modules.
Another breakthrough comes from Texas A&M, where researchers have developed a 3D-printable composite of phase-changing paraffin wax and light-sensitive liquid resins. In powder form, the paraffin is evenly mixed throughout the resin, creating a pliable paste suitable for 3D printing. The light-activated property of the resin allows the composite to be cured into a rigid material with UV light. The even distribution of the paraffin and the lack of leakage concerns enable a composite mix of up to 70% PCMs. Preliminary tests reveal a 40% improvement in thermal response compared with non-PCM versions due to the high proportion of PCMs. Emily Pentzer, a materials scientist at Texas A&M, imagines this additive manufacturing method as a versatile technique for adding PCM capability to new and existing building components. “The ability to integrate phase-change materials into building materials using a scalable method opens opportunities to produce more passive temperature regulation in both new builds and already existing structures,” she said.
Translating PCMs’ thermal characteristics into tangible performance metrics—including how PCMs perform in hot and cold climates—is fundamental to the materials’ widespread adoption. A 2021 comprehensive survey indicated that PCMs function best in hot climates. However, a 2023 study by the Kaunas University of Technology in Lithuania revealed that PCMs in cooler climates outperform their warm counterparts. The Kaunas team conducted sixteen simulations in three European latitudes: Copenhagen, Milan, and Athens. Employing the criterion of energy payback periods, or the time required for operating energy savings to offset PCM costs, the researchers found that PCMs delivered the shortest energy payback in colder locations. The team also prioritized the retrofit of existing structures in its assessment of PCM applications. “The thermal performance assessment of existing buildings is highly valuable information, which can be useful when making renovation decisions,” explained senior project researcher Eglė Klumbytė.
Despite these advancements, wider implementation of PCMs in construction remains a work in progress. However, the benefits PCMs bring are nothing new. For example, the Kaunas team refers to Socrates’ 2,500-year-old description of climate-attuned building methods when describing its strategies. “Back then, [Socrates] indicated that the northern wall of a building needs to be thicker compared to the southern, thus our idea that wall orientation is crucial when considering its structural composition is related to that of Socrates.” In this way, PCMs can represent just not a modern innovation but a continuation of a longstanding, commonsense, age-old aspiration to create buildings in harmony with their environments.
The views and conclusions from this author are not necessarily those of ARCHITECT magazine.
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