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Scientific American: New Air-Conditioning Technology Could Be the Future of Cool
New Air-Conditioning Technology Could Be the Future of CoolStandard AC units cool buildings but contribute to global warming. New technology aims to change that
By Lauren Leffer on August 29, 2023
This past July was the hottest recorded month in human history. Heat waves smashed temperature records worldwide and even brought summer temperatures to Chile and Argentina during the Southern Hemisphere’s winter. It’s more than just a matter of sweaty discomfort. Severe heat is the deadliest of all weather events; in the U.S. alone, it kills more people each year than floods, tornadoes and hurricanes combined. As climate change worsens, access to artificially cooled spaces is rapidly becoming a health necessity—and an issue of basic human rights.
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For example, some newer air conditioner designs pull moisture from the air with desiccant materials (similar to the silica gel in the packets you might find in a bag of jerky or a bottle of pills). The dried air can then be cooled to a more reasonable temperature. This process can require some additional energy because the desiccant needs to be “recharged” using heat. But some companies, including the Somerville, Mass.–based start-up Transaera, recycle the heat generated by the cooling process to recharge the desiccant. Transaera claims that the system it is developing could use 35 percent less energy than the average standard AC unit.
Even bigger efficiency gains are possible when dehumidification is paired with evaporative cooling, which takes the energy-intensive process called vapor compression out of the equation altogether. Vapor compression—the system by which standard AC works—moves a refrigerant through a cycle in which it is variably condensed and expanded, enabling it to absorb heat from inside and release that heat outside. Conversely, evaporative cooling is a simpler process. It’s the same one through which sweating cools our skin: as water goes from liquid to gas, it absorbs heat. Swamp coolers, DIY devices in which a fan blows air over ice, work the same way. And in dry climates, people have used evaporative cooling for thousands of years. In ancient Iran, for instance, people engineered yakhchāls—large, cone-shaped clay structures with solar chimneys—which harnessed air circulation and the evaporation of adjacent water to lower temperatures so much that they could make ice in winter and store it through summer.
But this strategy also increases air’s humidity, so as a cooling system, it tends to work only when the weather is hot and dry; if humidity rises beyond a certain point, it cancels out the comfort gains of reduced temperature. To solve this, research groups, including Harvard University’s cSNAP team, have designed AC devices that use a hydrophobic barrier to perform evaporative cooling while holding back humidity. As a bonus, refrigerants—which are often greenhouse gases that are many times more potent than carbon dioxide—aren’t involved at all. “We expect to provide a 75 percent more energy-efficient air conditioner,” says Jonathan Grinham, an assistant professor of architecture at Harvard and one of cSNAP’s lead designers.
…
By Lauren Leffer on August 29, 2023
This past July was the hottest recorded month in human history. Heat waves smashed temperature records worldwide and even brought summer temperatures to Chile and Argentina during the Southern Hemisphere’s winter. It’s more than just a matter of sweaty discomfort. Severe heat is the deadliest of all weather events; in the U.S. alone, it kills more people each year than floods, tornadoes and hurricanes combined. As climate change worsens, access to artificially cooled spaces is rapidly becoming a health necessity—and an issue of basic human rights.
…
For example, some newer air conditioner designs pull moisture from the air with desiccant materials (similar to the silica gel in the packets you might find in a bag of jerky or a bottle of pills). The dried air can then be cooled to a more reasonable temperature. This process can require some additional energy because the desiccant needs to be “recharged” using heat. But some companies, including the Somerville, Mass.–based start-up Transaera, recycle the heat generated by the cooling process to recharge the desiccant. Transaera claims that the system it is developing could use 35 percent less energy than the average standard AC unit.
Even bigger efficiency gains are possible when dehumidification is paired with evaporative cooling, which takes the energy-intensive process called vapor compression out of the equation altogether. Vapor compression—the system by which standard AC works—moves a refrigerant through a cycle in which it is variably condensed and expanded, enabling it to absorb heat from inside and release that heat outside. Conversely, evaporative cooling is a simpler process. It’s the same one through which sweating cools our skin: as water goes from liquid to gas, it absorbs heat. Swamp coolers, DIY devices in which a fan blows air over ice, work the same way. And in dry climates, people have used evaporative cooling for thousands of years. In ancient Iran, for instance, people engineered yakhchāls—large, cone-shaped clay structures with solar chimneys—which harnessed air circulation and the evaporation of adjacent water to lower temperatures so much that they could make ice in winter and store it through summer.
But this strategy also increases air’s humidity, so as a cooling system, it tends to work only when the weather is hot and dry; if humidity rises beyond a certain point, it cancels out the comfort gains of reduced temperature. To solve this, research groups, including Harvard University’s cSNAP team, have designed AC devices that use a hydrophobic barrier to perform evaporative cooling while holding back humidity. As a bonus, refrigerants—which are often greenhouse gases that are many times more potent than carbon dioxide—aren’t involved at all. “We expect to provide a 75 percent more energy-efficient air conditioner,” says Jonathan Grinham, an assistant professor of architecture at Harvard and one of cSNAP’s lead designers.
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18 replies
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cSNAP: Eco-Friendly Air Conditioning
Evaporative-cooling-based system that uses a specially coated ceramic to cool air without adding humidity
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This technology is currently being de-risked at the Wyss Institute. It has been tested in real-world conditions at Harvard’s HouseZero, and showed that it effectively cooled indoor air even in extremely hot conditions. The team is combining their evaporative cooling system with additional innovations that pre-treat and dehumidify the input air, further maximizing its cooling capability and allowing it to be used in a wide variety of markets and climate zones around the world. The team plans to launch a startup to commercialize their technology, and is seeking a business development lead to join the project.
…
This technology is currently being de-risked at the Wyss Institute. It has been tested in real-world conditions at Harvard’s HouseZero, and showed that it effectively cooled indoor air even in extremely hot conditions. The team is combining their evaporative cooling system with additional innovations that pre-treat and dehumidify the input air, further maximizing its cooling capability and allowing it to be used in a wide variety of markets and climate zones around the world. The team plans to launch a startup to commercialize their technology, and is seeking a business development lead to join the project.
