INNOVATIVE TECHNOLOGIES FOR SUSTAINABLE COOLING

Whether we will be able to arrest further deterioration of the global environment or not that is a debatable question. But at present globally people are experiencing unbearable amount of heat, which is gradually becoming lethal at places. Naturally, the questions that arise include: What are our scientists doing? Is there any sustainable development to reduce heat in the interior places? And so on…

Lot of research works are being done to improve the situation at least internally, some of them have already started showing good results. This time, I will present here two such works that bid fair to improve the situation.

Development at the Argonne National Laboratory (US DOE)

Recently, researchers at the Argonne National Laboratory examined three different types of roofing strategies and their impact on near-surface temperature and cooling energy demand through regional modeling in the Chicago area.

They inform that concrete sidewalks, black asphalt streets, traffic, brick and steel buildings – these common city elements can retain heat and increase temperatures in a phenomenon called the urban heat island effect.

With increasingly warming temperatures during the summer months, urban cities like Chicago need to arm decision makers and communities with information about strategies to help keep their residents cool. One strategy involves something all buildings already have: a roof. Certain roofing materials can help cool the surrounding outside air and decrease the need for Air Conditioning (AC).

To help understand how climate is affecting urban communities, (as said before) researchers examined three different types of roofing strategies and their impact on near-surface temperature and cooling energy demand through regional modelling in the Chicago metropolitan area.

Detailing on the project, Rao Kotamarthi, Science Director for Argonne’s Center for Climate Resilience and Decision Science (CCRDS), informed, “We chose to run our model during a heatwave event – as opposed to average summer temperatures – so that we could maximize potential benefits where temperatures cross the 95^th percentile observed in a city for three consecutive days.”

The team ran a regional climate model simulating the Chicago metro area and three types of roofs: cool (painted a heat-reflecting white), green (vegetation) and solar panels. Rao said, “The cost between the roofs is approximately a factor of 3. Which option is the most cost effective to get the most benefit? If a community is deciding on a strategy, we can look at the model and give them an actual answer.”

They found that the three types of roofs reduced the near-surface temperature and AC consumption demand during daytime hours when air temperature is the highest. Cool roofs reduced the near-surface temperature by 1.5 degrees Celsius, followed by 1.2 degrees for green roofs and 0.6 degrees for solar panel roofs across the Chicago area.

Because all the roofing strategies offer cooling effects, they reduce AC consumption. Cool roofs reduced AC energy consumption the most, followed by green roofs and solar panel roofs. Energy demand was shown to be reduced by 16.6%, 14.0%, and 7.6%, when cool roofs, green roofs and solar panel roofs are deployed, respectively.

Overall, the large-scale deployment of cool roofs showed the best potential for cooling effects and cooling energy saving. They cost less than the other two technologies, and they do not require additional water. However, they are not helpful in managing stormwater loads as green roofs have the potential to do. Stakeholders can use results of the study to inform sustainable development approaches, lower summertime cooling energy demand, and help minimize greenhouse gas emissions in the long term over the Chicago region.

This work was conducted as part of the Community Research on Climate & Urban Science (CROCUS) Urban Integrated Field Laboratory. CROCUS is led by Argonne in partnership with academic and community organizations and civic and industry champions. Focused on the Chicago region, CROCUS studies urban climate change and its implications for environmental justice.

The results of this baseline study will help CROCUS communities plan and test mitigation options. The researchers will work closely with CROCUS community organizations and members.

And the results are a good starting point for what the researchers hope to achieve next, a city-scale and global-scale model for each of the roofing options. But how do you incorporate a green roof into a computer model? First, researchers will work to better understand green roofs by taking measurements at surface and building levels to improve on how a green roof is represented.

Detailing on the plan, Rao revealed, “We have very few measurements for green roofs. We need to measure how much energy goes in, how much goes out, and how much water it needs and how fast it retains it. We need these measurements to give us a complete understanding of the process so we can refine calculations and models.”

Researchers will measure the roofs of CROCUS partners throughout the city. For instance, Northeastern Illinois University has both roof types, while other partner buildings have solar panels.

Finally, the researchers want to improve the resolution of the model all the way down to street scale. Rao further explained that achieving this will help them see the difference between houses and streets, which is important because it will help answer questions such as, if a tree is planted, how much does it cool the nearby building and the pavement?

The team’s research used supercomputing resources at the Argonne Leadership Computing Facility (ALCF) and the National Energy Research Scientific Computing Center (NERSC).

Big strides in the Harvard University

The Wyss Institute at Harvard University is a research and development engine for disruptive innovation powered by bioinspired technologies with visionary people at its heart.

Wyss Institute and Harvard SEAS are jointly working on a solution called cSNAP, which is a biologically inspired, indirect evaporative cooling technology that uses water instead of refrigerant chemicals and consumes up to 75% less electricity than standard vapour compression units. Evaporative coolers have been around for millennia, but currently only work in hot, dry climates. cSNAP’s innovation is a multi-chambered ceramic heat exchange unit that is strategically coated with a proprietary material that isolates moisture from air as it’s cooled, reducing the temperature without adding humidity to the air.

cSNAP was tested in real-world conditions for the first time at Harvard’s HouseZero in August 2022, on one of the hottest days of the year. It achieved a coefficient of performance (COP – the ratio between the produced cooling power and the power needed to run the system) above 8 on-site and made the room where it was installed noticeably cooler.

Additional advantages of the system include its ceramic material base and low water use, which make it appealing for low-resource and desert settings, as well as its slim form factor that allows it to be unobtrusively clipped onto the wall of a building, or installed into a window frame for easy retrofitting. cSNAP has attracted significant attention from partners and competitors in the residential cooling and HVAC industries.

A more recent iteration of the system, which added a novel dehumidification technology to improve its cooling performance, was successfully tested at HouseZero in September 2023. The combined technology, called Vesma, has the potential to reach a COP of 10, whereas most standard A/C systems achieve a maximum of 3.5.

The Vesma team is initially focusing on the residential air conditioning market as the first of several promising applications. They are working to launch a startup to commercialize their technology, and are seeking inquiries from interested investors and partners.

Conclusion

In the scope of this small article, I have presented only two recent developments, but many more works are in progress across the globe. It is not only the scientists or technocrats, but also a number of individual experimenters are working today in this field.

These researchers have been working with indomitable spirit to improve the cooling systems and develop sustainable means for cooling, however, support of the investor community and above all strong political will can accelerate the process.

By P. K. Chatterjee (PK)