by Jackie Swift
“There is no way to separate energy from the environment,” says K. Max Zhang, Mechanical and Aerospace Engineering at Cornell University. “Here’s an example of what I mean: An apartment building in New York City has its heating system converted from a steam boiler running on diesel fuel to electric, air-source heat pumps. That change causes an energy system impact. You reduce the diesel usage but increase the electricity consumption, while making the overall energy efficiency much higher.”
“At the same time,” Zhang continues, “there’s an environmental impact as well. You reduce carbon emissions because the carbon intensity for diesel is much higher than for electricity, and you also reduce air pollution because burning diesel emits a lot more particulate matter (PM) into the air.”
This is a classic demonstration of the positive changes a clean energy system can make. It’s exactly the message Zhang wants to share with the broader world outside academia. He and his group are known as the Energy and Environment Research Laboratory. They are working on a range of energy research projects with potential to help mitigate air pollution, reduce greenhouse gas emissions, and address climate change.
Their work has become even more timely with the July 2019 passage of the New York Climate Leadership and Community Protection Act, which targets economy-wide, net-zero carbon emissions by 2050. “It’s a very green plan but a very daunting task,” says Zhang. “We don’t have a lot of years between now and 2050 to get this done.”
Solving Highway Pollution — Traffic, Particulate Matter (PM), Trees, Sound Walls
Zhang has been working on the nexus of energy and the environment since his dissertation in the early 2000s, when he looked at how PM from vehicle exhaust transformed physically and chemically near highways. These days, he and his lab are studying the impact of green infrastructure, such as trees and hedgerows, along highways to absorb PM from traffic-related emissions. “The layout of the trees matters,” he says. “If you plant the trees with sparse distribution, that kind of design can actually make the PM concentration behind the trees even higher. But if you plant them more densely, without much space between them, typically you have better results.”
“It’s a very green plan but a very daunting task. We don’t have a lot of years between now and 2050 to get this done.”
The researchers also found that combining the trees with a sound wall boosted the effectiveness significantly. “The sound wall pushes the plume up, and the trees then grab the particles,” Zhang explains. Their paper published in 2016 proposing the sound-wall-and-tree mitigation design has been cited over 100 times, indicating the intense interest in the topic.
Sound walls are very expensive, however, and only the Department of Transportation can build and maintain them since they are situated in the highway right-of-way. In another project, Zhang and his colleagues investigated the efficacy of a similar mitigation design, but one where the sound wall is replaced with a much-less-expensive fence that Zhang calls a LISS (Low-cost Impermeable Solid Structure).
“A LISS serves a similar purpose to a sound wall but at a much lower cost,” Zhang says. “It’s something communities themselves can adopt. The fence can be made of any material you can think of as long as it’s impermeable because we want a solid structure to push up the plume of particulate matter. A LISS is an example of what we call a science-driven design.”
To spread the word about his findings on highway pollution mitigation, Zhang joined with John Gallagher of Trinity College, Dublin, and Richard Baldauf, physical scientist/engineer in the Environmental Protection Agency’s National Risk Management Research Laboratory, to offer a series of international webinars on passive air pollution mitigation in the spring of 2019. They were surprised by the response. “We had over 1,000 unique attendees from more than 50 countries for the first three webinars,” Zhang says. “We had people attending from six continents. There’s a huge interest. We are trying to harness that interest, build a community, and make it sustainable.”
Zhang sees his work coming to fruition in the real-world in many ways. For example, the city of Detroit is on track to adopt the LISS design — adding inexpensive fencing to vegetation barriers — which he proposed.
A Hyper-Integrated Energy and Atmospheric System
New York State’s ambitious climate goals bring fundamental changes to the supply and demand sides of the energy system, which provide exciting research opportunities.
Zhang explains, “Under high renewable penetration scenarios, energy and atmospheric systems are hyper-integrated. Meteorology affects energy generation from solar and wind resources, energy demand from heating and cooling, and air pollution transport. We are reimagining how to design an integrated energy and atmospheric system-modeling platform to capture those changes. It is going to be very cool.”
The Tompkins County Energy Roadmap — A First
Before New York State passed the new greenhouse gas reduction bill, Tompkins County — where Cornell University’s Ithaca campus is located — had its own plan to reduce greenhouse gases by 80 percent by 2050. Zhang created an energy road map for the county, a first in the nation. “The Tompkins County Energy Roadmap looks at what areas contribute to greenhouse gas emissions,” Zhang explains. “It asks, ‘What are the strategies that can help us reduce those emissions and by how much can we reduce them?’”
Zhang’s work on the Energy Roadmap has already led Tompkins County to put in place new incentives and policies to achieve the reduction goals. The process of developing the documents required him to work with a steering committee representing a wide range of stakeholders within the community.
“I write a draft report with a team of students, and then the committee shares their thoughts about it,” he says. “Engaging community stakeholders with diverse perspectives takes time, but that’s where I learn the most. Having been in academia for so long, I feel the need to expose myself to more real-world settings, otherwise I’m not going to improve. I want to do something that will make a difference in the real world.”
Zhang’s research has been shaped by this engagement experience. A key recommendation in the Energy Roadmap to decarbonize the heating sector by providing heating that uses heat pumps powered by renewable electricity led Zhang’s group to undertake a project they call Smart Heat. They explore the potential for aggregating a large number of controllable heat pumps for providing high-quality power-system services to manage peak load and integrate renewable energy, while maintaining thermal comfort.
Zhang is working with a number of industry partners to create a living laboratory for heat pump research locally in Ithaca, New York. His group is also teaming with Taitem Engineering to convert the heating system of a 10-unit apartment building in Manhattan from diesel steam boiler to heat pumps and to quantify the energy, environmental, and economic impact of the conversion.
“I would not have appreciated the importance of renewable heat if I had not worked on the Energy Roadmap,” Zhang says. “We are at the beginning of electrification of the heating sector, and my group is fortunate to be in the front row.”