Key Points

• A workshop featuring five Penn experts focused on Red Days, which are declared when the regional electrical grid is likely to experience the greatest stress and peak demand for electricity.
• Penn routinely plans for Red Days by carefully managing cooling networks, coordinating action across offices, and encouraging individuals to lower energy use.
• Institutional and individual efforts to conserve energy on Red Days support responsible stewardship of the University’s resources.

Every summer, a handful of extremely hot days place extraordinary pressure on the regional electrical grid. At Penn, these days—known in the energy sector as Red Days or Peak Days—are planned for months in advance.

Although Red Days occur only 10–15 days per year at Penn, they influence everything from how reliably the grid operates to greenhouse gas emissions and institutional electrical costs. Red Day planning at Penn is a coordinated effort involving Facilities & Real Estate Services (FRES) and operational teams throughout the University that manage Penn’s buildings and energy systems.

That planning—and the reasons behind it—were the focus of a Red Day Readiness Workshop, held during Penn’s Earth Week 2026. Organized by the Utilities & Operations Subcommittee of Penn’s Environmental Sustainability Advisory Committee, the session brought together five speakers, including faculty leaders, operations specialists, and Penn Sustainability staff to explain how Red Days work, why they matter to Penn’s Climate & Sustainability Action Plan 4.0 (CSAP 4.0), and what the entire campus community can do and expect when they occur.

“Red Days have existed here for decades,” said event moderator Bill Braham, who is a professor of architecture, director of the Master of Environmental Building Design Program, and the co-chair of the Utilities & Operations Subcommittee. “They have energy and cost implications, and the reason we’re taking them on is they also have carbon implications.”

What Is a Red Day?

Red Days at Penn are designated between June 1 and September 30, on days when conditions indicate the regional electric grid is likely to be under peak stress. These are days when demand is expected to surge, potentially including an hour that ranks among the grid’s five highest electricity-usage hours of the summer. In practice, these are usually defined by some of the hottest and most humid afternoon hours of the summer (usually 4:00 – 7:00 p.m.) when offices are full and air-conditioning use surges across homes, businesses, and institutions throughout the Mid-Atlantic.  

In the Philadelphia region, these days are relatively predictable in the short term, and on average, Penn initiates a Red Day about 10–15 times per year. 

Solar projects like Great Cove I and II, developed through Penn's Power Purchase Agreement, connect directly to the electric grid. Image credit: AES

Why the Grid—and the Climate—Are Involved

At peak demand, when the normal supply of energy is stressed to meet higher-than-usual needs, the regional grid operator, PJM Interconnection, must draw on power plants that are normally held in reserve. These “peaker” plants are typically the least efficient sources of electricity generation and therefore are the most expensive to operate both from a cost and carbon emissions standpoint. 

“One of the first benefits of clipping peak demand is that it turns off the most expensive and dirtiest power plants on the grid,” said speaker Andrew Huemmler, senior lecturer in the School of Engineering and Applied Science. 

Reducing electricity demand during these critical hours supports the goals of Penn’s Climate & Sustainability Action Plan 4.0, which calls for refining Red Day strategies as extreme heat becomes more frequent with climate change. Even modest reductions, when coordinated across campus, can help stabilize the grid and limit emissions.

There Are Costly Implications

The cost of electricity reflects these same dynamics. Baseload energy sources such as nuclear, natural gas, coal, plus renewables like solar and wind can’t together meet the energy needs of the region on the hottest days of the year. To ensure reliability on those days, power purchasers pay a premium for energy supplied from peaker plants. All of this adds up to greater utility costs. 

“Many people go, ‘oh my God, we're paying power plants just to be there, but they don't produce very much electricity!.’ Well, when do you want electricity? You want electricity at peak. You really want it on the hottest day of the summer. So, you've got to pay for it,” explained Huemmler. 

Everyone pays for the costs of providing electricity in the quantities needed and during the times required. Residential customer billing typically does not break out the specifics of various cost components that comprise the total bill. However, commercial and industrial customers’ rate structures detail every cost associated with providing electricity. One significant category of the costs for providing electricity is known as demand or capacity charge. These costs are based on a customer’s Peak Load Contribution, which is calculated based on how much electricity an individual customer uses when the regional power grid as a whole is experiencing high (peak) usage. The actual calculation of Peak Load Contribution uses the average of the five customer peak demands that coincide with the five highest grid demand times. Basically, the less electricity used during these five times, the smaller the Peak Load Contribution, resulting in lower demand and capacity costs. The highest demand (for Penn) typically occurs later afternoon during the hottest/most humid days of summer.

“People wonder why there’s so much attention on a few days in the summer,” says director of Penn Sustainability Nina Morris. “It’s because those days matter disproportionately if we want to be responsible stewards of our resources.”

Operational staff at Penn carefully manage the University’s electrical demand on Red Days and every day. 

Penn Plans at the Campus Scale

Managing Red Days requires action by all on campus, and the University’s operational experts understand that their contributions are particularly influential.

FRES teams oversee more than 220 buildings and 18 million square feet, as well as nearly 300 acres of land. During the summer, the single largest driver of electrical load is cooling.

“The biggest control we have, from a facilities standpoint, is our chiller plants,” said workshop speaker and director of trades for FRES, Walt Molishus. “They account for roughly two thirds of our electrical load during the summer.”

Penn’s central cooling system, anchored by the Module 6 and Module 7 chiller plants, supplies chilled water through an underground network that is approximately 16 miles long. Because Red Days are driven by five one-hour peaks throughout the summer, operators can make precise, temporary adjustments to chiller output on hot days that significantly reduce demand while maintaining safety, research continuity, and general comfort.

Planning also extends to individual buildings. FRES works in advance with schools and centers to align expectations and, where possible, activities such as adjusting air-handling schedules, shifting energy-intensive housekeeping activities to different hours, reducing unnecessary lighting, and avoiding use of nonessential spaces during peak periods. These measures are proactive, coordinated, and designed to prevent disruptions rather than react to them.

Staff who lower or shut fume hood sashes used in research labs can help reduce Penn’s electrical use and promote lab safety.

Individual Actions Matter

While system-level decisions have the largest impact, individual actions provide critical support, especially when thousands of people act at once. 

On Red Days, key Penn building staff receive targeted communications with practical steps to reduce energy use during peak hours, which they then can cascade to relevant students, faculty, and staff in their networks. The messages often alert community members that “today is a Red Day, please help us save energy” and may include tips such as:

• Closing or lowering laboratory fume hood sashes when possible
• Closing blinds or shades on sunny sides of buildings
• Turning off lights and equipment in unoccupied spaces
• Powering down nonessential electronics
• Unplugging unused appliances

Designating staff or lab members to check spaces during peak hours can amplify these efforts. Individuals’ small actions and compromises, taken together, help ease strain on the grid.

"Every school and center is different. In lab buildings, for example, you're probably not going to be able to change temperatures or shut off lights in an area that's growing plants," said Andrew Zarynow, energy planning engineer at FRES and one of the workshop speakers. But in other spaces, such as in offices and libraries where greater variety in the environment can be tolerated and individuals have authority to control more, “you can have a profound impact by doing things like shutting off lights, coffee pots, copiers … or switching over a laptop to battery so it's not plugged in and using electricity." 

Penn’s Module 7 Chiller Plant connects to an approximate 16-mile underground distribution system that helps cool buildings throughout the University’s campus. Image credit: Penn University Communications

Action During a Few Days Can Make a Big Impact

Looking at the past three years between 2023 and 2025, Penn has achieved on average a nearly 8.5% load reduction during Red Day events as compared to normal operating conditions. These results demonstrate the effectiveness of Penn’s Red Day response program and the continued collaboration between Facilities, Operations, and campus stakeholders. Energy-conservation best practices promoted on Red Days can be helpful throughout the year—no matter where or when someone acts to lower energy use, it helps protect against excess.

“We need a stable grid for the good of everyone at Penn,” says Penn Sustainability’s Morris, “but also for the city and neighboring states. We are the largest private employer in Philadelphia and what all of us do on Red Days really matters—it’s part of Penn’s In Principle and Practice work that honors our deep connection with neighbors and the world.”

For a campus with round‑the‑clock activity, Red Days are a reminder that careful planning, university-wide communication, and collective action can make a measurable difference—often in just a few hours.