“Much of the residential building stock in the U.S. was built in the 1950s, ‘60s, and ‘70s, when people used gas furnaces to heat their homes, along with gas cooktops and water heaters,” said Elias Pergantis, a Ph.D. candidate in mechanical engineering advised by Profs. Kevin Kircher and Davide Ziviani. “Their electrical infrastructure only required breaker panels to handle 50 to 100 amps for the whole house.”

Today’s newest electrified appliances, such as heat pumps and electric water heaters, are much more efficient and environmentally friendly. But if they all operate at once, an older home’s breaker box might not be able to handle the peak loads. “This is especially a problem in the Midwest,” said Pergantis, “which is generally a colder climate, and has more than eight million homes with insufficient breaker panels.”

In short, older homes can’t use new technology like heat pumps without upgrading their breaker panels. And that can cost $2,000 to $10,000 per home, in addition to the cost of the heat pump itself.

Pergantis has another solution, which involves software rather than hardware. “Our idea is to use smart controls to reduce the peak loads by disaggregating them,” he said. “For example, we heat the water at night, and then run the heat pump during the day. So the house is using the same overall amount of electricity, but the peaks are spread out so there’s no chance of tripping the breaker.”

To test his theory, Pergantis ran an experiment at the DC Nanogrid House, a 1920s-era West Lafayette home that has been retrofitted with electrical appliances and sensors. Pergantis first built a model of when electrical peaks occur, based on the years of real-world data they’ve gathered from people living in the house.

Then he put the model to the test. In January 2024, he implemented his control strategy for a month, adjusting electrical appliances so that their peak usage never overlapped. “It was the coldest part of the year,” said Pergantis. “Outdoor temperatures dipped to -4 degrees Fahrenheit. But the indoor temperature stayed at a comfortable level the entire month, and we only exceeded 100 amps once (but still in the safe zone). Compare this to the previous January, when the house would often exceed 120 amps, which would trip the breaker on most older homes.”

And it didn’t require massive changes. The experiment only involved a few sensors monitoring two high-draw appliances: the electric heat pump and the electric water heater. All other electrical systems were unaffected. “This kind of system can be implemented in older homes, without any major change of lifestyle for people,” he said. “That’s important to lower the barrier of entry to heat pumps and other electrification.”

The DC Nanogrid House easily accommodated the experiment, since it’s already outfitted with sensors and smart controls. But to duplicate the results of this successful test in real-world homes would require some regulatory changes. “In the U.S., we don’t currently have a standardized system for the breaker panel to talk with the water heater, which also talks with the heat pump and the cooktop,” Pergantis said. “There are ‘smart’ thermostats, but they’re not yet ‘smart’ enough to coordinate all these appliances. But as we’ve shown in our experiment, a small amount of automatic control and be a huge money saver for older homes.”

The ultimate goal for Pergantis, the DC Nanogrid House, and Purdue’s smart-building community is to lower the barrier of entry for all people to electrify their homes. “If we can make the process easier and less expensive, people will adopt it,” he said. “It will save them money, and help create a better climate for all of us.”

Pergantis presented this research at the 2024 Herrick Conferences, hosted by Purdue University. Watch the video here:

Protecting residential electrical infrastructure through advanced control: The first field results
Elias N. Pergantis, Levi D. Reyes Premer, Alex H. Lee, Priyadarshan, Haotian Liu, Eckhard A. Groll, Davide Ziviani, Kevin J. Kircher
ABSTRACT: Electrifying vehicles and residential appliances can significantly reduce greenhouse gas emissions in areas with clean electricity. However, the electrical infrastructure in most older houses was not designed to accommodate peak current draws from large loads, such as space heating, water heating, and vehicle charging. Upgrading a house’s circuit breaker panel and/or electrical service (the wires that connect a home to the utility) can be a significant barrier to rapid electrification. This study develops a novel two-level control architecture that robustly maintains the total current draw in an all-electric home within the safe limits of existing panels and service. The control system adjusts the temperature set-points of an electric resistance water heater and an air-source heat pump. The high-level controller adjusts set-points over a receding forecast horizon, while the low-level controller monitors the real-time conditions and switches off appliances if necessary. The system is tested over 31 days in an occupied, 208 m² house in a cold climate. Test conditions include outdoor temperatures as low as -20 . The controller successfully maintains the whole-home current within the safe limits of electrical panels and service rated at 100 A, a common rating for older US homes. The potential value of this work is to allow older homes to safely electrify without upgrading electrical panels or service. If electrical codes permit, this could save a typical homeowner on the order of two to ten thousand dollars and eliminate significant delays.

Source: Elias Pergantis, epergant@purdue.edu, Kevin Kircher: kkirche@purdue.edu

Writer: Jared Pike, jaredpike@purdue.edu, 765-496-0374