Electricity-monitoring technology surges forward at Carnegie Mellon

Credit: Maria Raffaele/Art Editor Credit: Maria Raffaele/Art Editor

Every month we pay for electricity. The bill we receive usually tells us two things: How much money we owe and how much power we’ve consumed. We know very little beyond those two things about our energy-consuming behavior for that month. For anyone trying to reduce his or her energy consumption, not knowing how to reduce electricity usage can hinder his or her strategy. However, researchers at Carnegie Mellon are currently developing a system that may be able to tell you how much energy each appliance in your home is consuming at any given time.

Mario Berges, an assistant professor in the civil and environmental engineering department, began his research by helping construct a system to monitor electricity usage in various buildings on the university’s campus. Berges and his colleagues initially implemented meters that would measure the amount of power going through individual circuits. Circuits regulate the power going through many different outlets that may be located in different rooms. By turning every electric appliance on and off, Berges’ group was able to identify what the electric signal for each individual appliance looked like, creating an “electrical signature” for that appliance.

The problems with the setup, however, were that it was expensive, involved a lot of labor, and was not able to track changes in what was plugged in. For example, the electric signal from a specific outlet might be identified as “computer,” but if the computer were to be removed from that outlet and replaced with a lamp, the system could not make the correction by itself. Berges and his colleagues then began thinking of simpler, smarter, and less-intrusive monitoring systems.

“There’s a whole research area around the idea of taking non-intrusive measurements, which means taking measurements outside of the house [using the home’s electric meter]. From those measurements, you can infer what each appliance is doing based on how they consume the power,” Berges said.

The idea involved a technique known as non-intrusive load monitoring (NILM), which involved measuring the total electrical power usage of an entire building and deducing which appliances contributed that total power consumption using various communication and information technologies. This technique would be simpler and cheaper than installing monitoring systems on every circuit or outlet, but would need to be “trained”, or given information about the appliances in your house.

In a study that was recently published in the Journal of Industrial Ecology, Berges and colleagues proposed that the “training” of the system should happen when an electrician comes to your house to perform an energy audit in which the useage of your house’s electricity is evaluated.

“While you’re receiving an energy audit, you should be at the same time training the system, with the added benefit that you get all the [electrical] signatures there and you can leave the NILM in place, and it will collect the same data that that guy would collect in one day, but continuously,” Berges said. A prototype NILM system was tested in the study, and was found to correctly identify the power consumption of many household appliances, but had some trouble with appliances that were not present during the “training.”

Of course, there are several improvements that need to be made to this system. Even though an energy audit makes the “training” much easier, it still involves labor for the customer, which may deter interest. Also, there are some appliances on the market that do not have clear electrical signatures. They may have several different power levels that they cycle through, rather than one stable electric signal that is easy to detect by the NILM.

This research is a step in the right direction for providing useful energy-consuming information, and it also offers opportunities for other types of studies to be performed. The existence of this data could offer insight into topics like domestic human behavior or efficiencies of various household products.

Berges said, “There are many doors that open up, and it’s not only for consumers.”