Technology can make heating smarter, electricity greener and appliances more efficient.

Except when humans adjust their behavior to the technology.

Renovated homes and smart gadgets are part of a broad effort to tackle climate change. But here's the catch: People seem to relish using their new devices and comforts, often pushing energy consumption up and undermining the effort to reduce emissions of carbon.

Experts call it the "rebound effect."

One Danish utility knows it all too well. Engineers and technicians at Hofor, a city-owned company that supplies heat to a million residents in the greater Copenhagen area, crunch data from smart meters to better understand residents' consumption patterns. The research is critical for the utility, which is legally bound to lower general energy use as part of Copenhagen's ambitious push to become carbon neutral by 2025.

Hofor found that people changed the way they used energy in a freshly insulated and renovated building, cranking up the heat a few degrees. The behavior undermined expected energy savings.

"Spreadsheets and human behavior do not match," said Gorm Elikofer, chief customer officer at Hofor. "Humans say, 'Now we have more energy-efficient buildings so we can convert this to better comfort.'"

"The rebound effect is just human psychology, which makes it so hard to fix because the engineers can't really work on that" — Paul Voss, MD of Euroheat and Power

The most striking differences often follow extreme transformations to a home. A person used to living in a cold, poorly insulated, leaky home may rejoice at the opportunity to heat all rooms of the house knowing the energy won't escape and the building is state-of-the-art.

Danish consultancy Niras assessed 13 renovated buildings covering 100,000 square meters a few years ago and found results ranged from a 39 percent cut in energy use to an 18 percent increase. Elikofer pointed to a similar eye-opening result: An apartment building that received the Danish renovation prize in 2013 was supposed to see heating consumption drop by 75 percent, but reductions measured only 29 percent.

"If you put insulation in that wall, it will definitely lose less energy," said Adrian Joyce, secretary-general of EuroAce, the European Alliance of Companies for Energy Efficiency in Buildings. The issue, however, is how people choose to make use of those measures, he added.

The issue is not limited to heating. It's a mindset reflected in the choice of buying a bigger TV knowing it is more energy-efficient or not bothering to turn off a light because of the growing use of LED bulbs, said Paul Voss, managing director of Euroheat and Power, a lobby group in Brussels representing companies in the district energy sector.

"The rebound effect is just human psychology, which makes it so hard to fix because the engineers can't really work on that," he said.

Samuel Leupold, CEO of wind power for Dong Energy, compares it to the way food labels work.

"It’s like when you buy mayonnaise," he said. "If it says 'light' on it with reduced calories, I tend to take more."

Technology and innovation also have increased the use of renewable-based electricity in people's homes, erasing the notion that using too much power is bad for the environment.

"I can see that with my kids," Leupold said. "I was brought up in a way that, when you leave a room, you immediately switch off the light because in those days, electricity was expensive and you probably had the sense that maybe it was not generated in the most environmental way."

Now it's more difficult to control energy use because electricity is cheaper, and "at the same time you can have a clean conscience because it is renewable [energy]," he added.

A 2015 academic article in the Renewable and Sustainable Energy Reviews journal found that "consumer choices and behavior are, to a large extent, driven by cognitive biases, heuristics and other 'predictably irrational' tendencies."

"Yet these cognitive biases and motivational factors are often overlooked by practitioners and policymakers seeking to promote energy efficiency and conservation," it added.

Gorm Elikofer said a regulatory system that limits the excessive use of heating could save about 10 percent of unnecessary energy consumption.

Education can be part of the solution, though people may not heed what they are told.

"People should be given guidance so they can decide consciously what they are going to do," said Joyce of EuroAce. "But you are running into the problem of people resisting to be told what to do."

Elikofer at Hofor found that "it is very difficult to do anything with the consumers."

Instead, he added, the solution is to educate the people setting up the heating system in the basement of the buildings. Elikofer said a regulatory system that limits the excessive use of heating could save about 10 percent of unnecessary energy consumption.

"The task is not to make people freeze," he said, but to keep things within reasonable bounds.

"It is like speed limits on the highways," Elikofer said. "Why should you be ridiculous?"

Joyce said technology can help overcome some of these issues: If a person opens the window while the heat is on, a smart gadget could detect that and shut off the heat.

"Smart systems are only as smart as the programmers," he said.

This article is part of a POLITICO Special Report: Connected Citizens.