Commercial buildings could cut their heating and cooling electricity use by an average of 57 percent with advanced energy-efficiency controls, according to a year-long trial of the controls at malls, grocery stores and other buildings across the country. The study demonstrated higher energy savings than what was predicted in earlier computer simulations by the same researchers.
“We’ve long known that heating and cooling are among the biggest energy consumers in buildings, largely because most buildings don’t use sophisticated controls,” said the study’s lead researcher, engineer Srinivas Katipamula of the Department of Energy’s Pacific Northwest National Laboratory. “But our tests of controls installed at real, working commercial buildings clearly demonstrate how much more energy efficient air-conditioning systems can be.”
Sitting on the roofs of many commercial buildings are shiny metal boxes containing heating, cooling, ventilation and air conditioning (also known as HVAC) units. These are pre-made in a factory and have all their components inside a box, leading the industry to call them “packaged” HVAC units. Another kind of commercial HVAC, called air handling units, have long used sophisticated controls to ensure they work as efficiently as possible. But packaged units are often allowed to run for hours on end, even if they aren’t needed, and receive little maintenance.
Packaged HVAC units consume the same amount of electricity each year as 8 million U.S. residents, or about 2,600 trillion British thermal units of energy. All those ignored and often-inefficient HVAC systems add up, creating higher power bills and contributing to the nation’s greenhouse gas emissions.
Putting an idea to the test
Katipamula and his PNNL colleagues have spent their careers thinking up ways to reduce energy use in buildings. In 2011, they set out to adapt the controls already found in air handling HVAC units for use in packaged rooftop HVAC units. The goal was to enable packaged units to automatically adjust their operations based on conditions inside and outside a building. Using sensors and variable-speed motors, the controls decide when and how fast ventilation fans should run, and if the units can use naturally cold air from the outside instead of mechanically cooling indoor air.
While the PNNL team was evaluating how these controls could work, they learned a few companies were simultaneously and independently in the process of developing such advanced controls. During the summer of 2012, the team installed one of the commercially available control kits on 66 rooftop HVAC units at eight volunteer commercial buildings in Washington state, Ohio, California and Pennsylvania. The buildings included shopping malls, grocery stores, big-box stores and a medical clinic. The installed devices, manufactured by Transformative Wave of Kent, Wash., were chosen because they most closely resembled the advanced controls PNNL had envisioned.
Real energy savings
Katipamula and his colleagues found that, compared to standard operations, the HVAC units using advanced controls cut their energy use by an average of 57 percent. The actual energy savings ranged from 20 to 90 percent. Larger buildings such as malls, which need bigger HVAC units, saved more energy than smaller buildings. And buildings that ran ventilation fans more, such as stores open long hours, tended to save more energy.