Commercial buildings could cut their heating, ventilating and air conditioning (HVAC) electricity use by an average of 57 percent with advanced energy-efficiency controls, according to a year-long trial of advanced controls at malls, grocery stores and other buildings across the country. The study, conducted by the Department of Energy’s Pacific Northwest National Laboratory (PNNL), demonstrated higher energy savings than predicted in early computer simulations.
Sitting on the roofs of many commercial buildings are HVAC boxes known as packaged HVAC units. 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.
In 2011, Srinivas Katipamula, the study’s lead researcher, and his colleagues at PNNL set out to adapt the better 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.
“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,” Katipamula said, “But our tests of advanced controls installed at real, working commercial buildings clearly demonstrate how much more energy-efficient air conditioning systems can be.”
While the PNNL team was evaluating how these controls could work, they learned that a few companies were in the process of developing advanced controls. During the summer of 2012, the team installed one of the commercially available and energy-efficient control kits on 66 rooftop HVAC units at eight volunteer commercial buildings in California, Ohio, Pennsylvania and Washington. The PNNL team 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, saved more energy than smaller buildings. And buildings that ran ventilation fans more, such as stores that are open long hours, tended to save more energy.
When using the national average energy costs, researchers found all the field-tested HVAC units would have saved an average of $1,489 annually per unit. It would take a building owner three years to recoup the cost of buying and installing advanced controls with these average cost savings.
“I’m proud to see the advanced controls my colleagues and I evaluated not only work in the real world, but produce significant energy savings,” Katipamula said. “We hope commercial building owners will be inspired by these tangible savings and install advanced controls in their rooftop HVAC units.”