A Pacific Northwest National Laboratory team found commercial buildings could cut their heating and cooling electricity use by an average of 57% with advanced energy-efficiency controls. The team built the results with a year-long trial of the controls at malls, grocery stores and other buildings across the country. The real world study demonstrated higher energy savings than the team had predicted in earlier computer simulations.
Lead researcher, engineer Srinivas Katipamula said, “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. 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 or gray metal boxes containing heating, cooling, ventilation and air conditioning (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.
Packaged Rooftop HVAC Units Example. Image Credit: Pacific Northwest National Laboratory.
Opposed to the packaged HVAC units is another type called air handling units that have long used sophisticated controls to ensure they work as efficiently as possible.
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The problem is 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 wasting the nation’s power generating capacity.
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.
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, 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.
Translating the energy savings into dollars saved depended on local power costs. Nationwide, energy costs an average of 10 cents per kilowatt-hour, though areas with abundant and inexpensive power supplies often pay less and large cities with greater energy needs generally pay more. When using the national average, researchers found all the field-tested HVAC units would have saved an average of $1,489 annually per unit. The team calculated it would take a building owner three years to recoup the cost of buying and installing advanced controls with that average cost savings. Commercial buildings often have multiple rooftop HVAC units, so actual savings per building would depend on the number of units used.
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But the exact payback period depends on several factors. To help building owners weigh the costs, the research team developed a table that lays out which specific combinations of an HVAC unit’s size, the number of hours its fan runs daily and the local energy rate would result in a three-year or less payback period. The team concluded installing advanced controls in smaller units with a capacity of 15 tons or less could achieve a three-year payback in areas where energy costs 12 cents per kilowatt-hour or more, or where sufficient utility incentives were available.
Katipamula said, “I’m proud to see the advanced controls my colleagues and I evaluated not only work in the real world, but produce significant energy saving. We hope commercial building owners will be inspired by these tangible savings and install advanced controls in their rooftop HVAC units.”
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In reality though many owners aren’t paying the power bills. Buildings often, especially when more than one tenant is in occupancy, rent with terms where the tenant pays the electricity, other utilities, insurance and sometimes even the taxes. In these situations, almost everywhere, no disclosure is made to prospective tenants about the efficiency. Few landlords are interested in saving electricity when someone else pays the bill and they would have to invest more.
However that doesn’t point out that a few smart landlords could very well be more competitive with more efficiency. After all, those latter year savings could go to the landlord’s pocket instead of the power company’s.
By Brian Westenhaus of New Energy And Fuel
