According to the U.S. Department of Energy (DOE), approximately half of all U.S. commercial floor space is cooled by self-contained, packaged air conditioning units, most of which sit on rooftops. The U.S. Environmental Protection Agency’s (EPA) Energy Star — Small Business Guide reports that in 1981, rooftop units averaged 7.8 SEER performance. By 1995, the average value had jumped to about 10.7 SEER, and in 2008 the highest-efficiency rooftop unit operated at or near 13.5 SEER.

Today, rooftop units are performing at much more efficient levels. And the newer rooftop units are much more flexible than their predecessors, offering multiple functionality variables to help generate higher efficiency. Certain models, including Daikin McQuay’s Rebel commercial rooftop system, offer efficiencies up to 19.5 IEER.

“Over the past 10 years, rooftop unit manufacturers have begun increasing a unit’s efficiency by providing larger condenser coils, thus creating higher suction temperatures, a lower compressor head, as well as incorporating newer technologies such as variable volume or speed compressors and variable-speed condenser fans,” said Scott McGinnis, sales manager, Munters Corp. “This is much different from the past, when RTUs were built and offered with EERs in the lower single digits.”

Currently available rooftop units often feature variable air volume (VAV) capabilities, allowing a system to provide differing volumes of heating and cooling load based on need or call. These systems better manage temperature across multiple zones and offer reduced fan energy consumption.

Factory-installed microprocessor controls allow users to command capabilities from inside or outside the building. Scheduling and lockouts help dictate when the unit is operational depending on the time of day, day of the week, or based on temperature or weather conditions, which also contributes to a higher efficiency rating.

Erich Bauman, commercial product manager, Rheem Heating & Cooling Division summed it up by saying, “In today’s environment, producing better air really means producing air more efficiently.”

Minimum Efficiency Standards

Federally mandated minimum standards, created through the Energy Policy Act of 2005, were implemented Jan. 1, 2010. The standards raised minimum efficiency levels by 25 to 30 percent.

Minimum standards for small units (65- to 135-kBtuh) ranging in size from 5 to 11.25 tons, were raised from 8.9 to 11.2 EER for cooling systems, and from 8.9 to 11 EER for heating units and heat pumps.

Minimum standards for large units (135- to 240-kBtuh) ranging in size from 11.25 to 20 tons were increased from 8.5 to 10.6 EER for both heating and cooling systems.

Very large units (240- to 760-kBtuh) ranging in size from 20 to 63 tons were not prescribed to a previous minimum standard. The Energy Policy Act of 2005 established standards for very large units at 10.6 EER for cooling devices and 9.5 EER for heating systems.

“Since efficiency standards for rooftop units changed in 2010, we’ve seen some tremendous advancements in the past two years. Now, we have more efficient technologies that meet these standards, and innovations that can even control an environment’s humidity,” said Bauman. “In just a few years, motors and compressors have evolved to become more efficient than ever. We’ve seen them progress from single-speed systems, to multiple-speed, and now variable-speed — becoming more efficient with every change.”

The Energy Independence and Security Act of 2007 also created a federally mandated minimum standard of 13 SEER for rooftop units under 5 tons in size. The standard was implemented June 16, 2008.

“The baseline for minimum efficiency has been raised,” said Bauman. “Manufacturers, in turn, started developing products that reached new efficiency levels, and some manufacturers have gone above and beyond to deliver products that can provide measurable energy savings — leading to a faster payback on the investment.”

Brian Wathen, commercial marketing manager, unitary products group, Johnson Controls, said the change in minimum standards has led to major increases in efficiency. “We’ve seen minimum efficiency requirements increase approximately 30 percent since 2010,” he said. “New standards, combined with the switch from R-22 to R-410A, have driven efficiencies up drastically over the last several years.”

The Future

Many manufacturers insist efficiency will continue to be a driving force in rooftop units for years to come. “In the future we expect to see greater usage of ECM motors in all HVAC equipment, in addition to variable-speed compressors,” said Roxanne Scott, national product manager, Heat Controller Inc. “Both of these components contribute to efficient energy usage while maintaining a high degree of comfort within the conditioned space.

“We expect to see a continued emphasis not only on improved energy efficiency, but also on indoor air quality. Ventilation capabilities are receiving increasing attention, and we have found many improvements in the quality of filters.”

Bauman anticipates seeing greater diagnostic technologies embedded in commercial equipment. “Advanced diagnostics can help technicians more accurately assess any service issues and spend less time on service calls,” he said. “We also expect to see a continued migration away from copper heat exchangers to much more efficient, all-aluminum options, and foresee a continued research and development focus on products that employ more efficient indoor and outdoor blowers and systems.”

Bauman said he is confident a recovering economy will lead to a larger demand for rooftop business.

“As the economy continues to recover, a number of industries are modestly growing. Last year, we saw a lot of activity among public schools, since they were able to take advantage of some federal and state tax funding for upgrading to more energy-efficient HVAC systems,” he said. “One area that we’re closely monitoring for rooftop unit sales in 2012 is the full-service restaurant industry. Rheem just launched a product that specifically meets the needs of this sector because it provides both air conditioning and water heating, as 46 percent of a full-service restaurant’s operating costs are spent on HVAC and water expenses.”

Munters Corp.’s McGinnis said most commercial buildings have benefited from the industry’s recent push for efficiency.

“Schools, low-rise office buildings, dormitories, hotels, and churches are all growing sectors that are becoming more efficient while still keeping the simple, basic rooftop unit as the basis of their HVAC systems,” he said. “The future of the dedicated outdoor air supply rooftop unit is bright.”

Johnson Controls’ Wathen said his company’s products have been in demand across all commercial areas. “We’ve seen some health care business, specifically dealing with pharmaceutical sales, and small clinics,” he said. “We’ve also encountered some business through clothing and retail stores. Our national account continues to grow each year.”

To promote future high-efficiency upgrades, DOE developed an RTU Comparison Calculator, accessible at www.pnnl.gov/uac, allowing users to easily compare the energy and financial benefits of high-efficiency units to standard equipment.

“Investing in energy-efficient products for commercial buildings and factories is one of the most cost-effective ways for businesses to save money and compete in the global marketplace,” said U.S. Energy Secretary Steven Chu. “I’m excited to see manufacturers raising the performance bar to meet the genuine demand for energy-saving commercial air conditioners.”

Publication date: 6/11/2012