When the school board and town government of Bourne, MA, saw the unusually high utility bills for Bournedale Elementary School, they knew something had to be done.

Jonathan Nelson, town facilities director for the past two years, investigated the school’s HVAC system and quickly focused on two large rooftop units with inoperable ERV wheels that required replacement. The rooftop units were running at nearly peak capacity to compensate for the missing load reduction from the ERV components. In addition to poor efficiency, the two units were affecting comfort inside the school.  The system was able to properly heat the school during the winter months but unable to adequately cool the portions of the building that were utilized during the summer months.

Energy recovery wheels recycle energy from building exhaust to pre-treat fresh air prior to conditioning by an HVAC unit. When properly designed, a system featuring energy recovery allows engineers to specify smaller and more efficient heating and cooling units, with the balance of the required air load provided by the energy recovery devices.

Due to the missing ERV load, the two rooftop units at Bournedale Elementary School were working harder and using more energy than what was intended in the system design.

Nelson faced multiple challenges in replacing the inoperable ERV wheels at an acceptable cost. A primary concern was the tight space occupied by the wheels, which were placed into each unit before the initial system installation. The cabinet door of each unit was significantly smaller than the wheel itself, making the removal of the existing wheel and the installation of a replacement more difficult. The small door also blocked “slide out” access that enables a technician to remove the wheel from the cabinet to easily perform inspections, cleaning, or repairs.

Nelson came to this project with prior knowledge of the value of energy recovery wheels from his previous employment as a facilities manager in the health care industry. During his research of replacement solutions, he was mindful of the need for his maintenance staff to easily access the wheel once it was installed.

“I came at this problem from an economic and maintenance perspective,” he says. “I wanted an affordable replacement option for this unique physical space, and I wanted to be able to rely on the new wheel for years to come.”

He began his search for a more durable replacement for the two wheels by examining other rooftop units at Bournedale Elementary School that were functioning properly. The energy recovery wheels that were installed in the functioning units were manufactured by Airxchange Inc., in nearby Rockland, MA.

Nelson contacted Airxchange to discuss its line of energy recovery cassettes — which include a wheel, frame, motor, bearing, belt, and a pulley system. He was given personal guidance, including detailed specifications of the design load for each cassette from service engineers skilled at replacing existing wheels.

Nelson was also presented with a custom solution for installing the replacement cassette inside each unit without destructive altering of the cabinet walls or doors. While the energy recovery cassettes could be assembled inside the cabinet of each rooftop unit, Nelson was concerned that a lack of “slide out” access would prevent his maintenance staff from performing routine inspection or service; he considered converting the rooftop units to a slideout-cassette design.

The service engineers convinced Nelson that altering the cabinet would be an unnecessary expense because Airxchange’s segmented design enables access to all serviceable components, even if the entire cassette cannot be removed.

Airxchange also offered other benefits with the installation. Each cassette comes with a five-year warranty and an expected lifespan of 20+ years, depending on application and conditions. Also, each cassette comes with personal on-site supervision of the installation. Airxchange interfaces with sheet metal contractors and facility maintenance personnel to ensure a proper fit within the unit.

The Airxchange service engineers arrived after the existing wheels and surrounding sheet metal structure were dismantled and removed from the rooftop units. They worked with the building maintenance staff and the sheet metal contractor to ensure that the replacement cassettes were properly placed and secured.

The cassettes were assembled inside of each cabinet and tested for functionality. An Airxchange team member returned the next day to ensure that the newly fabricated sheet metal was properly directing the counterflowing airstreams through the cassette. The school maintenance staff was also given training on how to operate and maintain the cassettes.

According to officials, the ERV wheel replacement was a success thanks to careful planning by the Bourne facilities staff and the commitment from Airxchange.