Park Elementary School is located in Columbia, PA. It is a kindergarten through sixth grade public elementary school in the Columbia Borough School District with around 50 teachers and 500 students.In 2006, Park Elementary School’s aging HVAC system needed replacing. Each of the school’s classrooms were served by hot water heating only vertical unit ventilators and cooling only CAV, constant air volume, packaged DX rooftop units. The gymnasium, cafeteria, and administratives were served by CAV packaged DX rooftop units each with a hot water heating coil. Gary Trostle, the specifying engineer for the Columbia Borough School District, stated “For the Park Elementary School project, I wanted the replacement units to be energy efficient, provide a more comfortable environment for the students and teachers, and improve the school’s indoor air quality, including meeting the current ventilation code requirements.” One potential replacement solution proposed was standard VAV, variable air volume, packaged DX units with hot water reheat VAV terminal units for the classrooms and administratives and standard CAV packaged DX rooftop units with hot water heating coils for the gymnasium and cafeteria. It would be a low initial cost solution that would be easy to install and be able to meet the ventilation code requirements. However, this solution would not improve occupant comfort because the units would still have compressor staging, and thus would not be able to tightly control the air temperature supplied to the VAV terminal units resulting in classroom temperature swings and uncomfortable students and teachers. The units would also only be moderately more inert. Another potential replacement solution proposed was hydronic cooling and heating VAV and CAV rooftop air handlers. With the installation of a chiller plant the system would be more inert than the previous system. This solution would improve occupant comfort and indoor air quality because the air handlers would be able to match the buildings temperature and humidity loads with their modulating water valves and be able to meet the ventilation code requirements. However, the high cost of the air handlers, chiller plant, their installation, and the system maintenance made this solution nearly infeasible.
The AAON® Solution
Noting the issues with these proposed solutions, Troy Schr, an AAON sales representative with HC Nye Co., presented Trostle with the replacement solution of AAON RM Series packaged DX units with AAONAIRE® total energy recovery wheels and Digital Scroll™ compressors. “Including factory installed energy recovery wheels and Digital Scroll™ compressors on the units,” Schr commented, “substantially improved the units’ energy and ability to provide occupant comfort.” For heating the CAV units and VAV terminal units included hot water heating coils. Because RM So 100% out-side air, meeting the ventilation requirements would not be a problem. The units would also include additional indoor air quality improvement features including double wall construction and 4” ers. Finally, the AAON solution would require no more installation or maintenance costs than the proposed standard packaged DX rooftop unit solution. Therefore, be-cause the AAON RM Stively met all of Trostle’s replacement goals, Park Elementary School decided to go with the AAON RM Series solution.