Report Released: Commercial Roof-top Units in Minnesota

Apr 21, 2017

CEE has released a final report on its research with Seventhwave into efficiency in commercial roof-top HVAC units: Commercial Roof-top Units in Minnesota — Characteristics and Energy Performance.

Packaged roof-top units (RTUs) are ubiquitous on commercial buildings throughout the United States because of their low capital cost, reliability, and well-developed service and distribution network. There is anecdotal evidence, however, that these systems tend to operate inefficiently and sub-optimally. To validate or refute this evidence, the project team conducted a multilevel field study to characterize both new and existing RTUs in Minnesota and monitor the energy performance of existing RTUs.

C9TGPgKXoAE14IS.jpgThe first stage of this project, conducted by the project lead, Seventhwave, characterized both existing RTUs and the new/replacement market. CEE conducted the second stage of the project, which monitored existing RTU energy performance.

Research results suggested recommendations for Minnesota’s Conservation Improvement Programs (CIP). One recommendation is expanding the Minnesota Technical Reference Manual (TRM) to include a wider scope of RTU-related measures to aid in the development of more comprehensive RTU programs. Many other efficiency options that are now available, such as demand control ventilation, improved economizers, and energy recovery ventilation, could also be added to a comprehensive RTU program.

Utility rebates for RTUs have historically been based on exceeding a minimum level of efficiency, but only at maximum energy usage. Since RTUs don't typically operate at maximum capacity around the clock, however, it is important to find efficiencies when energy use is lower too. Developing rebates based on the Integrated Energy Efficiency Ratio (IEER) — to account for efficiency when the energy load is less — would benefit utility programs whose priority is annual energy savings.

This project was supported in part by a grant from the Minnesota Department of Commerce, Division of Energy Resources through the Conservation Applied Research and Development (CARD) program. The project was co-funded by CEE in support of its nonprofit mission to advance research, knowledge dissemination, and program design in the field of energy efficiency.

Related Links

Final Report: Commercial Roof-top Units in Minnesota
Webinar on project findings
Research project page