The objectives of this project are to demonstrate NETenergy’s Hybrid Rooftop Unit (RTU) and Thermal Energy Storage (TES) solution to 1) shift building electric load and reduce peak demand by 45% for four hours; 2) improve RTU efficiency by 10%; 3) extend equipment run hours by four times through shutting off the unit’s compressor when combined with local diesel generator, uninterruptable power supply, microgrid, or other distributed generations; and 4) demonstrate its reasonable system economics of a three to five year simple payback period.

Technology Description

NETenergy’s Hybrid RTU and TES use patented phase change composite as the thermal storage medium. Thermal storage is much smaller in size compared to typical ice storage installations. The phase change composite material has lower density than ice, a faster discharge rate, and an optimal freezing point. TES is integrated with a standard RTU to add load-shifting capabilities as well as improved RTU energy efficiency. The hybrid solution provides flexible operation depending on the needs of the building and the electric grid. It can charge and then discharge the thermal storage while still operating the compressor at a reduced capacity and flattens the load to reduce demand charges. This can provide 35% peak reduction for six hours, 45% for four hours, or 90% peak reduction for one to two hours. For a five-ton system, the solution comes with a ten fold reduction in size, weight, and cost than a typical ice thermal storage, and allows the solution to scale down to the ubiquitous market of three to twenty ton systems without the need to re-enforce rooftop load bearing capacity.


Department of Defense (DoD) installations have many mission-critical facilities that require continuous maintenance of temperatures and comfort of spaces- data centers, hospitals, laboratories, command centers, and others. Packaged RTU are commonly used to provide heating and cooling to maintain temperature and comfort to these facilities. There are more than 10,000 packaged RTUs in the U.S. Army and Airforce alone. RTUs rely on the commercial electrical grid for primary power. Although building-level diesel generators and uninterruptable power supplies may be available for these mission-critical facilities as back-up power, the capacity to support the heating, ventilating, and air-conditioning equipment may be limited depending on cost and other factors. More frequent and stronger natural disasters can cause prolonged power outages and wholesale electricity prices to spike. The benefits of this technology include DoD installation electric energy demand cost reduction, improved resilience in facility operations during long-duration grid outages, as well as a reduced carbon footprint.

  • Rooftop Units (RTU),

  • Thermal Energy Storage (TES),