Rooftop units (RTU) are commonly employed natural gas-fired furnaces that meet minimum federal efficiency standards, and yet rarely exceed the annual fuel utilization efficiency of about 80%. RTUs with heat pumps use the same compressors that provide cooling in the summer and operate in reverse to provide heat in the winter. Heat pumps operate very efficiently in warmer weather; however, they deliver less heat at lower efficiency as outdoor temperatures decrease. This is a challenge for cold region applications. Dual fuel RTUs combine the advantages of heat pump efficiency at mild and colder temperatures with gas-fired equipment, which can be called upon in very cold conditions. In addition, the utility structure and rates are very different across the U.S. This variability plays an important role in selecting and optimizing an RTU paired with a furnace or a heat pump due to the direct relationship between operational unit cost and utility rate structure.

This field demonstration pilot project includes the following objectives:

1. Evaluate the operation and feasibility of dual fuel RTUs in commercial/light commercial buildings versus the available baseline RTUs from efficiency, operating cost, return on investment (ROI), and demand response perspective.
2. Provide insight on Adaptive Control System design for the building and adjusting change over temperature for the hybrid RTU equipment based on weather and utility rates/rate structures to reduce operational cost of the unit and ROI of the project.

Due to their ability to provide heating from electricity or natural gas sources, hybrid RTUs may enhance military installation readiness and energy resilience. These technologies need demonstration to validate the potential and benefits in Defense applications.

This project includes a detailed research and development demonstration to assess the benefits of dual fuel RTU application in military installations. This will be accomplished through a pilot installation at a training facility in Fort Gregg-Adams, VA with a focus on measuring three impact areas to inform the system’s controller and resulting operational efficiency:

• Energy efficiency optimization
• Operational cost impact
• Reduction in imported energy

In this pilot, Gas Technologies Institute Energy will install four hybrid RTUs (20 tons each) at Fort Gregg-Adams, VA site with the following specifications:

Daikin Applied “Rebel” DPS020 Packaged Heat Pump RTUs with:

• 208V/3-phase/60 Hz Single point power with non-fused disconnect
• 0-100% Comparative [ID1] [RK2] (aka differential) enthalpy economizer
• Stainless steel gas heat exchanger – Modulating 12:1 Turndown

Condensing section with:

• Heat pump operation leveraging R-410A refrigerant (R-32 preferred, if available and in production by Daikin) [ID3] [RK4] 
• Variable Speed Inverter Compressor
• Direct drive condenser fans
• Microtech III controller with Building Automation System communication card

Additionally, the hybrid RTU will be controlled by an adaptive smart thermostat (provided by BKR Energy) leveraging a cloud service to obtain weather data. The adaptive controls can also be configured so facility managers can control how they operate their system, such as lower operating cost, lower imported energy, or some balance between the control parameters.

Hybrid RTUs combine the advantages of heat pump efficiency at mild temperatures with gas-fired equipment, which then can be called upon in cold conditions. These systems have a changeover point to move from the electric heat pump to the gas heating, which can be controlled based on utility rates, or to respond to electric grid signals in times of winter peak demand. 

Projected benefits are:

• 10%-25% reduction in site-based energy use.
• 15%-30% reduction in operating energy costs compared to baseline.
• 10%-20% reduction in imported energy.

(Project Completion - 2026)