Integrated Energy Systems (IES) are an emerging approach to self-powered HVAC and water heating that integrate fuel-fired and electrically powered equipment with Distributed Energy Resources (DER) and energy storage. In this paper, the authors describe hybrid and grid-interactive IES designs and approaches that serve to balance energy grid supply and demand while exploiting multiple energy resources in ways that improve overall operating cost and efficiencies, minimize emission levels, and provide resilient systems in the built environment.

IES includes a myriad of equipment combinations including traditional furnaces, water heaters and heat pumps, on-site power from small-scale combined heat and power and photovoltaics, as well as electrical and thermal energy storage. Individually, these systems have key attributes including high efficiency, low cost of operation, delivered comfort, and energy resilience. However, operated in isolation, the equipment can only provide those attributes some of the time. A comprehensive approach including laboratory, modeling, and field research indicates proper configuration and control of these systems, and when grid connected, can demonstrate far better performance integrated and connected than when isolated.