Bosch has developed and demonstrated a novel direct current (DC) microgrid system that maximizes the efficiency of locally generated photovoltaic energy while offering high reliability, safety, redundancy, and reduced cost compared to equivalent alternating current (AC) systems. Several demonstration projects validating the system feasibility and expected efficiency gains have been completed and additional ones are in progress. This paper gives an overview of the Bosch DC microgrid system and presents key results from a large simulation study done to estimate the energy savings of the Bosch DC microgrid over conventional AC systems. The study examined the system performance in locations across the United States for several commercial building types and operating profiles. It found that the Bosch DC microgrid uses generated PV energy 6%-8% more efficiently than traditional AC systems.

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Heather Burpee with the University of Washington's Integrated Design Lab reviewed an earlier draft of this report.The authors extend their thanks to their NREL colleagues Kyle Benne and Michael Sheppy for conducting formal internal reviews of this document, and to Stefanie Woodward and Sara Havig for providing editing assistance.Thousands of EnergyPlus simulations were run to fully debug and finalize the energy models referenced by this report. This would not have been possible without the support of the NREL High Performance Computing Center managed by Jim Albin and Wesley Jones. Additional thanks go to Torri Lopez of the NREL High Performance Computing Center for helping to install and maintain the software necessary to perform energy simulations on the Windows High Performance Computing cluster.Finally, several other NREL colleagues provided valuable guidance and information during the modeling process, either directly or through their past work. Ian Doebber contributed insights, particularly heating, ventilation, and air conditioning insights, gained through his work on previous healthcare projects. Jennifer Scheib provided electric lighting data. Kyle Benne provided programming and automation assistance, and Brent Griffith contributed invaluable EnergyPlus modeling and debugging assistance.ii Executive SummaryThe Commercial Buildings Group at NREL developed this Technical Support Document under the direction of the U.S. Department of Energy Building Technologies Program. It documents the technical analysis performed and the resulting design guidance that will enable large hospitals to achieve whole-building energy savings of at least 50% over ANSI/ASHRAE/IESNA Standard 90.1-2004. This report also documents in detail the modeling methods used to demonstrate that the design recommendations meet or exceed the 50% energy savings goal. MethodologyTo account for energy interactions between building subsystems, we used EnergyPlus (DOE 2010) to model the predicted energy performance of the baseline and low-energy buildings to verify that 50% energy savings are achievable in all climate zones. EnergyPlus computes building energy use based on the interactions between climate, building form and fabric, internal gains, and heating, ventilating, and air conditioning systems. The percent energy savings values presented in this document are based on a nominal minimally code-compliant building, as described in Standard 90.1-2004, and utilize a whole-building site energy use intensity metric (Torcellini et al. 2006).The following steps were used to determine 50% savings:1. Define architectural-program characteristics (design features not addressed by Standard 90.1-2004) for a typical large hospital, thereby defining a single prototype model. 2. Create baseline energy models for each climate zone that are elaborations of the prototype model and are compliant with Standard 90.1-2004, using industry feedback to strengthen the inputs for the baseline models. 3. Create low-energy models for each climate zone by applying a list...

NOTICEThis report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.Available electronically at http://www.osti.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: (ASHRAE 2004b). The AEDG-K12 was developed in collaboration with the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), the American Institute of Architects (AIA), the Illuminating Engineering Society of North America (IES), the U.S. Green Building Council (USGBC), and the U.S. Department of Energy (DOE). U.S. Department of EnergyThe AEDG-K12 is the second AEDG for K-12 school buildings; the first was part of a series of six AEDGs targeting 30% energy savings over levels achieved by following the ANSI/ASHRAE/IESNA Standard 90. 1-19991- (ASHRAE 1999. The guides in the 30% energy savings series are: Each guide provides user-friendly design assistance and recommendations to design, architectural, and engineering firms to achieve energy savings. The AEDG-K12 includes prescriptive recommendations by climate zone for the building envelope; fenestration; lighting v systems (including interior and exterior electric lights and daylighting); plug, process, and phantom loads; commercial kitchen equipment; service water heating (SWH); HVAC systems; building automation and controls; outdoor air treatment; and measurement and verification (M&V). Additional savings recommendations are also included, but are not necessary to achieve the 50% savings goal. These are provided for renewable energy systems and alternative HVAC systems.The objectives in developing this TSD were to:• Document the development of the baseline and low-energy K-12 school facility energy models.• Document the modeling assumptions needed to verify 50% energy savings.• Present the recommendations for achieving at least 50% savings over Standard 90.1-2004.• Validate that the recommendations result in 50% or greater energy savings by climate zone.• Document the process used to develop the AEDG-K12. AEDG-K12 Development ProcessThe AEDG-K12 was developed by a PC representing a diverse group of professionals. Guidance and support were provided through collaboration of ASHRAE, AIA, IES, USGBC, and DOE. PC members were...