Net-Zero Energy Buildings: A Classification System Based on Renewable Energy Supply Options

NOTICE This 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. Executive Summary A net-zero energy building (NZEB) is a residential or commercial building with greatly reduced energy needs. In such a building, efficiency gains have been made such that the balance of energy needs can be supplied with renewable energy technologies. Past work has developed a common NZEB definition system, consisting of four well-documented definitions, to improve the understanding of what net-zero energy means. For this paper, we created a classification system for NZEBs based on the renewable sources a building uses. A building that offsets all its energy use from renewable resources that are available within the footprint is at the top of the NZEB classification system at an NZEB:A. A building that achieves an NZEB definition through a combination of on-site renenewables and off-site purchases of renewable energy credits is placed at the lowest end of the NZEB classification at an NZEB:D. We also look at how this classification relates to the previously developed NZEB definitions. The goal of this type of classification is to encourage NZEB owners and NZEB designers to first use all possible cost-effective energy efficiency strategies, and then use renewable sources and technologies that are located on the building and at the site. We have provided for lower classes of NZEB to include buildings whose energy use exceeds the renewable energy available at the site. This NZEB classification system is applicable to both single building projects as well as a set of buildings in a community or campus.