ASHRAE Journal - September 2009 - 24

What Is a Net Zero Energy Building? Calibrating expectations is a foundation for success in any net zero energy building (NZEB) project. In the broadest sense, an NZEB is a residential or commercial building with greatly reduced energy needs. In such a building, efficiency gains enable the balance of energy needs to be supplied with renewable energy technologies. But this broad definition leaves plenty of room for interpretation—and for misunderstanding among the owners, architects, and other players in an NZEB project. Agreeing to a common definition of NZEB boundaries and metrics is essential to developing design goals and strategies. To improve clarity, the National Renewable Energy Laboratory has created two foundational references: Zero Energy Buildings: A Critical Look at the Definition (August 2006) documents four NZEB definitions: net zero site energy, net zero source energy, net zero energy costs, and net zero energy emissions.11 Zero Energy Buildings: A Classification System based on Renewable Energy Supply Options (July 2009) classifies NZEBs based on the renewable energy sources used. At the top of the classification system is the NZEB:A—a building that offsets all of its energy use from renewable energy resources available within the footprint. At the lowest end is the NZEB:D—a building that achieves an NZEB definition through a combination of on-site renewables and off-site purchases of renewable energy credits. Table 1 and the sidebar “Net Zero Energy Building Definitions” summarize the four NZEB definitions and four energy-use classifications. There is no “best” definition or energy-use accounting method; each has merits and drawbacks, and the approach for each project should be selected to align with the owner’s goals. But across all NZEB definitions and classifications, one design rule remains constant: tackle demand first, then supply. NZEB owners and designers should first use all possible cost-effective energy efficiency strategies and then incorporate renewable energy, weighing the many possible supply options available and giving preference to sources available lesson learned from some of the initial NZEBs is that peak demand issues are even more pronounced than in typical buildings. 8 While NZEBs have large PV systems that offset significant energy use, their demand for grid power peaks in the evening, during morning warm-up, or when a cloud blocks the sun. As a result, NZEBs often do not offset peak demand. To address the potential poor load factors of NZEBs, more research is needed on energy storage and its effect on large-scale NZEB penetration scenarios. With energystorage integration, flatter load profiles, and better load factors, utilities will be much more agreeable to the con24 ASHRAE Journal Net Zero Energy Building Definitions • Net Zero Site Energy: A site NZEB produces at least as much renewable energy as it uses in a year, when accounted for at the site. • Net Zero Source Energy: A source NZEB produces (or purchases) at least as much renewable energy as it uses in a year, when accounted for at the source. Source energy refers to the primary energy used to extract, process, generate, and deliver the energy to the site. To calculate a building’s total source energy, imported and exported energy is multiplied by the appropriate site-to-source conversion multipliers based on the utility’s source energy type. • Net Zero Energy Costs: In a cost NZEB, the amount of money the utility pays the building owner for the renewable energy the building exports to the grid is at least equal to the amount the owner pays the utility for the energy services and energy used over the year. • Net Zero Energy Emissions: A net zero emissions building produces (or purchases) enough emissions-free renewable energy to offset emissions from all energy used in the building annually. Carbon, nitrogen oxides, and sulfur oxides are common emissions that NZEBs offset. To calculate a building’s total emissions, imported and exported energy is multiplied by the appropriate emission multipliers based on the utility’s emissions and on-site generation emissions (if there are any). within the building footprint. Use of on-site renewable options over off-site options minimizes the overall environmental impact of an NZEB by reducing energy transportation, transmission, and conversion losses. In addition to efficiency measures, demand-side strategies may include renewable energy sources that cannot be commoditized, exported, or sold, such as passive solar heating, daylighting, solar ventilation air preheaters, and domestic solar water heaters. Typical supply-side generation options include photovoltaics, solar hot water connected to a district hot water system, wind, hydroelectricity, and biofuels. cept of large numbers of buildings with significant on-site generation capacity. Energy consumption in our nation’s commercial building sector will continue to increase until buildings can be designed to use energy efficiently and produce enough energy to offset their growing energy demand. DOE has set an aggressive goal to create the technology and knowledge base for cost-effective net zero energy commercial buildings by 2025, and we are gratified to have many industry leaders joining us in this quest. We invite commercial architects, engineers, and owners to use the Zero Energy Buildings Database and to contribute their own data to make it an increasingly useful tool. ashrae.org September 2009

ASHRAE Journal - September 2009

Table of Contents for the Digital Edition of ASHRAE Journal - September 2009

ASHRAE Journal - September 2009
Contents
Commentary
Industry News
Letters
Meetings and Shows
Getting to Net Zero
Feature Articles
How High Can You Go? Building Height and Net Zero
Lab for Learning
Solar Hot-Water Heating System: Lessons Learned
50th Anniversary—Low Pressure Steam Heating Systems
Building Sciences
Products
Emerging Technologies
People
Classified Advertising
Advertisers Index
ASHRAE Journal - September 2009 - ASHRAE Journal - September 2009
ASHRAE Journal - September 2009 - Cover2
ASHRAE Journal - September 2009 - 1
ASHRAE Journal - September 2009 - 2
ASHRAE Journal - September 2009 - Contents
ASHRAE Journal - September 2009 - 4
ASHRAE Journal - September 2009 - Commentary
ASHRAE Journal - September 2009 - Industry News
ASHRAE Journal - September 2009 - 7
ASHRAE Journal - September 2009 - 8
ASHRAE Journal - September 2009 - 9
ASHRAE Journal - September 2009 - Letters
ASHRAE Journal - September 2009 - 11
ASHRAE Journal - September 2009 - 12
ASHRAE Journal - September 2009 - 13
ASHRAE Journal - September 2009 - 14
ASHRAE Journal - September 2009 - 15
ASHRAE Journal - September 2009 - Meetings and Shows
ASHRAE Journal - September 2009 - 17
ASHRAE Journal - September 2009 - Feature Articles
ASHRAE Journal - September 2009 - 19
ASHRAE Journal - September 2009 - 20
ASHRAE Journal - September 2009 - 21
ASHRAE Journal - September 2009 - 22
ASHRAE Journal - September 2009 - 23
ASHRAE Journal - September 2009 - 24
ASHRAE Journal - September 2009 - 25
ASHRAE Journal - September 2009 - How High Can You Go? Building Height and Net Zero
ASHRAE Journal - September 2009 - 27
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ASHRAE Journal - September 2009 - 32a
ASHRAE Journal - September 2009 - 32b
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ASHRAE Journal - September 2009 - 36
ASHRAE Journal - September 2009 - 37
ASHRAE Journal - September 2009 - Lab for Learning
ASHRAE Journal - September 2009 - 39
ASHRAE Journal - September 2009 - 40
ASHRAE Journal - September 2009 - 41
ASHRAE Journal - September 2009 - 42
ASHRAE Journal - September 2009 - 43
ASHRAE Journal - September 2009 - Solar Hot-Water Heating System: Lessons Learned
ASHRAE Journal - September 2009 - 45
ASHRAE Journal - September 2009 - 46
ASHRAE Journal - September 2009 - 47
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ASHRAE Journal - September 2009 - 51
ASHRAE Journal - September 2009 - 52
ASHRAE Journal - September 2009 - 53
ASHRAE Journal - September 2009 - 50th Anniversary—Low Pressure Steam Heating Systems
ASHRAE Journal - September 2009 - 55
ASHRAE Journal - September 2009 - 56
ASHRAE Journal - September 2009 - 57
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ASHRAE Journal - September 2009 - Building Sciences
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ASHRAE Journal - September 2009 - 80
ASHRAE Journal - September 2009 - 81
ASHRAE Journal - September 2009 - Products
ASHRAE Journal - September 2009 - 83
ASHRAE Journal - September 2009 - Emerging Technologies
ASHRAE Journal - September 2009 - 85
ASHRAE Journal - September 2009 - 86
ASHRAE Journal - September 2009 - 87
ASHRAE Journal - September 2009 - 88
ASHRAE Journal - September 2009 - 89
ASHRAE Journal - September 2009 - People
ASHRAE Journal - September 2009 - 91
ASHRAE Journal - September 2009 - 92
ASHRAE Journal - September 2009 - Classified Advertising
ASHRAE Journal - September 2009 - 94
ASHRAE Journal - September 2009 - 95
ASHRAE Journal - September 2009 - Advertisers Index
ASHRAE Journal - September 2009 - Cover3
ASHRAE Journal - September 2009 - Cover4
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