In April 2023, ASHRAE released ANSI/ASHRAE Standard 228-2023, Standard Method of Evaluating Zero Net Energy and Zero Net Carbon Building Performance, a new standard that sets a standard calculation method for a building or group of buildings to qualify as “zero net energy” and “zero net carbon”. The standard defines the calculation of energy and carbon use in terms of source metrics rather than site metrics. Site metrics, such as site energy use, capture the energy use or emissions directly attributed from power or fuel imported onto a building site. Source metrics apply a multiplier to site metrics to additionally account for energy losses during the upstream generation, distribution, and transmission processes, capturing gross building energy use impacts and emissions more effectively. In Standard 228, source metrics can be calculated using annual average source factors or hourly multiplier data where available. The use of source metrics in Standard 228 thus creates more stringent thresholds of renewable energy use or emissions reductions and offsets for buildings vying to claim net zero status. The standard, however, also establishes off-site allowances for buildings that are unable to install and produce adequate renewable energy in order to fulfill the zero net energy or zero net carbon standard.
Standard 228 was developed based on existing ASHRAE Standards, including Standard 105, that establishes methods of determining, expressing, and comparing building energy performance and greenhouse gas emissions. The Standing Standard Project Committee for Standard 228 (SSPC 228) will publish continuous version updates to include addenda and revisions of this new standard as needed.