ANSI/RESNET/ICC 1580-2025 Standard for Calculating CO2e Emissions Based on Metered Data, for Operational Ratings

As organizations, building owners and energy managers face increasing pressure to measure, disclose and reduce greenhouse gas emissions, accurate and defensible accounting has never been more important. This standard establishes a rigorous, standardized methodology for calculating CO2e emissions using actual metered energy consumption data bringing clarity and consistency to operational carbon reporting.

Designed to complement asset-based approaches such as ANSI/RESNET/ICC 301—2025, this standard fills a critical gap by addressing emissions based on real-world performance rather than simulation. It provides a practical framework for facilities, portfolios and organizations seeking to quantify year-over-year emissions reductions, comply with disclosure mandates and align with energy management systems, such as ISO 50001. By leveraging long-run marginal emissions data and an evidence-based forward-looking methodology, this standard enables meaningful comparisons across reporting years while reflecting evolving grid conditions.

Whether applied to a single building, a multi-site enterprise or an industrial facility, this standard supports credible, transparent and technically sound operational carbon accounting empowering organizations to demonstrate measurable progress toward climate and performance goals.

Topics Covered in This Book:

• Purpose, scope and applicability of operational CO2e emissions accounting.
• Definitions and terminology essential to emissions reporting.
• Methods for calculating emissions from hourly metered electricity consumption.
• Treatment of fossil fuel use and standardized combustion emission factors.
• Procedures for calculating emissions savings relative to a normalized baseline.
• Application of long-run marginal emission rates (LRMER) using Cambium data.
• Levelization methodology, evaluation period and real social discount rate.
• Requirements for renewable energy accounting, including on-site generation.
• Limitations and treatment of renewable energy credits (RECs).
• Alignment with ISO-based energy management systems and building performance standards
• Referenced standards, including ASHRAE 90.2 and related RESNET/ICC standards.