855773644-LEED-v5-BD-C-Reference-Guide-Launch-Edition - Page 228

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ASHRAE 90.1 4.2.1 COMPLIANCE PATH: APPENDIX G PERFORMANCE RATING METHOD (PRM)

ASHRAE 90.1, Appendix G Performance Rating Method (PRM) uses a stable baseline methodology that supports comparison of building performance across versions of ASHRAE 90.1 using a variety of performance metrics. Using the PRM, an energy modeler can develop a single set of ASHRAE 90.1, Appendix G Baseline Building Design and Proposed Building Design models to document compliance with this prerequisite, with EAc3: Enhanced Energy Efficiency, and with any code requirements linked to ASHRAE 90.1-2016 or later or IECC-2018 or later.

The stable baseline methodology in the PRM requires a Performance Index (PI) less than or equal to the Performance Index Target (PIT), with further adjustments and limitations addressing on-site renewable energy. The scale for the Performance Index ranges from one to zero, where one represents a baseline building that minimally complies with ASHRAE 90.1-2004 requirements, and zero represents a net-zero building.

Calculate the Performance Index Target using the results of the baseline building model completed under the PRM protocol, and the Building Performance Factor (BPF) for the project type and climate zone. The BPFs are provided in ASHRAE 90.1, Table 4.2.1.1 for the energy cost metric.

Refer to the Building Envelope Backstop section for further guidance addressing limitations on envelope trade-offs when applying the PRM Method. Also, refer to ASHRAE 90.1-2022 G1.2.1(b) for similar requirements limiting trade-offs from interior lighting power.

Major renovations Major renovations have slightly less stringent Performance Index Targets than New Construction, determined by multiplying published BPFs by a factor of 1.05 (See ASHRAE 90.1- 2019, Addendum cr or ASHRAE 90.1-2022 4.2.1.3 ).

Appendix G PRM. Alternative Metrics in Lieu of Energy Cost

Although the ASHRAE 90.1, Appendix G PRM references a cost metric, the energy modeler may instead demonstrate EAp2: Minimum Energy Performance compliance for the PRM using the future source energy metric referenced in EAc3: Enhanced Energy Efficiency, or a site energy metric, or a current source energy metric. Substitute all PRM references to cost with the new metric. Building Performance Factors to assess compliance must be specific to the metric and the referenced version of ASHRAE Standard 90.1 .

U.S. Green Building Council LEED v5 Reference Guide for Building Design and Construction, April 2025 Launch Edition 218