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meet the prescriptive requirements. ASHRAE 90.1-2019 compliance is achieved if the proposed design’s energy cost is no greater than the budget. For ASHRAE 90.1-2022, an additional improvement below the ECB must be met based on an adjustment referencing the prescriptively required “energy credits” from Section 11. Refer to the Building Envelope Backstop section for further guidance addressing limitations on envelope trade-offs when applying the ECB Method.

The ECB Method may not be used to demonstrate improvement in regulated energy savings for EAc2: Enhanced Energy Efficiency.

ASHRAE 90.1 4.2.1 compliance path: Appendix G PRM stable baseline For initial buildouts and substantial alterations, this path holistically evaluates building performance including base building systems and systems modified in the project scope. Projects locating in underperforming buildings will have difficulty showing compliance using this path.

For initial buildouts and substantial alterations, ASHRAE 90.1, Appendix G PRM utilizes 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 EAc2: 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 PI ranges from one to zero (1–0), where one (1) represents a baseline building that minimally complies with 90.1-2004 ASHRAE requirements and zero (0) represents a net zero building.

The PIT is calculated using the results of the baseline building model completed in accordance with the PRM protocol and the BPF for the project type and climate zone. The BPFs are provided in ASHRAE 90.1, Table 4.2.1.1 for the metric of energy cost.

Substantial alterations have slightly less stringent PITs than new buildings, 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, performance calculations for other alterations (90.1-2022 G3.3) For other alterations (alterations that are not initial buildouts or substantial alterations), the stable baseline methodology does not apply. The methodology is similar to ASHRAE 90.1-2010,

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