Performance cost index

The Performance Cost Index (PCI) is a metric introduced in ASHRAE Standard 90.1-2016 to evaluate the energy performance of a building. It's a key part of the standard's Performance Rating Method (Appendix G), which allows for a flexible, whole-building approach to code compliance.

The PCI is a simple ratio that compares the annual energy cost of a proposed building design to the annual energy cost of a baseline building design.

PCI Calculation

The formula for the PCI is:

PCI = Baseline Building Performance / Proposed Building Performance​

Where,

• Proposed Building Performance: The calculated annual energy cost of the building as it is designed. This is determined through energy modeling and includes costs for all end-uses, such as HVAC, lighting, and plug loads.
• Baseline Building Performance: The annual energy cost of a fictional, minimally code-compliant building. In ASHRAE 90.1-2016 and later versions, this baseline is fixed at a stable level of efficiency (roughly equivalent to the 90.1-2004 standard), regardless of the current code edition.

The formula for the target PCI is:

PCIt = [BBUEC + (BPF x BBREC) - PRE] / BBP

Where,

• BBUEC:  Baseline building unregulated energy  cost
• BPF:  Building performance factor from Table 4.2.1.1.
• BBREC:  Baseline building regulated energy cost
• PRE:  Prescriptive renewable energy
• BBP:  Baseline building performance

A lower PCI value indicates a more energy-efficient building. To comply with the standard, a project's calculated PCI must be less than or equal to a target PCI (PCI_t) specified in the standard for its climate zone and building type.

The metric's importance lies in its ability to provide a consistent, universal benchmark for building energy performance. By keeping the baseline fixed, the PCI allows for a clear, year-over-year comparison of efficiency improvements between different editions of the ASHRAE standard and for use in beyond-code programs like LEED.