ASHRAE 90.1-2019 Appendix G

Performance modelling beyond the code minimum

Appendix G under 2019 changes shape. The baseline is now anchored to a 2004 reference, and Performance Cost Index is measured as improvement over that fixed target. It is how beyond-code and stretch programs measure real progress.

Fixed 2004 baseline generated from your proposed model
Four-orientation baseline simulation, averaged
PCI and PCI-t for LEED and stretch-code targets
End-use cost tables and G3.1 rule documentation
3D building model showing geometry with blue walls, teal roofs, and orange adjacent structures in a grid layout within a design software interface.
Stable baseline, sharper targets

Built to show how much better

Appendix G under ASHRAE 90.1-2019 continues the anchored-baseline approach introduced in 2016. Your baseline is generated from your proposed model but held against a 90.1-2004 reference of prescriptive requirements, so PCI numbers stay comparable across code cycles. Under 2019 you also report PCI-t, comparing against the code-cycle target for beyond-code programs. LEED, jurisdictional stretch codes and voluntary rating programs all lean on these numbers. It is the most work of the three pathways, and for anything beyond baseline compliance it is the one you actually want.
Digital floor plan highlighting Diesel Tank Room in green, adjacent to Diesel Pump Room and MSB Room, with navigation and editing tools on the interface.
Fixed 2004 Baseline

The big change in the 2016 version of Appendix G, carried through 2019: the baseline no longer updates with each code cycle. It is anchored to 90.1-2004. That gives beyond-code programs a stable reference to point at.

Digital architectural floor plan interface showing Level B1 layout with highlighted Access Room and editing tools for opacity and color on the blueprint.
Climate Zone Weather

Same weather file for baseline and proposed. TMY3 for the site or an ASHRAE equivalent, applied identically to both simulations.

Screenshot of betterbuilding software showing a tags panel with categorized building elements like windows, walls, floors, roof, and retail, alongside a level navigation menu on the left.
PCI and PCI-t

Under 2019 you report both PCI (proposed against the 2004 baseline) and PCI-t (proposed against a code-required target for the current cycle). LEED, jurisdictions and stretch codes typically want a PCI-t below a stated threshold.

Screenshot of a building management software interface showing a list of building levels with options to edit, duplicate, or access roof geometry for Level 03.
Glazing as Designed

Proposed glazing modelled exactly as specified. The 2019 baseline still caps window-to-wall ratio, which is where large-facade projects continue to pick up their margin.

3D building model in Betterbuilding software showing color-coded wall shading and window elements with controls and a simulations panel on the right.
Shading and Site

Real geometry in the proposed. Baseline has no external shading and cardinal-averaged orientation. Passive design still earns credit.

User interface of Betterbuilding software showing solar panel renewables settings including surface coverage 100%, cell efficiency 18%, azimuth 0°, tilt 5°, and row size 1.55 meters, with a rectangular solar array preview on the right.
System Type Baseline

Table G3.1.1-3 sets baseline HVAC by building type and area. The 2019 tables include more system options than 2016, particularly for heat pumps, so the baseline you compare against may not be what you remember.

Betterbuilding interface showing Wall tags and detailed settings for External Wall and Internal Wall, including R-value, solar absorptance, exposure, thickness, density, and heat capacity sliders.
Unregulated Loads

Plug loads, process energy and receptacles held identical on both sides. They still hit the cost totals, which is why regulated-only PCI is usually the more instructive number.

Betterbuilding software interface showing Spaces tab with building zones and settings for Occupants including Design Level, Activity Level, Air Velocity, Work Efficiency, and Clothing Method.
Four-Orientation Runs

Baseline simulated at all four cardinal orientations and averaged. Proposed runs once in its actual orientation. Same overhead as 2016: four extra simulations, no shortcut.

Betterbuilding software interface showing energy consumption summary for Example Building with proposed versus reference data, including bar charts and tables of electricity use by category and monthly energy breakdown.
PCI Report

End-use cost tables for both models, PCI and PCI-t calculations, baseline system justification, and every G3.1 rule applied. Reviewers will read all of it.

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