Appendix G PRM Rules

Appendix G Performance Rating Method Rules and OSSTD-PRM

The “Create ASHRAE 90.1-2019 PRM Model” measure provides a detailed implementation of the rules of the Appendix G Performance Rating Method. Below are some of the key changes that are applied by the tool when creating the Baseline and Proposed model:

Rules for Baseline Model
  • Apply baseline envelope rules
    • Space conditioning type
    • Constructions
    • Insulation levels
    • Window-to-wall ratio
    • Skylight-to-roof ratio
    • Infiltration
  • Apply baseline lighting rules
    • Lighting power
    • Lighting occupancy sensor control
  • Determine and create baseline HVAC systems
    • Remove user model HVAC
    • Determine baseline HVAC based on building type and Appendix G rules
    • Create new baseline HVAC systems
    • Apply special rules for computer rooms and laboratories
  • Size HVAC systems
    • Apply HVAC efficiencies
    • Apply fan power adjustments
    • Apply baseline HVAC controls
  • Rotate building model through cardinal directions
  • Check for unmet load hours and rectify, if needed
  • Handle additional compliance data
    • Multiple building types
    • Plug load measures
    • Elevators
    • Exterior lighting
    • Interior lighting exceptions
    • Number of systems per zone
Rules for Proposed Model
  • Apply proposed envelope rules
    • Infiltration
  • Apply proposed lighting rules
    • Residential lighting power
  • Remove pipe losses for SWH
  • Adjust computer room equipment schedules