ASHRAE 90.1 Appendix G PRM Modelling

This section outlines the procedures involved in setting up proposed and baseline building models in accordance with ASHRAE 90.1 Appendix G PRM. In the text below "Appendix G" refers to ASHRAE 90.1 Standard Appendix G.


Tip: See also the DesignBuilder LEED and ASHRAE 90.1 Appendix G User Guide


Note: you will need the DesignBuilder LEED / ASHRAE 90.1 module to access this functionality.

Add new site

Add new building

Constructions and Glazing

Opaque construction templates


Glazing templates

Create 3-D building model

Geometry convention

It is important for ASHRAE 90.1 based-work that the proposed and baselines buildings have identical floor areas and zone volumes. The easiest way to ensure this is to use the Simple geometry convention for both buildings. With the Simple template the block geometry drawn gives the exact surface geometry and zone volumes to be used in the simulation. This means that when you copy the proposed building to create the baseline building the zone geometry will be correct even after loading the baseline constructions.


If instead you used the External measurements template for example you would find that the baseline building surface areas, floor area and zone volumes would be different after loading the baseline constructions because these generally have a different thickness to those selected for the proposed building.


Note: When loading an activity template, it will update the lighting schedule.


Utility costs


EnergyPlus provides a "LEED Summary" report which is displayed on the Summary tab after the simulation if the appropriate option is checked on the Output tab of the Simulation options dialog under the Summary Tables header.

Convert an Existing Simulation Model to an ASHRAE 90.1 Model

To convert a standard EnergyPlus model to be treated as a proposed building go to the Regions tab at site level and set the Mandatory energy code to one of the ASHRAE 90.1 energy codes. You will be warned to check that the ASHRAE climate zone is correctly set. The default climate zone can be overridden at site level under the Location header.

Unmet hours

"Unmet hours" of a building are the summation of the number of hours when the heating or the cooling set point temperature of a zone is not met either by the HVAC system or by the plant. The data is provided in the Summary report as:


Understanding/Interpreting/Calculating the number of unmet hours:


When each zone is unmet in the specified hours as beside


Zone 1 unmet during hours: 6 8 14 16

Zone 2 unmet during hours: 6 8 12 16

Zone 3 unmet during hours: 7 8 12 13


Total number of unmet hours of the building: 7 hrs and not 12 hrs.


6 7 8 12 13 14 16



The above information on Unmet hours is sourced from a post by Ashu Gupta (and subsequent posts) on the bldg-sim mailing list