ASHRAE 90.1 Appendix G PRM Reference

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.

 

The main sources of documentation on using DesignBuilder for ASHRAE 90.1 Appendix G PRM work are:

 

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 ASHRAE 90.1 Geometry convention for both buildings. With this 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.

Lighting

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

HVAC

Baseline DX Cooling Coil Efficiency Input

From the ASHRAE 90.1 Standard, all HVAC equipment in the baseline building design shall be modelled at the minimum efficiency levels, both part load and full load. The efficiency rating that includes the supply fan energy shall be adjusted to remove the supply fan energy so that supply fan energy can be modelled separately. To help meet this requirement, for baseline systems that use DX cooling coils, i.e., systems #1 through #6, the COP input can be calculated using a simple ASHRAE COP calculation tool.

 

 

You can download the COP calculation tool from our website. Thanks to Germán Campos from Ecoeficiente for providing it!

Note: The calculation requires a sizing run as the cooling capacity is a mandatory input to the program.

Utility costs

Outputs

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:

Example

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.

Diagnosing Excessive Unmet Hours

Possible causes of unmet load hours are as follows:

 

 

To help identify and fix the issue, the following checks can be made: