2.1 Simulation General Requirements

2.1.1 General

This document lists the building descriptors that are used in energy simulations. Users must provide valid data for all descriptors that do not have defaults specified and that apply to parts of the building that must be modeled.

2.1.2 Definition of Building Descriptors

Building descriptors provide information about the proposed design and the baseline building. Building descriptors are discussed in the generic terms of engineering drawings and specifications in order to avoid bias toward one particular energy simulation engine. However, the building descriptors in this chapter are compatible with commonly used simulation software. Other building descriptors may be substituted as long as the input restrictions and definition of the baseline building conditions are consistent.

Each energy simulation program has its own way of accepting building information. EnergyPlus, for instance, uses a comma delimited data file called IDF. DOE-2 uses BDL (building design language) to accept information. It is the responsibility of the COMNET software developer to translate the generic terms used in this chapter into the “native language” of the simulation program used by the software. Figure 2.1.2-1 illustrates the flow of information.

Figure 2.1.2-1: Information Flow

2.1.3 Building Envelope Descriptions

The user shall provide accurate descriptions for all building envelope assemblies including exterior walls, windows, doors, roofs, underground walls and floors. However, the following exceptions apply:

• Any envelope assembly that covers less than 1% of the total area of that assembly type (e.g., exterior walls) need not be separately described. If not separately described, the area of an envelope assembly must be added to the area of the next most similar assembly of that type.
• Exterior surfaces whose azimuth orientation and tilt differ by no more than 45º and are otherwise the same may be described as a single surface or described using multipliers. This specification would permit a circular form to be described as an octagon.

2.1.4 Treatment of Building Descriptors Not Fully Addressed By This Document

The goal for this document is to provide input and baseline rules covering a full range of energy-related features encountered in commercial buildings. However, this goal is unlikely to ever be achieved due to the large number of features that must be covered and the continuous evolution of building technologies.

Building systems or components not described in this document shall be modeled in the baseline building as meeting the mandatory and prescriptive requirements of Standard 90.1, Sections 5 through 10. If there are no mandatory or prescriptive requirements for a system or component not described in this document, it shall be modeled in the baseline building the same as in the proposed building. Any uncertainty regarding appropriate modeling assumptions must be resolved so that the impact is conservatively assessed; for example, so as to make it less likely rather than more likely that rated building energy performance will be lower.

When a simulation program does not model a design, material, or device of the proposed design, an exceptional calculation method shall be used if approved by the rating authority. 

2.1.5 Space Use Classification

Space use classifications determine the default or prescribed occupant density, occupant activity level, receptacle power, service water heating, lighting load, area-based minimum outdoor ventilation air, daylighting setpoints, and operating schedules used in the analysis. Process loads and refrigeration loads are also provided for applicable space types. The user shall designate space use classifications that best match the uses for which the building or individual spaces within the building are being designed.

Space use classifications shall use either the building area method or space-by-space method, but the two types of classifications shall not be combined within a single analysis. The building area method assigns assumptions based on average values within typical buildings of the designated type. The building area method is recommended when detailed space planning information is unavailable. More than one building area category may be used in a building if it is a mixed-use facility.

The space-by-space method uses the area categories developed for the 90.1 lighting requirements. The space-by-space method can be used whenever design information is available with the necessary detail. The user may override the default assumptions for some building descriptors dependent on the space use classification with supporting documentation. Details are provided in Section 3 of this manual.