1.4 Modeling Assumptions on Building Operation

When calculating annual energy use, it is necessary to make assumptions about how the proposed building is operated and the level of energy services required by the tenants.  Operating assumptions include thermostat settings, number of occupants, receptacle loads, process loads, hot water loads as well as schedules of operation for HVAC systems, lighting systems and other systems. Sometimes these data are known with some certainty and other times (for instance for speculative buildings), it is necessary to make estimates. 

When the proposed design energy performance is compared to the baseline building energy performance, these modeling assumptions are generally the same for both models, so the impact of making the right assumptions is less critical. However, for programs like ENERGY STAR and ASHRAE’s bEQ, the choice of assumptions is critical. In these cases, it is important that the modeling assumptions be consistent with the underlying empirical data upon which the baseline energy performance is based. The default COMNET assumptions are selected to be as close to these average conditions as possible.  The COMNET modeling guidelines are supported by the technical appendices described below.

Table 1.4-1: COMNET Technical Appendices



A – Building Descriptors

Tabular summary and classification of building descriptors. 

B – Modeling Data

Modeling data and assumptions by building type and space use.

C – Schedules

Default and prescribed schedules of operation.

D – Construction Materials

Default construction materials library.

H – Equipment Curves

Spreadsheet that summarizes and graphs the default equipment performance curves referenced in the Modeling Guidelines and Procedures.