Utility rate inputs and calculating energy costs

Simple utility rate estimates may be used, however if one of the goals of the simple box modeling analysis is to estimate the energy cost impact of design alternatives, then realistic utility rates are important. This is especially true for buildings that will be on time-of-use electricity rates. Some designs are better than others at reducing energy consumption during peak demand periods, and they might provide greater cost savings than energy savings.

Simple utility rate estimates are often estimated in terms of $/kWh and represent an average rate over the course of the year. However these rate estimates do not account for the variation in charges for when the electricity is used, or the peak power (demand) used by the building.

Detailed rate structures can be input in BEM models that account for:

• Energy charges
• Demand charges
• Block charges
• Time of use periods

Information Sources

The ideal source of input information is the actual rate from the utility that will be providing electricity and gas to the building. Many utilities post rate descriptions on their websites. The client may be able to provide you with the rate structure in effect for the project, depending on the project stage. Otherwise, some good sources of rate data include:

• The OpenEI database - publishes detailed rate information for many locations
• The Energy Information Administration - publishes average energy rates for different parts of the United States.