Under the performance approach, the energy use of the building is modeled using a compliance software program approved by the Energy Commission. Program users and those checking for enforcement should consult the most current version of the user’s manuals and associated compliance supplements for specific instructions on the operation of the program. All compliance software programs, however, are required to have the same basic modeling capabilities.

More information on how to model the mechanical systems and components are included in Chapter 9, Performance Approach, and in the program vendor’s compliance supplement.

The compliance rules used by the computer methods in generating the energy budget and compliance credits are based on features required for prescriptive compliance. Detailed information can be found in the Nonresidential Alternative Calculation Methods (ACM) Approval Manual.

There are minimum modeling capabilities required for programs that are used for the performance approach. All certified programs are tested for conformance with the requirements of the Nonresidential ACM. The designer has to use an approved program to show compliance.

Compliance is shown by running two models: a base case budget building that nominally meets the mandatory and prescriptive requirements and a proposed building that represents the actual proposed envelope, lighting, and mechanical systems of the building. To create a level playing field the base case and proposed designs are compared using the same assumptions of occupancy, proscribed climatic conditions and operating schedules. The results are compared using standardized time of use rates, or TDV of energy cost.

The proposed building complies if its annual source Energy and TDV energy is less than or equal to that of the budget building. Reference Appendix JA3 describes the derivation of the TDV energy multipliers.

Compliance in the Performance Approach is across all building systems. The design team can use more glass than with the prescriptive approach and comply by making a more efficient HVAC system. Energy can be traded off between prescriptive requirements in the envelope, HVAC system, indoor lighting, and covered processes.

The alternative calculation method defines the modeling rules for developing the base-case model of the building and mechanical systems. The base-case HVAC system(s) is modeled on a system(s) according to occupancy type, floor area of building, number of floors, and zoning.

The following are some examples of how to get credit in the Performance Approach from HVAC systems:

• Use of high efficiency equipment that exceeds the minimum requirements of §110.1 and §110.2
• Application of economizers where they are not required
• Oversizing ducts and pipes to reduce fan and pump energy
• Use of heat recovery for space or water heating
• Use of thermal energy storage systems or building mass to move cooling off peak
• Reduce reheating and recooling

Use of thermally driven cooling equipment, such as absorption chillers.