Under the performance approach, the energy use of the building is modeled using a compliance software program approved by the California Energy Commission. This section presents some basic details on the modeling of building mechanical systems. 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 detailed in the Nonresidential Alternative Calculation Methods (ACM) Approval Manual and are based on features required for prescriptive compliance.
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 just meets the mandatory and prescriptive requirements and a proposed building that represents the actual building's proposed envelope, lighting and mechanical systems. To create a level playing field the basecase 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 Time Dependent Valuations (TDV) of energy cost.
The proposed building complies if its annual TDV is less than or equal to that of the budget building. Reference Appendix JA3 describes the derivation of the TDV energy multipliers.
It is important to note that 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 Envelope, HVAC, Indoor Lighting and Covered Processes.
The ACM defines the modeling rules for developing the base-case model of the building and mechanical systems. The base-case HVAC system(s) are based on the proposed HVAC system(s) according to the following specific characteristics:
•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.