'In addition to the mandatory measures (Section 1.6.1), the Standards provide two basic methods for complying with nonresidential energy budgets: the prescriptive approach and the performance approach. The mandatory measures must be installed with either method, but note that mandatory measures may be superseded by more stringent measures under the prescriptive or performance approach. Commissioning requirements added in §120.8 are mandatory for buildings greater than 10,000 square feet.
With either the prescriptive or performance compliance paths, there are mandatory measures that must always be met. Many of the mandatory measures deal with infiltration control, indoor and outdoor lighting, or sign lighting; other mandatory measures require minimum insulation levels and equipment efficiency or requirements for refrigerated warehouses. The minimum mandatory levels are sometimes superseded by more stringent prescriptive or performance requirements.
The prescriptive approach (composed of prescriptive requirements described in Chapters 3, 4, 5, 6, 7, and 10) is the most direct approach of the two. Each individual energy component of the proposed building must meet a prescribed minimum efficiency. The prescriptive approach offers relatively little design flexibility but is easy to use. There is some flexibility for building envelope components, such as walls, where portions of the wall that do not meet the prescriptive insulation requirement may still comply as long as they are area-weighted with the rest of the walls, and the average wall performance complies. If the design fails to meet even one of the requirements, then the system does not comply with the prescriptive approach. In this case the performance approach provides the most flexibility to the building designer for choosing alternative energy efficiency features.
A. Building Envelope. The prescriptive envelope requirements are determined by the envelope component approach. This approach is described in detail in Chapter 3 this manual. The stringency of the envelope requirements varies according to climate zone and occupancy type.
B. Mechanical. The prescriptive mechanical requirements are described in detail in Chapter 4. The prescriptive approach does not offer any alternative approaches, but specifies equipment, features and design procedures that must be followed.
C. Indoor Lighting. The prescriptive lighting power requirements are determined by one of three methods: the complete building method, the area category method, or the tailored method. These three approaches are described in detail in Chapter 5 The allowed lighting under the Standards varies according to the requirements of the particular building occupancy or task requirements
D. Outdoor Lighting. The Outdoor Lighting Standards are described in Chapter 6. They set power limits for various applications such as parking lots, pedestrian areas, sales canopies, building entrances, building facades and signs. The Standards also set minimum requirements for cutoff luminaires and controls. Outdoor lighting compliance is prescriptive in nature and is determined by the lighting application type (general and specific) and the lighting zone for each application. Detailed information on the outdoor lighting power allowance calculations is found beginning in Section 6.4.
The performance approach (Chapter 11) allows compliance through a wide variety of design strategies and provides greater flexibility than the prescriptive approach. It is based on an energy simulation model of the building. The Standards specify the method for determining an energy budget for the building.
The performance approach requires an approved Computer Software program that models a proposed building, determines its allowed energy budget, calculates its energy use, and determines when it complies with the budget. Design options such as window orientation, shading, thermal mass, zonal control, and building configuration are all considered in the performance approach. This approach is used because of the flexibility and because it provides a way to find the most cost-effective solution for complying with the Standards.
The performance approach requires that the annual TDV energy be calculated for the proposed building or space, and be compared to the TDV energy budget. The performance approach may be used for envelope or mechanical compliance; envelope and mechanical compliance; envelope and indoor lighting compliance; or envelope, mechanical and indoor lighting compliance. It is not applicable to outdoor lighting, or to indoor lighting in the absence of envelope compliance. The performance path is not available for sign lighting, exempt process load, some covered process loads (e.g. refrigerated warehouses), or solar ready applications.
TDV energy is the “currency” for the performance approach. TDV energy not only considers the type of energy that is used (electricity, gas, or propane), but also when it is used. Energy saved during periods when California is likely to have a statewide system peak is worth more than energy saved at times when supply exceeds demand. Appendix JA3 of the Reference Joint Appendices has more information on TDV energy.
Three basic steps are involved:
A. Design the building with energy efficiency measures that are expected to be sufficient to meet the energy budget. (The prescriptive approach requirements provide a good starting point for the development of the design.
B. Demonstrate that the building complies with the mandatory measures (see Chapters 3, 4, 5, 6, 7, 8, 9, and 10).
C. Using an approved calculation method, model the energy consumption of the building using the proposed features to create the proposed energy budget. The model will also automatically calculate the allowed energy budget for the proposed building.
If the proposed energy budget is no greater than the allowed energy budget, the building complies.
If performance approach will be used for additions and alterations, see Chapter 11 for details.