In 'addition to the mandatory measures (Section 1.6.2), the Energy Standards provide two basic methods for complying with low-rise residential energy budgets: the prescriptive approach and the performance approach. The mandatory measures must be installed with either of these approaches, but mandatory measures may be superseded by more stringent measures under either approach.
A. The prescriptive approach, composed of a climate zone dependent prescriptive package ( Section 1.6.3), is less flexible but simpler than the performance approach Each 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. For example, if a portion of a wall does not meet the prescriptive insulation requirement, an area-weighted average of all walls can be used to meet the prescriptive requirement
B. The performance approach (Section 1.6.4) is more complicated but offers considerable design flexibility. The performance approach uses an approved software program to model a proposed building and compare it to a calculated energy budget. Performance compliance is based on window efficiency and orientation, shading from overhangs, space-conditioning equipment and water-heating system efficiencies, and house configuration. This approach is popular with production builders because of its flexibility and it provides a way to find the most cost-effective solution for complying with the Energy Standards.
For additions and alterations, see Chapter 9 for details of compliance approaches that are available.
With either prescriptive or performance compliance, there are mandatory measures that must always be met. Some deal with infiltration control and lighting; others require minimum insulation levels or equipment efficiencies. New for the 2019 Building Energy Efficiency Standards are mandatory measures that require R-20 insulation values for 2’ x 6’ wood-framed walls, air-filtration devices on most ducted mechanical systems, and kitchen range hoods meeting airflow and sound ratings specified in ASHRAE 62.2. For detailed information on these changes, see applicable sections within this manual.
Minimum mandatory levels are sometimes superseded by more stringent prescriptive or performance approach requirements. For example, if mandatory measures specify R-22 ceiling insulation and the prescriptive approach is used, then R-38 ceiling insulation (depending on climate zone) must be installed. Conversely, the mandatory measures may be of a higher efficiency than permitted under the performance approach; in these instances, the higher mandatory levels must be installed. For example, a building may comply using the performance computer modeling only R-7 insulation in a raised floor, but R-19 must be installed because that is the mandatory minimum.
The prescriptive requirements are represented in Table 150.1-A (single family) or 150.1-B (multifamily). The prescriptive approach is the simplest but least flexible compliance path. New in 2019 is a requirement for a PV system. See Chapter 7 for more information on solar generation, community solar, and battery storage.
The prescriptive approach is a set of predefined performance levels for various building components. Each component meets or exceeds the minimum efficiency level specified in Table 150.1-A or 150.1-B and related footnotes in the Energy Standards. In some climate zones, these prescriptive requirements specify that many cooling system types are HERS-tested to verify that they have the correct refrigerant charge.
The performance approach, also known as the computer compliance method, requires that the building meet both an efficiency EDR and a total EDR. (Additions and alterations continue to meet a time-dependent valuation [TDV] energy budget.) The efficiency EDR is the efficiency of the building without the benefits from any solar generation. The total EDR includes the building and the effects of solar generation plus any solar electric generation.
Annual Time-Dependent Valuation (TDV) energy be calculated for the proposed building and compared to the standard TDV energy budget. 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 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. Reference Joint Appendix JA3 has more information on TDV energy.
The use of Energy Commission-approved software represents the most detailed and sophisticated method of compliance. While this approach requires the most effort, it also provides the greatest flexibility. The programs automatically calculate the energy budget for space conditioning and water heating, and the minimum required PV size to receive credit toward meeting the efficiency EDR. The budget is determined from the standard design, a computer model of the building using prescriptive requirements. The computer software allows manipulation of the proposed building’s energy features to achieve compliance. See Chapter 8 of this manual for more information on the performance method.