8.1   Overview

This chapter explains the performance method of complying with the Standards. The method works by calculating the Time Dependent Valuation (TDV) energy use of the proposed design and comparing it to the TDV energy use of the standard design (the budget). The standard design is a building with the same size as the proposed design, but incorporating all features of Prescriptive Package A. The energy budget includes water heating, space heating, and space cooling. Lighting is not included in the performance calculations. If the proposed design uses equal or less TDV energy than the standard design, then the building complies.

Computer programs used for compliance are certified by the Energy Commission as being capable of calculating space conditioning and water heating energy use in accordance with a detailed set of rules. The computer programs models the thermal behavior of buildings by calculating heat flows into and out of the various thermal zones of the building. The computer programs certified by the Energy Commission must demonstrate their accuracy in analyzing annual space conditioning and water heating energy use of different building conservation features, levels and techniques. This method provides maximum flexibility because the building designer may trade-off the energy performance of different building components and design features to achieve compliance. Making a building more efficient will result in lower utility bills and usually improved comfort. The performance approach provides the ability to test different options and choose the best strategy to reduce your overall energy budget. With today’s wide choice of high efficiency materials, equipment and controls there are many opportunities to make a building more energy efficient. Improving the building envelope provides several opportunities for improving efficiency, in particular with measures related to window placement, location, and efficiency. In space conditioning there is not only equipment with very high efficiency for space heating and cooling but also many innovative system types that eliminate the need for ducts, combine space and water heating together, or use advanced designs that can dramatically improve the building’s overall performance. Improved water heating system efficiency includes wide range equipment that can significantly increase efficiency, and improvements to the distribution system can drastically reduce energy losses.

The performance method is the most popular compliance method under the Standards, with more than 95 percent of building permit applications for newly constructed buildings being submitted in this manner. The method is especially popular with production homebuilders because they can optimize performance and achieve compliance at the lowest possible cost. This chapter provides only a general overview of the performance method. Each computer program that is certified by the Energy Commission is required to have a compliance supplement that provides more detailed information regarding the use of the software for compliance purposes. The requirements for the compliance supplement along with other requirements for approved computer programs are documented in the 2013 Residential ACM Approval 'Manual.

For a detailed discussion of the performance method with additions and alterations, see Sections 9.5, 9.6 and 9.7.