Title 24 Overview
The 2019 California Energy Code outlines two primary methods of compliance: Prescriptive and Performance. The Prescriptive Method requires that each element of a building be analyzed individually and meet the minimum requirements described for each. For building envelopes, this typically, this can be completed by using code prescribed charts and tables that outline minimum U-values for walls, windows, roofs, etc and configuring these system to meet this minimum . The Performance Method analyzes the building as a whole to predict energy usage in comparison to an acceptable standard. Computer modeling is typically required to make accurate prediction or yearly energy use. Each method has a set of mandatory requirements that must be met in order for the building to be regarded as energy compliant.
The 2019 California Energy Code includes sections that have provisions and mandatory requirements for all occupancies. They also have provisions that detail mandatory requirements for non-residential, high rise residential and hotel/motel buildings, and provisions that define mandatory requirements for low-rise residential buildings. For each system in the building that can significantly impact energy use, these provisions outline the mandatory requirements for both compliance methods.
Nonresidential, High-rise Residential and Hotel/Motel Buildings
As an example, the non-residential Chapter of the Energy code has provisions that relate to each of the energy related building systems as summarized below.
The Standards have both mandatory measures and prescriptive requirements that impact the design of the building envelope. These requirements establish a minimum level of performance for each envelope system. It should be noted that where designs may exceed these minimum provisions, they can be recognized for credit in the performance approach. These variations in designs are typical called compliance options. Compliance options have eligibility criteria that must be satisfied before compliance credit is offered.
Generally, exterior masonry walls will require some insulation in most climate regions in the state if the prescriptive provisions are used for design. Uninsulated exterior masonry walls may be used in many building configurations if the performance method are used for design. See the prescriptive design example in the following section.
Indoor lighting is one of the prime systems consuming energy (kilowatt-hours) in a commercial building, representing about a third of yearly electricity use. The Standard provisions limit this energy use but with the intent of maintaining minimum levels lighting quality and levels suitable for most common task work. The Standards are the result of the involvement of many representatives of the lighting design and manufacturing community, and of building departments across the state. A great deal of effort has been devoted to making the lighting requirements practical and realistic.
The outdoor lighting and sign energy standards conserve energy, reduce winter peak electric demand, and are technically feasible and cost effective. They set minimum control requirements, maximum allowable power levels, minimum efficacy requirements, and require cutoff classification for large luminaires. The lighting power allowances are based on current Illuminating Engineering Society of North America (IESNA) recommendations for the quantity and design parameters of illumination, current industry practices, and efficient sources and equipment that are readily available. Data indicates that the IESNA recommendations provide more than adequate illumination. The Standards do not allow tradeoffs between outdoor lighting power allowances and interior lighting, HVAC, building envelope, or water heating.
The Standards requirements for mechanical systems set minimum performance criteria for these systems in an effort to reduce energy consumption while maintaining occupant comfort. This has been accomplished by 1) Maximizing equipment efficiency, both at design conditions and operation 2) Minimizing distribution losses of heating and cooling energy through construction requirements 3) Optimizing system control to minimize unnecessary operation and simultaneous use of heating and cooling energy. The Standards also recognize the importance of indoor air quality for occupant comfort and health. To this end, the Standard requirements for outdoor air ventilation must be met during all operating conditions.
Domestic Hot Water
The energy used to heat water for use in a building can be significant. Standby losses and demand both impact this use. Typically more than a quarter of a gas water heater system’s total energy use is caused by standby losses. However, when the system fuel is natural gas, there are no generation losses as are associated with electricity. Fuel type is very important in determining water heating energy use. While natural gas, LPG or oil can be burned directly to heat water, electricity is typically generated in a power plant. Approximately two thirds of the source energy used to generate electricity is lost in the generation and distribution processes. Any electric water heating system must automatically account for the inefficiency of the fuel type. Standard electric water heaters are not considered energy efficient for this reason. Electric heat pump water heaters, however, are closer to the efficiency of typical gas systems, because they use the outdoor air as a heat source in heating water. The relative values of the losses associated with different sources of energy are integrated into the performance method
Low-rise Residential Buildings
Similar provisions are provided for low-rise residential buildings but the provisions are tailored to systems and building configuration that are typically used in these applications.
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