The second method for Code compliance allowed by the California Code is the Performance Method. 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. This method also has additional mandatory requirements that must be met in order for the building to be regarded as energy compliant.
The following sections summarizes the whole building performance approach to compliance. It includes a discussion of computer methods, the procedures involved in determining the energy budget and the proposed building’s energy use, and how to plan check performance compliance.
In the Performance Method, compliance is shown when the Time Dependent Valuation (TDV) energy of the proposed design is less than or equal to the TDV energy of the standard design. The standard design is a building like the proposed design, but is configured to comply exactly with both of the mandatory measures and the prescriptive requirements in the code. The Performance Method is the most flexible compliance path and is likely to produce building designs that perform closer to predicted. The energy performance of a proposed building design is determined using actual building geometry and site placement. Credit for certain conservation features, such as a daylighting atrium, thermal mass, energy storage and other more elaborate energy conservation methods not address in the prescriptive approach can be accounted for with this approach.
Beginning with the 2005 Standards, the “currency” for assessing building performance is time dependent valued (TDV) energy. TDV energy replaces source energy, which has been the currency since the California Energy Commission first adopted standards in 1978. TDV, sets a variable values to energy depending on the time it is used. This means that electricity saved on a hot summer afternoon (peak demand) will be worth more in the compliance process than the same amount of electricity saved on a winter morning. It was found that the value assigned to energy savings using TDV more closely reflects the market costs for electricity, gas, propane, and other energy sources and provides an incentive to designs, such as thermal storage or daylighting, that are more effective during peak periods. Detailed TDV data is available from the California Energy Commission upon request.
Approved compliance computer programs calculates TDV energy for three main building components: HVAC , lighting , and domestic hot water generation. It does not include energy for plug loads from computers (even though a default value for the internal gains from plug loads are modeled in the hourly computer simulation), vertical transportation, garage ventilation, outdoor lighting or other miscellaneous energy uses. These energy uses are assumed to be relatively constant in typical designs and are not part of the design compliance process. It should be noted that when calculating the TDV energy use of the proposed building, if a feature of the building is not included in the building permit application, the energy use of that feature is assumed to be equal to that of the standard energy budget prescriptively allowed by the Code. That means that if a permit is submitted for a shell building (envelope only), and the performance approach is used to demonstrate compliance, trade-offs cannot be made between the envelope and the mechanical or lighting system.
The rules for performance compliance are identical to those for all other nonresidential and high-rise residential buildings. The area of each function must be input into an approved compliance program along with its corresponding envelope, mechanical, and indoor lighting features. The computer software program is used to calculates an energy budget (standard design compared to proposed design). The proposed design must be less than or equal to the standard design for the building to comply.
Note that air barriers are a requirement for all nonresidential buildings and cannot be traded off in the Performance Compliance approach. Air barriers are assumed to achieved by a continuous air barrier that seals all joints and openings in the building envelope and is composed of one of the following:
- Materials having a maximum air permeance of 0.004 cfm/ft².
- Assemblies of materials and components having an average air leakage not exceeding 0.04 cfm/ft².
- An entire building having an air leakage rate not exceeding 0.40 cfm/ft2.
Although some wall exterior wall systems are required to have a minimum amount of insulation, mass masonry wall system can be uninsulated.
Lighting Energy Budget (non residential)
Lighting power allotments are the established maximum lighting power that can be installed based on the compliance approach used, the building type, and building area. Lighting power allotments for an application are determined by one of the following four compliance approaches:
A. Prescriptive approach – Complete Building Method: This method can be used when the entire 90 of the building is one nonresidential building occupancy type. With this method you use a maximum single lighting power density value governs the entire building or tenant space. See table below.
B. Prescriptive approach – Area Category Method: In this method different lighting power density values are assigned to each of the primary function areas of a building.
C. Prescriptive approach – Tailored Method: This method uses layers of lighting power allotments depending on the space and tasks. Lighting power allotments are determined room-by-room and task-by-task. The Tailored Method and the Area Category Method can be used in conjunction with each other.
D. Performance approach: The performance approach incorporates one or more of the three previous methods which set the appropriate lighting power allotment used in calculating the building’s custom energy budget.
The performance approach allows energy allotments to be traded between space conditioning, mechanical ventilation, indoor lighting, service water heating, envelope, and covered process loads. Such trade-offs can only be made when permit applications are sought for those systems involved. For example, under the performance approach, a building with an envelope or mechanical ventilation system that is more efficient than the prescriptive efficiency requirements, may be able to meet the energy budget for a standard designed building with more lighting power than allowed under the three prescriptive lighting approaches.
EnergyPro – Software for Performance Based Compliance
EnergyPro is a commercial software product that is available to users via subscription and a fee. EnergyPro is an energy analysis software that may be used to document compliance with California’s 2019 Residential and Nonresidential Building Energy Efficiency Standards (Title 24, Part 6). EnergyPro specializes in building energy performance modeling and is the only commercial software approved for 2019 Nonresidential and Residential buildings. ASHRAE 90.1 Standards, as well as residential and nonresidential Green Building rating systems, such as GreenPoint Rated, and LEED are also integrated into the system.
EnergyPro is the only software package to generate the new California Energy Commission (CEC) 2019 online Prescriptive forms. The software is made up of an interface that includes an interactive “Building Tree”, different Libraries and residential and nonresidential calculation models.
- In-depth summary of the version 8 Energy Pro Software, with a prescriptive residential example
- How-to guide for Energy Pro 8
- Simple Nonresidential Performance Compliance Method Example with Energy8Pro