This topic 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. The basic procedure is to show that the Time Dependent Valuation (TDV) energy of the proposed design is less than or equal to the TDV energy of the standard design, where the standard design is a building like the proposed design, but one that complies exactly with both of the mandatory measures and the prescriptive requirements. The performance method is the most detailed and flexible compliance path. The energy performance of a proposed building design can be calculated according to actual building geometry and site placement. Credit for certain conservation features, such as a daylit atrium, cannot be taken in the prescriptive approach, but could be evaluated with an approved computer program.
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, as the name implies, values energy differently depending on the time it is used. This means that electricity saved on a hot summer afternoon will be worth more in the compliance process than the same amount of electricity saved on a winter morning. The value assigned to energy savings through TDV more closely reflects the market for electricity, gas, propane and other energy sources and provides incentives for measures, such as thermal storage or daylighting, that are more effective during peak periods. Joint Appendix III provides more information on TDV energy and detailed TDV data is available from the California Energy Commission upon request.
The compliance software calculates TDV energy for three main components; the space conditioning energy use, the lighting energy use, and the service water heating energy use. 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. The key component of calculating the TDV energy use of the proposed building is that if a feature of the building is not included in the building permit application, the energy use of that feature is equal to that of the standard energy budget. 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.
Space Conditioning Energy Budget
The space conditioning budget is defined in §141(a)1, as “... the TDV energy used for space conditioning in a standard building in the climate zone and city in which the proposed building is located, calculated with a method approved by the Commission...”The space conditioning energy budget is automatically determined from the program user’s inputs from the corresponding elements of the proposed design. This budget is automatically re-calculated each time a compliance run is done.
Lighting Energy Budget
The lighting energy budget is defined in §141(a)2, as “...the TDV energy used for lighting in a standard building calculated with a method approved by the Commission...” The budget consists of the lighting power used by a building based on one of the following criteria:
(1) When no lighting plans or specifications are submitted for permit, and the occupancy of the building is not known, the standard lighting power density is 1.2 W/ft2. (2) When no lighting plans or specifications are submitted for permit and the occupancy of the building is known, the standard lighting power density is equal to the corresponding watt per ft2 value derived in the complete building method. (3) When lighting plans and specifications are submitted for permit, the standard and proposed lighting power density is equal to the corresponding total allowed lighting power (in watts) calculated using either the complete building method, the area category method, or the tailored method (§146(b)1, 2 or 3). A complete set of lighting plans and prescriptive forms are required for use of the tailored lighting method in the performance approach.
For all occupancies except hotel guest rooms and high-rise residential living quarters, the proposed lighting power density is expressed in W/ft2. For residential occupancies (hotel guest rooms or high-rise residential buildings), the approved computer program will set the proposed lighting power density and the standard design LPD at the same the value as specified in the ACM Approval Manual.
Service Water Heating Energy Budget
The service water heating energy budget is defined in §141(a)3 as “...the TDV energy used for service water heating in a standard building calculated in the climate zone in which the proposed building is located, calculated with a method approved by the Commission...” The budget consists of the service water heating energy used by a building assuming the service water heating system meets both the mandatory and prescriptive requirements for water heating. The service water heating TDV energy use is calculated using a method described in the ACM Manual using the proposed building service water heating system. This system must be consistent with plans and specifications submitted in the building permit application For high-rise residential buildings, the water heating TDV energy budget is calculated using the methods and assumptions documented in the Residential ACM Manual. The procedure is the same as for low-rise residential buildings.