Time dependent valuation

Time dependent valuation (TDV) is a metric used for the California energy code (Title 24, Part 6). TDV considers many factors including the cost of energy but also the environmental and societal costs associated with energy use.

The concept behind TDV is that energy efficiency measure savings should be valued differently depending on which hours of the year the savings occur, to better reflect the actual costs of energy to consumers, to the utility system, and to society. The TDV method encourages building designers to design buildings that perform better during periods of high energy cost. Higher hourly TDV values tend to occur during peak demand periods (e.g. hot summer days), reflecting increased strain on the power grid and the associated environmental impacts during these peak hours.

Hourly TDV factors exist for each fuel source (electricity, natural gas) with different factors in each climate zone, and different factors for residential vs. commercial buildings.

TDV was used starting with the 2005 version through the 2022 version of Title 24. Starting with the 2025 version of Title 24, it was replaced with a new metric called Long-Term System Cost (LSC).

Uses for TDV

TDV is used for two main purposes:

1. Code development—prescriptive measures in the code are developed by demonstrating that they are cost effective, using the TDV metric.
2. Code compliance—projects pursuing the performance approach must compare the TDV of the proposed building to the TDV of a baseline building (the "Standard Design") and demonstrate that the proposed building has a lower TDV. Note that starting with the 2022 code, performance approach projects must also demonstrate compliance with a second metric—hourly source energy.