CBECC-Res 2019 calculates compliance for a proposed design based on its energy design ratings (EDRs). An EDR is generally calculated as the annual integrated time-dependent value (TDV) of energy (across fuels) of a building relative to a common reference design (based on the 2006 International Energy Conservation Code) (Wilcox, 2017). Accordingly, the EDR is a unitless score, generally between 0 and 100, with a lower score being better.
EDR scores are based on the total annual-TDV of a design relative to the total annual-TDV of the reference design. Annual-TDV is the sum across hours of the net energy used in that hour multiplied by that hour’s TDV.
The EDR for a specific design is (generally) calculated as the ratio of the design’s annual-TDV and the reference building’s annual-TDV:
Compliance for a proposed design in CBECC-Res 2019 has two requirements:
1. The EDR of the building design, ignoring contributions from renewable generation and battery storage (except for the self-utilization credit described below), must be lower than the EDR of the code prescriptive standard design (also ignoring contributions from renewable generation and battery storage). These EDRs are called the “Efficiency EDR” for the respective proposed and standard designs. The intent of this requirement is to encourage designs that reduce loads in addition to generating energy.
2. The EDR of the final design (including contributions from renewable generation and battery storage) must be lower than the EDR of the code prescriptive standard design (also including contributions from renewable generation and battery storage). These EDRs are called the “Final EDR” for the respective proposed and standard designs.
A minimum of five annual-TDV calculations are required to evaluate the compliance of a specific proposed design:
1. Proposed design “Efficiency” TDV
2. Proposed design “Final” TDV
3. Standard design “Efficiency” TDV
4. Standard design “Final” TDV
5. Reference design TDV (the common denominator in all EDR calculations)
The specific computations that produce the EDR from annual-TDV totals are described in the 2019 Residential Alternative Compliance Method (ACM) Reference Manual (CEC, forthcoming). Because the reference design annual-TDV is used in the calculation of all EDRs, the compliance of a building design can generally be determined when the TDV of the proposed design is lower than the TDV of the standard design, for both the “Efficiency” and “Final” simulations (though this is not strictly the case due to some small adjustment factors used to determine EDR). The standard design is also described in the ACM.