Page 10 - Zero Net Energy Case Study Homes-Volume 1

ZERO NET ENERGY CASE STUDY HOMES
INTRODUCTION
(Right) The HERS Index rat- ing for a candidate Zero En- ergy Ready Home (ZERH) that meets all prescriptive require- ments and achieves a point total of 65. If the home can ac- commodate a right-sized solar PV system to drop the HERS Index rating to zero, then it would be considered Zero En- ergy Ready according to the federal program.
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Zero Net Energy Case Study Homes: Volume 1
3. California Variant of Metrics for “Zero Energy Homes”
The California Energy Commission (CEC) has established a similar rating system for residential projects, though without all the prescriptive requirements for the design and construction as the federal ZERH program. Rather, the California program uses primarily certified energy modeling on the project design features to calculate an Energy Design Rating (EDR), which is “aligned with” RESNET and the HERS Index scale. This EDR calculation by the energy model includes both energy use and energy production by any solar PV system that is included as part of the design, so it is capable of representing the annual net-energy performance of the residential project. (Some residential projects may also comply via a “prescriptive path”, as described in the 2016 Residential Compliance Manual4, in which case an efficiency EDR is not calculated.)
Peculiar to the structure of the California energy code, however, the energy model calculation uses the TDV-ZNE metric to output a number on the HERS Index scale corresponding to the “energy performance” of the residential project (or rather, as noted above in the section on Technical Metrics, corresponding to the value of the energy performance.) On this scale, the “baseline” number of 100 corresponds to the TDV energy performance of a building project meeting the building envelope requirements of the 2006 International Energy Conservation Code (IECC). A score of zero (EDR = 0) means that a residential project can be labelled “Zero- Energy”, or rather more precisely, “Zero TDV Energy”. Such a project’s design would combine a high level of energy efficiency and a solar PV system such that the modeled annual net-energy performance of the project (using the CEC-certified software and the TDV metric) is net-zero or net-positive.
As with the federal rating system for certification of a “Zero Energy Home”, the California rating index, EDR=0, is not based on data measurements of the built project for at least one full year and therefore the project cannot be regarded as verified ZNE. The EDR system, like the cor- responding federal program, is a method of labeling a residential project in a particular location before occupancy.
https://www.energy.ca.gov/2015publications/CEC-400-2015-032/CEC-400-2015-032-CMF. pdf, pp. 1-17.
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