Page 12 - Zero Net Energy Case Study Homes-Volume 1

ZERO NET ENERGY CASE STUDY HOMES INTRODUCTION
• Are certified under one of a number of qualifying ZE asset rating programs (e.g., the federal ZERH program or the California Zero Energy Homes rating system).
To be listed as one of these three types in the NZEC database of the inventory of ZNE buildings, the project must have “documentation” that indicates that the project satisfies the criteria for that type of ZNE project. The “documentation” required is not specifically described on the NZEC website, and is in fact not required to be actual annual energy performance data. “Documenta- tion” can be the results of an energy model for the project. Also, this documentation does not actually have to be submitted (whether energy model or utility data) in order to list the project in the NZEC inventory; the submittal for the project simply has to indicate which category is appropriate based on the project. NZEC is therefore an honor system rather than a system of ZNE verification.
5. Metric for Annual Energy Use: “Energy Use Intensity (EUI)”
One other metric deserves brief mention: Energy Use Intensity, or EUI, expressed in kBtu/sf per year. A State-funded technical study7 in 2012 found that ZNE was technically achievable with EUI values varying (by climate zone) from 11.5 to 17.3 for single-family homes, and from 16.0 to 18.6 for low-rise multifamily homes. The projects in this book have EUIs ranging from 7.4 (Mer- itage, in Fontana) to 18.6 (Oak Haven, in Ojai), providing further validation of the achievability of ZNE in practice, not just in theory. (Note that because EUI is a per-square-foot metric – not a per-occupant metric – it will tend to be higher for smaller than for larger homes.)
Zero Net Energy Residential Projects As Defined for this Case Studies Book
The broad and inclusive national listing of zero-energy projects in the NZEC database is valu- able in showing the relatively rapid transformation of building industry practice in the number and types of ZNE residential projects. This case studies book utilizes a somewhat stricter defi- nition of ZNE, however, in evaluating the overall performance of the project and its inclusion in this book. Specifically, the case study project must have measured energy data for at least one full year and must account for all energy use, both electric and gas, with the gas energy use shown to be offset by the on-site renewable energy system.
We have, however, partially adopted NZEC’s concept of “Zero-Energy Ready” by including projects that, according to the measured data collected for one year, are performing less than ZNE as a total housing group in spite of an initial goal of achieving ZNE, but for which individual housing units within the larger group are indeed ZNE performers as verified by the energy performance data. That is, these case study projects are either verified Site-ZNE in whole or in part according to actual measured and recorded data for one full year. In one case, there is ample roof space to add solar PV panels that, according to the measured data, would bring the residential project to full “Zero-Energy” performance by NZEC categorization.
Selection of the ZNE Case Study Buildings for this Book
Because the California housing industry is so diverse, ranging from the small builders to the corporate developers, as well as in project types from small renovation to dense multi-family housing, projects were selected to obtain representative examples from each category. The planning, approval and financing of each are very different, and these factors very much influence the ZNE design decisions and ultimate performance of the built project. As such, as part of each individual case study, these issues are discussed in the detail necessary to understand these influences.
7 “The Technical Feasibility of Zero Net Energy Buildings in California”, Arup, et al. 2010.
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Zero Net Energy Case Study Homes: Volume 1