Page 8 - Zero Net Energy Case Study Homes-Volume 1

ZERO NET ENERGY CASE STUDY HOMES INTRODUCTION
Introduction
This book is the fourth in a series on case studies of zero net energy (ZNE) buildings developed under the direction of the California Public Utilities Commission to support the adoption of ZNE building practices1. It is the first one that profiles residential projects, but shares the same ob- jectives and approach as the preceding volumes. Each case study focuses on the process of decision-making that resulted in the solution as it was built, and offers a detailed analysis of the project’s performance, along with the all-important lessons learned.
This volume presents details about the design, construction and performance of five Zero Net Energy (ZNE) residential projects in California. Each project is representative of a particular housing type of the residential market in California: single-family home (renovation), single- family home (new), subdivision tract housing, modular (factory-built) housing and low-rise multi- family affordable housing.
Within this simple summary are contained several complex distinctions that are important to understand before beginning to focus on these individual projects. The descriptive term, zero- net-energy, for example, has several different meanings, especially in the residential sector among institutions and government agencies that track progress in this area. The regulatory environment has different metrics for ZNE, as broad goals are defined and action plans are developed. The housing industry itself consists of different producers, from small local builders to corporate production companies, giving rise to different criteria for decisions.
This Introduction section will clarify these distinctions and set the common basis for each of the case studies that follow.
Metrics of Zero Energy Residential Projects
1. Basic Technical Metrics.
Depending on how the accounting of energy use over the course of a year is done, there are three distinct technical definitions of what is meant by a zero net energy or ZNE project currently used in practice: Site ZNE, Source ZNE and TDV ZNE. (“TDV” or “Time-Dependent Valuation” is the definition used in California’s building code.)
As a practical matter, all three definitions have several aspects in common. First, the accepted time frame for ZNE accounting is one calendar year: a project is ZNE if the energy consumption equals renewable energy production over a one-year period. Second, the dominant form of renewable energy production selected is solar photovoltaic (PV) energy; there are other sources that would meet the renewables definition, but they are rarely selected as the most cost-effective and practical solution at the building level. Third, “at scale” deployment of ZNE residential projects presumes that the buildings are grid-connected. Though not a definitional requirement, grid-connectivity provides the most practical and cost-effective means of meeting ZNE performance targets.
A Site ZNE building has an on-site renewable energy supply, and the amount of energy used by the building over the course of a year is equal to the amount of energy supplied by the on-site system. For grid-connected buildings, the power drawn from the utility grid equals the power exported to the utility grid. This is known as Site ZNE since the line of transaction is drawn at the building site boundary. It is the one ZNE metric that can be directly metered and measured.
1 The three earlier ZNE case study books, Zero Net Energy Case Study Buildings, Volume 1, (2014), Volume 2 (2016), Volume 3 (2018) can be found at: https://www.amazon.com/s/ref=nb_ sb_noss_2?url=search-alias%3Daps&field-keywords=zero+net+energy+buildings
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Zero Net Energy Case Study Homes: Volume 1