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

ZERO NET ENERGY CASE STUDY BUILDINGS, VOL. 1 INTRODUCTION
Introduction
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Zero Net Energy Case Study Buildings: Volume 1
This monograph provides information about six non-residential buildings that were designed and built to perform at zero net energy (ZNE) consumption over the course of a year. Each has proven to be successful at achieving that level of performance, or better, for at least one year of post-construction occupancy.
Design of zero net energy (ZNE) buildings is a relatively new area of work within the professional community of building designers and only a small number of these designs have been built within the U.S. Fewer still have been occupied long enough to collect sufficient monitored data about their energy use and on-site renewable energy supply to demonstrate that the designs were in fact successful examples of ZNE performance. The first early successes are therefore valuable sources of insights and information about design process, design strategies, post-occupancy building issues and corrective measures taken to ensure actual ZNE performance.
This last point is one principal focus of these ZNE case study buildings, namely to present in some detail the problems discovered from reviewing the metered data once the building was occupied and what changes were made to the building and its use patterns in response to this information. Indeed, as discussed later in this publication, one of the common discoveries was that there were even problems with the monitoring systems, which delayed the analysis, diagno- sis and correction process.
As the case studies illustrate, architects and engineers generally have the skills and experience to design ZNE buildings provided that this objective is consistently embraced in the early part of the process and involves integrated disciplines with each early decision-making step. Success is also the product of adhering to the following general four-step process, as will be illustrated by each of the case study buildings:
• Set the energy performance target
• Design to this target
• Build to this design
• Monitor, diagnose and correct actual performance
Before delving into the individual case study buildings, however, it is important to define terms, especially what is meant by the term, “ZNE building”.
Definition: A Zero Net Energy Building — A Question of Accounting and Metrics
Depending on how the accounting of energy use over the course of a year is done, there are multiple definitions of what is meant by a zero net energy or ZNE building currently used in com- mon practice. This Introduction section describes three principal definitions of ZNE:
• “Site” ZNE
• “Source” ZNE
• “TDV” ZNE, the “Time Dependent Valuation (TDV)” metric in use in California’s building
code.
The six case study buildings in this monograph use the “Site” ZNE energy accounting method. As ZNE is brought into building energy codes, however, and as ZNE rating and certification methods evolve, it is useful to understand the alternative methods of “Source” ZNE as well as the “TDV” metric for ZNE now in use 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: energy consumption equals renewable energy production over a one-year period. Second, the dominant form of renewable energy pro- duction 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 solu-