Zero Energy Buildings: A Critical Look at the Definition

TLDR

A net zero‑energy building (ZEB) is a building whose energy needs are largely met by renewable sources, yet there is no universally accepted definition, and how the goal is framed influences design choices and the validity of claimed success. The paper investigates what zero energy means, why a clear definition is essential, and how progress toward the ZEB goal has been made using current low‑energy buildings. The authors examine four documented definitions—net‑zero site energy, net‑zero source energy, net‑zero energy costs, and net‑zero energy emissions—applying each to a dataset of low‑energy buildings to assess their implications. The study demonstrates that the chosen ZEB definition significantly affects design outcomes, reveals large disparities among definitions, and shows how utility rate structures influence zero‑energy scenarios.

Abstract

A net zero-energy building (ZEB) is a residential or commercial building with greatly reduced energy needs through efficiency gains such that the balance of energy needs can be supplied with renewable technologies. Despite the excitement over the phrase “zero energy,” we lack a common definition, or even a common understanding, of what it means. In this paper, we use a sample of current generation low-energy buildings to explore the concept of zero energy: what it means, why a clear and measurable definition is needed, and how we have progressed toward the ZEB goal. The way the zero energy goal is defined affects the choices designers make to achieve this goal and whether they can claim success. The ZEB definition can emphasize demand-side or supply strategies and whether fuel switching and conversion accounting are appropriate to meet a ZEB goal. Four well-documented definitions—net-zero site energy, net-zero source energy, net-zero energy costs, and net-zero energy emissions—are studied; pluses and minuses of each are discussed. These definitions are applied to a set of low-energy buildings for which extensive energy data are available. This study shows the design impacts of the definition used for ZEB and the large difference between definitions. It also looks at sample utility rate structures and their impact on the zero energy scenarios.