Zero Energy Buildings

Indian Institute of Technology, Delhi

Zero energy buildings

Environmental Engineering

Ankit Agarwal

Prateek Deshmukh

Rahul Agarwal

Varun Pal Singh Kohli

Amrit Juneja

24-3-2008

CONTENTS

ABSTRACT 4

INTRODUCTION 5

I. Boundary Definitions and Energy Flows 6

II. Definitions 9

III. How definition influences design 11

IV. Conclusion 14

V. References 16

LIST OF TABLES

I. Table 1 7

II. Table 2 15

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. We lack a common understanding or a common definition for the phrase “Zero Energy Building”. In this paper, we use a sample of current generation low-energy buildings to explore the concept of zero energy: what it means and why a clear and measurable definition is needed. The way the zero energy goal is defined affects the choices designers make to achieve this goal and whether they can claim success. A ZEB can be defined in different ways relating to cost, energy, or carbon emissions and, irrespective of the definition used, different views are taken on the relative importance of energy generation and energy conservation to achieve energy balance. This study shows the design impacts of the definition used for ZEB and the large difference between definitions.

“Using ZEB design goals takes us out of designing low-energy buildings with a percent energy savings goal and into the realm of a sustainable energy endpoint,” and the goals that are set and how those goals are defined “are critical to the design process,” with the definition influencing designers who strive to meet it. “Because design goals are so important to achieving high-performance buildings, the way a ZEB goal is defined is crucial to understanding the combination of applicable efficiency measures and renewable energy supply options.”

INTRODUCTION:

A zero energy building (ZEB) or net zero energy building is a general term applied to a building with a net energy consumption of zero over a typical year.3 Four well-documented definitionsвЂ"net-zero site energy, net-zero source energy, net-zero energy costs, and net-zero energy emissionsвЂ"are studied; pluses and minuses of each are discussed. Although zero energy buildings remain uncommon in developed countries, they are gaining in importance and popularity. The zero-energy approach is promoted as a potential solution to a range of issues, including reducing carbon emissions, and reducing dependence on fossil fuels. Most ZEB definitions do not include the emissions generated in the construction of the building which would usually invalidate claims of reducing carbon emissions.

A building approaching zero energy use may be called a near-zero energy building or ultra-low energy house. Buildings that produce a surplus of energy during a portion of the year may be known as energy-plus buildings.

Zero-Energy Buildings: Boundary Definitions and Energy Flows

The tagline of the ZEB concept is that buildings can meet all their energy requirements from low-cost, locally available, nonpolluting, renewable sources. For a building to be classified as a ZEB it should generate enough renewable energy on site to equal or exceed its annual energy use. The following questions arise while designing a Zero Energy building.

How to Account for the Energy Balance?

A ZEB implies that the energy generated on the site must be equal or in excess of its annual energy usage. There arises two obvious cases-

(a) When the on-site generation does not meet the loads then a ZEB can typically use traditional non renewable energy sources such as the electric and natural gas utilities

(b)When the on-site generation is greater than the building’s loads, excess electricity should be stored so that it can be used later at the time of deficit. Alternatively it is exported to the utility grid. By using the grid to account for the energy balance, excess production can offset later energy use. Achieving a ZEB without the grid would be very difficult, as the current generation of storage technologies is limited.

Off-grid buildings cannot feed their excess energy production back onto the grid to offset other energy uses. As a result, the energy production from renewable resources must be oversized at all times. In many cases (especially during the summer), excess generated energy cannot be used.

Assumption: We assume that excess on-site generation can always be sent to the grid. However, the grid may not always need the excess energy. In this scenario, on-site energy storage would become necessary.

Selecting the best technology from available Supply-Side renewable energy Technologies

Typical examples of various supply-side renewable energy technologies available for ZEBs today include PV, solar hot water, wind, hydroelectric, and biofuels. All these renewable sources are favorable over conventional energy sources such as coal and natural gas, but their relative preference depends upon the availability of the technology within the building footprint or at the site. Table 1 shows this ranking in order of preferred application. The principles applied to develop this ranking are based on technologies that:

• Minimize overall environmental impact by encouraging energy-efficient building designs and reducing transportation and conversion losses

• Will