Definition and Design of Zero Energy Buildings

*Yuehong Lu, Xiao-Ping Zhang, Zhijia Huang, Jinli Lu and Changlong Wang*

## **Abstract**

The wide application of renewable energy system (RES) in buildings combined with numerous financial incentives on RES paves the way for future zero energy buildings (ZEB). Although the definition of ZEB still lacks a national building code and international standards, the number of ZEB projects is still increasing worldwide which seems to be the pioneer ZEB buildings. However, due to the intermittency of the renewable resources, various uncertain parameters, and dynamic electricity price from the grid, how to select the renewable energy system for buildings is one of the challenges and therefore becomes an extensive concern for both researchers and designers. In addition, questions like how to achieve the target of zero energy for different types of buildings, should the building be designed as an independent ZEB or a group of buildings to be a ZEB cluster, and how to make building owners actively involved in installing enough RES for the building are still on the air. This chapter will present a comprehensive view on several key issues related with ZEB, that is, definition, evaluation criteria, design method, and uncertainty analysis, and the penalty cost scheme is also proposed for consideration as one policy to assist the promotion of ZEB.

**Keywords:** renewable energy, optimal design, zero energy building, robust method, feed-in tariff, penalty cost

### **1. Introduction**

Building energy consumption is generally recognized as one of the main sectors contributing to the whole primary energy consumption and greenhouse gas emissions in the world, which greatly raise public awareness on building energy conservation in recent years. Green building (GB), low-energy building (LEB), and nearly/net-zero energy building (ZEB/nZEB/NZEB) are widely developed for the advantages of low-energy demand in the building, efficient energy system operation, and integration of renewable energy system [1–5]. In addition, numerous incentive policies, such as investment subsidies, feed-in tariff, net-metering schemes, etc., have been applied to promote the application of renewable energy sources [6–16], thus paving the way for future zero target for buildings.

The concept of ZEB/nZEB is extended from autonomous buildings that are targeted to operate off-grid by installing enough solar PV and/or wind turbine for the generation of all the energy the building required to include grid-connected ZEB that is aimed to balance annual energy exchange with the grid. The off-grid ZEB has also been named "autonomous" or "stand-alone" building as shown in

**Figure 1.** *Basic elements in the definition of off-grid zero energy building.*

**Figure 1**, which can be defined as "Zero Stand Alone Buildings are buildings that do not require connection to the grid or only as a backup. Stand-alone buildings can autonomously supply themselves with energy, as they have the capacity to store energy for night-time or wintertime use" [17].

The on-grid ZEB is a "grid-connected" or "grid-integrated" net-zero energy building that is connected to one or more energy infrastructure as shown in **Figure 2**; it can be defined as "Zero Net Energy Buildings are buildings that over a year are neutral, meaning that they deliver as much energy to the supply grids as they use from the grids. Seen in these terms they do not need any fossil fuel for heating, cooling, lighting or other energy uses although they sometimes draw energy from the grid" [17].

However, no national ZEB codes and international standards have been developed since numerous proposed approaches spotlight different aspects of ZEB. The metric applied for the "zero" balance is a vital issue since it affects how renewable energy system will be selected to achieve this goal. Torcellini et al. [18] introduced four different nZEB definitions, including site nZEB, source nZEB, emissions nZEB, and cost nZEB, as defined below:


**41**

i.e.∑ i

**Figure 2.**

i.e.∑ i

**2. Incentive policies**

*Definition and Design of Zero Energy Buildings DOI: http://dx.doi.org/10.5772/intechopen.80708*

consumption and RES generation to be equal:

*Basic elements in the definition of on-grid net-zero energy building.*

Exported\_energy(i) × weight(i)‐∑

Generation\_energy(i) × weight(i)‐∑

different countries till 2013, as shown in **Figure 3**.

the specific investment upfront cost.

policies on RES in different countries are described as follows [6]:

Net energy <sup>=</sup> /Generation/‐/Load/≥ 0

The concept of balance can be defined in the following mathematical equations, the balance between export and import energies (Eq. (1)) or the balance between load and generation (Eq. (2)) [19]. The balance between load and generation is generally used as a basic requirement during the design phase of ZEB. By contrast, the balance between export and import energies is particularly useful for evaluating its matchability between load and generation and the interaction between building and grid. In the previous study, most studies defined "net" as the building energy

Net energy = /Export/‐/Import/ ≥ 0 (1)

Imported\_energy(i) × weight(i) ≥ 0

(2)

Load\_energy(i) × weight(i) ≥ 0

i

i

Substantial policies and regulations have been provided to support the installation of RES power plants and thus simulate the widespread of ZEB applications. Under the support of these policies, an increasing number of ZEB case studies have been conducted, and there are over 360 ZEB projects which had been identified in

The continued growth in ZEB projects is mainly driven by the progressive financial incentives on renewable energy promotion, which is summarized for several countries from different parts of the world, as shown in **Table 1**. The main support

• Investment subsidies: Based on a percentage of the renewable energy output or

#### *Definition and Design of Zero Energy Buildings DOI: http://dx.doi.org/10.5772/intechopen.80708*

*Green Energy Advances*

**Figure 1**, which can be defined as "Zero Stand Alone Buildings are buildings that do not require connection to the grid or only as a backup. Stand-alone buildings can autonomously supply themselves with energy, as they have the capacity to store

The on-grid ZEB is a "grid-connected" or "grid-integrated" net-zero energy building that is connected to one or more energy infrastructure as shown in **Figure 2**; it can be defined as "Zero Net Energy Buildings are buildings that over a year are neutral, meaning that they deliver as much energy to the supply grids as they use from the grids. Seen in these terms they do not need any fossil fuel for heating, cooling, lighting or other energy uses although they sometimes draw

However, no national ZEB codes and international standards have been developed since numerous proposed approaches spotlight different aspects of ZEB. The metric applied for the "zero" balance is a vital issue since it affects how renewable energy system will be selected to achieve this goal. Torcellini et al. [18] introduced four different nZEB definitions, including site nZEB, source nZEB, emissions

• Site nZEB: A site nZEB produces at least as much energy as it uses in a year when

• Source nZEB: A source nZEB produces at least as much energy as it uses in a year when accounted for at the source. Source energy refers to the primary energy

• Emission nZEB: A net-zero emission building produces at least as much emission-free renewable energy as it uses from emission-producing energy sources.

• Cost nZEB: In a cost nZEB, the amount of money the utility pays the building owner for the energy the building exports to the grid is at least equal to the amount the owner pays the utility for the energy services and energy used over the year.

energy for night-time or wintertime use" [17].

*Basic elements in the definition of off-grid zero energy building.*

energy from the grid" [17].

**Figure 1.**

nZEB, and cost nZEB, as defined below:

used to generate and deliver the energy to the site.

accounted for at the site.

**40**

The concept of balance can be defined in the following mathematical equations, the balance between export and import energies (Eq. (1)) or the balance between load and generation (Eq. (2)) [19]. The balance between load and generation is generally used as a basic requirement during the design phase of ZEB. By contrast, the balance between export and import energies is particularly useful for evaluating its matchability between load and generation and the interaction between building and grid. In the previous study, most studies defined "net" as the building energy consumption and RES generation to be equal:

$$\text{Net energy} = \text{/Export} / \text{-} \text{/Import} / \approx \text{0} \tag{1}$$

$$\begin{aligned} \text{i.e.} & \sum\_{\mathbf{i}} \text{Expected\\_energy(i)} \times \text{weight(i)} \cdot \sum\_{\mathbf{i}} \text{Imported\\_energy(i)} \times \text{weight(i)} \neq 0\\ \text{Net energy} &= \text{/Generation} / \text{-} / \text{Load} / \text{\&} \tag{2} \\ \text{i.e.} & \sum\_{\mathbf{i}} \text{Generation\\_energy(i)} \times \text{weight(i)} \cdot \sum\_{\mathbf{i}} \text{Load\\_energy(i)} \times \text{weight(i)} \geq 0 \end{aligned} \tag{2}$$
