1、Alexi Miller is a Senior Project Manager at New Buildings Institute (NBI) in Portland, OR. Jim Edelson is the Director of Codes and Policy at NBI. Zero Net Energy Buildings and the Grid: The Future of Low Energy Building-Grid Interactions Alexi Miller, P.E. Jim Edelson ASHRAE Associate Member ASHRAE
2、 Associate Member ABSTRACT As zero net energy (ZNE) and other low-energy buildings become increasingly common, it is important to consider how different ZNE strategies can interact with local electricity grids. The electricity grid was built as a one-way street, with energy flowing from the power pl
3、ant to buildings. But widely distributed renewable energy systems and other cutting-edge building technologies will change that equation as the grid transitions to a transactive energy framework with integrated demand-side management. Demand response (DR) technologies and grid-sensitive design featu
4、res in ZNE buildings will be critical to enabling the successful integration of these facilities into the grid at a large scale. The paper describes three tiers of DR and renewable energy technology integration in commercial buildings: 1. Conventional buildings with one-way energy flows or conventio
5、nal net metering2. Moderately responsive buildings with interactive demand response capacity3. Fully grid-integrated buildings with active and passive efficiency and demand response features, often with onsite renewable energyThis third tier represents the buildings of the future. These buildings in
6、tegrate grid-sensitive design features, fully dispatchable DR across major end-uses in the building, and carefully designed and installed renewable energy technologies that are intended to improve the relationship between the building and the electricity grid. These buildings, whether operating at a
7、 ZNE level or not, must be explicitly designed with both active and passive features and technologies to optimize the interactions between buildings and the utility grid. Passive design strategies such as building orientation, daylighting, and passive space conditioning, are the foundational step an
8、d should be implemented as much as practicable. Active strategies such as night ventilation, thermal storage, or DR will also be instrumental and can allow buildings to be used when necessary as storage for the grid. Renewable energy systems should be carefully chosen and designed to interact well w
9、ith the grid. The paper differentiates between renewable-oriented and efficiency-oriented ZNE building typologies and discusses their impacts. The paper presents a framework for employing design strategies and measures that ensure buildings of the future can benefit from, and support, the grid moder
10、nization efforts that will occur throughout the life of the buildings. Finally, policy recommendations to improve future building-grid interactions are offered. INTRODUCTION Policies, programs and market developments have dramatically changed the prospects for Zero Net Energy (ZNE) buildings over th
11、e past decade. There is burgeoning market interest in ZNE, and policies and programs can foster and grow that interest through leadership, direct support, and the reduction of risks and uncertainties. Actual ZNE construction to date is still relatively new, and only a small percentage of building co
12、nstruction now has a goal of ZNE. However, efforts are increasing, with a doubling in the number of commercial ZNE buildings over the last few years (NBI 2014). ZNE homes and buildings have been designed and constructed by a growing number of design teams and builders and are spread throughout a num
13、ber of climate zones and political jurisdictions, including (in North America) 39 US states, three Canadian provinces, and the District of Columbia. Figure 1 Growth in ZNE projects from 2012 to 2015 (NBI) ZNE buildings have now passed the “proof of concept” stage, with more ZNE buildings being const
14、ructed as well as larger and more complex buildings. One important question now is how to garner the significant benefits of rapidly increasing the numbers of ZNE homes and buildings through policies and programs while adding to the stability, rather than the instability, of the energy delivery syst
15、ems throughout North America. The analysis and recommendations below depict a pathway for best advancing ZNE buildings in light of their impacts on the grid. Almost all existing ZNE policies follow from broader climate or energy policies enacted by state legislatures, governors, mayors and city coun
16、cils, but usually with regard only to energy consumption, not considering the impact on the grids. California is a notable exception, with its value of energy (Time Dependent Valuation-TDV) dependent on the time-of-day use; but even there, the extreme patterns of consumption in ZNE buildings are not
17、 fully considered. The US Department of Energy, states and local governments can all contribute to the development of a Path to ZNE that considers development of a ZNE building stock that works well for the energy delivery infrastructure. Utilities and program administrators can operate successful Z
18、NE pilots with this purpose in mind. Even building codes are at the early stages of considering changes that could better support ZNE in the future and can also be guided with this same dual objective (energy and grid) in mind. This paper first frames the ZNE building impact in a general sense and t
19、hen describes the different impacts of “Renewable-oriented” versus “Efficiency-oriented” ZNE buildings. A synthesis and set of technical recommendations are then presented, including examples of where and how the various strategies may be optimal. The paper concludes by exploring potential policy re
20、search and policy development avenues. We hope this paper provides useful information to expand the role of ZNE buildings in achieving carbon and efficiency policy goals while also working to help the grid smoothly integrate distributed energy generation and very low-energy buildings. TWO TYPOLOGIES
21、 FOR ZERO NET ENERGY BUILDINGS As zero net energy buildings become increasingly common, it is important to consider how different ZNE strategies can interact with local electricity grids. Although a building may generate enough renewable energy onsite to offset the imported energy used over the cour
22、se of the year, at any particular time it is very unlikely that the generation is actually equivalent to the usage. Integrating demand response (DR) technologies and grid-sensitive design features into ZNE buildings is critical to enabling the large-scale integration of these facilities. This paper
23、will examine the two major typologies in ZNE buildings as they relate to the grid. To understand the relationship of buildings to the grid in general, three tiers of DR and renewable energy technology integration in buildings can be identified: Tier 1. Conventional buildings with one-way energy flow
24、s or conventional net metering: These buildings comprise the great majority of buildings and have no DR technologies, grid-sensitive design features, or other smart features. These buildings may be equipped with renewable energy sources such as PV panels, but the panels are typically designed for ma
25、ximum annual production, and the building imports energy as needed throughout the day and year. Tier 2. Moderately responsive buildings with some DR capacity: These buildings have some DR technology installed, typically associated with discrete end-uses. For example, there may be controllers install
26、ed on heating, ventilation, and cooling (HVAC) or lighting equipment to allow the building to participate in demand response programs through load aggregators by shedding load at specific times based on automated instructions from a third party. Tier 3. Fully grid-integrated buildings: These buildin
27、gs are carefully designed, and interactions with the electricity grid have been considered during the design process. The buildings integrate grid-sensitive design features, fully dispatchable DR across all major end-uses in the building, and carefully designed and installed renewable energy technol
28、ogies that are intended to facilitate a positive relationship between the building and the electricity grid. These three tiers of DR and renewable energy integration can play out differently in various applications. However, within the generic category of ZNE buildings there are two fundamental typo
29、logies: Renewable-Oriented ZNE buildings and Efficiency-Oriented ZNE buildings. The different features commonly seen in these two approaches interact differently with the grid, and each approach offers its own opportunities and challenges. Features of Renewable-Oriented ZNE Buildings Renewable-orien
30、ted ZNE buildings may be designed as such or may be a conventional (Tier 1 or 2 in the above list) building retrofitted with significant renewable energy generation. These buildings, of course, generate as much energy onsite as they consume on an annual basis. The path to achieving this goal involve
31、s more active strategies as well as more renewable generation to account for a higher energy usage relative to efficiency-oriented ZNE buildings. These buildings are generally more likely to exhibit both high peak usage and high peak generation. Renewable-oriented ZNE buildings typically have higher
32、 overall energy usage when compared to their efficiency-oriented peers. (When compared with a run-of-the-mill building, these buildings clearly stand out as energy efficient and high performing.) To compensate for their higher energy usage, these buildings tend to have more renewable energy generati
33、on capacity installed onsite. These buildings are likely to fall into Tier 1 or Tier 2 of the above list: net-metered buildings, which may be moderately responsive with some DR capability. In order to optimize the impacts these buildings have on the electricity grid, more active strategies are neede
34、d. For example, active DR strategies, like those often delivered by an Energy Services Company (ESCO) or a DR aggregator, may be implemented so that the building can respond to specific load shedding or curtailment events by adjusting the operation of its mechanical systems. Other active systems suc
35、h as night ventilation or thermal storage are well suited to improve the grid-sensitivity of these buildings. The load shape impacts of these buildings and their renewable energy systems can be very significant. Jim Lazar published a paper in January 2014 titled “Teaching the Duck to Fly” in which h
36、e discusses the impacts of increasing renewable energy generation on Californias energy grid and outlines ten strategies that can significantly ameliorate the potential problems these changes will pose (Lazar 2014). Figure 1 shows the predicted load shape on an illustrative day in southern Californi
37、a in 2020. (Lazar notes: “this illustrative day is a light load; a heavy renewable energy generation day such as one that might be experienced in the spring or fall and is not intended to represent a normal or summer peak day. It is selected to illustrate the opportunities available to meet a challe
38、nging situation.” That is, this represents something of an extreme case at this point in time and for the near future.) The blue line shows the total load on the system. The red line, often called the “Duck Curve,” shows what could happen if the state achieves its Renewable Portfolio Standard (RPS)
39、goals in 2020 without careful consideration of how to accommodate renewable energys impact on the load shape. A renewable-oriented ZNE building will be more likely to exacerbate the swings within the duck curve, without incorporating significant DR capabilities. Figure 2 The Sitting Duck: CA loadsha
40、pe on an illustrative day in 2020 before and after renewables (Lazar). Features of Efficiency-Oriented ZNE Buildings Efficiency-oriented ZNE buildings are typically designed from the ground up to be as efficient as possible and include only enough onsite renewable energy generation to cover the mini
41、mal needs of the building. These buildings are likely to fall within Tier 2 or Tier 3 of the above list (moderately or fully grid-integrated buildings) and are generally more energy efficient than their renewable-oriented peers. The integrated design process common in these buildings offers opportun
42、ities to ensure that grid-sensitive design elements are incorporated. Passive design strategies tend to play a bigger role in efficiency-oriented ZNE buildings than in renewable-oriented ZNE buildings. These design strategies are grid-sensitive and by definition do not require intervention by a thir
43、d party such as a building operator or ESCO. Some examples of passive design strategies often employed in these buildings are daylighting, building orientation, high insulation levels, and passive heating and cooling. That is not to say that efficiency-oriented ZNE buildings cannot make use of activ
44、e strategies. Buildings in this category, and those in Tier 3 in general, are good candidates for DR strategies such as load curtailment and for active load management strategies such as thermal storage. These strategies are generally implemented in the building at the design stage. One benefit of i
45、ncorporating grid-sensitive design strategies into buildings such as these is that the building becomes significantly more independent and reliable. The degree of independence depends on the particular energy efficiency and demand response strategies employed, but for the most part, a building with
46、passive technologies implemented will be better able to withstand extreme events (such as a power outage) and will be inherently better suited to respond to price signals such as those sent by time-of-use energy pricing. The grid impacts of efficiency-oriented ZNE buildings can be ameliorated in lar
47、ge part by grid-sensitive design strategies and operational choices. The effects of these strategies and choices can flatten out the load shape significantly and can help reduce the peak demand issues illustrated in Figure 1 above (the Sitting Duck). Figure 2 shows the predicted load shape on an ill
48、ustrative day in California in 2020just as Figure 1both before (red) and after (green) the adoption of Lazars ten recommended strategies. In this case, the duck has taken flight (resulting in significantly lower peak demand and less dramatic ramping rates), with positive impacts for the utilities an
49、d society as a whole. (The ten strategies recommended by Lazar include strategies at the utility-wide scale as well as the building level. Nonetheless, the impact of grid-sensitive building design has effects similar to these.) Figure 3 The Flying Duck: The impact of multiple strategies on an illustrative days load shape in 2020 (Lazar). How Can These Two ZNE Building Typologies Coexist? There is space for both renewable-oriented ZNE buildings and efficiency-oriented ZNE buildings. Because of the different effects the two design approaches can have on the grid, it is important to
