1、Meli Stylianou is a Project Leader at Natural Resources Canadas CanmetENERGY research facility in Varennes, Quebec Smart Net Zero Energy Buildings and Their Integration in the Electrical Grid Meli Stylianou ABSTRACT Two largely related innovation drivers are challenging the conventional way of desig
2、ning and operating commercial buildings: the need to reduce energy consumption and the need to reduce electrical demand. The first driver has provided momentum towards the design of Net Zero Energy Buildings (NZEBs), while the second towards the operation of buildings that are responsive to signals
3、from the electrical grid. NZEBs emerged as the drive to lower energy consumption made the integration of renewable energy in buildings commercially feasible in a number of jurisdictions. New tools are now facilitating the implementation of collaborative processes targeting designs that lower energy
4、consumption to the point where it is possible to design buildings that, over a year, generate as much energy as they consume. The second driver emerged as electrical network operators and utilities provided financial incentives to building owners to reduce, during specific periods, their electrical
5、demand in response to signals from the electrical grid. These incentives are fuelling the development of Demand Responsive Buildings (DRBs), buildings that are operated in response to these signals to shed or shift their demand, making the released electricity available to the grid. Until recently b
6、uildings have been operated as passive loads of the electrical grid. DRBs, however, have expanded the range of building operation and are increasingly shifting the role of buildings from passive loads of the electricity networks towards that of active participants that not only shift or shed electri
7、cal demand but also store and generate electrical energy. Whereas the emphasis on NZEB research has been largely on how to design buildings to lower their energy consumption to reach net zero energy levels, the emphasis on DRBs has been on how to operate them in a way to lower their electrical deman
8、d during specific periods. Given the potential for NZEBs to adversely affect grid stability due to their inherently low power factors, operating strategies developed for DRBs would need to be integrated to NZEBs to counteract this effect. This paper discusses these “Smart NZEBs” and explores the rel
9、ationship between NZEBs and DRBs in the context of the Smart Grid. It also provides an overview of technologies that will facilitate the emergence of Smart NZEBs, such as Building Information Modeling and the application of open communication standards. INTRODUCTION According to the IEA ECBCS Strate
10、gic Plan for 2007-2012 (IEA - ECBCS, 2008), worldwide energy consumed by the built environment varies from 50-70% of the worlds total energy consumption. The significance of electrical generation, transmission and distribution dedicated to the built environment is underlined by recent data. In the U
11、.S., for example more than 70% of electricity generated is consumed by residential and commercial buildings (DOE, 2009), while the Ontario Power Authority (OPA) estimates that more than 30% of the peak demand in Ontario is due to the commercial building sector (Rowlands, 2008). Demand Side Managemen
12、t (DSM) programs in this sector have been dealing primarily with energy efficiency by improving envelope insulation levels and substituting individual components such as windows, boilers and chillers for more energy efficient ones. Their objective is to reduce the energy consumed with the resulting
13、lowering of greenhouse gas LV-11-C039322 ASHRAE Transactions2011. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Volume 117, Part 1. For personal use only. Additional reproduction, distribution, or transmission in e
14、ither print or digital form is not permitted without ASHRAES prior written permission.emissions and utility baseloads. These DSM programs, driven primarily by climate change concerns, have been expanded over the last few years to include programs that address the reliability and efficiency of electr
15、ical networks. These two types of programs, representing the drivers of climate change and grid reliability have provided the momentum for new ways of designing and operating buildings represented by two emerging frameworks, namely the Net Zero Energy Building and the Demand Responsive Building. The
16、 present paper will examine the relationship of these two frameworks to the electrical networks and provide an overview of how they could converge into a new paradigm that combines their low energy and demand responsiveness characteristics. NET ZERO ENERGY BUILDINGS (NZEB) NZEBs are defined in this
17、paper as buildings that are highly efficient and which over a year generate as much energy from renewable sources as they consume. They have evolved over time as concerns about climate change have been driving the energy reductions in buildings to levels where the amount of energy consumed can make
18、on-site renewable energy generation commercially feasible. This framework has been gaining ground with national and international efforts currently under way to develop technologies and processes that will allow the NZEBs widespread implementation (IEA, 2010). The momentum towards NZEBs has benefite
19、d from the collaborative approach towards design developed in the early 1990s by Canadas C2000 program called Integrated Design Process (IDP) (Zimmerman, 2006). This process is in contrast to the conventional design approach which is a linear process with architects determining the building form, or
20、ientation and other building envelope characteristics before handing this design over to the mechanical engineer who designs the HVAC system (Torcellini et al, 1999). IDP, however, has provided the means to bring the design of the envelope and electromechanical systems into a process that allows the
21、 designed building performance to exceed that of its component systems. Mismatch of generation and consumption The vision of NZEB has traditionally considered two components: highly energy efficient building design and renewable energy generation. The first component strives to reduce the energy req
22、uired by the building as much as possible, while the second one provides the balance of the energy requirements. However, issues arise due to the mismatch between the generation of renewable energy and its consumption. One of the ways to meet this mismatch of generation and consumption is through th
23、e use of the electrical grid as a means to store excess electrical energy. Over the last decade, a number of utilities have provided building owners with the ability to send excess electrical energy back to the grid under a variety of contractual arrangements, from net-metering (Hydro Quebec, 2010)
24、to feed-in tariffs (OPA, 2010). This arrangement provides a significantly more cost effective method of storing energy compared to electrical batteries. In the case of Ontario (and other locations worldwide), this way of dealing with the mismatch between energy generation and consumption is also fin
25、ancially beneficial for the building owners, since generation of electricity from the sun can be worth as much as 80.2/kWh, regardless of time of generation and electricity use. The ability to store excess electricity by transferring it to the grid, however, could pose significant problems to utilit
26、ies as a high penetration of NZEBs could affect grid stability (Crawley et al, 2009). This is because peak demand in NZEBs is significantly more pronounced than in typical buildings (Torcellini, 2006). The potential stability problem stemming from a high penetration of NZEBs is best illustrated by t
27、he figure below. Figure 1 presents the peak day for Oberlin College, (Torcellini et al, 2006), a building approaching net zero energy levels of performance. During this particular winter day, the morning peak tops 140kW. However, around 14:00, the energy collected due to the passive solar and intern
28、al gains of the building has reduced significantly the need for additional energy from the building ground source heat pump. This coincides with the peak electricity generation of the building photovoltaic system, with a resulting return of 20kW to the electrical network. As a result, the design of
29、this building creates a two way flow of electricity and a swing of more than 160kW over a period of five hours. 2011 ASHRAE 323Figure 1: Oberlin College peak heating season utility demand, PV production, and end use (Torcellini et al, 2006) This load profile, in particular the high demand swing comb
30、ined with the two way electricity flow, is markedly different from the profile of typical buildings. If this effect is multiplied a large number of times, as it would be in the case with significant penetration of NZEBs, it could create problems with the stability of the electrical distribution netw
31、orks, as these networks are currently generally operated to handle steady and predetermined electrical generating capacity and relatively predictable consumption patterns. Therefore, operating the NZEBs systems in a manner that smoothes out this type of load profile would contribute in maintaining n
32、etwork stability in the case of high NZEB penetration. DEMAND RESPONSIVE BUILDINGS (DRB) The use of building operation as the means to counteract electrical grid instabilities is currently used in a number of jurisdictions across North America through the development of Demand Response (DR) programs
33、. The U.S. Federal Energy Regulation Council (FERC) defines Demand Response (DR) as “Changes in electric usage by end-use customers from their normal consumption patterns in response to changes in the price of electricity over time, or to incentive payments designed to induce lower electricity use a
34、t times of high wholesale market prices or when system reliability is jeopardized” (FERC, 2010). Although these DR programs were originally developed for industrial users, concerns regarding reliability and efficiency of the networks have expanded them to include residential and commercial buildings
35、. The financial incentives of these programs have precipitated a marked increase in the attention paid to how commercial buildings are operated. This in turn has contributed to the development of demand responsive buildings (DRB), i.e., commercial buildings that have the capacity to modify their ope
36、ration in response to pricing or other signals from their service provider/utility by releasing electrical demand. 324 ASHRAE TransactionsLinking buildings to the grid DRBs are linked to the grid by their ability to receive and act on utility signals. Typically, DRBs receive price or other signals f
37、rom its utility and react by modifying their operation in response to them. The result is the lowering of the building electrical demand during the period defined by the signals, preferably with minimal impact on the occupants comfort (Figure 2). Figure 2: Typical impact of DR control strategies on
38、a building load curve Typically large commercial buildings are equipped with Building Energy Management Systems (BEMS) enabling them to program alternative operating sequences. These alternative sequences generally include raising the zone temperature setpoints, lowering air handling unit static pre
39、ssure setpoints, or lowering the building lighting levels. When these sequences are activated the electrical energy demand of the building is shifted or, in the case of lowering lighting levels, eliminated. The Lawrence Berkeley National Laboratory (LBNL) has studied extensively the possibilities of
40、fered by buildings in reducing their electrical demand using automated approaches (Motegi et al, 2007; Kiliccote, et al, 2009). In order to fully automate the process from the utility to the building, LBNL has developed the Open Automated Demand Response Communications Specification (LBNL and Akuaco
41、m, 2009), a communications model designed to facilitate sending and receiving of Demand Response (DR) signals from a utility or independent system operator to electric customers. Using the above communications specification, the building is linked through a two way communication link to the service
42、provider and reacts to the service providers signal by using its control systems (Figure 3). The signal from the service provider is received by the BEMS as shown in Figure 3. This signal, which could be an indication of the level of DR (low, medium, high) or the real electricity price is then proce
43、ssed by the BEMS which activates the pre-programmed set of alternative control strategies aimed at reducing the facilitys electrical demand. 2011 ASHRAE 325Figure 3: Building to Grid conceptual model The ability of the building to react to the signal is highly dependent on its BEMS and the electro-m
44、echanical systems in place. A BEMS with a high degree of granularity, that is the ability to control the system down to zone temperature controls, would be able to modify the operation of the electromechanical systems in a more effective manner than one that has control only over major equipment. Si
45、milarly, the inclusion of systems having the ability to modulate (e.g., variable speed drives and dimmable lighting ballasts) in the original building design contributes significantly to the responsiveness of the building. It is interesting to note that similar system design characteristics are impo
46、rtant in ensuring that the building reaches net zero energy performance. THE PARADIGM SHIFT: BUILDINGS AS CONSUMERS, GENERATORS AND STORAGE OF ENERGY The two-way electricity flow between NZEBs and the distribution networks, as well as the two-way communication link between DRBs and the utilities, ra
47、dically modify the relationship between buildings and the electrical network. Buildings are no longer passive loads, but become active participants in what is emerging as the Smart Grid. While the need to minimize energy consumption that drove the emergence of NZEBs is an objective that has been on
48、and off in the public eye since the first energy crisis in the 1970s, consideration of buildings in the context of electrical grid reliability is a relatively recent development. This new relationship of the building to the electrical grid makes the two way electricity flow of NZEBs, and the two way
49、 communication link of DRBs part of a larger consideration for network operators. As many state governments in the US start requiring renewables in the electricity supply mix, increasing levels of intermittent renewable energy generation are 326 ASHRAE Transactionscoming on line. In fact a comparison of capital costs for different electrical generation technologies by Ipakchi and Albuyeh, (Ipakchi and Albuyeh, 2009), demonstrates that the capital cost of inherently intermittent technologies is going to be reduced over time, creating operational challenges for the transmissio
