1、2010 ASHRAE 37ABSTRACTBuilding emulators couple computer simulations to realcontrol hardware, creating a useful tool for studying buildingcontrol system performance. The National Institute of Stan-dards and Technologys (NISTs) Virtual Cybernetic BuildingTestbed (VCBT) is a whole building emulator de
2、signed tosupport research in a variety of topics linked to the concept ofa “cybernetic building”, where numerous building controlsystems are integrated together and with outside entities suchas utility providers. The design and use of the VCBT isdescribed in the context of specific research projects
3、 involvingbuilding system commissioning, automated fault detection anddiagnostics.INTRODUCTIONThe concept of developing building emulators, asimulated building shell and simulated heating, ventilation,and air-conditioning (HVAC) equipment combined with realbuilding automation and control system hard
4、ware, as a tool forstudying building control system performance emerged in thelate 1980s. Early work led to an international collaborativeeffort to explore variations of building emulator designs andapplications in Annex 17 of the International Energy Agency,Energy Conservation in Building and Commu
5、nity Systemsprogram (Kelly and May 1990; Haves et al. 1991; Vaezi-Nejadet al. 1991; Karki 1993).Building emulators have found limited use as researchtools, training aids for control systems users, and for controlsystem performance evaluation. (Liebecq et al. 1991) and(Kaerki and Lappalainen 1994) de
6、signed prototype emulatorsto test such aspects as accuracy, time-step, zone temperaturecontrol changes and tuning loop parameters. (Larech et al.2002) developed a test method for evaluating HVAC control-lers by emulation. (Brambley et al. 2005) discuss emulationfor training, FDD, operational strateg
7、izing, and optimalcontrol and state that “Computer emulation of building condi-tions that are fed into controllers will speed the adoption ofnew technologies by providing a resource for testing control-ler hardware under a complete range of conditions.”Building emulators vary in design details but c
8、ommoncharacteristics include real-time simulation linked to a hard-ware interface that couples the simulated building and simu-lated mechanical equipment to the controllers. Digital-to-analog converters are used to convert simulated sensor infor-mation such as temperatures, pressures, and flows into
9、 elec-trical signals that are wired to the sensor input terminals of thecontrol hardware. Analog-to-digital converters are used toconvert analog control signals into digital values that are fedinto the simulation. Digital inputs and outputs are used forswitching and status signals. The overall effec
10、t from theperspective of a building controller is that it “thinks” it isreceiving real sensor input and controlling real building equip-ment; but, in reality, the sensor data and equipment are simu-lations. A building emulator combines the reproducibility andflexibility of simulations with the real
11、performance constraintsof actual control hardware.The development and widespread use of the BACnetcommunication protocol standard (ASHRAE 2008; Bushby1997) combined with rapid advancement in the capabilities ofcomputer control hardware for building applications has madepossible a new generation of “
12、cybernetic building systems.”Cybernetics is the science of communication and controltheory that is concerned especially with the comparative studyof automatic control systems (Websters, 2009). A cyberneticbuilding integrates building automation and control systemsThe Virtual Cybernetic Building Test
13、bedA Building EmulatorSteven T. Bushby, MSc Michael A. Galler, MScFellow ASHRAE Member ASHRAENatascha Milesi Ferretti, PE Cheol Park, PhDMember ASHRAESteven T. Bushby is leader, Michael A. Galler is an engineer, and Natascha S. Castro and Cheol Park (retired) are mechanical engineersof the Mechanica
14、l Systems and Controls Group at the Building and Fire Research Laboratory, National Institute of Standards and Technology,Gaithersburg, MD.OR-10-006 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116
15、, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. 38 ASHRAE Transactionsfor comfort control, energy management, and fire detection,security, and transport systems. It also
16、 integrates the buildingsystems with outside service providers and utilities. Cyber-netic building systems offer the potential for significantlymore energy efficient building operations, lower maintenancecosts, and improved occupant comfort and safety.The current generation of mechanical systems use
17、d forheating and cooing and their associated building automationand control systems almost never achieves their design effi-ciencies at any time during building operation and their perfor-mance typically degrades over time. For example, case studiesindicate that energy consumption for HVAC systems c
18、an bereduced 20% just by detecting mechanical faults and ensuringthat systems are operated correctly (TIAX LLC 2005). Addi-tional case study examples can be found in Ardehali et al.(2003). The vision of cybernetic building systems involves amuch more complicated web of potential building systeminter
19、actions and interactions between building systems andexternal entities such as utility providers than is typicallyfound in buildings today. In order to achieve the potential ofcybernetic buildings there is a need to understand the failuresof todays systems and ways to reliably take advantage of newo
20、pportunities that system integration provides.Buildings are complex systems of interacting subsys-tems. Most commercial buildings are “one-off” designs withunique operating needs. Interactions between subsystems canbe complex and are often not well understood. The industry isvery sensitive to the fi
21、rst cost of new technologies and perfor-mance goals such as energy efficiency, indoor air quality, andcomfort often conflict. There are no simulation tools that canrealistically capture all of the necessary details of a complexcybernetic building system. An emulator is needed that cancombine the str
22、engths of simulations with the constraints ofactual commercial control hardware and communication tech-nology. A real controller has constraints in memory, processorspeed, the number and size of the registers, the operatingsystem features, and the design choices made when creatingthe control algorit
23、hms. These constraints are very importantwhen trying to test and demonstrate the feasibility of algo-rithms that are intended to be embedded in the controllers.THE NIST VIRTUAL CYBERNETIC BUILDING TESTBEDThe NIST Virtual Cybernetic Building Testbed (VCBT)is a whole building emulator designed with en
24、ough flexibilityto be capable of reproducibly simulating normal operation anda variety of faulty and hazardous conditions that might occurin a cybernetic building. It serves as a testbed for investigatingthe interactions between integrated building systems and awide range of issues important to the
25、development of cyber-netic building technology including:Automated commissioning of building systems;Automated fault detection and diagnostics (FDD) ofbuilding systems and components;Optimization strategies for interacting building systems;Communication and interaction between building sys-tems and
26、utility providers to manage energy loads andrespond to real-time price fluctuations;Development of communication standards for providingbuilding system information to emergency responders;Development of decision support tools to aid emergencyresponders; andExtension of BACnet capabilities to new app
27、lications.The VCBT control hardware consists of BACnet productsfrom multiple companies that are used for HVAC control,lighting control, physical access control, and fire detection.The BACnet network topology is an internetwork of allnetwork types commonly found in BACnet systems. Figure 1is a photog
28、raph of the VCBT control hardware.The interface between the control hardware and the build-ing simulation permits the use of multiple simulation tools sothat the simulation tool can be selected based on features thatmatch the nature of the problem being investigated. For exam-ple, investigations of
29、building system responses to fire eventsuse a simulation tool whose primary strength is accuratelyrepresenting fire physics, and investigation of fault detectionin HVAC system components uses a simulation tool thatprovides detailed representation of HVAC system componentswhere faults can be introduc
30、ed.The VCBT provides a way to emulate an entire building,including its various automation and control systems, in thelaboratory. It provides a way to examine the interactions of theFigure 1 Virtual Cybernetic Building Testbed control hard-ware. Shown in the photo are the data acquisitionunit in the
31、lower left, a range of HVAC control prod-ucts, a fire detection and alarm system, and on thefar right some biometric devices that are part of anaccess control system. Not shown are other accesscontrol devices and a lighting control system. 2010, American Society of Heating, Refrigerating and Air-Con
32、ditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. ASHRAE Transactions 39various
33、systems and to see how the building reacts underadverse events, such as equipment failure or a fire. Tests canbe conducted under reproducible, carefully controlled condi-tions, including weather, without endangering the safety orcomfort of occupants in a real building. The VCBT can beused to test ne
34、w concepts for control strategies and prototypeproducts in a way that is economical, efficient, and convenient.VCBT ArchitectureThe VCBT software components run in a real-time,distributed, multi-platform environment. Each component canpotentially be run on a variety of computers, except for the data
35、acquisition and control unit which requires special hardware.The software components can be distributed across differentmachines for operational convenience or, if needed, toincrease parallelism in the processing to meet real-timesynchronization constraints with the building controllers. Theplatform
36、 currently used is Windows XP, but past platformsused include Windows NT, Windows 95/98, and Sun Solaris1.The software components were designed to facilitate migra-tion to alternative computing platforms. A variety of computerprogramming languages, including C, C+, Visual C+,FORTRAN, Java, and Virtu
37、al Reality Modeling Language(VRML) are used. Figure 2 depicts the logical interrelation-ships and data flows for the VCBT software components.All of the component models communicate with theCenter which serves as the heart of the distributed system andthe main user interface. It serves as a reposito
38、ry for sharedinformation that is used to couple the simulations, exchangeinformation with the data acquisition unit, and control timing.Because real building controllers are used, each simulationmust run in real time.The Center manages the activation and deactivation of allcomponent models used in a
39、 run, and coordinates all data flowto and from the models. It keeps time for the models andsynchronizes the time on the BACnet controllers with thesimulation time. Using the Center, an operator can choosewhich component models to use for a particular run, which ofthe available computers should be al
40、located to run eachcomponent, the weather data to be used for a particular run,and controls the initiation of any simulated faults. The opera-tor can view data from any of the component models in realtime, and view the status and any error messages from any ofthe component models used. When performi
41、ng a run with afire, the instruction to ignite the fire comes from the Center.Bi-directional data exchange takes place through aCommon Object Request Broker Architecture (CORBA)connection depicted in Figure 2 by thick green arrows. Mostof the component models have a wrapper written in C and C+(red s
42、hell) with the actual models written in FORTRAN andcalled from the C/C+ wrapper code. The Center also commu-nicates directly with HVAC controllers via a BACnet connec-tion (thin blue arrow).The HVACSIM+component is used to simulate theHVAC mechanical systems. The Building Shell model, whichis implem
43、ented using HVACSIM+, is used to calculate heattransfer through the building surfaces, and to provide outdoortemperature and humidity information. ZFM-HVAC is used tosimulate the effects of a fire in the virtual building, includinginteractions with the HVAC systems. The HVACSIM+ andBuilding Shell mo
44、del components are used when the purposeof the emulation is to study details of the HVAC control systemperformance. The ZFM-HVAC model is used when thepurpose of the emulation is to study response to fires. Theseoptions are mutually exclusive. More details about HVAC-SIM+and ZFM-HVAC are provided be
45、low.The Data Logger is the communication interface to thedata acquisition system and, indirectly, the real buildingcontrollers. The simulated values that represent sensor inputsto the controllers are converted by the digital-to-analogconverter of the data acquisition system into analog inputsreprese
46、nted by either DC voltages (0 V to 5 V) or DC currents(4 ma to 20 ma). The ranges for each input and output on thecontrollers are known to the Data Logger, so the input valuescan be converted from the value sent from the Center to thecorrect voltage. To the building controllers this input is indis-t
47、inguishable from a real sensor. There is a capability to scalevalues to other ranges as needed. The output values of theBACnet controllers that represent inputs to the virtual buildingsystem component models are read by the digital voltmeterthrough multiplexers. The output voltage range of eachcontr
48、oller is between 0 V and 10 V. The scaling for outputvalues is handled similarly to scaling for input values.1.Certain commercial equipment, instruments, or materials areidentified in this paper in order to specify the experimental proce-dure adequately. Such identification is not intended to implyr
49、ecommendation or endorsement by the National Institute ofStandards and Technology, nor is it intended to imply that thematerials or equipment identified are necessarily the best avail-able for the purpose.Figure 2 Logical diagram of VCBT software and commu-nications components. 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs p
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