This paper is a presentation of an 'instrument' for the optimization of the functionality and conservation of tertiary buildings. This technique has several different names: Building Automation Systems (BAS), Central Control and Monitoring System (CCMS) in English, and Gestion Technique du Bâtiment' (GTB) or Gestion Technique Centralisée (GTC) in French. With this technique it is possible to manage all the functions of a building, it is a modern instrument that introduces the concept of 'automation' in the operation of buildings using computerized procedures, earlier reserved for industrial processes. The system is structured with different automation levels with a distributed intelligence, each level characterized by a communication system (Fieldbus for the lowest and Ethernet for the highest level). In order to apply the BAS to CERN buildings it is necessary to evaluate the advantages, the CERN requirements and the integration with the several existing control and automation systems

Vairo, Antonio

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EUROPEAN LABORATORY FOR PARTICLE PHYSICSLABORATOIRE EUROPEEN POUR LA PHYSIQUE DES PARTICULESPresented at the 2nd ST WorkshopChamonix, France, February 2 - 5, 1999CERN-ST-99-February, 1999TECHNICAL MANAGEMENT FOR BUILDINGSA. VairoAbstractThis paper is a presentation of an ‘instrument’ for the optimization of the functionality andconservation of tertiary buildings. This technique has several different names: BuildingAutomation Systems (BAS), Central Control and Monitoring System (CCMS) in English,and Gestion Technique du Bâtiment’ (GTB) or Gestion Technique Centralisée (GTC) inFrench.With this technique it is possible to manage all the functions of a building, it is a moderninstrument that introduces the concept of ‘automation’ in the operation of buildings usingcomputerized procedures, earlier reserved for industrial processes. The system is structuredwith different automation levels with a distributed intelligence, each level characterized by acommunication system (Fieldbus for the lowest and Ethernet for the highest level). In orderto apply the BAS to CERN buildings it is necessary to evaluate the advantages, the CERNrequirements and the integration with the several existing control and automation systems.21 INTRODUCTIONThe technical management for buildings’ is a modern instrument for the optimizationof the functionality and conservation of tertiary buildings, minimizing the running costs. Thiskind of management is carried out by means of automation systems able to monitor and torule all, or a part, of the functions of the buildings.A management system for buildings has the following features:- field devices, able to monitor and control the functions of the building;- intelligent units, that send commands to the field devices, acquire and elaborate data;- communication system, that allows a correct communication between the severalentities;- software running the functions of the building.The main functions of a tertiary building controlled by a management system generally are:x electrical distribution;x heating, ventilation, air conditioning (HVAC);x alarms, access control;x lighting.The realization costs of these management systems must be justified by the benefits obtainedin the use of the building. The main benefits can be grouped in the following categories:x energy efficiency,x safety,x workplace conditions,x reducing operating costs.But there could be other reasons to install such computerized management systems; forexample, in North America in the early 1980s these management systems were installed inexisting buildings in order to increase the commercial value of those buildings.2 DEFINITIONSThe ‘Technical Management for Buildings’ includes different management systems thatcan be found on the market under different names. The differences are in strategy ofmanagement adopted and the main functions controlled. They also depend on the market ofdiffusion, the manufacturing firm and historical reasons. For instance, systems that have astheir main task the energy management of buildings include Energy Management System(EMS), Central Control and Monitoring System (CCMS), Energy Management and ControlSystem (EMCS). With the increasing use of computerized systems and with the evolution ofthe treatment of data, the type of management has changed.In this way from Central Control Systems (in French Gestion Technique Centralisée’)we get more developed management systems which are defined as Building AutomationSystems, Intelligent Building, and in French (Gestion Technique du Bâtiment).33 COMPARISON WITH INDUSTRIAL AUTOMATION SYSTEMSAll the building management systems have been derived from the industrial automationsystems with several differences. The communication system can be simpler because there isa lower complexity of the controlled process with less data to be transmitted, but it may haveto cover larger distances if there are buildings placed in an extended area. After it has beenset up, an industrial automation system can be considered stable. However, in tertiary systemsthere are often modifications and enlargements both of the controlled functions and of thecontrolled zone. For this reason, the building management system must have an openstructure that is easily modifiable.4 STRUCTURE OF THE SYSTEMA technical management system for buildings is the result of the installation of physicalcomponents and software. The system in the most general form is structured in three levels,as shown in Fig.1:x field level,x automation level,x management level.Figure 1: Three-level structure of a technical management system for buildings.This kind of architecture does not have a single control unit, but is characterized by adecentralization of several control and automation tasks that are carried out by ProgrammableLogic Controllers (PLC), named Local Processing Units (LPU).4.1 Field levelAt this level, there is the interface between the management system and the controlledphysical processes. By means of sensors and actuators, integrating or replacing the normaldevice, the system is able to acquire process data and to modify the process itself byexecuting the commands coming from the automation level; there is no ‘intelligence’ at this4level. The sensors convert a measure or the registration of an event to a representative signalto be sent to the upper level; the actuators have to execute the orders coming from theautomation level. All these instruments must therefore be equipped with devices able tocommunicate with the processing units by means of the field communication medium(fieldbus) and its communication protocol.4.2 Automation levelThis level has LPUs that may have more or less sophisticated tasks, from the simplecentre of communication between the management and the field level, to completelymanaging a process, for example the lighting system of a floor, transmitting at themanagement level only the data about the process.The most important tasks for the main LPUs are:x to rule the process, or a part of the process, following automation programs;x to acquire data from the field devices;x to transmit to the management level all or part of the data coming from the field;x to acquire from the management level the reference parameters for the automationprogram.The automation level can be organized with a main LPU at the head of a zone, or at thehead of a function of a zone, for example the air conditioning of a building.4.3 Management levelThe management level is formed by one or several central processing units. These arepersonal computers, communicating between themselves and with the automation level viaone or separated communication networks. A typical configuration for structuredmanagement systems is composed of several central processing units, each one dedicated to aspecial function, for example HVAC, power system, access control. These central controlunits carry out the most sophisticated tasks by means of software elaborating the data comingfrom the lower levels and the data entered by the user. At the present time modular computerprograms are available on the market that can be easily implemented and modified,improving the number of controlled functions or zones or the integration of the severalsubsystems. At this level there are the global management functions which elaborate the maindata of all the single processes. The most common of these functions are:x maintenance management, with scheduling of the interventionsand evaluation of the overall costs;x analysis of current or previous process operations;x data exchange with other systems, e.g. administrative database;x monitoring and displaying of operation mode and alarms;x faults statistics;x coordination of energy-saving operations of the different processes.54.4 Communication systemsSeveral technologies and standards are used at the present time. There are a largenumber of technologies, protocol communications and configurations on the market. There iscurrently no overall standardization.4.4.1 Connection between the local processing units and field devicesThe lowest level of communication is between processing units and sensors andactuators. These connections can be made with a discrete wiring from each field sensor oractuator to the unit. Many of the management systems for buildings use a large number ofI/O devices and operate over long distances. This leads to high wiring and installation costs;additional limitations are the reduced flexibility for system modification or extension and thelimited availability in the case of defective control units. To reduce costs and overcome theselimitations serial control systems known as fieldbus systems have been developed. Theseconsist of a simple cable supporting the feeding of the device and the communication.In a fieldbus system the processing units communicate with all the field devicesconnected with the bus. In this case the field instruments are equipped with a device whichallows the exchange of information in digital format, RS 232, RS422 or RS485 transmissionstandards. A fieldbus standard is characterized by the physical medium (usually a cable with2 or 5 conductors), the communication protocol and the communication strategy that involvesthe transmission speed and the complexity of the communication devices. In buildingmanagement systems both industrial fieldbuses and specific building automation buses areused. These have lower communication speed and data capacity but, at the same time, thecomplete system has lower costs and allows easy modifications.The choice of the fieldbus involves that all the devices forming the system must becompatible with its standards. There is also a strong dependence for future modifications,with the producer, or producers, following the specific standard.Table 1 lists some of the most common fieldbuses present on the market and used inbuilding management systems.Table1Common fieldbuses used in building management systemsName Main Firms Data rate Nodes Bus lengthControlled Area Network (CAN) Bosch, Allen Bradley 1 Mb/s : 50 kb/s 64 : 127 40 : 1000 mPROFIBUS Siemens, ABB,Landis &Gyr,Schneider Group500 : 93.7 kb/s 32 200 : 1200 mEuropean Installation Bus (EIB) Siemens, Phillips 9.6 kb/s 64 350 : 700 mBatibus Schneider Group,Landis & Gyr4.8 kb/s 75 300 mLon Works Echelon Corp. 1.25 : 0.078 Mb/s 64 130 : 2700 mWordFIP Cegelec, ABB 31.25 kb/s : 1 Mb/s 32 1900 : 750 m64.4.2 Connection between the management and the automation levelThe communication bus at this level is named ‘system bus’ or ‘process bus’ and it isrequired to have better performance than the bus used at the field level. At this level thepriority is not the acquisition data, but the exchange of more complex information. For thisreason other kinds of communication buses are used, with different technology, protocols andperformances. In more extended and structured management systems, with a large number ofprocessing units, there is a single communication network for the automation of amanagement level.4.4.3 Communication at the management levelThe communication network supporting this task is also called a LAN (Local AreaNetwork). At this level there is an exchange of information between computers and PLC witha large amount of data and a continuous flux. There is the need to have a medium that allowsgood transmission speed, long-distance transmission, and flexibility. For smaller systemswhere almost all the operator stations are located in the same area, it is possible to use a bussystem. But for an extended network the most common network used at this level is based onthe IEEE (Institute of Electrical and Electronics Engineers) 802.3 standard and usuallydefined with the name Ethernet.5 CERN SITUATIONOver the years, several systems of automation and control have been installed at CERN,for a variety of applications, and several kinds of fieldbus have been extensively used. In thisway the control and monitoring systems of various functions have been set up, also in a fewtertiary buildings, for example for HVAC systems, but these systems are run in anindependent way. The several systems are structured with two communication levels:fieldbuses connecting all the process devices and CERN’s LAN used as communicationmedium inside the management level and between the management and automation levels.The LAN is made up of an Ethernet network (Réseau Ethernet Service). The processing unitsof the several management systems of all the controlled processes are linked to this network.Each processing unit of the management level is able to communicate with its ownautomation level.6 EVALUATIONSThe evaluation of the usefulness of installing such management systems for buildings atCERN has to be executed by the users, by the people that are in charge of the management ofthe several functions and of the management of the site, examining the possible advantages,not only the economic ones. Nevertheless the estimation of the economic convenience musttake into account the cost and the payback time of the realization of the systems. This costincludes the costs of all the components: field devices, LPU, fieldbus and management unitswith suitable software. The problem of setting up the communication structure of the futureautomation systems or of coordinating the existing systems is simplified by the existence atCERN of the LAN covering almost all the site. But there are high costs, compared with anormal installation, in setting up a technical installation (electrical system, HVAC, etc.)7equipped with all the field and automation components necessary in order to be managed byan automation system. Consider the example, of a low-tension electrical switchboard of maindistribution with the following characteristics: In = 800 [A], one incoming circuit breaker andten outgoing circuit breakers. To be able to run it with such a management system, we haveto install components able to execute commands or to transmit their status or measures, acommunication device, a fieldbus and LPU able to carry out the communication with theEthernet network and simple automation functions. This involves an extra cost of about 15%in comparison with a normal switchboard, without considering the cost of the software andthe personal computer at the management level. The automation extra cost of automation iseven higher for secondary distribution switchboards: about 80% for a switchboard with oneincoming and twenty outgoing circuit breakers having In < 63 [A]. In existing buildings,generally, it is not possible to implement the existing installations; with controlled fielddevices instead it is necessary to replace them with new installations at high cost.7 CONCLUSIONSAt the present time at CERN, it is difficult to justify the cost of systematically installingglobal management systems for existing buildings. There is the eventuality that in the futurein some tertiary buildings there will be special requirements, which will be able to justify theinvestments. In that case it will be possible to realize computerized technical managementsystems for certain functions in existing or new buildings. It will also be possible to collectand coordinate all the control and automation systems of the tertiary buildings by a singlemanagement system.Bibliography[1] Building Automation System: Overall System Concept ( Siemens AG, 1996).[2] G. Schickhuber, O. McCarthy, Distributed fieldbus and control network systems.[3] M. Eyke, Building Automation Systems, Oxford, 1988.[4] Bati High Tech (Several issues).[5] Recommendations for the use of  P.L.C. at CERN, Working group on PLC, April 1998.[6] R. Carlson, R. Giandomenico, Building Automation Systems, 1991.[7] Recommendations for use of fieldbuses at CERN, Working group on fieldbuses, June1996.[8] B. Delfino, P. Pinceti, Il Fieldbus negli impianti eletrici, AEI, 1993.

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