1. Introduction of BMS
Building Management System (BMS) is to control and monitor building services systems in an efficient way by centralizing the control of individual systems ( 1.1). The systems include HVAC, Fire Services Lift, Escalator, Lighting, Electrical Distribution, Steam & Hot Water, and Plumbing & Drainage.
The main function of BMS is centralized control & monitoring and fault management. So it has another name call Central Control and Monitoring System (CCMS). The other functions are enhance interface & connectivity between systems, service response to customer, operator control of systems and graphical display to make the control of system more users friendly. Improve energy efficiency and operational efficiency. Allow capacity for future upgrades & expansions and automation. And related system Building Automation System (BAS) will be use on BMS.
2. Basic BMS Design
3-Levels BMS Architecture ( 2.1):
l Management Level – User can configure and monitor plant performance. Anticipate future trends, improve efficiency, and analyze management report.
l Automation / Controller Level – The location with greatest technical control requirement, and differentiate one from others. Controllers automatically perform their tasks from I/P and to O/P. Controllers can communicate with each other (Peer-to-Peer). Event based operation. The devices can function at the highest efficiency and no repetitive information is transmitted. Controllers only react with the Management Level when plant goes out of limits, and adjustments are made through a user interface.
l Field / Floor Level – Information is gathered through sensors and other intelligent devices. The information will be sent back to the controllers.
Third party equipment is integrated into the Automation and Field levels with control at the Management level.
Centrally controlled system ( 2.5) – A control system in which transmission is to a central computer and the reliance of all controls on a central computer.
Distributed control ( 2.6) – A control system in which control computations and intelligence are made at different locations and the result coordinated.
The constraints of BMS are network expansion, the limited variety of topologies and transmission media. The solutions are mixing of communication media (twisted pair, power line, radio, infra-red, fibre optics, coaxial). Complete implementation of OSI model. Using free topology, user-friendly software and development cost.
Topology affects system redundancy, communication protocol and system response time. The common system topologies such as: Bus, Star, Tree, Ring and Mesh.
Bus Topology ( 2.7) – All devices are connected to a central cable, call the bus or backbone. The advantage is much less cabling requirements. The brands using include Ethernet, Profitbus, ControlNet, LonWorks.
Star Topology ( 2.8) – All devices are conned to a central hub. Star networks are relatively easy to install and manage, but bottlenecks can occur because all data must pass through the hub. Cable fault affects one device only. But communication hub fault affects all devices. The brands using include Ethernet, Profitbus, ControlNet, LonWorks.
Tree Topology ( 2.9) – The topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs. Device at the highest point in the hierarchy controls the network. The brands using include Ethernet, Profitbus, ControlNet, LonWorks.
Ring Topology ( 2.10) – All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it. Same as bus network with both edges connect. The brands using include Token Ring, FDDI, Profitbus.
Mesh Topology (Fig 2.11) – Network topology which combines more than one basic topology such as bus, ring, or star. Good for redundancy. It will use lots of cable to connect every device with every device.
Considerations in Topology Layout for automating building with vast amount of points require well-designed network segmentation, in order to achieve a good performance & infrastructure. Well designed structured network by using repeaters, bridges or even better using routers to improve network reliability and simplify network troubleshooting. Some reasons why segmenting a network is important: Isolation of individual network segments in order to limit the propagation of a single fault to one segment and prevent this single fault from spreading out over the entire network. Different nodes demand different communication media and different network speeds but they all need to communicate with each other, which requires and interconnection between the different networking media. Increase the number of possible nodes in a single network and increase the number of possible nodes in a single network. Keep local traffic within one segment in order to avoid network traffic overload conditions which will make service like HVAC, lighting … malfunction.
There are three types’ configurations using in BMS:
1. Conventional configuration – Server workstations daisy chained with DDCs (usually using RS-485). Typical RS-485 Controller Level network ( 2.14) relatively low bandwidth (around 9600 bps). The limited nodes around 100, and the distance is lower than 1200m. Only for data transmission.
Controller Level Network
2. Ethernet-Based configuration – Use Ethernet as transmission media. Servers, Workstations and DDCs on the same Ethernet platform. Typical Ethernet-Based Network ( 2.15) with high bandwidth (typical 1Gbps backbone). Use IP Technology means open platform for various applications. Virtually no distance limitation. Always use for data, voice & video systems.
3. Hybrid configuration ( 2.16) – Non-hierarchy architecture with combination of different independent networks and interfaces. Various network topologies.
Networking – Protocol
Protocol ( 2.17) is a set of rules, which allows computer/controllers/devices to communicate from one to another. Proprietary Protocols developed by systems or computer manufacture to communicate to their OWN hardware and software over a recommended network. Open Protocols opening up protocols means disclosing procedures, structures, and codes and allowing other system developers to write interfaces and share data on their network. Acceptance of an open protocol depends on its quality, features, and services provided.
The OSI Seven Layer Model ( 2.18)
Each layer has a defined set of functions. The model provides a useful common reference to communicate protocol. Most communication protocols including those used in our field today use either all or some of the seven layers of the OSI model.
1. Network-capable Applications produce DATA.
2. Each protocol layer adds a header to the data it receives from the layer above it. This is called encapsulation. Encapsulated data is transmitted in Protocol Data Units (PDUs). There are Presentation PDU’s, Session PDU’s, Transport PDU’s etc.
3. PDU’s are passed down through the stack of layers (called the stack for short) until they can be transmitted over the Physical layer.
4. Any layer on one machine speaks the same language as the same layer on any other machine, and therefore can communicate via the Physical layer.
5. Data passed upwards is unencapsulated before being passed farther up.
6. All information is passed down through all layers until it reaches the Physical layer.
7. The Physical layer chops up the PDU’s and transmits the PDU’s over the wire. The Physical layer provides the real physical connectivity between machines over which all communication occurs.
2.18 OSI Seven Layer Model
The Physical layer provides for physical connectivity between networked devices. Transmission and receipt of data from the physical medium is managed at this layer. The Physical layer receives data from the Data Link Layer, and transmits it to the wire. The Physical layer controls frequency, amplitude, phase and modulation of the signal used for transmitting data, and performs demodulation and decoding upon receipt. Note that for two devices to communicate, they must be connected to the same type of physical medium (wiring). Ether to Ether, FDDI to FDDI etc. Two end stations using different protocols can only communicate through a multi-protocol bridge or a router. The physical layer is responsible for two jobs:
1. Communication with the Data link layer.
2. Transmission and receipt of data.
The Datalink Layer is the second layer of the OSI model. The datalink layer performs various functions depending upon the hardware protocol used, but has four primary functions:
1. COMMUNICATION with the Network layer above.
2. SEGMENTATION of upper layer datagrams (also called packets) into frames in sizes that can be handled by the communications hardware.
3. BIT ORDERING. Organizing the pattern of data bits before transmission (packet formatting)
4. COMMUNICATION with the Physical layer below.
This layer provides reliable transit of data across a physical link. The datalink layer is concerned with physical addressing, network topology, physical link management, error notification, ordered delivery of frames, and flow control.
Network Layer establishes and terminates connections between the originator and recipient of information over the network. Assign unique addresses to each node on the network. The addresses identify the beginning and end of the data transmission packets. Outbound data is passed down from the Transport layer, is encapsulated in the Network layer’s protocol and then sent to the Datalink layer for segmentation and transmission. Inbound data is de-fragmented in the correct order, the IP headers are removed and then the assembled datagram is passed to the Transport layer. The Network layer is concerned with the following primary functions:
1. Communication with the Transport layer above.
2. Management of connectivity and routing between hosts or networks.
3. Communication with the Datalink layer below.
Transport Layer maintain reliability on the network and enhances data integrity by delivering error-free data in the proper sequence. It may use a variety of techniques such as a Cyclic Redundancy Check, windowing and acknowledgements. If data is lost or damaged it is the Transport layer’s responsibility to recover from that error. Functions:
1. Communicate with the Session layer above.
2. Detect errors and lost data, retransmit data, reassemble datagrams into datastreams
3. Communicate with the Network layer below.
The session layer tracks connections, also called ‘sessions’. For example: keep track of multiple file downloads requested by a particular FTP application, or multiple telnet connections from a single terminal client, or web page retrievals from a Web server. In the World of TCP/IP this is handled by application software addressing a connection to a remote machine and using a different local port number for each connection. The session performs the following functions:
1. Communication with the Presentation layer above.
2. Organize and manage one or more connections per application, between hosts.
3. Communication with the Transport layer below.
The Presentation layer handles the conversion of data formats so that machines can ‘present’
data created on other systems. For example: handle the conversion of data in JPG/JPEG format to Sun Raster format so that a Sun machine can display a JPG/JPEG image. The Presentation layer performs the following functions:
1. Communication with the Application layer above.
2. Translation of standard data formats to formats understood by the local machine.
3. Communication with the Session layer below.
The application layer is the application in use by the user. For example: a web browser, an FTP, IRC, Telnet client other TCP/IP based application like the network version of Doom, Quake, or Unreal. The Application layer provides the user interface, and is responsible for displaying data and images to the user in a recognizable format. The application layers job is to organize and display data in a human compatible format, and to interface with the Presentation layer.
|Protocol||Intended Market||Controlled by||Developed by|
|BACnet||Buildings||ASHARE Committee||ASHARE Committee|
|DNP3||Utilities Power Generation||DNP3 Users Group||Westronic|
|EIB – European Installation Bus||Buildings||Siemens||Siemens|
|OPC – OLE for Process Control||Manufacturing||OPC Foundation||Microsoft and other companies|
|Profibus||Industrial, Buildings||EN50170, DIN19245||ABB, Siemens, Honeywell|
|CAN||Industrial, Buildings||ISO 11898/11519||BoschAG|
Message Frame Format
Fig 2.19 Message Frame Format
Master-Slave Protocol (2.20) – The control station is called “master device”. Only master device can control the communication. It may transmit messages without a remote request. No slave device can communicate directly with another slave device.
2.20 Master-Slave Protocol
Peer-to-Peer Protocol (2.21) – All workstations are loaded with the same peer-to-peer network operating system. Each workstation configured as service requester (client), service provide (server), or even BOTH.
2.21 Peer-to-Peer Protocol
Client-Server Protocol (2.22) – Client workstation are loaded with specialized client software. Server computers are loaded with specialized server software designed to be compatible with client software.
2.22 Client-Server Protocol
The CSMA/CE Protocol is designed to provide fair access to the shared channel so that all stations get a chance to use the network. After every packet transmission all stations use the CSMA/CD protocol to determine which station gets to use the Ethernet channel next. CSMA/CD likes a dinner party in a dark room: Everyone around the table must listen for a period of quiet before speaking (Carrier Sense). Once a space occurs everyone has an equal chance to say something (Multiple Access). If two people start talking at the same instant they detect that fact, and quit speaking (Collision Detection). IEEE 802.3 standard covers CSMA/CD.
Switched Ethernet – nodes are connected to a switch using point-to-point connections, When a frame arrives at the switch, the control logic determines the transmit port. If the transmit port is busy, the received frame is stored in the queue which is a First-in First-out (FIFO) queue. The memory to store pending frames is obtained from a shared memory pool. In case the memory is full, the received frame is dropped.
Networking – Cables
Copper wire pairs are the most basic of the data media.
• Two wire untwisted pair
The insulated wire conductors run in parallel, often in a moulded, flat cable. Normally used over short distances or at low bit rates, due to problems with crosstalk and spurious noise pickup. Performance in multiple conductor cables is enhanced by dedicating every second cable as a ground (zero volt reference), and by the use of electrically
1. A single wire is used for the signal transmission/reception
2. A common reference level/point is existed between the transmitter and receiver
3. It is the simplest connection technique but it is sensitive to noise, interference, loss, and signal reflection
4. It is suitable for short distance and low data rate application (Normally less than 200Kb-meter/s)
• Twisted Pair
The insulated conductors are twisted together, leading to better electrical performance and significantly higher bit rates than untwisted pairs. UTP is unshielded, like telephone cable, whilst STP is shielded and capable of higher bit rates. Systems using banetworkced signals obtain the highest bit rates.
1. Twisting or wrapping the two wires around each other reduces induction of outside interference
2. 1 to 5 twists per inch is quite typical • Cheap and moderate bit rate applications
3. For a few km distance the bit rate can be up to 10Mb/s, and 100Mb/s can be achievable for short distance applications like 100m
2.23 Two wire untwisted pair and Twisted Pair
Unshielded Twisted Pair (UTP):
•Composed of two of more pairs of wires twisted together
•Signal protected by twisting of wires
•Impedance of 100W
•Recommended conductor size of 24 AWG
2.24 Unshielded Twisted Pair
Cat5e: 100MHz ANSI/TIA/EIA-568-B.1
•Susceptibility to damage
•Limited flexibility for MACs (move, add and change)
•Distance limit of 10m
•Avoid in high traffic areas, heavy furniture locations, cross undercarpet power on top at 90 degrees
2.25 Cat3, Cat5e and Cat6 Cable
Screened Twisted-Pair (ScTP):
•Characteristic impedance of 100 W
•Four pair 22-24 AWG solid conductors
•Mylar/aluminum sheath around all conductors
•Drain wire that must be grounded
2.26 Screened Twisted-Pair
Shielded Twisted Pair (STP):
•Composed of two pairs of wires
•Metal braid or sheathing that reduce electromagnetic interference (EMI)
•Must be grounded
•Characteristic impedance of 150 W
•Conductor size is 22 AWG
•Electrical performance is better than UTP (300MHz bandwidth)
•Harder to handle – thick and heavy
2.27 Shielded Twisted Pair
Coaxial Cable (Coax): Composed of insulated center conductor with braided shied. It provides high degree of protection against EMI.
•Because the electrical field associated with conduction is entirely carried inside the cable; problems with signal radiation are minimized very little energy escapes, even at high frequency.
•There is little noise pick up from external sources. Thus, higher bit rates can be used over longer distances than with twisted pairs
2.28 Coaxial Cable
Series 6 (Video):
•Characteristic impedance of 75 ohms
•Mylar/aluminum sheath over the dielectric
•Braided shield over the mylar
•18 AGW solid-center conductor
2.29 Series 6
Series 11U (Video):
•Characteristic impedance of 75ohms
•Mylar/aluminum sheath over the dielectric
•Braided shield over the mylar
•14 AWG solid-center conductor or 18 AWG stranded-center conductor
2.30 Series 11U
•50 ohms characteristic impedance
•Multiple mylar/aluminum sheath over the dielectric
•Multiple braided shield over the mylar
•11 AWG solid-center conductor
2.31 Series 8
Series 58 A/U:
•50 ohms characteristic impedance
•Mylar/aluminum sheath over the dielectric
•Braided shield over the mylar
•20 AWG solid-center conductor
2.32 Series 58 A/U
Fibre Optics: Higher bandwidth and much lower signal loss than copper conductors. It used in the backbone or in horizontal runs of huge control network.
•The data is carried as pulses of light from a laser or high-power LED.
•Optical fibre is non-electrical, hence is completely immune from electrical radiation and interference problems. It has the highest bit rate of all media.
•The fibre consists of an inner glass filament, contained inside a glass cladding of lower refractive index, with an outer protective coating. In a step index fibre, there is a sudden transition in refractive index. A graded index fibre has a gradual transition from high to low index, and much higher performance.
•Most common fibres are multimode, where the inner fibre is larger than the wavelength of the light signal, allowing multiple paths to exist, and some dispersion to limit the obtainable bit rate. In single mode fibres, the inner fibre is very thin, and extremely high bit rates (several Gbps) can be achieved over long distances.
2.33 Fibre Optics
Multimode Fibre: Composed of a 50 or 62.5 micron core and 125 micron cladding. It commonly used in horizontal and intrabuilding backbones. It has distance limitation of 2000m. Often uses a light-emitting diode (LED) light source.
•The center core is much larger and allows more light to enter the fiber
•Since there are many paths that a light ray may follow as it propagates down the fiber, large time dispersion may occur which results in short distance applications or bandwidth reduction
•Because of the large central core, it is easy to couple light into and out of the this type of fiber
•It is inexpensive and simple to manufacture
•Typical value: 62.5/125
Multi-Mode Graded Index
•It is characterized by a center core that has non-uniform refractive index
•The refractive index is maximum at the center and decreases gradually towards the outer edge
•The performance is a compromise between single-mode step index fiber and multi-mode step index fiber
2.34 Multi-Mode Fibre
Singlemode Fibre: It composed of a 6 or 9 micron core and 125 micron cladding (say8/125 or 9/125). It used for distances up to 3000m. It uses a laser light source.
•Small core diameter so that there is essentially only one path that light may Take care,as it propagates down the fiber
• There is minimum time dispersion because all rays propagating down the fiber with the same delay time and results in wider bandwidth (i.e. high bit rate)
• Because of the small central core, it is difficult to couple light into and out of the this type of fiber
• It is expensive and difficult to manufacture
• Typical value: 9/125
2.35 Singlemode Fibre
|4-wire phone station wire||Quad RYGB||3kbps||300ft||RJ-11||Voice application|
|Flat Gray Modular||Flat Satin, tele. cable||13.3kbps||10-20ft||RJ-11 / RJ-45||Short data cables|
*Twist prevent interference
*Voice grade usually not for data
|STP||STP||16Mbps||100ft||RJ-45 / IBM data connector||*Shielding reduces interference
|Coax-thick||Frozen yellow garden hose||10Mbps||500ft||AUI||Original Ethemet cabling|
|Coax-thin||RG-58 Cheapenet||10Mbps||200ft||BNC||*Looks like cable TV
*Easier to work with than thick coax.
|Coax-then||RG-62||2.5Mbps||200ft||BNC or IBM data connector||Similar to RG-58, but not interchangeable|
|Fibre-optic cable||Fibre Glass||Several Gbps||Several km||SI / ST / SMA905 / SMA906||*Difficult to install
*Virtually error free
2.36 LAN Media Technology Analysis
The definition of open system is that system implements sufficient open standards for interfaces and services. It is supporting formats to enable properly engineered components to be utilized across a wide range of systems and to interoperate with other components. And that system in which products and services can be mixed and matched from set of suppliers; and supports free exchange of information/data between different systems without inserting gateways or proprietary tools. Some benefits from Interoperability:
•Devices can be shared among different subsystems.
•Reduce cost, shorten installation time, and reduce complexity as parts are being reduced.
•Devices in different subsystems can interact with each other; therefore, new breed of applications can be created easily.
•Owners can choose the best-of-breed products from different manufacture.
•Elimination of gateway dependency, especially during system upgrade.
•Allow move-add-change relatively easy, hence lower life-cycle costs.
The characteristics of open system are well defined, widely used, preferably nonproprietary interfaces/protocols; Use of standards which are developed/adopted by recognized standards bodies or the commercial market place; and definition of all aspects of system interfaces to facilitate new or additional systems capabilities for a wide range of applications.
The different between proprietary protocols and open protocols; For Proprietary protocols, most manufactures have their own proprietary protocols within their systems, so no communication between Systems unless a gateway is deployed. For open protocols, it allows systems of different manufacturers to communicate. Systems communicate with each other.
2.1 BMS – Open System – Modbus:
A high-level protocol for industrial networks developed in 1979 by Modicon (now Schneider Automation Inc.) for use with its PLCs. It is providing services at layer 7 of the OSI model. Modbus defines a request/response message structure for a client/server environment. It is the most commonly available means of connecting industrial electronic devices. Several common types of Modbus:
l Modbus RTU
n A compact, binary representation of the data.
l Modbus ASSII
n Human readable & more verbose.
n Very similar to Modbus RTU but is transmitted within TCP/IP data packets.
2.2 BMS – Open System – ARCent:
Attached Resource Computer NETwork (ARCnet) was founded by the Data point Corporation in late 1970s. ARCnet was one of the topologies used early on networking and is rarely used as the topology of choice in current LAN environments. ARCnet, however, still is a solid, functional and cost effective means of networking. Each device on an ARCnet network is assigned a node number. This number must be unique on each network and in the range of 1 to 255. ARCnet manages network access with a token passing bus mechanism. The token (permission to speak on the network) is passed from the lowest number node to higher number nodes in ascending order. Lower numbered addresses get the token before the higher numbered addresses. Network traffic is made more efficient by assigning sequential numbers to nodes using the same order in which they are cabled. Choosing random numbers can create a situation in which a node numbered 23 can be a whole building away from the next number, 46, but in the same room as numbers 112 and 142. The token has to travel in a haphazard manner that is less effective than if you numbered the three workstations in the same office sequentially, 46, 47, and 48, and the workstation in the other building 112. With this configuration, the packet stays within the office before venturing on to other stations. A maximum time limit of 31 microseconds is allotted for an ARCnet signal. This is also called a time-out setting. Signals on an ARCnet can travel up to 20,000 feet during the 31-microsecond default time-out period. You can sometimes extend the range of an ARCnet by increasing the time out value. However, 20,000 feet is the distance at which ARCnet signals begin to seriously degrade. Extending the network beyond that distance can result in unreliable or failed communication. Therefore, the time-out parameter and cabling distance recommendations should be increased only with great caution.
An ARCnet network is used primarily with either coax or twisted pair cable. Most older ARCnet installations are coax and use RG-62 A/U type cable terminated with 93 Ohm terminators. Twisted pair (UTP) installations are newer and use stranded 24 or 26 gauge wire, or solid core 22, 24, or 26 gauge type cable terminated with 100-Ohm terminators. Many ARCnet networks use a mix of both coax and UTP cabling. UTP cable is simple to install and provides a reliable connection to the devices, whereas coax provides a means to span longer distances. Typical ARCnet installations are wired as a star. ARCnet can run off a linear bus topology using coax or twisted pair as long as the cards specifically support BUS. The most popular star-wired installations of ARCnet run off two types of hubs:
1. Passive hubs cannot amplify signals. Each hub has four connectors. Because of the characteristics of passive hubs, unused ports must be equipped with a terminator, a connector containing a resistor that matches the ARCnet cabling characteristics. A port on a passive hub can only connect to an active device (an active hub or an ARCnet device). Passive hubs can never be connecte