Building Management Systems Essay
A BMS consists of software and hardware; the software program, usually configured in a hierarchical manner, can be proprietary, using such protocols as C-bus, Profibus, and so on. Vendors are also producing BMS’s that integrate using Internet protocols and open standards such as DeviceNet, SOAP, XML, BACnet and Modbus. A BMS is most common in a large building. Its core function is to manage the environment within the building and may control temperature, carbon dioxide levels and humidity within a building.
As a core function in most BMS systems, it controls heating and cooling, manages the systems that distribute this air throughout the building (for example by operating fans or opening/closing dampers), and then locally controls the mixture of heating and cooling to achieve the desired room temperature. A secondary function sometimes is to monitor the level of human-generated CO2, mixing in outside air with waste air to increase the amount of oxygen while also minimising heat/cooling losses. Systems linked to a BMS typically represent 40% of a building’s energy usage; if lighting is included, this number approaches 70%.
BMS systems are a critical component to managing energy demand. Improperly configured BMS systems are believed to account for 20% of building energy usage, or approximately 8% of total energy usage in the United States. As well as controlling the building’s internal environment, BMS systems are sometimes linked to access control (turnstiles and access doors controlling who is allowed access and egress to the building) or other security systems such as closed-circuit television (CCTV) and motion detectors.
Fire alarm systems and elevators are also sometimes linked to a BMS, for example, if a fire is detected then the system could shut off dampers in the ventilation system to stop smoke spreading and send all the elevators to the ground floor and park them to prevent people from using them in the event of a fire. In this report it is discussed the building management system (BMS) implemented in Administration Building of Trelleborg Lanka (Pvt) Ltd. It is a distributed control system with a computerized network of electronic devices.
The BMS was setup is to control, monitor and optimize building service such as Lighting, Air conditioning, Fire security, CCTV system, etc. Main objectives were as follows. ? Good control of internal comfort conditions ? Zonal control ? Increased staff productivity ? Effective monitoring and targeting of energy consumption ? Effective response to HVAC-related complaints ? Flexibility on change of building use ? Central control and monitoring of building ? Time saving ? Low operating cost ? Efficient use of building resources and services Rapid alarm indication and fault diagnosis Systems linked to the BMS represent 80% of a building’s energy usage. Fire alarm systems and elevators are also linked to the BMS, for example, if a fire is detected then the system could shut off dampers in the ventilation system to stop smoke spreading and send all the elevators to the ground floor and park them to prevent people from using them in the event of a fire. The BMS comprises: ? Power system ? Lighting system ? Heating, Ventilation and Air-conditioning system ? Security system Fire alarm system ? Elevators etc. 2. 0 SENSOR AND ACTUATORS USED ? Temperature Transducers [pic] [pic] ? Pressure sensors [pic] [pic] ? Humidity Sensor ? Differential Pressure sensors [pic] [pic] [pic] [pic] ? Humidity Transducers [pic] [pic] [pic] [pic] ? Level sensors ? CO2 sensor ? Flow Meter ? CCTV Cameras ? Light sensors ? Occupancy sensors ? Water Pumps ? Valve actuators ? Fans 3. 0 DETAILS OF CONTROLLERS/DDC USED Inputs allow the controller to read temperatures, humidity, pressure, air flow, and other essential factors.
The outputs allow the controller to send command and control signals to slave devices, and to other parts of the system. Inputs and outputs are digital or analog. The BMS is facilitated with a System/Network controller as this is a Supermarket/Office building. System controllers provide general purpose feedback loops, as well as digital circuits. System/Network controllers are applied to control more mechanical systems such as an Air Handler Unit (AHU), boiler, chiller, etc. Terminal Unit controller is used for control of lighting. |POINT SCHEDULE -BUILDING AUTOMATION SYSTEM (TRELLEBORG LANKA (PVT) LTD | | | | | | | | | | | |DIGITA|DIGITA|ANALOG |ANALOG| | | | | | |L |L |INPUT |OUTPUT| | | | | | |INPUT |OUTPUT| | | | | | | | |DI |DO |AI | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | [pic] 4. 0 SOFTWARE, GUI AND COMMUNICATION PROTOCOLS USED Open protocols were used. ? DeviceNet ? XML ? simple graphical interface 5. 0 DRAWBACKS OF THE SYSTEM ? Confusion is higher about responsibility of errors and faulty point identification when things go wrong since the open protocols were used. ? More than one points of contacts for any problem with BMS. ? Software and hardware was provided by different manufactures according to the requirements indicated in the point schedule. 6. 0 DISCUSSION
The BMS implemented in Administration Building of Trelleborg Lanka (Pvt) Ltd comprises above mentioned mechanical and electrical services in order to provide the facilities necessary for maintaining a comfortable working environment. Basic controls took the form of manual switching, time clocks or temperature switches that provide the on and off signals for enabling pumps, fans or valves etc. The purpose of the Building Management System (BMS) was to automate and take control of these operations in the most efficient way possible for the occupiers, within the constraints of the installed plant. The BMS is a “stand alone” computer system that calculates the pre-set requirements of the building and control the connected plant to meet those needs. Its inputs, such as temperature sensors and outputs, such as on/off signals are connected into outstations around the building.
Programmes within these outstations use this information to decide the necessary level of applied control. The level of control via the BMS is dependent upon the information received from its sensors and the way in which its programmes tell it to respond to that information. As well as offering a precise degree of control to its environment, it can be made to alarm on conditions that can’t meet specification or warn of individual items of plant failure. Occupancy times for different areas are programmed into the Building Management System such that the plant is brought on and off to meet the occupier requirements. These times are often under optimum start control.
This means that the chilled water pumps, AHU, etc are enabled, at a varying predetermined time, to ensure that the cooled space is at the set desired temperature for the start of the day. The Building Automation System therefore, based on the outside air temperature the space temperature and the building structure, determines the AC plant start time. Occupied, Unoccupied are the two operating modes for the building automation system. Occupancy is usually based on time of day schedules. In Occupancy mode, the BMS aims to provide a comfortable climate and adequate lighting, often with zone-based control so that users on one side of a building have a different thermostat than users on the opposite side.
A temperature sensor in the zone provides feedback to the controller, so it can deliver cooling as needed. Lighting can be turned on and off with the building automation system based on time of day by occupancy sensors and timers. One typical example is to turn the lights in a space on for a half hour since the last motion was sensed. A photocell placed outside a building can sense darkness, and the time of day, and modulate lights in outer offices and the parking lot. Air handlers mix return and outside air so less temperature change is needed. This can save money by using less chilled water. Some external air is needed to keep the building’s air healthy.
Analog temperature sensors have been placed in the space, the return and supply air ducts. Actuators are placed on chilled water valves, the outside air and return air dampers. The supply fan is started and stopped based on temperatures and building pressures combination. The “constant volume air handling unit,” are used. CAVs open and close dampers and water-supply valves to maintain temperatures in the building’s spaces. They cool the spaces by opening or closing chilled water valves that feed their internal heat exchangers. Generally one CAV serves several spaces. Chilled water is used to cool a building’s air and equipment. The chilled water system has two chillers and pumps.
Analog temperature sensors measure the chilled water supply and return lines. The chillers are sequenced on and off to chill the chilled water supply. Two cooling towers and pumps are used to supply cool condenser water to the chillers. The condenser water supply to the chillers has to be constant so, speed drives are used on the cooling tower fans to control temperature. Proper cooling tower temperature assures the proper refrigerant head pressure in the chiller. Analog temperature sensors measure the condenser water supply and return lines. The building automation system has alarm capabilities. If an alarm is detected, it is programmed to notify someone. Notification is through a computer and audible alarm.
Fire and smoke alarm systems are hard-wired to override building automation. The hot water system supplies heat to hot water heating coils. The hot water system has a boiler and pumps. Analog temperature sensors are placed in the hot water supply. The boiler and pumps are sequenced on and off to maintain supply. ———————– Name : A. P. W. Jayasekara(09/8660) P. G. C. Karunathilake(09/8663) W. M. A. S. Wijethunga(09/8678) T. N. Walpita(09/8676) Course : MSc in Electrical Engineering-Department of Electrical Engineering, University Of Moratuwa. Lec. By : Prof. Lanka Udawatta. Date : 2010-08-14 ASSIGNMENT Building Management System – EE5118