BAS for Energy Saving
The article highlights the effective utilization of BAS for energy saving opportunities related with HVAC system. It is to be understood that not necessarily fully automated BAS system will contribute entirely in energy saving as compared with partially automated BAS, whereas the energy efficiency should be taken into account at design engineering stage and then get the operation excellence through BAS…
- Swapnil S Deorukhkar
Building Automation is the automatic centralized intelligent monitoring & control of a building’s technical systems & services such as Heating, Ventilation and Air Conditioning (HVAC), lighting and other systems through a Building Management System (BMS) which is also known as Building Automation System (BAS). In today’s world of emerging technologies specific to the building energy consumption and managing the various services with remote operation control strategies and monitoring the same, building automation plays a vital role in effectively managing the various services. These services includes Central Air Conditioning equipment, Boilers, Hot Water Generators, Ventilation Fans, Exhaust Blowers, CCTV, Fire & Alarm System, Public Alarm System, Lighting, Lifts, Elevators, Escalators, DG Sets etc.
Since the major power consumption for a typical commercial building belongs to HVAC plant and could be around 60 % to 70 % of total facility power consumption, application of BAS for HVAC monitoring and control becomes more significant from energy saving and demand management perspective. The HVAC plant mainly consist of chillers or other central AC units and associated ancillary equipment such as primary, secondary chilled water pumps, condenser water pumps, cooling towers, AHUs, ventilation fans and TFAs etc. The type and capacity of air conditioning system depends on site dynamics. Controllers regulate the performance of various facilities within the building environment which includes:
• Mechanical Systems
• Plumbing Systems
• HVAC Systems
• Electrical System & Meters
• Security System
• Surveillance System
• Fire Alarm
Figure 1 illustrates the wide range of BAS applications to a commercial building.
Figure 1: The wide range of BAS applications to a commercial building
The building automation system should play a vital role in automating system operation and optimizing the energy consumption of these HVAC utility equipment either by efficient sequence of operation to maintain the desired cooling conditions and meeting the demand as well as meeting the load variations that are primarily due to occupational diversity or seasonal variations etc. Further, monitoring the operation and consumption data results in improving occupant control, lifecycle of utility equipment and reduced operating cost. Many upcoming new green buildings have now been built to accommodate BAS to get energy, air and water conservation characteristics.
This particular article will specifically highlight the effective utilization of BAS for energy saving opportunities related with HVAC system. It is to be understood that not necessarily fully automated BAS system will contribute entirely in energy saving as compared to partially automated BAS, whereas the energy efficiency should be taken into account at design engineering stage and then get the operation excellence through BAS.
BAS Integration & Connectivity
To get the required data from field devices or equipment, the communication needs to be established between Human Interface Unit which is the end user and field devices with the help of various controllers. Controllers are specific purpose based small computers with input and output capabilities. The input ports receive the signals from field devices and output ports transmit these signals to slave devices for further action. Direct Digital Control (DDC) system is the improved version of control systems which use microprocessors, software and electronic control devices. With the help of DDC the input data can be processed digitally and terminal devices can be effectively controlled. This is commonly used in present HVAC system controls especially for AHUs.
Most Building Automation networks consist of a primary and secondary bus which connects high-level controllers (these can be generic system or network type, terminal unit type or PLC based) with lower-level controllers, sensors, input-output devices and User Interface (generally, a computer workstation for human level interface device with graphical interface). This communication has been accomplished with the help of protocols. In networking, a communications protocol or network protocol is the specification of a set of rules for a particular type of communication. Various type of protocols are used such as ASHRAE’s BACnet protocol or LonWorks as open protocol. SNMP, TCP/IP and Modbus are also some of the specific protocols that are used for particular application based on the type of communication.
This is shown in figure 2 as a typical 3 Tier System Architecture for BAS:
Figure 2: Typical 3 Tier System Architecture for BAS
The field devices which can be various sensors and control devices which include temperature, humidity sensors, pressure transmitters, difference pressure switches, co2 sensors, flow switches, damper and valve actuators, vavs, occupancy sensors etc. The simple example is the photocell installed at a particular location of a building such as staircase, parking area etc will sense the darkness and occupancy and will operate accordingly. The terminal unit controller will receive the signal from photocell or lighting sensor and sends the signal for further process which executes the logic for written for corrective action to be taken and controls the lighting operation through BAS.
The first step towards this is to have as many field devices and sensors to get the required data point or parameter for monitoring or control from a central location. Physical connectivity between devices was historically provided by dedicated optical fiber, Ethernet, ARCNET, RS-232, RS-485 or a low-bandwidth special purpose wireless network. The I/O (Input-Output) summary points is then prepared. IO summary points (Input Output points) are the data points from field devices or equipment for communication purpose which can be digital input output points or analog input-output points. Analog inputs are used to read a variable measurement. Examples are temperature, humidity and pressure sensors which could be thermistor, 4–20 mA, 0–10 volt or platinum resistance thermometer (resistance temperature detector), or wireless sensors.
The user interface involves a workstation or PC having graphic interface with various dashboards or graphs or charts that are crucial for fist level information and further analysis. Complete navigation, monitoring and control can be made available through high level graphic interface. Data collection and reporting with BAS makes task for facility managers more efficient and professional with past trends and dashboards to analyze and troubleshoot the problems, since system failures gets reported in BAS system with correct associated information.
Following are the key benefits of BAS:
I. Simplifies installation
II. Commissioning and future expansion
III. Dramatically reduces implementation time & ensures proper operation
IV. Effectively reduces engineering and maintenance cost
V. Saves time and money for System Integrators
VI. Provides reliability and peace of mind to building owners and ensures energy efficient control strategies
VII. Real time monitoring and control of building operation and performance
VIII. Energy management and reporting
But the highest outputs from a BAS will come with efficient and appropriate design of HVAC equipment as per site dynamics as well as control strategies used for operation. For an example, application of VFD on air handling unit might not necessarily result in energy savings if the AHU is undersigned for an office room having fixed operating hours for which AHU is operated and the AHU is under-designed, which is just maintaining the desired room conditions during winter season only.
Another example is the application of VFD on primary chilled water pump and automating the same through BAS might not necessarily result in energy saving in case the chiller design is with low flow high Delta T and actual head is more than the designed head for a pump.
The lighting control for ON-OFF operation is also to be selected to suit the operation/business requirement such that the CCTV camera installed to capture activity at particular location will not get affected or have any business or security impact by switching OFF the lights.
Because of not having clear understanding of the system, it is observed that the manual override command is often used though having full fledge BAS system and equipment are manually controlled which violets the importance of BAS. This shows the need of understanding the present installed HVAC equipment and their operation as per site conditions then adding the necessary controls for effective and efficient operation of these utility equipment.
With all the field devices and control strategies made available for high end equipment, room automation which is an inherent part of BAS becomes more important to have better control which in turn reflects in further control of high side equipment & control of the same.
The Buildings having these facilities and effective operated BAS are termed as “Smart Buildings” and various ratings such as Silver, Gold, Platinum Green Building ratings or 1 to 5 Star ratings from BEE are available for a facility. This ultimately promotes users for saving more energy and contributing to saving the Environment by carbon reduction.
Hence, BAS is not only the enhanced single point control of the systems/equipment but is also a valuable source of information for facility managers and higher management from operation, historical data and any critical or failure incident point of view.
The various reports that can effectively be generated from BAS are:
• Operational data for an equipment/system (with available data points that are integrated with the system)
• Historical trend (graphs/charts) for consumption or variation of any operational parameter of an equipment/system
• Incident report
• Alarms and/or alerts
• Operating hours or ON-OFF trend
This is called as the advanced reporting system in today’s world of improved technologies.
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