Understand the Basic concept of BMS system

Understand the Basic concept of BMS system 

What is a BMS or Building Management System?
In a nutshell, BMS otherwise called as BAS or building automation is computer-based control system which reduces the manpower, automate the system, and saving the energy consumption in building by monitoring and controlling the mechanical and electrical equipment in modern day buildings or any industrial plants.
Not only that but BMS helps to
·        Increasing productivity.
·        Increasing the equipment lifetime and better performance.
·        Identifying the systems faults earliest.
·        Managing the hotel tenants in an effective manner.
Nowadays any modern-day buildings built with BMS to support facilities management to accomplish the maintenance and save the energy in building from one place of computers.

Any BMS software or system must provide the following facility to the operator

• Monitoring and controlling connected equipment in the building. 

• The alarm should be a popup in operator workstation for any critical faults in the system. 

• Any types of equipment on, off status and alarm should be logged or stored in PC to retrieve later.

• Scheduling the equipment to on and off automatically by preset time. 

• User interface graphics should be available in order to visualize the field equipment to monitor for BMS operator easily. 

BMS or BAS system monitor and/or controls the following system in buildings

• HVAC (Heating, Ventilation, and Air-conditioning or all supply and exhaust fans, ACs etc). 
• Lighting control system. 
• Fire alarm system. 
• Firefighting system. 
• Security control system. 
• CCTV system.
• Lift control system. 
• Pumping system. 
• Water tanks level. 
• Irrigation system. 
• Electrical meters.
• Water Leak detection system.
• Split units. 
• UPS units.
• VFD-Variable frequency drives. 
• VRF/VRV-Variable refrigerant flow or volume (both are same but each term copyrighted by a different vendor) 
• And any other system which has provision for BMS to control and monitor. 

Main components of the BMS System

1.     Hardware
·        DDC-Direct digital controller
·        Sensors
·        Actuators
·        Cables to connect sensors, actuators to DDC.
·        HMI display-Human machine interface.
·        PC Workstation
·        Server to save the large database.

2. Software

3. Networking protocols

·        Programming or configuration tools.
·        Graphics or User interface.
·        TCP/IP– Transfer control protocols/Internet Protocol.
·        BACnet– Building automation controller network-ASHRAE
·        Modbus
·        LONworks
·        CANbus
·        and numerous protocols available.
Don’t worry about the various protocols, this all protocol doing the same task to transfer data from one device to another device. 

BMS System architecture in the modern-day building

However, BMS System controls and monitor all the electrical and mechanical systems in buildings from BMS workstation or HMI(Human Machine Interfaces), but not directly because each system has its own functionality and unique purpose like

• HVAC System helps to facilitate and provide comfortable and healthy air conditioning to tenants.
• The lighting control system which has a variety of lightings in buildings that needs to be on and off effectively and save energy while tenants not available.
• CCTV helps to facility management to secure the building
• Access control systems may also be used to control access into certain areas located within the interior of buildings.
• A fire alarm system is the life safety system to warn people by audio and visual to protect their lives from fires, smoke, carbon mono oxide and other toxic elements for the human.
• In case of fire Firefighting system aims to protect human life and property in the building by a large amount of water and other gas.
• UPS is to provide to the uninterrupted power supply in the building for electrical equipment.
• Pumping system used in the building to pump the water to the required area.
• still tons of systems evolved in the modern-day building to facilitate the people.

All systems have its own controllers and processing system due to the different functionality of each system.

So BMS controllers or device designed for controlling and monitoring the HVAC system and other small systems and integrate all other systems through dedicated networking protocols like BACnet, Modbus etc.

General BMS System architecture with Levels

• Management Level: This is the front end for operator and engineer used to visualize the graphics for controlling and monitoring the systems which have computer workstation, server, web browser, printers.

• Automation Level: BMS Router and other main controllers connected in building network integrate third-party system and connect BMS devices

• Field devices Level: this is Level where BMS controllers connect to field systems sensors, actuators, and other panel circuits to monitor and control.

Simple Real Time example for BMS System

Any modern day building client provides huge specifications for BMS System, whereas here I am going to take simple requirement to monitor and control the sequence of Air Handling unit. 

Let us see below the requirement of the client to monitor and control the sequence in BMS System.

Before we go detailed about how to design the BMS System for the requirement. let us see some basics components of the AHU-Air handling unit.

AHU is an HVAC system which consists of the duct, fan, filter, cooling coil, heating element,humidifier, sound attenuators, dampers, valves and many more to regulate the air into the room by heating, ventilation and conditioning to distributes the conditioned air through the building and returns it to the AHU and also called as centralised AC in modern-day building.

Duct – It is the collection of metallic tubes that interconnected and distributes the heated/cooled air to the required rooms.

In order to monitor the duct air temperature in fresh, return and supply duct. we have to install the duct temperature sensor in the duct.

Fan Motor– Blower is used to circulate the air from fresh and return duct to the supply duct.

This fan motor controlled and monitored by the separate electrical panel by the designed electrical circuit with help of electrical relay and contactor and providing an option to BMS system to

• On/Off the fan.

• Monitor the fan running status.

• Monitor the Fan motor overload fault status and many more.

Filter– It is one of the main components in AHU to prevent the dust and dirt particles to enter in the AHU.

When the AHU fan motor started, the fresh outside air supplied into the duct where filter components used to filter the dirty particles continuously and in order to monitor the filter extreme dirty condition,

DPS switch is used to install across the filter and provide a signal to BMS when the filter gets dirty(technically DPS-Differential pressure switch will send the signal to BMS when the pressure reached more than pre-set across the filter and this same function can be used to monitor the fan status.

Now we Read about How DPS used to monitor fan and filter status

Heating/Cooling element- It is used to cool or heat the water that entered in the coil so that air in the duct can be heated or cooled based on the user requirement.

Either heating or cooling water enters into the coils are controlled and monitored by valves on the pipe with help of valve actuator.

Dampers- An HVAC damper is a movable plate, located in the ductwork, that regulates airflow and directs it to areas that need it most.

Damper opening and closing position controlled electrically with the help of damper actuators and this actuators have terminal for control from BMS and terminal to monitor the feedback of position.

System Description:

The variable speeds Air Handling Units are used to serve air conditioning need for all area of buildings

The Air Handling Unit comprises:

·        Variable Speed Supply Fan

·        Chilled water coil with the 2-Way modulating control valve

·        Duct mounted supply air pressure sensor

·        Outdoor & re-circulating Air modulating damper

·        Carbon dioxide sensor.

·        Supply and Return Air temperature sensors

·        Supply air differential pressure switch

·        Differential pressure switches for 2 set of filters

System Monitoring and Alarm:

      ·        Software alarms shall be generated at the operator workstation whenever the run status of the supply fan (with differential pressure switch) does not match the current command state.
·        A failure alarm shall occur when the run status of the load shows no operation and the load has been commanded to be on.
·        An advisory alarm shall occur when the run status of the load shows operation and the load has been commanded to be off. All alarms shall be recorded in an alarm log for future review. Provide 15 seconds (adjustable) time delays before generating an alarm.

The sequence of Operation

a. Auto Mode:

When the AHU start is in AUTO mode (i.e. selector switch installed in the MCC must be in Auto Position), the unit is started and stopped from the BMS via a time schedule or BMS override command. When the start for the AHU is initiated, the control program residing in the controller follows the following sequence

Start-Up:

The following sequence follows with a preset time interval per interlock equipment start-up:
1) Check Supply fan trip signal – Normal State
2) Supply Air Damper –Open Position
3) Outdoor Air Damper –Open Position
4) Return Air Damper – Open Position

5) Once the above conditions are satisfied, AHU is enabled to start in Auto mode or using a plant enable button on the graphics in manual mode by the operator. Once enabled, BMS will automatically command supply fan to start.

6) Supply Fan shall start and it’s associated Interlock equipment in sequence. Through the signal from the Diff. Airflow Switch, if airflow is detected, the System will continuously run, if No airflow is detected by the DP Switch, the Supply Fan will de-activated and send an Alarm to the DDC – for “No Airflow” and shut down the whole system including its associated interlocks. If the Air flow switch signal is proved ‘ON’ then BMS will enable control loops.

b. Shutdown Mode:

When the shutdown command for the AHU is initiated, the control program residing in the controller follows the following sequence.
1) Send Stop command to stop the supply fan
2) The outdoor air, return and supply air damper move to close
3) Move chilled water valve to close position

c. Manual (Hand) Mode:

When the AHU is the manual mode, the fans are started and stopped from the AHU control panel. Other control except for fan on/off control shall function as per the Auto mode.

d. Fire / Smoke Mode:

Fire condition is determined by the Fire Alarm Control Panel. AHU will automatically shutdowns the whole system with associated interlocks.

AHU Control

The control program, on the feedback of air handling unit operation, initiates the control algorithm. This algorithm consists of three controls. Each temperature, pressure and ventilation control has its own control loop. The pressure control loop is used to modulate the speed of the supply air fan hence supply air flow. The control loops design to function as per following explanation:

a. Temperature Control loop:

The supply air temperature installed in the duct will relay the measured signal (temperature) to the DDC controller, the DDC controller compares this signal with set-point (adjustable by the operator from BMS central) and generates an analog output to the 2-way modulating cooling valve. Based on the difference between the two values, a proportional-integral program will determine the percentage of the cooling coil valves opening to achieve the desired condition. The default set-point value for the supply air temperature is 13ºC (Adjustable).

b. Pressure Control loop:

The supply air pressure sensor shall be installed in the duct  will relay the measured signal (static pressure) to the DDC controller, the DDC controller compares this signal with the set-point (adjustable by the operator from BMS central) and generates an analog output to the variable frequency drive (VFD) of the supply air fan. Based on the difference between the two values, a Proportional-Integral program will determine the percentage of the fan speed to achieve the desired pressure. The set-point value for the supply air pressure for each AHU shall be adjusted.

c. Ventilation Control loop:

Demand control ventilation employs return air carbon dioxide controlling strategy.

A single carbon dioxide sensor sense carbon dioxide concentration in the return air duct and sent to the DDC controller, the DDC controller compares the signals with return air carbon dioxide concentration (Default carbon dioxide level difference value 400 ppm).

Then DDC controller generates an analogue output to the outside air dampers and returns air damper to modulate, based on the difference between the values, the Proportional integral program will determine the percentage of the modulation of outdoor and return air dampers.

Minimum outdoor air quantity shall be governed either by building pressurization requirement (Input from Building differential pressure sensor) or 20% of the Maximum outdoor requirement of the AHU.

Alarms:

The following minimum alarms shall be generated on BMS
1) Filter Dirty Alarm: This is generated when pressure drop on each filter exceeds the set value to indicate dirt accumulate at filters.
2) Fan Trip Alarm: A normally open “NO” volt free contact at the MCC panel when closed will generate an alarm at the BMS indicating that the fan is tripped
3) Fan Fail: In case the supply air fan fails to start or if the differential pressure switch across

supply fan is not giving the signal according to the command due to any reason then alarm shall be generated. In case of a fan fail alarm on the BMS, due to abnormal behaviour, the DDC controller will latch the alarm. The operator has to acknowledge (reset) the alarm on the BMS once the trouble has been checked and removed. The operator shall not be able to start the AHU until the alarm s acknowledged and reset.

4) Temperature High & Low: Temperature HIGH and LOW alarms shall be generated if the supply/return air temperature rises above or falls below the supply /return air temperature alarm limit.

List of Input and output points are required for the above-discussed sequence of operation for AHU

Some basic terms of digital electronics

• Analog Input: Analog inputs can come from a variety of sensors and transmitters. You can measure a whole bunch of different things. The job of the sensor or transmitter is to transform that into an electrical signal. Here are a few of the things you can measure with analog sensors:

·        Level

·        Flow

·        Distance

·        Viscosity

·        Temperature

• Digital Input: It allows a microcontroller to detect logic states either 1 or 0 otherwise called as VFC-Volt free contact.
• Analog Output: In automation and process control applications, the analogue output module transmits analogue signals (voltage or current) that operate controls such as hydraulic actuators, solenoids, and motor starters.
• Binary Output: it is nothing but relay output from the controller to trigger on and off any equipment.

Now its time to choose the DDC controllers based on the above input and output point list.

Any BMS controllers manufacturer must have the basic controllers types of analogue input-output, binary input, and output controllers either dedicated controllers or mixed of all types in a single controller.

For the above applications, we need to choose controllers that should accommodate 17 AI, 6 BI, 5 AO, and 1 BO(Note that temperature and humidity are two different analogue input)

Once controllers are designed, we need to calculate power load for each controller (available in controller datasheet) and field devices to choose the right transformer rating for our DDC panel.

Next things are to write a program for our controllers to accomplish the above sequence,

First, we need to change English words into the flowchart then we can change it later on the different programming language that required for BMS vendors either ladder logic or functional block or plain English and etc.

Whatever it is any BMS program functionality that will not go beyond the basic digital logic gates.

Flowchart for AHU Control sequence of operation

SSA Integrate - Fire alarms and BAS

SSA Integrate - Fire alarms and BAS

The integration of Building Automation System and fire alarm systems can result in overall reduction in equipment, installation, and maintenance costs while still maintaining the level of safety required for these systems to operate. 

With the advent of smart building technology, heating, cooling, electrical, lighting, security, and other systems need monitoring and intercommunication for optimized efficiency and operation. With sophistication comes the need for a building automation system (BAS) to allow for nearly seamless operation of these various interrelated equipment.

When the fire alarm system takes control of equipment that is not a listed component of the fire alarm control unit, the fire alarm system must either override the natural operating mode of the building equipment or pass off that command via a simple switch or data communications to the building mechanical systems. Likewise, each manufacturer’s BAS has its own protocol for monitoring conditions and communicating operational commands to maintain the proper building environment and efficiency. There are also standard open communication protocols such as LonTalk and BACnet that can be used to communicate with a multitude of equipment from various manufacturers in order to achieve an integrated building system. 

The communication protocol for a fire alarm control unit to communicate to and from its indicating (input), initiating (output), and sometimes notification appliances is typically an analog or digital communications signal carried over what is referred to as a signaling line circuit (SLC). Because communications signals are typically proprietary protocol, each SLC is dedicated to a specific manufacturer’s equipment and cannot include connection of incompatible devices that use a different signal protocol.

Therefore, in order to integrate system alarm and control functions with the BAS in a manner other than relay logic, fire alarm system manufacturers had to also design and support the open communication protocols used for building automation, in a manner that would not compromise the integrity or the operation of the fire alarm system. This process of sharing information between both fire alarm and BAS came to be known as bridging, or open gateway processing. Because of the strict code and listing requirements of fire alarm systems, much of this communication has been primarily limited to one-way communication. However, some manufacturers of both fire alarm and BAS do produce equipment such as gateways that are listed for bi-directional communication with their equipment. 

Make a case of a building with separate building automation and fire alarm systems: When the building engineer receives a call from an occupant complaining about increased temperature or whistling air within the ductwork and finds that the fan is shut down or a damper is closed, the building engineer is more apt to call a controls contractor to investigate the problem before he calls their fire alarm service provider. Should the problem be related to an override of controls by the fire alarm systems, not only does the building engineer have to wait for the controls contractor to diagnose the problem, he also has to call the fire alarm contractor to come out and fix the problem. This process can take time to correct; meanwhile, building occupants are uncomfortable and inconvenienced.

Sometimes this can even lead to finger-pointing between the two service providers as to whose problem it really is. In this scenario, the fire alarm control of a fan or a damper is required to be ahead of the hand-off-auto switch for the power to the equipment so the inadvertent shutdown of the equipment does not inhibit the operation of the fire alarm feature. A failure of the fire alarm system control relay could shut down the fan or close the damper without an alarm being present on the fire alarm system or fault condition occurring on the fire alarm control unit. 

Because many components that affect air and smoke movement within a building are shared between HVAC and fire alarm systems, let’s take a step backward in the evolution of the building process. When building systems are being commissioned for proper operation by either an authority having jurisdiction (AHJ) or an independent third-party group, coordination must occur between multiple trades. At this point in the construction process, each trade is independently looking to complete its own scope of work and more often than not is under pressure to finish the specific scope in a designated timeframe. Sometimes this leaves a disconnect between the fire alarm and mechanical trades that results in disruption during start-up and commissioning. 

The integrated system approach allows for those individuals responsible for controlling air movement to be focused on proofing and balancing the mechanical system, while the fire alarm contractors focus on the detection and annunciation of the alarm events. Much in the same manner as referenced in the previous example, the problems can get resolved more expeditiously and the systems can be brought on-line. 

If we focus on the installation of a building management system (BMS) and a fire alarm system, we see many similarities. Each of these control systems is classified as low-voltage systems that communicate to their respected devices through an analog or digital signal. Their wiring methods and materials are similar, and often their respective equipment is located in the same general area and is performing the same basic functions with one significant difference: the fire alarm system uses individual point addressable monitor and control modules while the BAS uses digital input/output driver assemblies that communicate with different protocols. 

Why is this important? Because the BAS still requires individual pairs of conductors to each point being controlled or monitored by the digital input/output module, resulting in more wire being needed and longer installation time.

When considering SSA system integration, the ability of the BAS to control a smoke control system operation falls under the auspice of the jurisdiction’s building code, often based on the model building codes. The IBC has been adopted by a large portion of the United States and is used in this article as an example. IBC Section 909 covers smoke control systems, the procedures for determining system parameters, the acceptable methods that may be used to accomplish smoke control, and the requirements to document the system’s actual performance. It recognizes that the smoke control system is a life safety system and must maintain the same high level of reliability required for any type of fire protection or fire alarm system.

Section 909 requires smoke control systems to be initiated by sprinkler system or smoke detection system operation, depending on the type of system being designed. It also requires systems providing control input or output to the mechanical smoke control systems to comply with Section 907 (Fire Alarm and Detection Systems) and NFPA 72: National Fire Alarm and Signaling Code, and states that such systems must be equipped with a control unit that complies with UL 864 and has to be listed as smoke control equipment.

Using a fire/smoke damper that is part of an engineered smoke control system complying with International Building Code Section 909 as an example, at each damper location we have a smoke detector for detection of smoke, an actuator that controls the opening and closing of the damper, and an end switch to provide positive confirmation of the damper open and closed position. Because the fire alarm system already needs to have circuitry to this location for individual smoke or duct smoke detectors, that same pair of wires can be used to monitor the open and closed position of the damper, essentially eliminating two pairs of wires back to the BAS controller. The position status signals of the damper can then be transmitted from the fire alarm system, through the gateway, and into the BAS along with the active alarm point information. This leaves the wiring to the actuator as the only BAS wiring needed at the damper location.

As another example, let’s use a stairway pressurization fan that is being controlled by a variable frequency drive (VFD). Typically, a VFD would be connected to the BAS via a digital signal while the fire alarm system would provide override of the VFD using dry contacts to stop it or put it into a smoke mode condition. Allowing the BAS to perform all of the control functions permits the adjustment of the fan speed through the BAS to regulate for atmospheric conditions by employing other equipment connected to the BAS, such a digital differential pressure sensors. Using the BAS solely for control eliminates any connection to the fire alarm system, with the activation commands being sent through the gateway.

Taking advantage of the aforementioned efficiencies gained by integrating the BAS with the fire alarm system requires planning in the design process. This planning process is the same whether it is a design build or a design assist type of project delivery. The building owner and operator must be involved in the process of establishing the design criteria or at the least have influence over it. In a typical design build or design assist process, the integration of these two systems is an afterthought and often never considered. The end user must be made to understand that the efficiencies gained by integration will pay dividends long into the lifecycle of the building.

Integrated systems require enough time to test and to verify that the system interoperability is functioning properly. It is important that the engineer as well as the installing contractor and the equipment vendors understand the impact of these requirements on providing an approved and code compliant installation. 

Due to the complexity of these systems and the required integration, testing must confirm that the functions and sequences work correctly under both automatic and manual modes.

The inspection and testing of integrated systems is usually exasperating and time-consuming, and often requires multiple rounds of retesting before all the deficiencies are corrected. This is often caused due to all of these different systems being completed late in the schedule and not enough time to “get the kinks out” prior to final testing. Anything that can expedite the commissioning process is beneficial to the overall project. 

One of the advantages of using the BAS as an integrated part of the smoke control system is the system’s ability to modify operating conditions to accommodate actual ambient conditions through the use of VFDs. The design of smoke control systems is based on many variable conditions, including temperature, wind conditions, and the quality or “tightness” of the construction. These conditions tend to make testing and adjusting of the smoke control system difficult at best.

Integrating BAS can help minimize test stress by adjusting the fan speed of individual fans through programming. In a situation of excessive stair pressurization, the individual fan can be adjusted to limit its airflow to the stair, resulting in a lower level of pressure affecting door opening forces. Similarly, for individual zone smoke control system performance, the fan speed can be adjusted on a zone-by-zone basis, based on the fire alarm signal received by the BAS. 

The downside to this operation is that the BAS controls are typically located remotely to the fire alarm control panel and the firefighters’ smoke control panel, both of which normally reside in a fire command room. BAS controls and system components are usually located for the convenience of the building’s staff and HVAC equipment. Under test conditions, additional personnel may be required to monitor the BAS controls to make any required modifications. 

While modifying fan output for each smoke zone condition is a more expedient method to obtain approval, it also provides future opportunities to inappropriately change the settings, possibly making the system ineffective. Care must be taken to limit access to this programming and provide logging procedures to document when and why changes are made.

Take a note: Fire condition is determined by the Fire Alarm Control Panel. AHU will automatically shutdowns the whole system with associated interlocks.

Question: How can the reliability of the fire alarm system be maintained while mixing data with other non-emergency inputs?

Answer: In reality the fire alarm system reliability is unaffected by other integrated systems when using the BACnet protocol due to the required use of the gateway interface. The gateway keeps the other signals on the network form affecting the fire alarm system.

Question: Building automation systems are more and more residing on an owner's IT network. If a BACnet gateway is used to interface to the fire alarm system, instead of hardwired connections, this device would reside on the owner's network which is likely not UL listed. Have you come across this concern?

Answer: The BACnet gateway itself is required to be listed, but not the system. So the fire alarm system devices or zones would be connected to the listed gateway and then the other side of the gateway would be connected to the network allowing the objects to be transmitted to the BAS, for example. Once again we are still required to use the listed gateway as the interface but the balance of the non-fire alarm system equipment does not need to be listed for fire alarm use. Having said that there are changes proposed to NFPA 72-2019 that would allow direct connection to the Ethernet or a network under certain conditions. These proposed changes have not yet been officially adopted.

Question: Do you recommend integrating the building fire alarm system and the BAS in an office building that undergo tenant fit-outs on a continuous basis?

Answer: With any system design in any building or occupancy planning is imperative. Knowing beforehand that the occupancy is to be offices and knowing that tenant fit-out occur on a regular basis, it is incumbent on the original system designer to include system changes and expansion in his or her design. Just because frequent changes to a system are expected does not preclude integrating all of the systems. It does require more coordination and provided that happens the systems should remain reliable.

Question: Does OEO override designated and alternate recall operation?

Answer: No, just the opposite. All recall features (elevator lobby smoke detectors for example) would input to the OEO controller and it would relinquish OEO or those floors in recall.

Question: How would elevator shunt trip for a sprinkled hoistway or elevator equipment room operation work into the OEO sequence of operation?

Answer: As stated previously, when these types of operations occur during or prior to OEO, these operations would take priority over the OEO and all OEO for the affected elevators would cease and all signs and voice messages would revert to “Do Not Use The Elevators, Use The Stairs” operation. 

Question: How would the use of BACnet interface to emergency control systems, requiring supervision of control wiring, address this code requirement?

Answer: NFPA 72-2019 (and previous editions) require supervision to within 3 ft of the controlling device or no supervision if the device operation is fail-safe, meaning if the connection to the device is severed, the emergency device operates as required. The gateway could be determined as the connection to the controlling device and as long as that was within 3 ft of the controller it would be considered code-compliant. This is unlikely to happen and other design considerations will need to be considered to ensure that the performance of the emergency control system is code compliant. Given the many types of configurations, there can be no one definitive answer to the problem until the actual field condition is evaluated.