Showing posts with label BAS. Show all posts
Showing posts with label BAS. Show all posts

Wednesday, April 14, 2021

Intelligent Building Looks

 Intelligent Building Looks

Over the past 20 years, many different buildings have been labeled as intelligent. However, the application of intelligence in buildings has yet to deliver its true potential. For the last three decades, the so-called intelligent buildings (IBs) were only a conceptual framework for the representation of future buildings. However, today, IBs are rapidly becoming inherent constituents of influential policies for design and development of future buildings. Undeniably, urbanized areas are expected to be highly influenced by IBs in order to promote smart growth, green development and healthy environments (Hollands 2008; Choon et al. 2011; Berardi 2013a). Various studies have tried to map the evolution of the concept of IBs (e.g. Clements-Croome 1997, 2004; Buckman, Mayfield, and Beck 2014). In essence, the emergence of information and communication technology (ICT), together with the development of automation, embedded sensors, and other high-tech systems are key elements in IBs (Kroner 1997).
 
"For commercial developments, intelligent-building technologies can result in above-market rents, improved retention, higher occupancy rates, and lower operating expenses," says Arindam Bhadra president and founder SSA Integrate.
 
Technology is changing what’s possible for buildings. With the advent of smart building technology, heating, cooling, electrical, lighting, fire/life safety, and other systems need monitoring and intercommunication for optimized efficiency and operation.
Learning objectives:
·         Distinguish the differences between smart buildings and their counterparts.
·    Demonstrate the benefits of system integration as they relate to smart buildings.
·        Apply smart building techniques in various commercial buildings in a general building example.
 
Most infrastructure systems deployed in today's buildings are inherently "smart," with self-contained logical control that includes embedded performance optimization and self-diagnostic algorithmic features. While it is understood that intercommunication of these systems provides tremendous opportunity in optimizing building operation efficiency, it is necessary for the engineer to think beyond the building automation system (BAS) as the link to systems interoperability. With sophistication comes the need for a BAS and building controls that allow for nearly seamless operation of this interrelated equipment. Smart buildings and smart cities integrate the design of the infrastructure, building and facility systems, communications, business systems, and technology solutions that contribute to sustainability and operational efficiency.
 
Today's truly intelligent buildings interoperate on a common converged network where data is shared through an open-source platform. Middleware collects, analyzes, and communicates in a two-way fashion with the smart systems to best optimize the building response and enhance the occupant experience. To do this effectively and efficiently, the engineer must bring together and align more stakeholders than in the past.

The BAS, with control over the building's HVAC systems, has long been viewed as the core smart system in a commercial building. However, modern construction contains many more inherently smart devices and subsystems. Electromechanical timers for irrigation and lighting control have given way to microprocessors with real-time clocks and the ability to network together. Racks of clicking elevator-control relays have been replaced by robust and reliable programmable logic controllers. Multiple networks crisscross the building, each one connecting its specific group of devices, such as surveillance cameras, card readers, or fire alarm initiating and notification devices. Audio/video systems have grown from stand-alone racks of analog-source electronics to building wide distribution of digital content. Ever more stringent building energy codes essentially mandate that networked microprocessor lighting control systems be installed instead of an array of interconnected sensors and power packs.

Smart features—such as microprocessor control, the ability to network together, and some form of user interface and configuration software—can now be found in irrigation systems, plumbing equipment, all sorts of submeters (including electricity, natural gas, domestic water, and hydronic energy), and even fire extinguishers and exit signs. The next generation of smart devices, coming to market under the Internet of Things (IoT) banner, promises the next stage in the evolution of building performance monitoring with wireless communication, low-power or completely battery-free operation, low cost, small form factor, and a wide range of esoteric applications.

These IoT devices frequently report to the vendor's cloud-based application for processing, analysis, reporting, and user interface. Google's $3.2 billion purchase of Nest is a clear indication of the bullish outlook tech firms have for future investment in building technology and the convergence of building systems and the information technology (IT) department.

Benefits of integration

Smart devices and IoT technologies are the conduits to capture better and more relevant building data; however, if that data remains solely contained within the boundary of the original smart building system—BAS, lighting control system, electrical power monitoring system, vertical transport system, etc.—the power of the collected data cannot be fully realized. These independent "silos" of smart devices are, at best, inefficient to install, manage, and maintain. Each is typically sold and installed by a separate contractor, each is operated or monitored by a unique software system, and the massive collection of disparate specialty devices makes it all but impossible for the average facility operator to become adequately trained to maintain most of it properly.

However, if these specialty devices become enabled to share their data through an open-source data platform, smart building systems become collectively intelligent and their effectiveness increases exponentially. When elevators, HVAC systems, lighting controls, and other systems are integrated with intelligent building platforms, they move beyond the collection of data to allowing communication across the systems to foster efficiency. Strong building data is the foundation of the intelligent building platform, which turns the collected data into building intelligence that can be applied to foster smarter use of the built environment.

Two generic examples take advantage of common scheduling and occupancy/vacancy programming across these systems, as well as provide occupants with more control over their space.

1.  Example No. 1: HVAC zones within the building can be reset to a "standby" condition during normal working hours either by time schedule or when unoccupied as sensed by a zone occupancy/vacancy sensor. During this "standby" mode, the associated HVAC equipment serving the respective zone will revert to an intermediate, relaxed temperature setpoint and the lighting can be reduced or turned off completely—all reducing energy consumption.

2.   Example No. 2: During off-hours, should an occupant (or occupants) enter the space, the elevator controls can signal the respective zone for which the occupant is destined and the associated HVAC and lighting controls—just in that zone—can be automatically activated to temporary occupancy. Once the occupant is in the zone, the occupancy/vacancy controls will adjust the HVAC and lighting controls as the occupant moves through or changes zones.

The real power of each smart device gets unlocked when incorporated into an intelligent building software platform. The traditional approach to integrating systems has been to expand the HVAC-centric BAS, but there are practical limits to what a building management system can achieve. Due to the wide variety of devices and applications for integration in a modern building, it is becoming more common to forgo the traditional approach and to, instead, provide a dedicated intelligent building platform separate from the building management system. In this approach, the intelligent building platform acts as a master to the various specialty devices and subsystems.

The traditional building management system (i.e., temperature control system) remains an integral part of the mechanical systems. The building management system is specified within the mechanical division of project specifications and is typically provided by a subcontractor to the mechanical contractor.

In similar ways, lighting controls are specified within the electrical division and provided by the electrical subcontractor, and plumbing controls are specified within the plumbing division and provided by the plumbing contractor, etc.

Key features of an intelligent building software platform are:

·        Multiple protocol capability to allow flexibility in procurement of the various subsystems and devices

·  A common object/data model to encourage the normalization of the assortment of protocols and subsystems into a consistent framework

·    Open-source software to enable software development to extend the core features 

·   Open distribution to ensure that the owner/end user will have maximum future flexibility when expanding or maintaining the system

·        A suite of software features that match up with owner requirements, which could include advanced visualization/user interface, dashboards targeting managers and occupants, fault detection and diagnostics, energy analytics, advanced reporting capabilities, and performance optimization capabilities.

Stakeholders

The best conditions for success when creating an intelligent building occur when the goals of the diverse stakeholders can be aligned with intelligent building goals at the project outset. Just as it is necessary for a project team to find agreement on basic architectural programming details like location, size, height, and cost before any detailed construction drawings can be drafted, the "size and shape" of the intelligent platform must be agreed upon before any meaningful design can begin.

Unfortunately, current practice is often to skip an initial programming phase with the stakeholders at the table. Instead, each subsystem design engineer or design-build contractor creates a solution in a vacuum or with minimal coordination between disciplines, and the opportunity to develop the most value at the lowest cost is lost. Much later in construction, as the various stakeholders come to the table, features get added in a patchwork manner, leading to higher costs and unfortunate compromises that result in a system with diminished effectiveness.

Avoiding this situation requires pulling together people from the organization who may be unfamiliar with the design and construction process and who may have never before been asked to envision the technology features of a building, and conducting early workshops or design charrettes. Quite a bit of education often is required at these early meetings, because many team members will need an understanding of what is possible. The potential positive results can be huge. When the team of traditional early-stage participants, such as architects, engineers, and general contractors, are all aligned around a set of minimum requirements for intelligence, the intelligence becomes a part of the DNA of the project.

There are a limited number of stakeholders for a traditional building management system, including operating/engineering staff, building-management staff, and perhaps energy-management staff. In an intelligent building paradigm, there are many more stakeholders that should become involved, because an intelligent building is able to deliver benefits across a much wider spectrum. Of course, the specific involvement on any project will depend greatly on the individual experiences and expectations of each stakeholder, from end user/occupant, to IT and network technicians, to corporate management-level executives, to regulatory compliance officers.

Some of the stakeholders in a modern building may be new to the idea of an intelligent building, and may be accustomed to performing their job functions without real-time software. For these stakeholders, additional conversations will be necessary to educate them and to encourage active involvement in the project.

A brief summary of the benefits of intelligent building strategy implementation:

·    Improved operational efficiency/use. This class of stakeholders (facilities manager, operations manager) is focused on keeping the building functioning on a day-to-day basis. Inwardly, they are concerned with occupant satisfaction, ease of operation, access to critical systems information, and productivity of the maintenance staff. The visibility provided by the intelligent building platform allows a real-time and more organized response to maintenance concerns, making their jobs easier and improving their ability to keep the occupants comfortable and happy. These stakeholders are concerned with the productivity of the non-staff occupants in the building and strive for optimal building comfort. They want access to information about the effectiveness of the building’s spaces and how integration can improve productivity.

·  Reduced utility consumption. Beyond improved maintenance practices that can reduce the amount of wasted energy, the aggregation and analysis of data from devices, such as power meters alongside HVAC controls, within the intelligent building platform can allow a facility to predict its utility demand and implement more focused energy-management strategies to maximize efficiencies and minimize costs. Facilities can reduce their dependency on the power utility grid when these strategies include the installation of onsite renewable energy sources, such as solar and wind. The power of integration is ultimately optimized when this intelligence from the building platform is used to drive a net zero facility.

·      Improved financial performance. Expanding from the objectives of those stakeholders concerned with operational efficiency, knowing the financial effects of operational inefficiencies can foster more informed decisions. More efficient responses to operating problems can lower the maintenance costs and inevitably promote a more optimal, therefore, more energy-efficient and cost-effective operation. Customized reports comparing financial metrics across the entire enterprise also can be provided to the financial stakeholders who are interested in how the intelligent building systems are impacting the company’s financial metrics and the bottom line revenue/profitability.

·   Enhanced occupant experience. These stakeholders (end user, owner, facilities manager, operations manager) are concerned with the comfort and safety of the building occupants. Many studies have associated a strong link between occupants’ comfort and productivity levels. These stakeholders also want the intelligent building to help disseminate messages during an emergency, including pre-action and warnings. Additionally, they are interested in how the building’s intelligence can be leveraged to maintain proper access control and improve emergency communications as well as tenant/employee attraction and retention.

·    Sustainability. Sustainability stakeholders are concerned with energy and water efficiency, utility optimization, and how to reduce emissions and save resources. These stakeholders will want to show performance data from throughout the intelligent building in lobby displays to promote the building’s sustainability initiatives.

·  Competitive advantage and value. When increased efficiencies, lower resource consumption, and positive financial performance are coupled with an engaged, empowered, and seamless occupant experience, real estate value and competitive advantages are created. A building where systems are integrated and converged is capable of capturing embedded opportunities that create value through both continuously improving performance and the ability to respond to marketplace desires and demands.

·     Prestige/recognition. Prestige and recognition are motivations for multiple stakeholders who want to create a high-profile image for the building, company, and/or community, showcasing the company’s commitment and dedication to all occupants, visitors, and investors.

Visualizing success

Strong visualization tools organize and present the building data so that stakeholders can better understand the building to make necessary adjustments for optimization. Individual dashboards for each of the building’s stakeholders can be built to concentrate on targeted data sets. For example, the day-to-day building operator will need the most inclusive dashboard that features an overall picture of the facility as well as certain granular-level statistics specific to each facility, while the financial stakeholder will want to know how the day-to-day numbers play out in the overall budget.

How a Smart Building may function

If a building is not performing to its designed standard, than a smart building should be able to gather information as to why and adapt to perform differently in the future. This ‘adaptableness’ should span across the four main principles of building progression. See below Figure.

·   Intelligence: the methods by which building operation information is gathered and how to respond

·    Enterprise: the methods by which a building uses information that is collected to improve occupant and building performance   

·        Materials: the building’s physical form

·        Control: the interaction between the occupants and the building

Building Management Pillar

Example 1

Example 2

Enterprise

Combining hardware, and software to overcome fragmented non-proprietary, legacy systems.

Integrating BMS and real-time systems with smart analytics to predict building faults before the BMS picks up an alarm.

Materials

Based on occupancy counts, a smart building could close or open zones during periods of low or high occupancy.

Adapting to future climate conditions by replacing features that can account for change.

Control

Warning occupants of the likely temperature of their building before they set off from home

Using real-time environmental information to enable occupants to see what part of the building suits their preferences best.

Cost and budget issues

With all the features and benefits that have been described, why are more buildings not incorporating the truly intelligent, converged building system approach? One common misperception is that it must cost more. If the intelligent concept is an afterthought and is applied as an overlay late in the building design process, there indeed could be a budgetary impact. However, if the intelligent building concept is a key initiative considered from the project inception and supported by the project owners and stakeholders, the individual smart systems can be planned and designed to minimize—and even remove—the budgetary impact.

Early involvement allows the project to eliminate common redundancies, such as multiple parallel networks, multiple software systems configured to create separate user interfaces, and even multiple electrical installation subcontractors. Early involvement also enables the many granular design decisions to be made in alignment with the overall intelligent goals. This can result in the elimination of costly details with marginal incremental benefit, with a corresponding budget shift into items that deliver maximum value. At the same time, it can prevent design-time gaps in the planning of smart systems that are sufficient to attain the intelligent goals, reducing costly last-minute change orders.
 
As an example, a recent client engaged Environmental Systems Design as a partner for the design of its new headquarters facility early in the project. This client recognized building occupants have high expectations in regards to their modern built environment. This client committed to providing their employees, colleagues, and customers a heightened experience in terms of efficiency, comfort, safety, and increased productivity through the implementation of the intelligent building concepts.
 
Environmental Systems Design was tasked with developing, designing, and delivering an intelligent building platform. Early involvement, in-depth coordination across all trades, and unwavering client support has led to an intelligent building design that will be implemented in a cost-neutral way when compared with the initial budgetary line item costs for the individual mechanical, electrical, plumbing (MEP), and associated systems. The intelligent building design will integrate BAS (HVAC temperature control), an intelligent lighting control system, vertical transport systems, and building metering and submetering onto one common, converged platform where fault detection, diagnostics, building analytics, and informational dashboards are applied to deliver on the efficiency, comfort, safety, and productivity initiatives identified and agreed upon by the project stakeholders.
 
The demand for building intelligence through a converged platform is being recognized by building owners and operators as a primary and future-oriented component of meeting market expectations, creating value, and maintaining a competitive advantage. The intelligent facility of today and tomorrow will be strikingly different even from that of the current, high-performance building. While both feature smart MEP systems and the latest equipment optimization, the intelligent building will stand out behind the scenes for its ability to collect data from each disparate system, collaborate it into dashboards for individual stakeholders, and—most importantly—to use the collected data to impact the building positively and enable continuous improvements.

India’s Coolest Buildings

Below is the list of some of the coolest buildings of India.
1) i-flex solutions, Bangalore - Located at C.V Raman Nagar Bangalore,
2) Signature Towers, Gurgaon
3) Adobe-India’s Headquarters - Adobe-India’s Headquarters is located at NOIDA
4) Gateway Tower Gurgaon
5) Gigaspace IT Park Pune
6) HSBC Building Pune
7) Infinity Towers, Kolkata
8) Infosys Multiplex, Mysore
9) Statesman House, Delhi

Top Green Buildings In India

Green buildings are becoming an integral part of modern India. Maharashtra has 334 LEED-certified green buildings, while Karnataka and Tamil Nadu have 232 and 157 buildings, respectively.


1.   Suzlon One Earth, Pune
2.   CII- Sohrabji Godrej Green Business Centre, Hyderabad
3.   Jawaharlal Nehru Bhawan, New Delhi
4.   Raintree Hotel, Chennai
5.   ITC Green Centre, Gurgaon
6.   Infinity Benchmark, Kolkata
7.   I-Gate Knowledge Centre, Noida
8.   Biodiversity Conservation India Ltd. (BCIL), Bangalore
9.   Olympia Tech Park Chennai

Ref:


Sunday, November 1, 2020

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.
  1. Software
  1. 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