Components of BMS

Components of BMS 

A Building Management System (BMS)—also known as a Building Automation System (BAS)—is a computer-based control system installed in buildings to monitor and manage the Mechanical, Electrical, and Electromechanical services. These services typically include:

·        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. 

·        Lift control system. 

·        Pumping system. 

·        Water tanks level. 

·        Irrigation system. 

·        Electrical Energy meters.

·        Water Leak detection system.

·        Split 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. 

The primary goal of a BMS is to ensure efficient, safe, and reliable building operations, while also optimizing energy consumption and reducing operational costs.

Architecture Overview

BMS systems are built using a layered architecture:

1. Field Layer

✓Sensors and actuators (temperature sensors, motion detectors, relays, etc.)

2. Control Layer

✓DDC (Direct Digital Controllers) that receive inputs and control outputs.

3. Supervisory Layer

✓Workstations or servers that provide the graphical user interface (GUI).

4. Enterprise Layer

✓Interfaces with other systems like EMS (Energy Management System), DCIM, CMMS, etc.

 

Typical BMS Layout
[ Sensors ] ↔ [ DDC Controller ] ↔ [ BMS Server/SCADA ] ↔ [ Operator Workstation ]

 

Major Components

🔸 1. Sensors: These devices gather real-time data from the environment and send it to controllers. Common types:

✓Temperature Sensor Measure air, water, or room temperature

✓Humidity Sensor Track moisture levels in the air

✓CO₂ Sensor Monitor air quality and occupancy

✓Water Quality Sensors is analyze chemicals, pH levels, and other water parameters for environmental management. 

✓Pressure Sensor Detect duct or chilled water pressure

✓Occupancy Sensor Detect human presence in rooms

✓Hall effect sensors are used for position detection and occupancy sensing, such as determining if a door or window is open or closed, or if a motorized shade is in a particular position.

✓Flow Sensor Monitor fluid movement in pipes

✓Light Sensor Detect ambient lighting

✓Air Quality Sensors is measure gases like carbon monoxide to control ventilation system

✓Smoke/Leak Detector Smoke, gas, water leak Fire systems, water leak detection

✓Electrical relay and contactor

✓Current Sensors monitoring instruments find utility in the measurement of the electric current

✓DPS Differential pressure switches for ventilation and air conditioning (not for fuel gases) are for filter, fan or air flow monitoring in air conditioning and ventilation systems,

✓Energy Meter is a device that measures and monitors electrical or thermal energy consumption within a building. The meters collect energy consumption data and transmit it to the BMS's controllers.

✓Digital Sensors report on/off status, such as door contact switches or flow switches, or send pulses for counting events like water flow.

✓Analog Sensors provide a continuous, variable output, like thermistors or 0-10V signals, for detailed measurements of temperature, humidity, or pressure.

Signal Type Description Used With

✓Analog 0–10V Voltage proportional to value Temperature, CO₂

✓Analog 4–20mA Current loop, more stable Pressure, level

✓Digital (Dry Contact) ON/OFF or pulse count Flow switches, alarms

✓Resistive (NTC/PT100) Resistance changes with temp Thermistors, RTDs

🔸 2. Actuators
Actuators execute commands from controllers to adjust mechanical operations.
Type Function
✓Valve Actuators Open/close water or air valves
✓Damper Actuators Control air flow in ducts
✓Relay Modules Turn on/off electrical loads

🔸 3. Controllers (DDC – Direct Digital Controllers)
✓Controllers process inputs from sensors and determine outputs to actuators.
✓Local controllers: Installed near equipment (e.g., AHUs, chillers)
✓Programmable: Logic can be customized per application
✓Real-time processing: Executes control loops continuously
✓Supports communication: Modbus, BACnet, or proprietary

Panel Element Description
✓DDC Controller Main logic unit
✓Terminal Blocks Wiring terminations
✓Circuit Breakers Protection for I/O modules
✓Relays and Contactors For switching loads (pumps, fans)
✓24VDC Power Supply Supplies power to controllers/sensors

🔸 4. Field Devices
Combination of input/output modules, power supplies, fuses, and interface terminals mounted inside control panels.
✓Analog Input (AI): e.g., 4-20mA, 0-10V sensors
✓Digital Input (DI): e.g., dry contact, flow switch
✓Analog Output (AO): e.g., control signals to valves
✓Digital Output (DO): e.g., relay signal to pump/starter

🔸 5. User Interface Devices
a) Operator Workstations
b) Touch Panels / Mobile Apps

🔸 6. Network Infrastructure
BMS requires stable communication between field devices, controllers, and servers.
Type Example
✓Serial RS-485 (Modbus RTU, BACnet MSTP)
✓Ethernet/IP BACnet/IP, Modbus TCP
✓Fiber Optic Backbone for large campuses
✓Wireless Wi-Fi, LoRaWAN, Zigbee (modern IoT)

🔸 7. Server & Database System
🔸 8. SCADA/GUI Software

Extra innings - 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.

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 the 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 from entering 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 to monitor the filter extreme dirty condition.

DPS switch is used to install across the filter and provide signals 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.

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 the help of the 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 these actuators have terminal for control from BMS and terminal to monitor the feedback of position.