Simplifying BMS Design Basics

by
Ashwini Karkara
BAS Consultant & Engineers

Building Management System-: Begin with the basics
BMS – Building Management system
Building Automation system
A Building Management System (BMS)
is a blend of hardware & software based
is a blend of hardware & software based
control system installed in buildings to
control and monitor the building’s
mechanical, electrical & other utility
equipment

Building Services
Services Equipments
Mechanical system HVAC , Plumbing , Fire Fighting, STP
Electrical System Electrical DB’s/Lighting control & monitoring,
Generator set, UPS
Utility & Life Safety Lifts, Fire Alarm System,

Tenant
Billing
Maintenance Management
System
Access Control
AC System
Ventilation and
Exhaust Air
System
Public Address &
2-Way
Communication
System
Fire Detection and
Control System
Generally the Systems Controlled and Monitored By BMS
IBMS
Central Monitoring
Access Control
System
Lighting Control
System
PHE System
Electrical/ DG/
UPS System
Elevator System
Central Monitoring
Systems
Asset Tracking
System / TAM
System
CCTV and Security
System

Basic of Instrumentation
• Us our Body and its parts
• Our Body Reflexes

In BMS
INPUTS:- Sensors
Temperature (of room)
Humidity (of room)
Flow Rate (chilled Water)
Flow Rate (chilled Water)
Pressure (of Fire Hydrant)
Level (of a Tank)
Run status (Pumps, Fans)

Temperature Sensors
– Sensing technologies
• Thermistor
– Accurate over limited
range
– Point type only
– Used for space
temperature
• Nickel Wire
– General purpose sensor
– Point or averaging type
– Used for space or duct
– Application Issues
• Mount inside thermal well for water
temperature
• Mount return air sensor away from
fresh air stream
• Mount space temperature sensor :
– At 1500 mm height
– On inside wall
– Away from direct sun or other
heat sources
• Ensure off-coil sensors are far
– Used for space or duct
• Platinum
– High accuracy / linearity
– Point type only
– Precision applications
• Ensure off-coil sensors are far
enough away from coil
• Outdoor air temperature sensors
require sunscreen
• Calibrate using precision resistor,
validate using digital thermometer
• Know mounting scope of
responsibility

Pressure Sensors
– Air Static Pressure
• Used to control VFD based on
VAV duct static
• Must be mounted in region of
laminar flow; five duct diameters
from restrictions
• Active sensor
– Water Static Pressure
• Used to monitor pressure at top of
sprinkler riser
• Commercial grade sensors can leak
– Water Differential Pressure
– Air Differential Pressure
• Used to calculate airflow from
velocity pressure
– PVELOCITY = PTOTAL - PSTATIC
– CFM = 4005 * AREA *
(PVELOCITY / K FACTOR)½
• Used in VAV boxes and air flow
monitoring stations
– Water Differential Pressure
• Used to control bypass valve or VFD
• When controlling bypass, best to
mount at last AHU
• Do not try to save costs by using
two static pressure sensors
• Calculation error of same magnitude
as signal may ocur.

Other Sensors
 Waterflow
 Mount in region of laminar
flow; five diameters from
restrictions
 Many technologies:
 Annubar
 Paddlewheel
 Carbon monoxide
 Control car park ventilation fans
 Carbon Dioxide
 Used as indirect indicator of
indoor air quality
 Paddlewheel
 Electromagnetic
 Turbine
 Humidity
 Used to measure the Relative
Humidity in air.
 Some humidity sensors comes
with in built temperature
sensors also.
indoor air quality
 Electrical Transducers
 Current Transducers
 Voltage Transducers
 Lux Level Sensors
 To measure the intensity of
light.
 MOTION SENSOR

In BMS
OUTPUTS:- Control
Valves
VFD Speed Command
Air Dampers Actuators
ON-OFF Command (Fans,
Pumps, Boilers)

INPUTS & OUTPUTS
INPUTS e.g
Analouge (varying-reading)
AI
Temperature, Humidity, Water Flow , Air
Flow , Tank Level, Energy KW, Voltage,
Current, Pressure, pH, Conductivity
Digital (Binary-ON or OFF)
DI or BI
Status (on/off, airflow , run, open/close)
Alarm
Trip
Trip
OUTPUTS e.g
Analouge (varying-positioning)
AO
Fan Speed regulating (0 to 100%)
Chilled water valve control (0 to 100%)
Digital (Binary-ON or OFF)
DO or BO
Command (on/off, open/close)

I/O
Building management system relies on 4 types sensory information to make a control decision
Analog inputs : are used to read a variable measurement. Examples are temperature, humidity and
pressure sensor which could be thermistor, 4-20 mA, 0-10 volt or platinum resistance thermometer
(resistance temperature detector), or wireless sensors.
Digital input : indicates if a device is turned on or not. Some examples of a digital input would be , an air
Digital input : indicates if a device is turned on or not. Some examples of a digital input would be , an air
flow switch, or a volt-free relay contact.
Analog output : controls the speed or position of a device, such as a variable frequency drive, a I-P
(current to pneumatics) transducer, or a valve or damper actuator. An example is a chilled water valve
opening up 25% to maintain a setpoint.
Digital outputs : are used to open and close relays and switches. An example would be to turn on the
parking lot lights when a photocell indicates it is dark outside.
A typical Mid Size Building may have 800 -2000 sensory points also known and I/O points.
A complex Building like an Airport may have more than 5000 points

DDC Controllers
 Types of DDC controllers
 Fixed function
 Configurable
 Text programmable
 Graphic programmable
 Point Definition
 Ranging (linear, calculated,
 Control Loops
 Proportional plus integral control
commonly used
 Other software routines used in
local control logic
 Minimum, maximum, average,
calculator, etc.
 Psychometric calculations
 Timing (delays, pulses, etc.)
 Ranging (linear, calculated,
polynomial)
 Filtering (smoothing and
debounce)
 Interlocks
 Timing (delays, pulses, etc.)
 Boolean and comparator
operators
 Time clock and backup schedules

Outputs
Analogue
Inputs
The Controller maths
logic
PID
Alarms
Times
Logs
Time control
for boilers,
chillers etc.
Modulating or
on/off valves
Analogue
Temperature
Pressure
Humidity
Digital
Run / fault
Pulsed
Meters

Typical BMS for Lighting Control
Sl.
No
IO Description AI DI AO DO FIELD DEVICE
1 Room Lights Circuit 1 &2 & 3 On/Off 0 0 0 2 To the 6Amps light phase of each circuit
2 Room Motion Status 0 1 0 0 Dual PIR Sensor to sense motion
3 Room Lux level 1 0 0 0 Room Mounted Lux Level
4 Room AC start/Stop 0 0 0 1 To Window AC electrical starter panel
5 AC Run Status 0 1 0 0 Current Switch across Window AC phase.
TOTAL 1 2 0 3

Control Logic for Lighting Control
• Based on the Time Schedule for occupancy the BMS
DDC shall switch on the room lighting.
• Same logic operates only if Occupancy sensor senses
any motion in the room.
any motion in the room.
• The LUX level of room is sensed and based on high lux
level the room light circuits (nearest to windows) are
switched on first and then if lux level still increases the
second circuit is switched OFF.

Control Logic for AC Control
• Based on a Time Schedule AC phase can be allowed to
pass through the AC starter.
• AC run status shall be monitored through a current
switch which shall provide a contact in case AC
switch which shall provide a contact in case AC
compressor is taking load .

Typical BMS for Water System
Sl.
No
1 Ground Tank Low , Medium and High Level 0 3 0 0 Level Switch in underground tank
2 Raw Water Pump On/Off 0 0 0 1 Through Raw Water Pumps starter
3 Raw Water Pump Auto/manual Status 0 1 0 0 Through Raw Water Starter Panel
Auto/Manual Switch
4 Raw Water Pump Run Status 0 1 0 0 Current Switch across Pump phase.
5 Overhead Tank Low , Medium and High Level 0 3 0 0 Level Switch in overhead tank.
6 Transfer Water Pump On/Off 0 0 0 2 Through transfer Water Pumps starter
7 Transfer Water Pump Auto/manual Status 0 2 0 0 Through Transfer Water Starter Panel
Auto/Manual Switch
8 Transfer Water Pump Run Status 0 2 0 0 Current Switch across Pump phase.
TOTAL 0 12 0 3

Control Logic for Water System
• The Ground Floor Tank Low , Medium and High Levels
are measured. If ground tank level is between Low to
High the raw water pump is switched on till it achieves
High level.
• If Overhead tank level is between Medium and Low
level the transfer pump shall be switched on to fill the
overhead tank till level is High.
• Failure of any pump shall automatically switch on the
standby pump.

Typical BMS for AHU
Sl.
No
1 AHU On/Off 0 0 0 1 AHU panel to accept 2A NO contact
2 AHU Run Status 0 1 0 0 Differential Pressure Switch across blower
3 AHU Auto/Manual Status 0 1 0 0 Pot . free contact @ AHU Panel
4 AHU filter Status 0 1 0 0 Differential Pressure Switch across filter
5 Return air temperature 1 0 0 0 Duct type temperature sensor
6 2 Way chilled water modulating valve control 0 0 1 0 2 way Modulating Valve
7 Chilled water return header flow rate 1 0 0 0 Flow meter
TOTAL 2 3 1 1

What is a Building Automation System?
 A BMS system collects the operating information required for intelligent building
management.
 It analyses the operation of the building systems by viewing all important
temperatures, humidities and equipment status.
 Further to collection of these data, the BMS presents these data on the screen with
full color
• Automates some control strategies such as turning equipment On/Off according
to a time schedule – ensures energy savings
• Allows an operator sitting at the BMS work station to view key information about
the building – improves building operations
the building – improves building operations
• Allows an operator sitting at the BMS work station to control some of the
equipment in the building – improves building operations allowing remote control
/ over-ride where necessary
• Maintains an audit trail of what happened and when it happened – improves
building management by means reporting and traceability
• Maintains historical data for selected information (like temperature, humidity
..etc) – improves building management by means reporting and traceability
• Alerts the operator at the BMS work station when readings fall outside of normal
range (i.e. breaker trips, temperature too warm, etc.) – improves building
management by having a faster reaction time to problems
• By doing the above and more a BMS system saves manpower, ensures productive
occupants (especially in an office environment), prolongs equipment life, and the
most important of all saves energy. diagrams (graphics) for the ease of
understanding.

BMS Protocols
BMS system manufacturer divided predominantly into two different
protocols, mentioned below-
• BACnet - A Data Communication Protocol for Building Automation and
Control Networks developed by ASHRAE. It gives freedom to client to
connect all BACnet compliant devices and ease in commissioning &
configuring.
configuring.
• Lonworks -Lon Works is actually a family of products originally developed
by the Echelon Corporation. At the core of this technology is a proprietary
communications protocol called Lon Talk. Here one needs to buy license for
each individual controllers & devices. Commissioning requires software key
(dongle) all the time for commissioning & configuration.
• Modbus is developed by Modicon in 1979. It is used to establish master-
slave/client-server communication between intelligent devices. It is a de
facto standard, truly open and the most widely used network protocol in the
industrial environment and devices.

System Architecture IP- 1 Tier Where all controllers are connected
to HMI on LAN.
TCP/IP
Server
Bacnet over IP
963 Software with
Bacnet Protocol
Client
Client
DDC 1
P1-service
DDC 2
P2-service
DDC 3
P3-service
Sub Station
Control Room
Portable Operator
Terminal
P1- Gnd
Third Party Integrator for APFCR
relays, ACB, DG switchgear, BTU,
multi data meter, KWH meters,
VFD, Chiller, DG, UPS, Boiler & Jet
fan
3rd Party 3rd Party 3rd Party
P1- 2nd flr P1- 3rd flr P1-4th flr P1- 5th Flr
P1-Upper
Basement
P1-Lower
Basement
P1- 1st flr Multi protocol
integrator
DDC 1
DDC 1
DDC 7
DDC 1
DDC 1
DDC 9
DDC 1
DDC 11
DDC 1 DDC 1
DDC 2
DDC 1
DDC 2
DDC 3
Hotel Mall Office

DDC 1 Lower Ground (Pump Room)
System Architecture.
Server
DDC 4 Diesel Generator (LT Room- Ground Floor)
DDC 2 &3 Lower Ground Floor (Lighting Control)
Main Supervisory Controller (EINC)
Supervisory Software 963
DDC 5 & 6 Electrical (LT Room – Ground Floor)
DDC 4 Diesel Generator (LT Room- Ground Floor)
DDC 7 &8 Ground Floor (Lighting Control)
DDC 9 & 10 First Floor (Lighting Control)
DDC 11 &12 Second Floor (Lighting Control)
DDC 13 ( Terrace Tanks) & DDC 14 (Fire Hydrant)

RS 485 – 2Tier
Level1-: where all controllers are connected
to each other in daisy chain fashion & then
after they connect to router or gateway.
Level2-: When router or gateway is connected
to any HMI for monitoring & controlling.
to any HMI for monitoring & controlling.

Building Automation System Software
Alarms
User Interface
and Password

Energy
Operations
Maintenance
Supervisory Controller (processing)
Operator Workstation (long term storage)
Operator Workstation
Where this feature resides





Control Logic
Demand Limiting
and Duty Cycling
Historical Data
Graphics
Scheduling

Supervisory Controller
DDC Controller
Operator Workstation
Supervisory Controller (processing)
Operator Workstation (long term storage)














BMS Typical BOQ-
It can be categorized in 3 broad categories-
1. BMS controllers, Softwares, POT(Portable Operator
Terminal),integration & PC.
2. Field Devices- It comprises different kind of sensors,
switches, actuators, Transmitters etc
switches, actuators, Transmitters etc
3. Cables & conduits

1. BMS controllers, Software's, POT
(Portable Operator Terminal), for integration & PC.
• Controllers selection can be done based on the IO (Input Output) requirements directly
just to match AI(Analog Input), AO(Analog Output), DI(Digital Input), DO(Digital
Output) in the layman’s language.
• Integration to collect the data from different devices.

2. Field Devices-
Comprises different kind of sensors, switches,
actuators, Transmitters
BMS
Areas
Category
Type
Sub-
Category
Application
AHU(Airside) Temperature(cum
Humidity/RH)
Sensor Room To know the actual Temp inside without cooling
Duct
To know flowing air Temp(& RH) inside duct for
supply & Return Air
Differential Pressure Across AHU Fan to check it is on or off physically,
Differential Pressure
Switch Air
Across AHU Fan to check it is on or off physically,
across filter to check the status
Valve & Actuators Across cooling coil
Chillers, cooling
towers(Waterside)
Temperature(cum
Humidity/RH) Sensor Immersion
To Know water temperature from the chillers & to the
chillers
Outside To Know outside temp & RH
Differential Pressure
Switch Water
Across Pumps to check it is on or off physically, across
filter to check the status
Others
Level Transmitters Water To know the water level
Oil To know the oil level
CO2, CO sensor Room To know the air quality as in parking lot

3. Cable
It generally can be categorized in two different applications-:
• Signal/Control Cable: From different field devices to controllers &
from Controllers to field devices to control the equipments
• Communication Cable: cable between different controllers, routers
& gateways for the purpose of intercommunication between
& gateways for the purpose of intercommunication between
controllers.
• Integration cable: cable required for monitoring of third party
devices.

Cable Selection
BMS
Areas Category Cable Type Application
AHU Duct, Room Temp sensor 2c x 1 sqmm shielded Passive Temp(2c) signals from sensor to controllers
Temp cum humidity sensor 4c x 1sqmm shielded
Passive Temperature(2c) & Active(2c-power) RH measurement
from sensor to controllers
DP Switch for Air 2c x 1 sqmm shielded Passive Temp(2c) signals from switch to controllers
AHU FAN VFD 2c x 1 sqmm shielded Run status
2c x 1 sqmm shielded On/off status
2c x 1 sqmm shielded Relay output for VFD On/OFF Operation
Valve & Actuator 5c x 1sqmm shielded Control & Power (3c power and command) & Monitor (2c)

Integration
BMS
Areas Category Cable Type Application
Integartion DG
2c x 1.5 sqmm twisted pair
shielded
Integration is only to collect data from different devices to monitor
& generate reports
UPS
shielded
& generate reports
VAV's
shielded
& generate reports
2c x 1.5 sqmm twisted pairIntegration is only to collect data from different devices to monitor
Electrical Panels
shielded
& generate reports
Chillers
shielded
& generate reports
Security & Fire Alarm
system
shielded
& generate reports
Elevator
shielded
& generate reports

BMS Design Aspects
Basic data required before you start system design:
1. Input / Output summary for all subsystems, which need to either monitor or control.
2. Selection of appropriate field devices.
3. All integration devices & respective point details which has to be monitored.
4. Signal & Communication cable route layout (at least tentative).
5. Panel (Enclosure for controllers) location, BMS PC location.
Steps to follow for designing-:
1. Select the suitable controllers required for the requirement.
2. Select the enclosure to mount those controllers, which includes power supply for controllers & other wirings for field device
connection.
3. Now start with the AHU designing which includes signal & control cabling requirement for different field device selection as
per the requirement.
4. A typical AHU generally requires following field devices-Temperature cum Humidity sensor (or only Temp) in return & supply
duct. Differential Pressure Switch (For Air) across the AHU Fan, Filter, Actuators for AHU Line.
5. A typical AHU will have following wiring connection- Connection to all Field devices, Connection to electrical panels as per
I/O, connection to VFD’s.
6. A typical Chiller side will have following field devices-Immersion type temperature sensor (for supply & return pipes),
Butterfly Valve & Actuator in each chiller supply, differential Pressure sensor across main supply & return .
7. A typical chiller will have connection to all field devices, chiller panels, Pump VFD’s.

BMS Commissioning Aspects –
Air Side Commissioning- It comprises individual commissioning of AHU (Air handling Unit), CSU
(Ceiling Suspended Unit), Fans & associated field devices.
• We need to measure each field devices value during AHU commissioning as first task to make
sure all field devices are working & then all points can be put in a logic.
Water side commissioning – It comprises individual commissioning of Water cooled chillers, Air
cooled chillers, Cooling towers, Primary pumps, Secondary pumps, VFD’s & associated field
devices
devices
• We need to measure each field device value & other connected points value individually before
putting them into logic.
Integration of Air side & water side in a logic-This is to integrate all independent system in logic.
Which can work automatically based on the user defined parameters without any conflict of
individual system functionality.

BMS Commissioning Aspects
Integration of monitoring points-
• This is to collect all data in BMS system for the purpose of monitoring only.
• PICS details i.e mapping details to be taken from respective equipment supplier.
• Protocol significance for integration purpose-whenever we say one device supports Modbus over
RS485, here RS 485 signifies physical channel (cable type) & communication port while Modbus
signifies data pattern. Therefore all devices in a loop must support same protocol & configure to
the same.
• Cable used for integration is 2 core x 1.5 sqmm shielded
• Cable used for integration is 2 core x 1.5 sqmm shielded
• All monitored devices have to be looped in daisy chain connection to RS-485 port. Devices can
support different communication over different protocols. We need to make sure whenever making
a loop all devices should support same communication & protocol type. for instance Modbus over
RS485.
Client User interface (UI)
• Client can change parameters as temperature & humidity from UI as per the comfort level & all
basic information can be viewed on the UI.

Simplifying BMS Design Basics

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