6-Bms & Hvac Systems

Ibrahim kshanh www.ibrahim.kshanh.name

بسم الله بسم الله الرحمن الرحيمالرحمن الرحيم

Ibrahim kshanh www.ibrahim.kshanh.name

BMSHVAC

Evolution of

SYSTEMS With

Name of Presenter : Ibrahim Elsayed Kshanh

Title : Maintenance Specialist

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Contents1-Introduction To BMS

- BMS Objectives

2-HVAC Systems

- HVAC Control

- BMS Def.

- Building Automation & BMS (Supervisory Controls)

- DDC Control

-Control Theory (DDC Algorithm)

-Control Concept

-Modes of Control

-Control Valves & Valve Authority Concept

3-HVAC Automation

4-HVAC Instrumentation

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BuildingManagement

System

HVACSecurityAccess

Fire Others

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BMS Central Management

• Energy Management Techniques

• Maintenance Reports

• Automatic Alarm Reporting

•Long Term Trend data storage

Objective of BMS

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BMS

and HVAC Systems

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Self Contained

Unitary Units Central Systems

Ex: AC split units .VRV,…[Space Thermostat]

Or Electronic Control

Used when the first cost is more important than the operating cost

-Central Supply Subsystem

-End Use Zone Subsystems-Combination Ex: : Chiller or Boiler & AHU,FCU

Central AHU & VAV

HVAC

Heating, Ventilating and Air Conditioning System

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HVAC Control

HVAC:Heating, Ventilating and Air Conditioning System

Temperature (T): 20—25 C

Relative Humidity (RH) : 20% -- 60%

Pressure (P) : Slightly Positive

Ventilation : Air Quality

Comfort Condition

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HVAC Control

Chiller3

Chiller2

Chiller1

2-W

AY

LO

AD

S

Secondary Chilled Water Pumps

* * * *

Condenser

Evaporator

* * * *

Condenser

Evaporator

* * * *

Condenser

Evaporator

Primary Chilled Water Pumps

Condensed Water Pumps

Chilled & Condensed Water System

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AHU Control

An air handling unit (AHU)

air flow is from the right to left in this case. Some AHU components shown are:

1-Supply duct

2-Fan compartment3-Vibration isolator

4-cooling coil

5-Filter compartment6-Mixing box air duct

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AHU Control

MCC

Panel

M

M

M

M M

TSM

SM

CO2

AO

AO

AO

DI

AO

DIAI

DIAI

DO

DDC

Control Panel

Supply air

Exhaust airReturn air

E

H

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Chilled Water System Pressure Control

ControllerPID Loop

VFD

Main Return Header

Primary .Ch.W .Pumps

2-W

ay

Load

s

L

H L

H L

Secondary Ch.W.Pumps

DP

Main Supply Header

Chiller

Chiller

Chilled water system control

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DDC Control

• Electronic, Microprocessor Based

More accurate than pneumatic type

• With Free programmable SW Package

• Implementation of Energy Management techniques

• Open Protocols

Flexibility (sp, schedule ,override)

Energy cost saving

Promotes Integration

• Strong Alarm, Trends Capabilities

Facilitates Diagnostic and troubleshooting

• Web Based Provide Remote Access

Digital Microprocessor Based Controllers

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Building Automation & BMS (Supervisory Controls)

LCP/DDC LCP/DDC LCP/DDC LCP/DDC

Supervisory Control

Management level Network

Field level Network

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Control Theory

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Control Concept

The aim of The control is:

• To keep certain variable (Controlled Variable) within a desired value (set point) using certain calculations or programming instructions (Algorithm) that results in a corrective action (Control Signal) that affects the controlled variable directly or through another controlled variable (Automatic Control) in order to achieve a full system balance and overall desired performance

• To Maintain System Stability

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Controller)Algorithm(

Final Control Element

Process)Final Control Element(

External Disturbance

Sensing Element

Fe

ed b

ack

Clo

sed

loop

Co

ntro

l Corrective signal

Manipulated variable

Set point

Controlled variable

Implemented Control Loops

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1-Two-Position Control

On/Off Control

OnOff

Cycle

Time

Control Signal

Off Value 22

On Value 18

Diff

ere

ntia

l -

/+2

Set Pont:20

Zone Temp.

Time

Heating On/OFF Control:

Control Signal1 for T≤ Tmin

Zero for T≥ T max

Disadvantages: -Control Overshooting -Results in Cycling Process

Under shoot

Duty Cycle

Over shoot

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2-Time Proportioning Two-Position Control

Signal Converter

Analog Controller

Output 4-- 20 mA

Two Position Pulses with duty cycle

0%--100%

ControllerProcess Error

Signal

460540

ON Off

Control

Signal

On Off

Off

On

Cycle

Time

T ≤ 460

T =480

T≥540

T =500

T =520

460

Under shoot Pro

por

tiona

l Ban

d -

/+

40

Over shoot

Set Point:500

540

Proportional Band

1-Reducing the Average Power being supplied to a Heater

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2-Eleminates Cycling 3-Minimizing Offset

Application:

Heating Current Valve

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3-Floating /Three Position Control

ActuatorP

Controller

Common

DO2(OFF)DO1(ON)

Inlet Van

Damper

remain

openremainopen

remain close

Set point

Damper

position

Dead band

Time

Static Pressure

Damper Position is Linear and proportional to the On/Off Pulse Durations

Example :

Static Pressure Control

Pulse Duration

Time

DO1/2

Fully Open

Fully Closed

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4-Proportional Control (P)

From Process

Control Point

T

-

Set Point

TControl Signal = K p* Error K p :Controller Gain

4 – 20 mA

0—10 Vdc

Cooling Coil

Valve

To Process

Manipulated Variable

GPM

0% 100%50%

Set PointM : Bias or Manual Reset

+M

Cooling

Error

Control Output

Kp

M

Linear Relation

Time

ControllerKp

Error Signal

Control Signal Continuou

s

AO

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Proportional Control (P)

Throttling Range

Control Point T

Actuator Position

Set poin

tOffset

Control Point T

Time

Set Point

50%

100%

0%

Cooling

T1 T2

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5-Integral Control (PI)

•Automatic Reset

Eliminates offset

Cooling

Control Point (F)

50%

100%

0%

Actuator Position

Throttling Ranges

SP1

L1

SP2

L2

SP3

L3

Multiple Final Control Element Position for each

controlled variable value

The actuator final position depends on:

• Proportional Band (depends on actual load)

•Deviation signal Amplitude (E) and duration (dt)

Control Signal = K p* Error +

K I ∫e. dt

K I :Integral/Reset Gain

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Offset

Time

Control Variable

T

• Fast Response

• Zero st.st Error

• Excessive overshoot or integral windup

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gpm

AHU Control

P Temp. Control Loop

C

M

ControllerP

.

Controlled Variable

Compensation Sensor

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6-Derivative Control (PID)

Control Signal = K p* e+ K I ∫e. dt +Kd de/dtKd: Derivative Gain

Offset

Time

Control Variable

T

• Oscillation damping

• Noise Sensitive

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HVAC Instrumentation

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HVAC Control Valves

Control valves in HVAC are motorized valves commanded by BMS control signal , used to regulate the flow of the operating fluid that affects certain HVAC parameter

AHU Control

M

Controller

T

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Controllability

Output Energy

BTU 100%

50%

The best controllability is achieved by keeping Linear relationship between the Control output (which considered as the valve stroke ) and the output cooling

The controllability curve depends upon two c/cs,the valve flow c/cs & the cooling coil flow c/cs

Valve Opening100%50%0%

4mA Control Signal

20mA

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Typical Coil Characteristics:

O/P Energy%

BTU

Flow%

gpm

100%

At Const.

Water Temp.

Air Temp.

Coil Surface Area.

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Valves Flow Characteristics:

Flow%

Valve Stroke%

100%

100%Quick Opening

Linear Relationship

Equal Percentage

Theoretical /Inherent c/cs

Assuming Const.ΔP with flow

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Combined Valve & Coil Characteristics:Cooli

ng%

Flow %

100%

100%

Coil

Flow%

Valve Stroke%

100%

100%

Valve

Equal Percentage curve

Cooling%

Valve Stroke%

Coil Curve

Valve Curve

Best Controllability

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Flow%

Valve Stroke%

100%

100%

Equal Percentage valve Inherent C/Cs

Q = Qmax R) ]X/T-(1[

Q: Flow Rate (gpm)

X: Valve Position (in.)

T: Max Valve travel (in.)

R: Valve Rangiability

= Max Flow / Min Controllable Flow

Theoretical /Inherent c/cs

Assuming Const.ΔP with flow

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Equal Percentage Installed C/Cs

Total Pump Head

ΔPv

Curve deviation due to:

1-As valve closes ΔPv increases

M

ΔPc

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2-As valve closes, More Pump Head will be appeared across the valve

Pump Flow C/Cs

Pump Head

Flow% 100%

100%

Pump

System Curve

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To minimize the variation in the valve pressure drop (ΔPv)

Size the valve for initial pressure drop (ΔP v100% ) as close as possible to the close off pressure drop (ΔP v 0% ) which is equal to

the Total Pump Head

More Excessive Pump Energy Cost

&Unpractical solution

Larger Required Initial Pump Head

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Valve Authority Concept

N=

Open Valve Pressure Drop (ΔP v100% )

Closed Valve Pressure Drop (ΔP v 0% )

N=

ΔP v100%

ΔP v100% + ΔPc100%

N=0.5

Total P.H.

ΔPv

M

ΔPc

N= )ΔP v100%(

2 )ΔPv100% (

- Δ Pc 100%Open : ΔP v 100% = P.H.

Close Off : ΔP v 0% = P.H. - 0

P.H.= ΔP v100% + ΔPc100%

ΔP v 100% ≥ Δ Pc 100%

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Flow%

Valve Stroke%

100%

100%

N=33%

N=50%

N=10%

N=1%

N=5%

Authority and Valve flow curve deviation

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Valve Sizing and valve Authority

Kv=

ΔPv

Q

Kv Selection

Lower Kv Higher Kv

Assumed to be equals to ΔPc i.e. N=0.5

Kv: Valve ability to pass the flow

Q : Flow (M 3/hr)

ΔPv: Initial Pressure drop across the valve (bar)

ΔPv ≥ ΔPc

N: from 0.5 to 0.7N: from 0.5 to 0.7

ΔPv ≤ ΔPcN: from 0.3 to 0.5N: from 0.3 to 0.5

From TheFrom The ControlControl Point of ViewPoint of View From TheFrom The EnergyEnergy Point of ViewPoint of View

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Thank YouThank You

Ibrahim Elsayed Ibrahim Elsayed KshanhKshanh

الرحيم الرحمن الله الرحيم بسم الرحمن الله بسم

علما ) ) زدنى ربى علما وقل زدنى ربى (( وقل

العظيم الله العظيم صدق الله صدق

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