PID Floating Control
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ASHRAE Hong Kong Chapter Technical Workshop
Fundamentals of HVAC Control Systems 18, 19, 25, 26 April 2007
© 2007 ASHRAE Hong Kong Chapter
Slide 1
About the Speakers “The Black Hairs”
Dr. Sam C. M. Hui Dept. of Mechanical Engineering, HKU Over 18 years of experience in teaching, research, consultancy & design
Mr. William Yick Business Development Director of Johnson Controls Over 30 years of professional experience in the HVAC controls
“The White Hairs”
© 2007 ASHRAE Hong Kong Chapter
Slide 2
Know The Instructor
Dr. Sam C M Hui – Dept. of Mech. Engg., The University of Hong Kong
PhD, BEng(Hons), CEng, CEM, MASHRAE, MCIBSE, MHKIE, MIESNA, LifeMAEE, AssocAIA HKU Dept. of Mechanical Engineering (4.5 years) HKU Dept. of Architecture (6 years) Asia Pacific Energy Research Centre, Japan (~1 year) PhD study (4 years) Associated Consulting Engineers (2 years)
Current role in ASHRAE:
President of ASHRAE Hong Kong Chapter
© 2007 ASHRAE Hong Kong Chapter
Slide 3
ASHRAE Study Guide
“Fundamentals of HVAC Control Systems” List price at US$150 Included for each participant of the workshop Divided into 10 chapters Typical structure of each chapter à Instructions à Study Objectives à Main Body à The Next Steps à Summary à Bibliography à Skill Development Exercises
© 2007 ASHRAE Hong Kong Chapter
Slide 4
Main Topics in Study Guide
1. Introduction to HVAC Control Systems 2. Basic of Electricity 3. Control Valves and Dampers 4. Sensors and Auxiliary Devices 5. Control Diagrams and Sequences 6. Self-Powered Controls 7. Electric Controls 8. Pneumatic Controls 9. Analog Electronic Controls 10. Digital Controls (* Practical considerations and applications are added too.)
© 2007 ASHRAE Hong Kong Chapter
Slide 5
Assumptions & Focus
Assumptions Audience knows the basic HVAC equipment & terminology Audience members have interest in HVAC control systems and may have some experience before or working on it now
Focus of this workshop Basic concepts of HVAC control systems Practical considerations and applications Updated with latest developments too, e.g. DDC system
© 2007 ASHRAE Hong Kong Chapter
Slide 6
Chapter 1 Introduction to HVAC Control Systems
© 2007 ASHRAE Hong Kong Chapter
Slide 7
Why We Need Controls?
To regulate the output of systems and equipment
Such as your car
For HVAC system, to regulate the movement of air, water, electricity to obtain desired indoor conditions
Also for energy management and safety
© 2007 ASHRAE Hong Kong Chapter
Slide 8
Control System Types
Self-powered controls Electric controls Pneumatic controls Analog electronic controls Digital controls
Direct Digital Control (DDC)
* Most control systems today use a combination of the 5 system types
Hybrid control system
© 2007 ASHRAE Hong Kong Chapter
Slide 9
Block Diagram of a Control Loop
© 2007 ASHRAE Hong Kong Chapter
Slide 10
Simple Heating System
© 2007 ASHRAE Hong Kong Chapter
Slide 11
Key Terms
Controlled variable Control point Setpoint Sensor Controlled device Process plant Controller Control loop Closed loop (i.e. w/ feedback) Open loop (i.e. w/o feedback)
© 2007 ASHRAE Hong Kong Chapter
Slide 12
Some Definitions
Automatic control system: A system that reacts to a change or imbalance in the variable it controls by adjusting other variables to restore the system to the desired balance. Controlled Variable: The quantity or condition that is measured and controlled. Controller: A device that senses changes in the controlled
© 2007 ASHRAE Hong Kong Chapter
Slide 13
[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings] © 2007 ASHRAE Hong Kong Chapter
Slide 14
Basic Types of Control Modes
Two-position control Floating control Modulating control
© 2007 ASHRAE Hong Kong Chapter
Slide 15
Two-Position Control
© 2007 ASHRAE Hong Kong Chapter
Slide 16
Two-Position Control With Anticipator
© 2007 ASHRAE Hong Kong Chapter
Slide 17
Step Control
© 2007 ASHRAE Hong Kong Chapter
Slide 18
Floating Control
© 2007 ASHRAE Hong Kong Chapter
Slide 19
P-I-D Control
© 2007 ASHRAE Hong Kong Chapter
Slide 20
Proportional-Only Control
© 2007 ASHRAE Hong Kong Chapter
Slide 21
P-I Control
© 2007 ASHRAE Hong Kong Chapter
Slide 22
Proportional Control
Proportional-Integral (PI) Control
Proportional-IntegralDerivative (PID) Control
[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings] © 2007 ASHRAE Hong Kong Chapter
Slide 23
Recommended control modes for HVAC system Application
Control mode
Space temperature
P, PID
Mixed air temperature
PI, Enhanced PID
Coil discharge temperature
PI, Enhanced PID
Chiller discharge temperature
PI, Enhanced PID
Air flow
PI (use wide proportional band & a fast reset rate), PID
Fan static pressure
PI, Enhanced PID
Humidity
P, possibly PI for tight control
Dewpoint temperature
P, possibly PI for tight control
[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings] © 2007 ASHRAE Hong Kong Chapter
Slide 24
Pulse Width Modulation
© 2007 ASHRAE Hong Kong Chapter
Slide 25
Time-Proportioning Control
© 2007 ASHRAE Hong Kong Chapter
Slide 26
Proportional Control (Gain and Loop Tuning – adjust the %gain to meet the specific application)
© 2007 ASHRAE Hong Kong Chapter
Slide 27
P-I Control (Loop Tuning is an “art”. Usually tune the P gain first, then adjust I gain to eliminate offset)
© 2007 ASHRAE Hong Kong Chapter
Slide 28
P-I-D Control (Derivative is seldom used because HVAC system response is rather slow.)
© 2007 ASHRAE Hong Kong Chapter
Slide 29
Proportional Control
© 2007 ASHRAE Hong Kong Chapter
Slide 30
Control Action & Normal Position
© 2007 ASHRAE Hong Kong Chapter
Slide 31
Sequencing
Typical control ranges: - Pneumatic = 3-13 psi - Electronic = 2-12 Vdc Control range (heating)
© 2007 ASHRAE Hong Kong Chapter
Control range (cooling)
Slide 32
Chapter 2 Basics of Electricity Introduce simple electrical circuits and common devices for controlling electrical power in HVAC systems. Some concepts of electronics are also helpful. Common devices: relays, transformers, starters
© 2007 ASHRAE Hong Kong Chapter
Slide 33
Simple Electrical Circuit V=IxR
© 2007 ASHRAE Hong Kong Chapter
P = V x I = I2 x R
Slide 34
Water Tank Analogy
© 2007 ASHRAE Hong Kong Chapter
Slide 35
Parallel Circuits
© 2007 ASHRAE Hong Kong Chapter
Slide 36
Series Circuits
© 2007 ASHRAE Hong Kong Chapter
Slide 37
Alternating Voltage
© 2007 ASHRAE Hong Kong Chapter
Slide 38
Simple AC Circuit
© 2007 ASHRAE Hong Kong Chapter
Slide 39
Capacitor in DC Circuit
© 2007 ASHRAE Hong Kong Chapter
Slide 40
Voltage & Current Out of Phase
© 2007 ASHRAE Hong Kong Chapter
Slide 41
Magnetic Field
© 2007 ASHRAE Hong Kong Chapter
Slide 42
Inductor in DC Circuit
© 2007 ASHRAE Hong Kong Chapter
Slide 43
3-Phase Voltage P = V x I x PF x √3
© 2007 ASHRAE Hong Kong Chapter
Slide 44
Transformer
© 2007 ASHRAE Hong Kong Chapter
Slide 45
120/208V Service (4-wire Wye Connected)
© 2007 ASHRAE Hong Kong Chapter
Slide 46
480/277V Service (4-wire Wye Connected)
© 2007 ASHRAE Hong Kong Chapter
Slide 47
Electromagnetic Relay (On/Off signal; a type of remote-controlled switch)
© 2007 ASHRAE Hong Kong Chapter
Slide 48
Simple DC Circuit With Relay
© 2007 ASHRAE Hong Kong Chapter
Slide 49
Multipole Relay
© 2007 ASHRAE Hong Kong Chapter
Slide 50
Single- & Double-Throw Contacts
© 2007 ASHRAE Hong Kong Chapter
Slide 51
Across-the-Line Motor Starter (Start/stop control and overload protection)
© 2007 ASHRAE Hong Kong Chapter
Slide 52
Starter With H-O-A Switch (H-O-A = hand-off-auto)
© 2007 ASHRAE Hong Kong Chapter
Slide 53
Starter With H-O-A Switch & Aux. Contact
© 2007 ASHRAE Hong Kong Chapter
Slide 54
Starter With Manual Start/Stop Buttons
© 2007 ASHRAE Hong Kong Chapter
Slide 55
Magnetic Starter With Life Safety Fan Wiring
© 2007 ASHRAE Hong Kong Chapter
Slide 56
Variable Speed Drives Inverter Variable Frequency Drive
VSD = variable speed drive ASD = adjustable speed drive VFD = variable frequency drive © 2007 ASHRAE Hong Kong Chapter
Slide 57
Sine-Coded PWM Waveform (PWM = pulse-width modulation)
© 2007 ASHRAE Hong Kong Chapter
Slide 58
Variable Speed Drive With Optional Starter (the starter is provided as a backup, in case the VSD fails)
© 2007 ASHRAE Hong Kong Chapter
Slide 59
Simple Relay Logic (Boolean logic notation, e.g. if (A or B) then C)
© 2007 ASHRAE Hong Kong Chapter
Slide 60
Relay Logic With Double-Throw Contact
© 2007 ASHRAE Hong Kong Chapter
Slide 61
Three-Way Light Switch
© 2007 ASHRAE Hong Kong Chapter
Slide 62
Symbols for Elec. Logic Devices
© 2007 ASHRAE Hong Kong Chapter
Slide 63
Voltage Feedback Bug (Ladder diagrams to show how devices are to be physically wired in the field.)
© 2007 ASHRAE Hong Kong Chapter
Slide 64
Correction for Voltage Feedback
© 2007 ASHRAE Hong Kong Chapter
Slide 65
Ladder Diagram
© 2007 ASHRAE Hong Kong Chapter
Slide 66
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