Fundamentals of HVAC Control Systems -...

Fundamentals of HVAC Control Systems

18, 19, 25, 26 April 2007

ASHRAE Hong Kong Chapter Technical Workshop

About the Speakers

Dr. Sam C. M. HuiDept. of Mechanical Engineering, HKUOver 18 years of experience in teaching,

research, consultancy & design

Mr. William YickBusiness Development Director of

Johnson ControlsOver 30 years of professional experience in

the HVAC controls

“The Black Hairs”

“The White Hairs”

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, AssocAIAHKU 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

ASHRAE Study Guide

“Fundamentals of HVAC Control Systems”List price at US$150Included for each participant of the workshopDivided into 10 chaptersTypical structure of each chapter

InstructionsStudy ObjectivesMain BodyThe Next StepsSummaryBibliographySkill Development Exercises

Main Topics in Study Guide

1. Introduction to HVAC Control Systems2. Basic of Electricity3. Control Valves and Dampers4. Sensors and Auxiliary Devices5. Control Diagrams and Sequences6. Self-Powered Controls7. Electric Controls8. Pneumatic Controls9. Analog Electronic Controls10. Digital Controls

(* Practical considerations and applications are added too.)

Assumptions & Focus

AssumptionsAudience knows the basic HVAC equipment & terminologyAudience members have interest in HVAC control systems and may have some experience before or working on it now

Focus of this workshopBasic concepts of HVAC control systemsPractical considerations and applicationsUpdated with latest developments too, e.g. DDC system

Chapter 1Introduction to HVAC

Control Systems

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

Control System Types

Self-powered controlsElectric controlsPneumatic controlsAnalog electronic controlsDigital controls

Direct Digital Control (DDC)

* Most control systems today use a combination of the 5 system types

Hybrid control system

Block Diagram of a Control Loop

Simple Heating System

Key Terms

Controlled variableControl pointSetpointSensorControlled deviceProcess plantControllerControl loopClosed loop (i.e. w/ feedback)Open loop (i.e. w/o feedback)

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

[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings]

Basic Types of Control Modes

Two-position controlFloating controlModulating control

Two-Position Control

Two-Position ControlWith Anticipator

Step Control

Floating Control

P-I-D Control

Proportional-Only Control

P-I Control

Proportional Control Proportional-Integral(PI) Control

Proportional-Integral-Derivative (PID) Control

P, possibly PI for tight controlDewpoint temperature

P, possibly PI for tight controlHumidity

PI, Enhanced PIDFan static pressure

PI (use wide proportional band & a fast reset rate), PID

Air flow

PI, Enhanced PIDChiller discharge temperature

PI, Enhanced PIDCoil discharge temperature

PI, Enhanced PIDMixed air temperature

P, PIDSpace temperature

Control modeApplication

Recommended control modes for HVAC system

Pulse Width Modulation

Time-Proportioning Control

Proportional Control

(Gain and Loop Tuning – adjust the %gain to meet the specific application)

P-I Control

(Loop Tuning is an “art”. Usually tune the P gain first, then adjust I gain to eliminate offset)

P-I-D Control

(Derivative is seldom used because HVAC system response is rather slow.)

Proportional Control

Control Action & Normal Position

Sequencing

Control range(cooling)

Control range(heating)

Typical control ranges:- Pneumatic = 3-13 psi- Electronic = 2-12 Vdc

Chapter 2Basics 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

Simple Electrical Circuit

V = I x R P = V x I = I2 x R

Water Tank Analogy

Parallel Circuits

Series Circuits

Alternating Voltage

Simple AC Circuit

Capacitor in DC Circuit

Voltage & Current Out of Phase

Magnetic Field

Inductor in DC Circuit

3-Phase Voltage

P = V x I x PF x √3

Transformer

120/208V Service(4-wire Wye Connected)

480/277V Service(4-wire Wye Connected)

Electromagnetic Relay(On/Off signal; a type of remote-controlled switch)

Simple DC Circuit With Relay

Multipole Relay

Single- & Double-Throw Contacts

Across-the-Line Motor Starter(Start/stop control and overload protection)

Starter With H-O-A Switch(H-O-A = hand-off-auto)

Starter With H-O-A Switch& Aux. Contact

Starter With ManualStart/Stop Buttons

Magnetic Starter WithLife Safety Fan Wiring

Variable Speed Drives -Inverter VariableFrequency Drive

VSD = variable speed driveASD = adjustable speed drive

VFD = variable frequency drive

Sine-Coded PWM Waveform(PWM = pulse-width modulation)

Variable Speed DriveWith Optional Starter

(the starter is provided as a backup, in case the VSD fails)

Simple Relay Logic(Boolean logic notation, e.g. if (A or B) then C)

Relay Logic WithDouble-Throw Contact

Three-Way Light Switch

Symbols for Elec. Logic Devices

Voltage Feedback Bug(Ladder diagrams to show how devices are to be physically wired in the field.)

Correction forVoltage Feedback

Ladder Diagram

Fundamentals of HVAC Control Systems -...

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