Download - ASHRAE Workshop Basics
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© 2007 ASHRAE Hong Kong Chapter Slide 1
Fundamentals of HVAC Control Systems
18, 19, 25, 26 April 2007
ASHRAE Hong Kong Chapter Technical Workshop
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© 2007 ASHRAE Hong Kong Chapter Slide 2
Chapter 5Control Diagramsand Sequences
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© 2007 ASHRAE Hong Kong Chapter Slide 3
Design Criteria - I
The control system:Must meet the needs of the processShould control the process as directly as possibleMust be designed to work with the HVAC system and vice versa
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© 2007 ASHRAE Hong Kong Chapter Slide 4
Design Criteria - II
The control system:Should minimize energy consumption while meeting process goalsMust meet the budgetMust be designed for maximum simplicityMust be easy to understand and maintain
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© 2007 ASHRAE Hong Kong Chapter Slide 5
Lower energy cost Lower operations cost
Increase flexibility Ensure quality building environment
Aims of HVAC Control SystemAims of HVAC Control System
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© 2007 ASHRAE Hong Kong Chapter Slide 6
Key Personnel
HVAC system designerResponsible for conceptual design, tendering, etc.
Controls vendor sales representativeProvide advice on control products & features
Mechanical contractorInstallation of mechanical parts
Electrical contractorInstallation of electrical parts
Controls contractorDetails of control system + part of the installation
Installation
Design, etc.
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© 2007 ASHRAE Hong Kong Chapter Slide 7
Typical Installation Tasks
Mechanical contractorInstallation of control valves, dampers, air and water measuring devicesProvision of control dampersInstallation of duct mounted smoke detectorsProvision of variable speed drivesProvision of starters for package equipment and special machinery (e.g. chiller)Provision of starters with thermal overload protection or motors with integral thermal overload protection
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© 2007 ASHRAE Hong Kong Chapter Slide 8
Typical Installation Tasks
Electrical contractor (the controls work)Motor startersFire alarm and life safety control relays and switches and all smoke detectorsWiring and mounting line voltage controlsPower to control panels
Controls contractorSelection of control valvesSelection of actuators for both valves and dampersControl and interlock wiring
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© 2007 ASHRAE Hong Kong Chapter Slide 9
Control Diagrams and Symbols
Symbols for HVAC system componentsRefer to ASHRAE Fundamentals Handbook 2005 Chp. 37, Abbreviations and SymbolsRefer to other local standards or guidelinesUsually specified in the contract drawings & documents
Generic control diagramsUsing generic symbols to describe and define the requirements of the control system
Shop drawings by contractorsSpecific hardware control diagrams
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© 2007 ASHRAE Hong Kong Chapter Slide 10
[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 11
Generic Symbols - I
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© 2007 ASHRAE Hong Kong Chapter Slide 12
Generic Symbols - II
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© 2007 ASHRAE Hong Kong Chapter Slide 13
Writing Control Sequences - I
Break the sequence into logical partsClearly indicate the control point and controlled device and how the setpoint is determinedConsider using enabling interlocksState the required/desired setpointsEach variable should be controlled by a single control loop
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© 2007 ASHRAE Hong Kong Chapter Slide 14
Writing Control Sequences - II
State how each device should be controlled when the system operates normally, shuts down and in emergenciesSpecify the normal position of important controlled devicesControl sequences should be as specific as possibleSimplify control sequences to avoid bugs
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© 2007 ASHRAE Hong Kong Chapter Slide 15
Single-Zone Air Handler
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© 2007 ASHRAE Hong Kong Chapter Slide 16
Single-Zone Unit WithDual Setpoint Thermostat
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© 2007 ASHRAE Hong Kong Chapter Slide 17
Typical VAV System
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© 2007 ASHRAE Hong Kong Chapter Slide 18
Control diagram of a VAV reheat system for year-round operation
[Source: Wang, S. K., 2001. Handbook of Air Conditioning and Refrigeration]
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© 2007 ASHRAE Hong Kong Chapter Slide 19
Pressure Independent Control
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© 2007 ASHRAE Hong Kong Chapter Slide 20
Chilled Water, Economizer and Hot Water Sequencing
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© 2007 ASHRAE Hong Kong Chapter Slide 21
Reset Schedule
(13 deg C)
F F
(18 deg C)
(13 deg C)
(16 deg C)
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© 2007 ASHRAE Hong Kong Chapter Slide 22
[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings]
Discharge air control loop with reset
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© 2007 ASHRAE Hong Kong Chapter Slide 23[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 24
Thermostat model of proportional control with deadbandand dual throttling range
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© 2007 ASHRAE Hong Kong Chapter Slide 25
Practical Examples forAir Handling System
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© 2007 ASHRAE Hong Kong Chapter Slide 26
Practical Examples forAir Handling System
Reference document:Honeywell, 1997. Engineering Manual of Automatic Control for Commercial Buildings - Heating, Ventilating, Air Conditioning, SI Edition., Honeywell, Inc., Minneapolis, MN, pp. 201-260.
Air Handling System Control ApplicationsAbbreviations and symbolsRequirements for Effective Control (general guidelines)Different HVAC processesASHRAE Psychrometric Charts
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© 2007 ASHRAE Hong Kong Chapter Slide 27
Practical Examples forAir Handling System
Typical format and design informationFunctional description (w/ diagram)FeaturesConditions for successful operationLimitationsSpecificationsPsychrometric aspects
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© 2007 ASHRAE Hong Kong Chapter Slide 28
Fan system start-stop control
[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 29
Fixed quantity of outdoor air control
Two-positiondamper
Return air
Deliver/supply air
[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 30
Mixed air control
[Source: Honeywell, 1997. Engineering Manual ofAutomatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 31
Economizer cycle control (outdoor air dry bulb)
[Source: Honeywell, 1997. Engineering Manual ofAutomatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 32
Economizer cycle control (outdoor air enthalpy)
[Source: Honeywell, 1997. Engineering Manual ofAutomatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 33
Economizer cycle control (outdoor air enthalpy)
[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 34
Economizer cycle control (outdoor air/return air enthalpy comparison)
[Source: Honeywell, 1997. Engineering Manual ofAutomatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 35
Mixed air control with economizer cycle
[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 36
Mixed air control with economizer cycle
[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 37
Economizer cycle control of space temperature withsupply air temperature setpoint reset
[Source: Honeywell, 1997. Engineering Manual of Automatic Control: for Commercial Buildings]
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© 2007 ASHRAE Hong Kong Chapter Slide 38
Designing Direct Digital Control (DDC) Systems
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© 2007 ASHRAE Hong Kong Chapter Slide 39
Design DDC systems
Design an effective DDC systemSimplicity & effective technical communication
Types of DDC signalsDigital output (DO), e.g. command to open a valveDigital input (DI), e.g. status signal from a fanAnalogue input (AI), e.g. room temperatureAnalogue output (AO), e.g. command to modulate a control valve
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© 2007 ASHRAE Hong Kong Chapter Slide 40
A simple DDC control system[Source: Shadpour, F., 2001. The Fundamentals of HVAC Direct Digital Control]
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© 2007 ASHRAE Hong Kong Chapter Slide 41
Componentsof a energymanagementsystem (EMS)with directdigital control(DDC)
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© 2007 ASHRAE Hong Kong Chapter Slide 42
Managementlevel
Control level
Operational level
Field level
Outstation, discrete controller
Sensor, switch, etc.
Central station
Central station communication via gateways
Levels of control in building energy management system
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© 2007 ASHRAE Hong Kong Chapter Slide 43
Example of system architecture for building management system
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© 2007 ASHRAE Hong Kong Chapter Slide 44
Six steps of DDC system design
System schematicControl point designationsPoint listDDC system architectureSequence of operationSpecifications
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© 2007 ASHRAE Hong Kong Chapter Slide 45
System schematic for a constant volume single zone AHU[Source: Shadpour, F., 2001. The Fundamentals of HVAC Direct Digital Control]
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© 2007 ASHRAE Hong Kong Chapter Slide 46
Control point designations for a constant volume single zone AHU[Source: Shadpour, F., 2001. The Fundamentals of HVAC Direct Digital Control]
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© 2007 ASHRAE Hong Kong Chapter Slide 47
[Source: Shadpour, F., 2001. The Fundamentals of HVAC Direct Digital Control]
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© 2007 ASHRAE Hong Kong Chapter Slide 48
An example of DDC system architecture[Source: Shadpour, F., 2001. The Fundamentals of HVAC Direct Digital Control]
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© 2007 ASHRAE Hong Kong Chapter Slide 49
Primary Bus
Primary Control Unit
OperatorInterface
WorkstationWeb
Server
Primary Control Unit
Secondary BusSecondary Bus
Central Plant Controller
Air Handler Controller
VAVBox
VAVBox
VAVBox
Lighting Controller
BACnetDevice
LonTalkDevice
System architecture of building automation system
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© 2007 ASHRAE Hong Kong Chapter Slide 50[Source: Shadpour, F., 2001. The Fundamentals of HVAC Direct Digital Control]
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© 2007 ASHRAE Hong Kong Chapter Slide 51
WorkmanshipQuantity of components
Material requiredSize of components
Quality of componentsLocation of devices
Indicate in specificationsShow on drawings
[Source: Shadpour, F., 2001. The Fundamentals of HVAC Direct Digital Control]
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© 2007 ASHRAE Hong Kong Chapter Slide 52
Useful References
Books:Honeywell, 1997. Engineering Manual of Automatic Control for Commercial Buildings - Heating, Ventilating, Air Conditioning, SI Edition., Honeywell, Inc., Minneapolis, MN.
http://customer.honeywell.com/Techlit/pdf/77-0000s/77-1200.pdf
Shadpour, F., 2001. The Fundamentals of HVAC Direct Digital Control: Practical Applications and Design, 2nd ed., Hacienda Blue, Escondido, CA.
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© 2007 ASHRAE Hong Kong Chapter Slide 53
Useful References
Research papers:Hui, S. C. M., 2007. Latest trends in building automation and control systems, In Proc. of the CAI Symposium 2007 on Intelligent Facility Management and Intelligent Transport, 28 March 2007, Hong Kong, 10 pages.
http://web.hku.hk/~cmhui/CAI-2007_SamHui.pdfSpitzer, D. W., 2002. Selecting flow measurement devices, HPAC Engineering, 74 (12): 52-59.
Website:DDC Online [www.ddc-online.org]