3ashrae workshop control samhui part 3
TRANSCRIPT
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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 4
Sensors and Auxiliary Devices
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2007 ASHRAE Hong Kong Chapter Slide 3
Control System Components
1. Sensing elements Temperature, humidity/moisture, pressure, flow, proof of
operation (e.g. for safety interlock)
2. Transducers Convert (change) sensor inputs and controller outputs
from one analogue form to another, more usable,analogue form, e.g. pressure-to-voltage
3. Controllers Receive inputs from sensors
Compares the input signal with the setpoint
Generates an output signal to operate a controlleddevice
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Control System Components
4. Actuators
A device that converts electric or pneumatic energy intoa rotary or linear action, e.g. for valves and dampers
(can be pneumatic or electrical controlled)
5. Auxiliary elements Transducers to convert signals from one type to another
(e.g. from pneumatic to electric)
Relays and switches to manipulate signals, electric
power and compressed air supplies to power the controlsystem
Indicating devices to facilitate monitoring of control
system activity
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[Source: Honeywell, 1997.Engineering Manual of Automatic Control: for Commercial Buildings]
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2007 ASHRAE Hong Kong Chapter Slide 6
[Source: Honeywell, 1997.Engineering Manual of Automatic Control: for Commercial Buildings]
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2007 ASHRAE Hong Kong Chapter Slide 7
Types of Sensors
Temperature sensors
Humidity sensors Pressure sensors
Flow sensors
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2007 ASHRAE Hong Kong Chapter Slide 8
Types of Temperature Sensors
Bimetallic
Fluid expansion Seebeck effect
Electrical resistance
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2007 ASHRAE Hong Kong Chapter Slide 9
[Source: Honeywell, 1997.Engineering Manual of Automatic Control: for Commercial Buildings]
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2007 ASHRAE Hong Kong Chapter Slide 10
Bimetallic Temperature Sensor
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2007 ASHRAE Hong Kong Chapter Slide 11
Mercury Switch
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2007 ASHRAE Hong Kong Chapter Slide 12
Rod-and-Tube Sensors
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2007 ASHRAE Hong Kong Chapter Slide 13
Capillary Sensor
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2007 ASHRAE Hong Kong Chapter Slide 14
Types of Humidity Sensors
Relative humidity sensors
Mechanical sensors Resistance-type sensors
Capacitance-type sensors
Dewpoint temperature sensors Saturated salt solution type Chilled mirror type
Wetbulb temperature sensors
Psychrometers
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2007 ASHRAE Hong Kong Chapter Slide 15
Chilled Mirror Dewpoint Sensor
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2007 ASHRAE Hong Kong Chapter Slide 16
Moisture Sensing Elements
Mechanical expand and contract as the
moisture level change ( hygroscopic ),e.g. nylon
Electronic change in either the
resistance or capacitance of the element Can be affected by temperature changes
Temperature compensation may be needed
A dew point sensor senses dew pointdirectly or detects condensation on a
cooled surface
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2007 ASHRAE Hong Kong Chapter Slide 17
[Source: Honeywell, 1997.Engineering Manual of Automatic Control: for Commercial Buildings]
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2007 ASHRAE Hong Kong Chapter Slide 18
Types of Pressure Sensors
Bourdon tube
Spiral tube Diaphragm sensor
Strain gauge
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2007 ASHRAE Hong Kong Chapter Slide 19
Bourdon Tube Pressure Sensor
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2007 ASHRAE Hong Kong Chapter Slide 20
Diaphragm Pressure Sensor
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2007 ASHRAE Hong Kong Chapter Slide 21
Flow Sensors
Sense the rate of liquid and gas flow Flow is difficult to sense accurately under all conditions
Selecting the best flow-sensing technique
for an application requires considering
many aspects Level of accuracy required
The medium being measured
The degree of variation in the measured flow
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2007 ASHRAE Hong Kong Chapter Slide 22
[Source: Honeywell, 1997.Engineering Manual of Automatic Control: for Commercial Buildings]
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2007 ASHRAE Hong Kong Chapter Slide 23
Types of Flow Sensors
Differential pressure flow sensors
Displacement flow sensors Passive flow sensors
Mass flow sensors
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2007 ASHRAE Hong Kong Chapter Slide 24
Orifice Plate Flow Sensor
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2007 ASHRAE Hong Kong Chapter Slide 25
Venturi Flow Meter
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2007 ASHRAE Hong Kong Chapter Slide 26
Pitot Tube Sensor
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2007 ASHRAE Hong Kong Chapter Slide 27
Air Flow Measuring Station
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2007 ASHRAE Hong Kong Chapter Slide 28
Averaging Pipe-Mounted
Pitot Meter
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Paddle Flow Switch
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2007 ASHRAE Hong Kong Chapter Slide 30
Inline Turbine Flow Meter
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2007 ASHRAE Hong Kong Chapter Slide 31
Target Meter
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2007 ASHRAE Hong Kong Chapter Slide 32
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2007 ASHRAE Hong Kong Chapter Slide 33
Ultrasonic Meter
Thermal Anemometer
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2007 ASHRAE Hong Kong Chapter Slide 34
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2007 ASHRAE Hong Kong Chapter Slide 35
Flow Measurement Devices
Selecting flow measurement devices Ref.: see the technical article
Spitzer, D. W., 2002. Selecting flow measurement
devices, HPAC Engineering, 74 (12): 52-59.
What flow meters measure (volume/mass)
Chilled water flow meters Differential pressure
Magnetic
Turbine Ultrasonic
Vortex shedding & fluidic
Selection criteria & considerations
Types of Auxiliary Devices
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2007 ASHRAE Hong Kong Chapter Slide 36
Relays
Fan and pump status switches
Timeclocks Wind-up t imers
Limit switches
Manual switches
High and low limit switches
Fire and smoke detectors
Indicating lights
Audible alarms Monitoring instrumentation
Time-Delay Relay Wiring
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2007 ASHRAE Hong Kong Chapter Slide 37
Limit Switch
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2007 ASHRAE Hong Kong Chapter Slide 38
Manual Rotary
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2007 ASHRAE Hong Kong Chapter Slide 39
Switch Configurations
Duct Smoke Detector
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2007 ASHRAE Hong Kong Chapter Slide 40
Alarm Horn and Light
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2007 ASHRAE Hong Kong Chapter Slide 41