Fundamentals of HVAC Control Systems

Transkript

1 ASHRAE Hong Kong Chapter Technical Workshop Fundamentals of HVAC Control Systems 18, 19, 25, 26 April ASHRAE Hong Kong Chapter Slide 1

2 Chapter 4 Sensors and Auxiliary Devices 2007 ASHRAE Hong Kong Chapter Slide 2

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 controlled device 2007 ASHRAE Hong Kong Chapter Slide 3

4 Control System Components 4. Actuators A device that converts electric or pneumatic energy into a 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 control system Indicating devices to facilitate monitoring of control system activity 2007 ASHRAE Hong Kong Chapter Slide 4

5 [Source: Honeywell, Engineering Manual of Automatic Control: for Commercial Buildings] 2007 ASHRAE Hong Kong Chapter Slide 5

6 [Source: Honeywell, Engineering Manual of Automatic Control: for Commercial Buildings] 2007 ASHRAE Hong Kong Chapter Slide 6

7 Types of Sensors Temperature sensors Humidity sensors Pressure sensors Flow sensors 2007 ASHRAE Hong Kong Chapter Slide 7

8 Types of Temperature Sensors Bimetallic Fluid expansion Seebeck effect Electrical resistance 2007 ASHRAE Hong Kong Chapter Slide 8

9 [Source: Honeywell, Engineering Manual of Automatic Control: for Commercial Buildings] 2007 ASHRAE Hong Kong Chapter Slide 9

10 Bimetallic Temperature Sensor 2007 ASHRAE Hong Kong Chapter Slide 10

11 Mercury Switch 2007 ASHRAE Hong Kong Chapter Slide 11

12 Rod-and-Tube Sensors 2007 ASHRAE Hong Kong Chapter Slide 12

13 Capillary Sensor 2007 ASHRAE Hong Kong Chapter Slide 13

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 2007 ASHRAE Hong Kong Chapter Slide 14

15 Chilled Mirror Dewpoint Sensor 2007 ASHRAE Hong Kong Chapter Slide 15

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 point directly or detects condensation on a cooled surface 2007 ASHRAE Hong Kong Chapter Slide 16

17 [Source: Honeywell, Engineering Manual of Automatic Control: for Commercial Buildings] 2007 ASHRAE Hong Kong Chapter Slide 17

18 Types of Pressure Sensors Bourdon tube Spiral tube Diaphragm sensor Strain gauge 2007 ASHRAE Hong Kong Chapter Slide 18

19 Bourdon Tube Pressure Sensor 2007 ASHRAE Hong Kong Chapter Slide 19

20 Diaphragm Pressure Sensor 2007 ASHRAE Hong Kong Chapter Slide 20

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 2007 ASHRAE Hong Kong Chapter Slide 21

22 [Source: Honeywell, Engineering Manual of Automatic Control: for Commercial Buildings] 2007 ASHRAE Hong Kong Chapter Slide 22

23 Types of Flow Sensors Differential pressure flow sensors Displacement flow sensors Passive flow sensors Mass flow sensors 2007 ASHRAE Hong Kong Chapter Slide 23

24 Orifice Plate Flow Sensor 2007 ASHRAE Hong Kong Chapter Slide 24

25 Venturi Flow Meter 2007 ASHRAE Hong Kong Chapter Slide 25

26 Pitot Tube Sensor 2007 ASHRAE Hong Kong Chapter Slide 26

27 Air Flow Measuring Station 2007 ASHRAE Hong Kong Chapter Slide 27

28 Averaging, Pipe-Mounted Pitot Meter 2007 ASHRAE Hong Kong Chapter Slide 28

29 Annubar Flow Sensor 2007 ASHRAE Hong Kong Chapter Slide 29

30 Paddle Flow Switch 2007 ASHRAE Hong Kong Chapter Slide 30

31 Inline Turbine Flow Meter 2007 ASHRAE Hong Kong Chapter Slide 31

32 Target Meter 2007 ASHRAE Hong Kong Chapter Slide 32

33 Ultrasonic Meter 2007 ASHRAE Hong Kong Chapter Slide 33

34 Thermal Anemometer 2007 ASHRAE Hong Kong Chapter Slide 34

35 Flow Measurement Devices Selecting flow measurement devices Ref.: see the technical article Spitzer, D. W., Selecting flow measurement devices, HPAC Engineering, 74 (12): What flow meters measure (volume/mass) Chilled water flow meters Differential pressure Magnetic Turbine Ultrasonic Vortex shedding & fluidic Selection criteria & considerations 2007 ASHRAE Hong Kong Chapter Slide 35

36 Types of Auxiliary Devices Relays Fan and pump status switches Timeclocks Wind-up timers Limit switches Manual switches High and low limit switches Fire and smoke detectors Indicating lights Audible alarms Monitoring instrumentation 2007 ASHRAE Hong Kong Chapter Slide 36

37 Time-Delay Relay Wiring 2007 ASHRAE Hong Kong Chapter Slide 37

38 Limit Switch 2007 ASHRAE Hong Kong Chapter Slide 38

39 Manual Rotary Switch Configurations 2007 ASHRAE Hong Kong Chapter Slide 39

40 Duct Smoke Detector 2007 ASHRAE Hong Kong Chapter Slide 40

41 Alarm Horn and Light 2007 ASHRAE Hong Kong Chapter Slide 41