Electric Valve Application

Refrigeration and Air Conditioning SystemsRefrigeration and Air Conditioning Systems

Tom BourquinProduct Manager - Electric Valves

February 14, 2012

Mechanical Valve Fundamental Forces

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Electric Valve Basics

• Electronically controlled• Non refrigerant specific• Non refrigerant specific• Wide load control capability

Relatively few valves cover• Relatively few valves cover multiple applications and capacity

• “Tight” superheat control• Tight superheat control• Direct temperature or pressure

control capabilitycontrol capability• Remote monitoring capability• Not restricted by physics• Not restricted by physics

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Heat Motor Valve

• Legacy electric valve design• Legacy electric valve design• Sensor reacts to refrigerant

temperaturetemperature• Control modulates energy to

valve heatervalve heater• Heater expands liquid and

modulates valve• Hysteresis and response issues

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Modulating Solenoid Valve

• Magnetic field modulated• Magnetic field modulated to control valve position

C t lt• Current or voltage modulation

• High hysteresis• Repeatability concernsp y

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Pulse Width Solenoid Valve

Val e is either open (energi ed)• Valve is either open (energized)or closed – no modulation

• Percent of time energized• Percent of time energized determines flow capacity

• Can cause “refrigerant hammer”• Can cause refrigerant hammer ,stressing system components• Applicable for larger systemsApplicable for larger systems

• Can have longevity concerns

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Stepper Motor Valves

• Controls in fine increments• Each step is a small fraction of

a revolution• Excellent resolution and

repeatability• Variation in step position is

not cumulative• Uni-polar and bi-polar motors• Internal and external stators

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Uni-polar step motors

• Permanent magnet rotors• Permanent magnet rotors• “Pull” control strategy

Only part of stator• Only part of stator windings used for each stepstep

• Lower torque output• Typically applied in• Typically applied in

smaller applications

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Conceptual Model of Uni-polar step motor

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Bi-polar step motors

• Permanent magnet rotors• “Push-Pull” control strategy• Higher torque output

• Suitable for any size application

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Conceptual Model of Bi-Polar Step Motor

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External Stator Step Motor Construction

• Stator is “dry” (external)• Electrical connections

are accessible• Stator is replaceable

• Rotor is “wet” (internal)• Magnetic field must pass

through large air gap to affect rotor• Reduces available power for a given

amount of materialM i i i i d d• Mounting is orientation dependent

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Internal Stator Step Motor Construction

• Stator and rotor are both “wet” (internal)( )• Electrical connections must be made

through a glass “feed-thru”• Actuator assembly and cable can be

replaceable• Air gap can be set to optimum dimension

• Maximizes power for material• Mounting can be independent of

orientation

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Typical Internal Stator Construction

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Digital Linear Actuators

• Step motor rotation• Step motor rotation converted to linear motion via anti-rotation device

• Can utilize a gear train to magnify torque and linear g y qforce, and increase resolution

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Significance of resolution

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4 55

5.56

6.5

2)

2.53

3.54

4.5

ON

S (

R-2

00.5

11.5

2TO

00 250 500 750 1000 1250 1500 1750 2000 2250 2500

EEV POSITION (STEPS)

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Electric Stepper Valve Control

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Electric Stepper Valve Control

• Electronic control has embedded algorithm• Superheat pressure and/or temperature control• Superheat, pressure, and/or temperature control• Standalone control or embedded in system hardware

• Sensors react to system temperature / pressure• Sensors react to system temperature / pressure• Control interprets data and modulates valve• Process repeats• Process repeats

continuously

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TXV Pulldown and Superheat Control

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EEV Pulldown and Superheat Control

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TXV versus EEV Superheat Control

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TXV versus EEV Superheat Control

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TXV versus EEV Superheat Control

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Mechanical / Solenoid Subcooler Control

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Mechanical / Solenoid Subcooler Control

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EEV / Mechanical EPR Subcooler Control

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EEV / Mechanical EPR Subcooler Control

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PID Control Algorithm

• 3 control methods in one• 3 control methods in one algorithm• Proportional – respondsProportional responds

to offset from setpoint• Integral – responds toIntegral responds to

change in offset• Derivative – responds p

to slope of adjustments

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Impact of PID on System Control

PID adjustment

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Impact of PID on System ControlPID adjustment

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System Control Strategy

• Ideal system control involves integrating all• Ideal system control involves integrating all component level controls• Allows for effective monitoring and eliminatesAllows for effective monitoring and eliminates

“control confusion”• Even without an integrated system control,Even without an integrated system control,

considering potential control scheme conflicts is important

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EEV Superheat Control – Suction Stop

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20

14

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8

10

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4

6

8

0

2

4

4 5 6 7 8 9 2 3 4 5 6 8 9 0 2 3 5 6 7 8 9 0 2 3 4 5 6 7 9 0 2 3 4 6 7 8 9 0 3 4 5 6 7 8 0

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7:24

7:25

7:26

7:27

7:28

7:29

7:31

7:3 2

7:33

7:34

7:35

7:36

7:38

7:39

7:40

7:41

7:4 2

7:43

7:45

7:46

7:47

7:48

7:49

7:50

7:52

7:53

7:54

7:55

7:56

7:57

7:59

8:00

8:01

8:0 2

8:03

8:04

8:06

8:07

8:08

8:09

8:10

8:11

8:1 3

8:14

8:15

8:16

8:17

8:18

8:20

8:21

EEV Valve Position – Suction Stop25

20

10

15

5

10

0

4 5 6 7 8 9 1 2 3 4 5 6 8 9 0 1 2 3 5 6 7 8 9 0 2 3 4 5 6 7 9 0 1 2 3 4 6 7 8 9 0 1 3 4 5 6 7 8 0 1

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7:24

7:25

7:26

7:27

7:28

7:29

7:3

7:3 2

7:33

7:34

7:35

7:36

7:38

7:39

7:40

7:4

7:4 2

7:43

7:45

7:46

7:47

7:48

7:49

7:50

7:52

7:53

7:54

7:55

7:56

7:57

7:59

8:00

8:0

8:0 2

8:03

8:04

8:06

8:07

8:08

8:09

8:10

8:1

8:1 3

8:14

8:15

8:16

8:17

8:18

8:20

8:2

Electric Valves – What’s Next?

• Stepper motor valves have been utilized for over 20 years but are still relatively immatureover 20 years, but are still relatively immature compared to mechanical valves• Advances in electronic controls are• Advances in electronic controls are

accelerating implementation• PID control is improving and is trending towardPID control is improving, and is trending toward

more “self-tuning” style controls• Creativity is becoming the limitation on systemCreativity is becoming the limitation on system

design

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Thank you!

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