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  1. #1
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    VAV damper actuator

    Modulating actuator or Floating actuator, which one is more common?

  2. #2
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    Dec 2007
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    I think the VAV controllers with built in actuators seem to be mostly floating actuators.

  3. #3
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    Floating, all about cost...so because floating is cheaper.
    "How it can be considered "Open" is beyond me. Calling it "voyeur-ed" would be more accurate." pka LeroyMac, SkyIsBlue, fka Freddy-B, Mongo, IndyBlue
    BIG Government = More Dependents
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  4. #4
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    Modulating is common on DDC, floating if pneumatic.

    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  5. #5
    Join Date
    Oct 2005
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    Honeywell design engineers state that floating actuators have a much longer life span in VAV applications than modulating.

  6. #6
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    It really depends on what you are using for controls.

    If simply a min-max. CFM and controlling temperature only, floating is preferred, if a CFM setpoint is being controlled by temperature offset, modulating (proportional) is typically utilized.

    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  7. #7
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    Everything I've ever done has been floating.

    If you want position, make a feedback input.

  8. #8
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    GT - teach me something. Now i am not talking feedback, only position control. My understanding of floating control, aka tri-state, is to drive something for for x time and stop it based on actuator stroke time. 3 wire control, power on one input drive ccw and power one the other input drive cw, and 3rd wire to common. It can have a 4th wire in the case of a spring return model in which the 4th wire is power to hold the actuator against the spring.
    Modulating control is 3 wire only power, common and signal whether it be spring return or not. The actuator drives exactly to the place based on the signal input, no timing required, send it to 1/2 the max input signal then it drives 1/2 stroke.
    So correct me if I am not following something here, but based on the previous information how would one have a floating pneumatic actuator?
    A signal pressure line simply pushing against a spring, no timing needed.
    Then the second explanation are you sure you're not getting that mixed up with with pressure dependent and pressure independent control? CFM control really has nothing to do with the actuator. Siemens, Invensys, CSI/INET, TAC and others have built hundreds of thousands of floating point controllers that have been controlled based on CFM.
    "How it can be considered "Open" is beyond me. Calling it "voyeur-ed" would be more accurate." pka LeroyMac, SkyIsBlue, fka Freddy-B, Mongo, IndyBlue
    BIG Government = More Dependents
    "Any 'standard' would be great if it didn't get bastardised by corporate self interest." MatrixTransform
    http://threedevilskennel.com/ - not my website.
    Versatile Hunting Dog Federation - www.vhdf.org/


  9. #9
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    Quote Originally Posted by crab master View Post
    GT - teach me something. Now i am not talking feedback, only position control. My understanding of floating control, aka tri-state, is to drive something for for x time and stop it based on actuator stroke time. 3 wire control, power on one input drive ccw and power one the other input drive cw, and 3rd wire to common. It can have a 4th wire in the case of a spring return model in which the 4th wire is power to hold the actuator against the spring.

    OK, a floating type actuator is less likely to keep calibrated and only bases its position on the input it's given (in other words, it has no idea where the hell it is at any given time) and in some instances have a tendency to "hunt" if not configured properly.


    Modulating control is 3 wire only power, common and signal whether it be spring return or not. The actuator drives exactly to the place based on the signal input, no timing required, send it to 1/2 the max input signal then it drives 1/2 stroke. The reason I say modulating (proportional) is "common" is because many controllers these days utilize a voltage signal to "put the actuator where we know it is going to be". This makes an emergency override easier if a component fails, like the pressure transducer, we can "set it" for a certain position until it can be looked in to.

    So correct me if I am not following something here, but based on the previous information how would one have a floating pneumatic actuator?
    A signal pressure line simply pushing against a spring, no timing needed.
    Then the second explanation are you sure you're not getting that mixed up with with pressure dependent and pressure independent control?Your right about that, a bad example for sure, I was referring to a pneumatic actuator controlled by a velocity controller, there is nothing proportional about those damn things....

    CFM control really has nothing to do with the actuator.Correct, just the choice of which to use. Siemens, Invensys, CSI/INET, TAC and others have built hundreds of thousands of floating point controllers that have been controlled based on CFM.
    They have also built hundreds of thousands of modulating actuators.

    I have worked on several clean rooms and labs with space differential transducers that require close control of the entering air and 90% of the time a modulating actuator is used, not floating. For an office space, floating control is fine, but they can be sloppy if not configured exactly right. Modulating takes some of the guess work out of it from an air balance standpoint. Especially with today's crazy control schemes with resettable duct static and supply air temperatures.

    Not trying to offend, just an observation...

    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  10. #10
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    There is one reason and one reason only that manufacturers use floating point actuators on VAV boxes: $

  11. #11
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    GT - no offense taken, just there is a lot of people that read these threads so I wanted to make sure explanations/definitions were correct.
    I agree with hundreds of thousands of modulating, but I'd put a fair amount of money that for VAV controllers and actuators there is more floating than modulating available and has been produced.

    Agreed with the floating timing/hunting comment, but many manufacturers address this by randomly driving the actuator for longer than the stroke time to help insure it goes to the zero position. Many do this after they sense the clutch has been pushed or after a power cycle as well. Another aspect for floating controllers made for the international market, many are set for 50 Hz timing by default, so that default of 230 seconds stroke time (or whatever it is) needs to be set to 185 seconds for our 60 Hz (faster) power for a 90 deg stroke. For less than 90 do the math, but a 45 deg stroke for an oval damper would be half of the timing at whatever Hz your at, so in my example 92.5 seconds.

  12. #12
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    VAV Actuator Floating question

    Over the last five years I have noticed that that most of the top 20 DDC brands are, or have, migrated away from floating (tri state) to analog actuators, with 0 to 10VDC becomming common place.

    With floating motors, I have seen some system VAV controllers lose track of damper position, and with 0 to 10vdc actuator outputs, there is less likelyhood of losing track of damper position (if your VAV zone controller doesn't have a damper position feedback input).

    Additionally, another trend is that many brands now incorporate damper shaft position feedback using an analog input. Both of these technology advances seem to be driven due to a common zone actuator manufacturing protocol that has lowered the cost to produce these analog VAV zone controllers with built in actuators.

    It actually takes less electronics to accomplish analog outputs compared to tristate actuator control, and that may be what is driving the newer generation away from floating actuator (using two binary outputs).

    Just my two bits. I am sure that others will may have a different opinion.
    "We are what we repeatedly do. Excellence, then, is not an act, but a habit" Aristotle

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  13. #13
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    Quote Originally Posted by dracula View Post
    Over the last five years I have noticed that that most of the top 20 DDC brands are, or have, migrated away from floating (tri state) to analog actuators, with 0 to 10VDC becomming common place.

    With floating motors, I have seen some system VAV controllers lose track of damper position, and with 0 to 10vdc actuator outputs, there is less likelyhood of losing track of damper position (if your VAV zone controller doesn't have a damper position feedback input).

    Additionally, another trend is that many brands now incorporate damper shaft position feedback using an analog input. Both of these technology advances seem to be driven due to a common zone actuator manufacturing protocol that has lowered the cost to produce these analog VAV zone controllers with built in actuators.

    It actually takes less electronics to accomplish analog outputs compared to tristate actuator control, and that may be what is driving the newer generation away from floating actuator (using two binary outputs).

    Just my two bits. I am sure that others will may have a different opinion.


    Thank you sir.......

    Must be a California thing???

    IMHO it does more with less....I have actually installed Johnson's VMA's using a proportional actuator, even though it would be way less expensive to utilize the floating built in deal....Just works with a bit more precision.


    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

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