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  1. #1
    Join Date
    Mar 2005
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    Building Static pressure

    I need to install a differential static pressure senser to control building static 1st part of my question, does the high pressure pitot tube go to the outside and low pressure pitot goes on the inside space. part 2 of my question, where is the most ideal location for the low and high pressure pitot tubes any direction would be great.......... THANKS

  2. #2
    Join Date
    Mar 2008
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    NC
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    High pressure tube should go inside the duct. Low is open to the space or ceiling plenum.
    2/3 down the duct (at least that's what all the literature will specify).

  3. #3
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    Dec 2010
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    For building pressure control - Hi press to space and Lo press to outdoors setpoint is typically .05" WC. control parts houses typically supply a space pressure reference wall plate with a barb fitting for Lo side connection and an outdoor atmospheric referencer with barb fitting for Hi side connection.
    As far as best location it depends on the application. IE 2 story versus 1 story offices, lab, hospital etc.. need more info on app and Im sure we can help

  4. #4
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    Sorry, was thinking vav. Try this link.


    http://hpac.com/ventilation-iaq/pres...mmercial-0210/

  5. #5
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    Mar 2005
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    Thanks for the response, it's a 2 story with about 40 vav's trying to keep space slightly positive, depending on time of year interier/exterier door's stay slightly open and as summer is approaching this seems to happen more often this time of year.

  6. #6
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    Quote Originally Posted by westendmechanical View Post
    Thanks for the response, it's a 2 story with about 40 vav's trying to keep space slightly positive, depending on time of year interier/exterier door's stay slightly open and as summer is approaching this seems to happen more often this time of year.
    Chilled water & hot water with AHU w/economizer, RTU w/economizer per floor & associated VAV's??

  7. #7
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    Mar 2005
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    Osiyo - great points and I do set them to the lowest setting 0.1" wc, but most 'specs' I've come across seem to favor 0.5. I like the bi- directional setting for trending purposes. I agree once your below 0.0" wc it doesn't matter much if your sensor is sensing correctly. Sometimes the sensor is off just a bit or being affected adversely so I like to test slightly positive and slightly negative according to the sensor aka some simple cracked door and paper tests just to see if air is going in or out then. Another thing I've recently found it useful for is alarming. > -0.025 at one building the gals have a hard time opening doors. So alarm at < -0.02" wc if > 5 minutes. Long story but building under construction yet and too many holes and during certain construction activities we can't bring in any outside air. Let's just say my trends were extremely useful in proving out a design flaw and a construction exhaust problem.
    On another job, my first real 'learner' on wind effects we were able to find the correlation between consistent wind speeds above a certain value and the building going negative. That's the building I found the center of the flat roof to be the ideal sensing location. Ever since if I can get my outdoor reference to such a location I will.

  8. #8
    Join Date
    Jan 2016
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    Do you need to increase the size of the outside pressure tubing if you are going to be sharing that reading with multiple sensors? I plan on using one outside pickup port for two sensors, and in some cases 4 would be ideal. if the run is less than 100" 1/4" should be fine even if i am splitting in the control cabinet to 4 difference sensors right?

  9. #9
    Join Date
    May 2012
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    I confess that I'm not a big fan of building space static pressure control but in the right application it can be made to work. A light commercial building such as a medical professional facility with a couple of air handlers is a reasonable application. Larger buildings with multiple air handlers probably deserve air flow tracking. (Yes, it's expensive and requires careful setup)

    There's a lot of good information in the thread:

    Filtering Inputs: Critical to good performance. The signal to noise ratio when measuring space pressure is poor. Smoothing the input will improve both the perceived performance and the actual performance. If your DDC product doesn't provide for filtering inputs you can use a rolling average of the measured input.

    Transmitter/Sensor selection: Given that you're trying to control to a small differential I strongly recommend using a bi-directional transmitter. If you were trying to control to a discharge temperature of 55 degrees you wouldn't select a temperature sensor that couldn't indicate less than 54 degrees. The output of your PID statement is going to be largely a function of deviation from setpoint. In order to accurately measure the deviation if the building goes momentarily negative a bidirectional transmitter will be necessary. When you select a bi-directional sensor read the spec sheet carefully. It seems that some manufacturers will note a transmitter as being "0-.1 iwc / bidirectional". In actual practice the sensor span may be -.1 to +.1 for a span of .2".

    Control Sequence: Hopefully your building envelope is tight and you're bringing in the required minimum amount of air for ventilation purposes. If so, controlling the speed of the return fan should suffice.

    Setpoint: .05" is a good starting point. Go lower if you can. You know that if the outside doors don't close properly you need to reduce the setpoint.

  10. #10
    Join Date
    Sep 2013
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    http://www.airmonitor.com/wp-content...1/BRO_SOAP.pdf

    This was spec'd on my last job. Replaced existing sensor and smoothed out the spikes amazingly well.

    However.
    1. Existing sensor was in a bad spot.
    2. New sensor is much higher in the air.
    3. 30' of 2" pipe essentially becomes your buffer.

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