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  1. #1
    Join Date
    Jul 2013
    Location
    Antwerp
    Posts
    13

    DPT always over filter?

    firts of all you have to know I'm a newbie first class in HVAC. so please be gently in your reply to what you might think: "that is a stupid question"

    An installation where humidity, temperature and pressure in a room are very delicate some VAV' are installed to remain the demanded pressure.
    to ensure the demands are met a DPT is installed over the VAV's. after a VAV are 2 filters.
    I understand that, to know if your filter is dirty, you install a DPT.
    Is that always done? if you have 2 filters, you install 2 DPT's? or is that just too much?
    will one DPT do the job and you just replace both filters at the same time?

    thanks in advance for your answer.

    kind regards
    Sam Vdh

  2. #2
    Join Date
    Nov 2006
    Location
    Desert Southwest
    Posts
    560
    Sam,

    If one filter is used as a pre-filter then I would install a DP on each filter.
    If you can't fix it with JB Weld, Duct Tape, and Ty Wire it has to be replaced.
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  3. #3
    Join Date
    Oct 2011
    Location
    Dallas, Texas
    Posts
    159
    The expectation is that one filter might get 'more dirty' faster than the other. Therefore you would want to know when they individually need replacing.

    The two filters you speak of, I am willing to bet, are not identical therefore it would not be wise to use just one differential pressure across both.

    The only stupid questions are the ones that are never asked...

  4. #4
    Join Date
    Jul 2013
    Location
    Antwerp
    Posts
    13
    Yes they are class G4 and H14.
    thanks for your replies.

  5. #5
    Join Date
    Mar 2005
    Location
    Pacific Time Zone
    Posts
    4,151
    As with the others across each would be preferred, but one could use one across both.

    You don't need a DPT (Differential Pressure Transducer) to know your filters are dirty. Multiple ways to do this such as differential pressure switch(es) set to trip above max differential pressure you want to see. The transducer(s) just gives you more detailed results.
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  6. #6
    Join Date
    Jul 2013
    Location
    Antwerp
    Posts
    13
    I've discoverd that for filter monitoring the use of a differential manometer is also done.
    anyone knows if Honywell has such instrument?
    I can' find it.

  7. #7
    Join Date
    Jan 2007
    Location
    Stongsville Oh
    Posts
    876
    Dwyer magnahelics are used as local indicators. They sell them in the ,1 to 1" range for filter delta p. VAV's are used to compensate for filter loading.Diff press transducers are used for ddc systems to write code that reads the press diff and an alarm is generated when the pressure exceeds x. I would check out dwyers website, they have photos and descriptions of many of there products which I use regularly.
    ckartson
    I didn't write the book I just read it!

  8. #8
    Join Date
    Jul 2013
    Location
    Antwerp
    Posts
    13
    [QUOTE=ckartson;16308351] VAV's are used to compensate for filter loading.Diff press transducers are used for ddc systems to write code that reads the press diff and an alarm is generated when the pressure exceeds x. /QUOTE]

    yes that much I know
    the instruments need to be local indicators and provided the DDC with an AI, so when the pressure exceeds x, BMS gives a warning to replace the filter.
    but there are A LOT of filters, the rest of the system is goign to be done with Honeywell equipment to it would be nice if the filter indicator is Honeywell as well.

  9. #9
    Join Date
    Jul 2011
    Location
    East coast USA
    Posts
    925
    one is enough even if you have a prefilter.

    Do you have a DDC controlling this Damper? and are you controlling/monitoring CFM and static?

  10. #10
    Join Date
    Jan 2007
    Location
    Stongsville Oh
    Posts
    876
    We sell Alerton controls wjich is a division of Honeywell now and as far as I know we use local indication by Dwyer and an inexpesive Dwyer 2 wire 4 to 20 ma sensor for the ai. I will try to find it on line.
    ckartson
    I didn't write the book I just read it!

  11. #11
    Join Date
    Jan 2007
    Location
    Stongsville Oh
    Posts
    876
    Name:  dwyer.jpg
Views: 132
Size:  97.4 KB

    Here is the differential press transmitter I was trying to think of. These can be purchased through Kele. They are small and work great for just that application.
    ckartson
    I didn't write the book I just read it!

  12. #12
    Join Date
    Jan 2007
    Location
    Stongsville Oh
    Posts
    876
    It really depends on the spec. Personally I hate filter switches and dpt because schools, hospitals etc. should have a maint program that doesn't rely on the computer to tell you to go do your job. IMHO!
    ckartson
    I didn't write the book I just read it!

  13. #13
    Join Date
    Jul 2011
    Location
    East coast USA
    Posts
    925
    Quote Originally Posted by ckartson View Post
    It really depends on the spec. Personally I hate filter switches and dpt because schools, hospitals etc. should have a maint program that doesn't rely on the computer to tell you to go do your job. IMHO!
    totally agree we call these "Idiot sensors"

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