purge ciircuit
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Thread: purge ciircuit

  1. #1
    Join Date
    May 2013
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    purge ciircuit

    hi, I am working on an air handle unit. I have previous contractor's project. I don't understand the purge control circuit. attachment is the circuit diagram. what is the purpose of this circuit? How does it work? what is the purge relay and warmup relay ( in the diagram) use for? EP is 310-24VAC. it is a way valves. and relay is RH2BULCAC24V. PE-1 is PNEUMATIC-ELECTRIC RELAY
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  2. #2
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    Jun 2006
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    What is EP-2, EP-3, EP-9, and EP-7 controlling? And most important what feeds X3 and X4.

    Basically EP-7 gets energized when power is at X3 and X4.....and PE-1 is closed. It remains energized until power is lifted from X3 and X4.

    Why.....need more details.

  3. #3
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    Dec 2006
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    Washington, DC
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    It sounds like it may be part of smoke purge from the fire panel. Just setup a similar one on core units with pneumatic actuators but not as many EP's.
    Quote Originally Posted by Qui-Gon Jinn (Star Wars Episode 1)
    "The ablilty to speak does not make you intelligent!"

  4. #4
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    Jul 2001
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    Canada
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    What type of area is the Air Handler serving ?

    I have had similar setups in a testing centre to PURGE odours out of rooms as well as stale air if the system was down for an extended time period.

  5. #5
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    Jan 2012
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    California
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    Without knowing what each device is it will be pure guess work. IE if R-1 starts the fan then the TDR-1 allows the EP's to open dampers first before ventilation. The signal from the EP's would be typically fed to a high signal selector and would open the dampers if they were NC. If they were in a smoke system they should fail open possibly and the EP dumps main air to do that. My point is just a ton of options for doing anything. Without knowing what every device is hooked up to and how it's all guess work.

  6. #6
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    May 2013
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    thanks for replying my post. and sorry for missing detail. Name:  Untitled2.jpg
Views: 79
Size:  97.0 KB . it is a BMS design for single duct air handle unit. this is full design diagram. the only thing i don't understand is the purger circuit. the relay 1 they called it purge relay. Relay 2 they called it warm up replay. part no is RH2BULCAC24V. TDR-1 is a time relay. Part NO is 438USA. what is PE-1 uses for? is it used for protection purpose? point 9a and 9b i think is digital output from controller. why relay 2 has normal open and normal close switch in diagram. Can anyone explain more detail how this purge circuit work to me? appreciate.

  7. #7
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    May 2013
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    11
    the pic is not clear. please check the pdf file
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  8. #8
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    May 2013
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    this pdf file is more clear
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  9. #9
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    Jun 2006
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    New Jersey
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    I don't see R-1 or R-2 in schematic. And that is a nasty schematic to follow. But with what you said, the new drawing, and the previous drawing. Your purge relay drives your OA dampers open and return air dampers......it also drives your VAV's 100%. No purge relay.......your VAV's will drive 100% with morning warmup(R-2).

    My best guess.

  10. #10
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    Nov 2005
    Location
    Shreveport, Louisiana
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    I disagree that is an easy diagram to read. I will have to take some pics of some around here....
    UA Local 141

  11. #11
    Join Date
    May 2013
    Posts
    11
    I read the operation sequence. and I guess how it work. first. controller send digital signal to EP enable through 9A 9B . PE close. EP2 is connected to outdoor damper and spill damper. these dampers are fully closed. EP3 is connected to return damper. Return damper is fully opened. EP9 is connected to vortex damper. Vortex damper is fully opened. when controller send digital signal to warmup enable digital output through DO6. it energize relay coil R2. Normal switch R2 is close and Normal close switch R2 is open. EP7 which is connect to vac box is fully open. then. morning warmup start. after a setup time, warmup signal and EP enable are false in BMS. Normal switch R2 is open and Normal close switch R2 is close. Dampers go to set up position by controller. and time delay TDR1 is close. Relay coil R1 is energize. the normal open switch R1 in Supply fan and return fan is close. The fans start. morning warmup is finished.

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