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  1. #1
    I have a VAV box with a boiler coiler in it with a duct

    supply of 55 degrees. How hot would the coil need to be

    to get a 100 degrees out of the runs?

  2. #2
    Join Date
    Sep 2002
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    Hampton Roads, Virginia
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    1,631
    double post
    "There are 10 types of people in the world.. those who understand binary, and those who don't."

  3. #3
    Join Date
    Sep 2002
    Location
    Hampton Roads, Virginia
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    1,631
    You could do it with 101º water if the coil had enough rows, static pressure would need to be higher to push the air thru' this 20-40 row coil. Truthfully, there is not enough info to answer the question, need airflow, coil size and rows etc.
    "There are 10 types of people in the world.. those who understand binary, and those who don't."

  4. #4
    I have a building that puts out constant heat during the

    winter. The outside stat brings on the boiler and the fan

    boxes for the coils. My RTU is constantly putting out

    55 degrees to the building for the vav boxes to cool the

    rooms down. Well, my one problem is in one space there

    are 3 rooms that has one vav box with a heat coil and no

    perimeter heat. What I'm wandering is my supply to the

    building suppose to be higher than 55 degrees? Because

    it'll bring in outside air in the winter time.

  5. #5
    Join Date
    Mar 2004
    Location
    CHICAGO SUBURBS
    Posts
    464
    You can run your rtu discharge temp at a higher temp as long as it will not hurt other zones in the building. I have a building that has a combination of vav and cav zones and if I don't run the discharge @ 60 deg in middle of winter, the cav zones won't reheat enough.I think that is what your asking.
    Some people swear by me and some at me

  6. #6
    Join Date
    Jun 2006
    Posts
    147
    I would try increasing the DAT setpoint until I got complaints from interior zones then back it down. Is your boiler on a reset schedule? Turn the water temp up. I have a VAV system that was converted from a old constant volume system and with the increased volume of air I have problems getting enough heat out of some coils. You will probably have to lower the temp again next summer. Ken

  7. #7
    Join Date
    Oct 2001
    Posts
    6,966
    drop the box on that 3 zone perimeter area and install a fan powered VAV...when you call for heat the VAV 55F will damper off and the fan will pull rturn air to supply the zones plus your wet coil temp. then without touching the rooftop and effecting the other interior zones on the cooling side.maintain your 55F on that rooftop and work the space heat generated within especially on the perimeter where it is missing baseboard.
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  8. #8
    Join Date
    Mar 2003
    Posts
    7,326
    you would need much more info to get the correct answer. you dont necessarily need 100 degree air to heat that area. design supply air temp? hot water temp? cfm, heat loss, type of box? etc.

  9. #9
    Join Date
    Jul 2006
    Posts
    68
    Originally posted by flange
    you would need much more info to get the correct answer. you dont necessarily need 100 degree air to heat that area. design supply air temp? hot water temp? cfm, heat loss, type of box? etc.
    Flange is right, we need more information. If the system is designed right, you shouldn't have to change th DA-temp. Don't know if you system is pnuematic or ddc. Your vav box should have heating cfm setpoint. Typical boiler water temps are from 160-180 degrees, should vary if based on a outdoor air reset schedule. Make sure your reheat valve is opening fully. Need to fully test out vav box, check all the above mentioned by flange.

  10. #10
    Join Date
    Jul 2005
    Location
    Orange County, NY
    Posts
    936
    Lets assume this VAV box supplied 1000 CFM with an inlet air temp. of 55 Deg. To achieve a 100 Deg. Discharge air your coil would have to supply 48,600 Btu/hr.

    Furthermore, assuming a 180 Supply water temp., the flow rate (GPM) thru the coil would be about 5 with a 20 Deg. Split.

    Core

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