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  1. #1
    Join Date
    Aug 2006
    Posts
    2,603

    LED Lighting Verses VAV Reheat??

    We have a building that the lights run 16 hours a day, all the Fluorescents are in drop ceilings, all the incadescent spot cans are in plaster ceilings. Ceiling is the return plenum. VAVs are Parallel Boxes, fan comes on via a call for heat. Modulating controls bring on Staged Electric reheat, as the demand for heat increases. On really cold days we get, "we're too cold call." The temperature is always just within specs. of a minimum of 68 F, when we get the calls. While I applaud the switch to LEDs, I question why this building was picked. Has anyone else had experiance with Reheat and LEDs??

  2. #2
    Join Date
    Feb 2013
    Location
    Phoenix, AZ
    Posts
    198
    Quote Originally Posted by madhat View Post
    While I applaud the switch to LEDs, I question why this building was picked.
    Perhaps there were energy incentives offered by the utility or maybe something to do with LEED certification?

    While the reduced heat gain might tend to reduce occupant comfort in the colder months, I imagine they looked at energy savings during the cooling season as well. Perhaps overlooked during the retrofit is that the HVAC is sized according to total load (which includes lighting). Now that the heat gain from lighting load is reduced - Oops...

  3. #3
    Join Date
    Jan 2013
    Location
    Central Arkansas
    Posts
    79
    Not long ago we had a similar call but found a vav that had never been turned on in a 10 year old building, also found one box that a high limit was burned out.

  4. #4
    Join Date
    Dec 2006
    Posts
    303
    If the lighting was that big of a factor in heating the space, I think your design engineer screwed up

  5. #5
    Join Date
    Feb 2006
    Location
    SouthEastern Virginia
    Posts
    1,075
    Put a discharge air reset program on your air handlers and base the reset on return air. I would try 62 degrees DAT based on your lowest return air temperature setpoint like 69 or 70 degrees. This will help the reheat situation.
    It might get loud!

  6. #6
    Join Date
    Jul 2011
    Location
    East coast USA
    Posts
    981
    If i understand correctly. When you switched to LEDs your lost the heat load from the other lights and your plenum temp is colder then it was and the reheats cant overcome the DT. Seen this happen many years ago...When there was a push to retrofit the lights in a commercial office building..during the winter they saw an increase in heating cost because we lost so much heat from the lights.

    anyway, i would imagine you have a RTU w/no heat and perimeter heat, with VAV some with Electric heat strips? if so, you may find adding plenum heaters will help. Unless you have other ways to warm up the supply air or plenum air

  7. #7
    Join Date
    Aug 2006
    Posts
    2,603
    We have a DX Split System with no heat. No perimeter heat, and an open stair case that's three stories tall. Add a huge Copella with windows in it at the very top. We run reheat on the First Floor, which is under ground in the back, almost year round. Hardly ever run reheat on the top floor. So we have a big problem that just got worse.

  8. #8
    Join Date
    Jul 2011
    Location
    East coast USA
    Posts
    981
    Quote Originally Posted by dlove View Post
    If i understand correctly. When you switched to LEDs your lost the heat load from the other lights and your plenum temp is colder then it was and the reheats cant overcome the DT. Seen this happen many years ago...When there was a push to retrofit the lights in a commercial office building..during the winter they saw an increase in heating cost because we lost so much heat from the lights.

    anyway, i would imagine you have a RTU w/no heat and perimeter heat, with VAV some with Electric heat strips? if so, you may find adding plenum heaters will help. Unless you have other ways to warm up the supply air or plenum air
    Have you checked to see the reheats are working correctly? but over all, adding reheats to the area complaining its cold is the only way. fans running during Occupancy and making sure you have proper air flow. (may need to balance). But if your returns air temp is low, not much else you can do but add heat to the effective areas.

  9. #9
    Join Date
    Aug 2006
    Posts
    2,603
    I played with the return dampers and things are better. I have air flowing up the stairway. As long as they don't complain about the slight noise increase from the top floor return I'm good.

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