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  1. #14
    Join Date
    Dec 2003
    Posts
    2,395
    One last thought. Do the fans run when its cold outside? If they dont I cant see how cutting them off on occation would be a problem

  2. #15
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,365
    Quote Originally Posted by chadtech View Post
    Hi guys, looking at a 1.5M sq. ft. distribution center which has some PLC controls for there large rooftop exhaust fans which provide ventilation. The problem they have with the current setup is the fans will run when the outside air humidity is really high and cause the warehouse concrete slab to sweat and become slick as owl s&%t. Looking for some controls sequence suggestions. I am thinking maybe a concrete slab temp sensor, and then a indoor dewpoint sensor. With a adjustable setpoint that will lock out the fans if the slab temps comes within 3 or 4 degrees of indoor dewpoint. Think that will work ok?
    Stoping in the fans will not eliminate the problem.
    Maybe reduce the fan's air flow and turn on the dehumidifiers would be a safer strategy.
    1,000 cfm ventilation of infiltration/ventilation needs 2 lbs of dehumidification per hour per 1^F dew point reduction.
    If you have a natural air change in 12 hours depending on the wind and doors opening.
    40,000 cfm natural infiltration requires 80 lbs. of dehumidification per hour for 1^F dew point reduction. You may need a 2-3^ F reduction in dew point.
    If you know the fan capacity, you can calc the amount of dehumidification. Heating the air does not change the dew point. Cooling tends to cool the slab also which does not help the problem. Fans directed to the floow may help because it helps warms the concrete. Dehumidification with the ventilation off is best.
    Also consider the potiential for moisture absorption by the materials in the warehouse. Moisture may damage the these materials.
    The lowest cost high capacity and efficiency dehus are the free standing large dehumidifiers like the Santa Fe MAX. 10 units located throughout the space could reduce the dew point 2-3^F possibly.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  3. #16
    Join Date
    Jul 2001
    Location
    Canada
    Posts
    1,810
    1 of my customers has 2 large DRY storage warehouses , 1 is 8 years old the other 4 years old. Built from the same plans & specs only difference is the OLDER one had a vapour barrier put down before the concrete floors were poured. Guess which one has the WET floor syndrome.

  4. #17
    Join Date
    Oct 2003
    Location
    Michigan
    Posts
    724
    Quote Originally Posted by Control Man View Post
    1 of my customers has 2 large DRY storage warehouses , 1 is 8 years old the other 4 years old. Built from the same plans & specs only difference is the OLDER one had a vapour barrier put down before the concrete floors were poured. Guess which one has the WET floor syndrome.
    Ding Ding Ding there is more to the issue than controls.
    Beware of the prophet trying to make a profit.

    There is less oxygen from knee level to the floor! Check it out next time you tie your boots.

  5. #18
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,365
    Quote Originally Posted by Control Man View Post
    1 of my customers has 2 large DRY storage warehouses , 1 is 8 years old the other 4 years old. Built from the same plans & specs only difference is the OLDER one had a vapour barrier put down before the concrete floors were poured. Guess which one has the WET floor syndrome.
    Concrete with an epoxy seal on surface gets slick immedeately when below the dew point of the air. Concrete with out sealer will pass a small amount of moisture via capirally movement of moisture to the dry side. I would suspect that a moisture barrier on the bottom of concrete would eventually have the same effect.
    Non the less, keeping the dew point of the air 1^F below the surface temp of the concrete eliminates the moisture condensation. A good dehumidifier is worth its weight in gold, thus the high price for those Therma-Stor dehus? (Humor)
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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