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  1. #1
    Join Date
    Mar 2005
    Location
    Georgia
    Posts
    389

    Distribution center concrete floor sweating

    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?

  2. #2
    Join Date
    Aug 2012
    Posts
    2,754
    I don't think your exaust fans are causing your floors to sweat. Is the distribution area air conditioned?

  3. #3
    Join Date
    Mar 2007
    Posts
    380
    This is definately off topic, but I thought owl turds were dried out pellets?

  4. #4
    Join Date
    Aug 2012
    Posts
    2,754
    Maybe the employees are sweating so much it is accumulating on thefloor. Just a thought.

  5. #5
    Join Date
    Feb 2008
    Location
    Purcellville Va.
    Posts
    746
    Infrared radiant heaters to keep the slab dry and humidty down.

  6. #6
    Join Date
    Dec 2003
    Posts
    2,432
    I think you are on the right track. You just want to turn off the fans when the slab temp is below the dew point of the outside air. I would do what you said, but control them on outdoor humidity instead of indoor.

  7. #7
    Join Date
    Dec 2001
    Posts
    216
    how old is the facility and has this been a problem since day one? I had a project for Hershey Chocolate that was 1.6M sq/ft cold storage and it took 9 months to get the moisture out of the precision pour floors. We never had "pooling" of moisture on the floors but our rate of humidity removal was extremely high. what climate / region is this facility in?

  8. #8
    Join Date
    Mar 2005
    Location
    Georgia
    Posts
    389
    Its not air conditioned, facility is located in GA. The building is not new, probably 6 years old. Radiant heaters would surely work but we were just trying to come up a control sequence to run the exhaust fans which are pulling all the humidity in. Does anyone think CO2 will be a problem? Thanks for the feedback.

  9. #9
    Join Date
    Dec 2001
    Posts
    216
    If they are running combustion based equipment such as propane powered forklifts then yes air quality will go bad real quick depending on the density use. If the forklifts are battery powered the key thing here is making sure that the ventilation rates in the charging areas are maintained. If the charging areas for battery powered equipment are in an isolated room / area that is independent of the "big box" this will be an advantage.

    what is the pattern to this problem? I.E. does it happen after a cool night when the temps rise rather quickly in the morning and the concrete mass has fly wheel affect and is still cool from the night ventilation? etc.....

    is this a tilt up building with concrete walls, built up block walls, or insulated manufactured panels?

  10. #10
    Join Date
    Aug 2006
    Location
    Ohio
    Posts
    2,092
    What are you using for make up air for your ventilation?

    I would temper the make up air coming into the building.

    If you have no make up then there is half your battle.

    Looking into controlling the ventilation sequence could get you tied up with CO issues (propane forklift), hydrogen buildup (battery charging stations), CO2, or a host of other air quality issues associated with the plant.

    I think your make up air is the main issue here, without control of it you are at the mercy of mother nature in this warehouse.

  11. #11
    Join Date
    Jul 2008
    Posts
    1,481
    Quote Originally Posted by chadtech View Post
    ... 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?
    it is the dew point of the air yr interested in very close to the slab.
    measure the floor temp and inside RH at the slab air interface and look it up on a psychrometric chart. you will find out.
    The only way to get rid of the problem is to either cool the air, and strip moisture out (move left[ish] on the psych chart)
    Or raise the temp of the slab (further up the saturation line)

    If you dont have buckets of cooling or heating, it sounds like dumping moist warm air from inside to outside is the only available solution.
    1 + 1 = 3 ( *** for very large values of 1)

    ...everybody wants a box of chocolates and long stemmed rose

  12. #12
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,642
    http://www.weather.com/maps/maptype/...name=undefined

    The dew point in GA is 70^F right now. The concrete slab is <70^F. What is going to fix this? How about a couple large dehumidifiers? Check out the Ultra-Aire 205. One will handle +5,000 Sqft. of space. Pulls out +8 lbs. of moisture per hour. Lowering the indoor dew point 1^F below the slab temp will eliminate the condensation. It like magic.
    http://www.thermastor.com/
    There a couple other dehus out there that will work, Hi-E Dry 200, and Quest/
    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"

  13. #13
    Join Date
    Dec 2003
    Posts
    2,432
    With such a large (1.5 m sq ft) I just cant see any reasonable solution besides turning off the fans when its humid enough to cause the problem. Maybe monitor co also and let this over-ride the humidity control. I am envisioning large wall louvers where the air is entering the building? Does the problem occur everywhere or just in front of the louvers?

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