What is a “Sweating Slab”?
Believe it or not, concrete slabs can sweat and this is a well documented phenomenon. Most simply stated, concrete sweating (aka “sweating slab syndrome”) refers to condensation the develops on the surface of a concrete floor inside an industrial building, not subjected to outside weather conditions.
Why Do Concrete Slabs Sweat?
Condensation collects on a concrete slab because the temperature of the slab is at or below the dew point temperature of the ambient air inside the building. This situation occurs most often during times of the year when outdoor temperatures can change by 10F or more within just a few hours. While outdoor temperatures may change significantly within just a few hours, the concrete floor temperature is much different. Some studies indicate the temperature of a concrete floor can lag several weeks behind the ambient air temperature. Example - If the concrete floor temperature is 70F today, and the inside air temperature increases to 90F(and remains at 90F), it can take several weeks for the concrete floor to reach a temperature close to 90F (the air temperature).
How Can Industrial Fans Mitigate Sweating Slab Syndrome?
When the indoor air temperature rises significantly over a short period of time, the much colder concrete slab will cool the boundary layer of air just above the slab to or below the dew point temperature. Once the dew point temperature is reached, the moisture in the air will condense, leaving droplets of water on the floor (resulting in a sweating slab). The condensation process can be prevented by installing ceiling mounted industrial fans in areas sweating slabs are often an issue. Industrial fans move air from the ceiling, down to the floor and across the floor in all directions. This air movement disrupts the boundary layer of cooler air just above the slab, preventing the air from reaching the dew point temperature. If the boundary layer air above the floor never reaches the dew point temperature, the condensation process is prevented (no sweating slabs).
All Industrial Fans HVLS Fans Are Not Equal
An industrial fan must be capable of moving air across a large area of the floor to be an effective mitigation solution. Remember, the boundary layer of air just above the floor must be constantly disrupted by airflow to prevent the condensation process. Most reputable industrial fan and commercial fan manufacturers provide air velocity profiles for each fan they make. Air velocity profiles provide data on the air speeds you can expect for a variety of different distances from the fan. This information will help you decide if a fan will be effective for your particular situation (comparing the air velocity data with expected mounting height of the fan, distance of the floor, etc). Some fan manufacturers will only provide this information upon request. So, if you can’t find air velocity profiles on the fan manufacturer’s website, be sure to submit a request.