Ceiling Fans for Summer Cooling in Industrial Facilities
When using industrial ceiling fans during the summer months you really do need to think of what you’re trying to accomplish. As a result of the natural process of warm air rising and cold air falling, there is a big temperature difference between the floor and ceiling in all manufacturing plants and warehouses. This temperature difference can be very large, especially in high ceiling facilities. Typically, the ceiling air temperature will be 1/2 to 1 degree F warmer for every foot in height during the winter. However, during the hot summer days, super heating of the upper ceiling areas of a factory occurs due to the effects of the sun and any heat producing plant equipment, both of which boost this difference in air temperature between the floor and the ceiling.
Conventional practice for summer cooling in manufacturing and warehousing facilities has been to circulate the cooler air near the floor area horizontally among workers in order to allow the evaporative cooling process to work the most efficiently. The evaporative cooling that we “feel” occurs as moving air travels over our moist skin, causing that moisture to evaporate, resulting in a lower temperature at the skin’s surface, making us feel much cooler. The feeling of coolness experienced while working outside in a breeze on a hot summer’s day is exactly what the evaporative cooling process is all about. But as the ambient air temperature increases, often along with humidity levels, the cooling effect of moving air is hampered and becomes less effective, unless the air speed is increased. And even then, it is only effective to a certain point before real discomfort occurs.
Lately there has been a strong promotion for the use of large HVLS type (High Volume, Low Speed) ceiling fans for the summer cooling of workers. These fans are very effective for balancing out the temperature differential by mixing the cooler floor air with the hot ceiling air. The result is a much warmer floor area temperature, which is desirable, but only during the cold winter months. However, driving hot air down vertically onto workers in the summer months is very counterproductive and uncomfortable. All ceiling fans mix the hot ceiling air with the cooler floor air, as these illustrations show below:
But during the summer months, the standard recommendations from many of the HVLS type ceiling fan manufacturers is to continue to use these fans for air circulation, which results in driving that super hot ceiling air down to the plant floor and onto the workers.
The only way to attempt to compensate for this increased ambient temperature at the floor area is to increase the air velocity. Ceiling fans blowing hot air down from such a high distance operate at a relatively low speed (HVLS = High Volume, Low Speed) so increasing their relatively low air speed is difficult or impossible to do. You must increase the air velocity significantly in order to aid the evaporative cooling effect in the resulting increased floor area temperature environment.
For the most cost effective and efficient summer cooling in a factory setting, the cooler floor air must be circulated horizontally, not vertically, among workers.
Optimally, hot stratified ceiling air should be ventilated out of the building, but in any case, must not be mixed with the much cooler air located at the plant floor. Horizontally circulating this cooler air using industrial air circulators near the floor areas also allows the workers to “adjust” both the direction and speed of the air for their maximum comfort.
Industrial air circulators will not cause the undesirable summer mixing of the hot ceiling air with the cooler floor air. Only the cooler floor air is circulated among the workers, resulting in a much more comfortable and consistent work area temperature.
By Mark Janisse
Mark Janisse has over 35 years experience in the field of Industrial Air Circulation and Ventilation. Mr. Janisse is the Director of North American Sales at Jan Fan Inc.