Using large-diameter, low-speed fans to make your plant more comfortable
June 26, 2012
Summertime and the factory is even hotter. Here’s a look at one option for making conditions more tolerable and safer for your workforce.
With all their heat-producing machinery and processes, manufacturing facilities can be very hot, uncomfortable, and unsafe workplaces. This can be especially true in the summer months. Studies have shown that improved occupant comfort leads to increased productivity and that worker productivity decreases as temperatures rise above 77 degrees F.1
A comfortable environment also improves employee retention, which is a critical factor in an industry that’s struggling to find workers.
The following FAQs provide answers about improving your operation’s comfort using large-diameter, low-speed fans.
Feeling comfortable depends on more than just air temperature. Human thermal comfort takes into account numerous environmental factors, including temperature, thermal radiation, humidity, and air speed as defined by ASHRAE Standard 55-2010 (American Society of Heating, Refrigerating, and Air-conditioning Engineers), along with personal factors such as activity level and clothing.
When the temperature and humidity rise, the body’s ability to cool itself decreases. Reducing the amount of clothing worn is greatly valued, and incorporating natural ventilation where applicable can help. Granted, in the manufacturing industry, reducing activity level generally is not an option, and many jobs require protective clothing. However, applying gentle, nondisruptive, nonturbulent airflow from large-diameter, low-speed fans can aid the evaporative cooling process and help to maintain employee comfort even in hot conditions.
Large-diameter, low-speed fans do not increase or reduce the amount of humidity in the space, nor will they change the temperature of the air. The airflow provides a cooling effect on occupants, similar to a natural breeze. Additionally, a fan can distribute or even out any humidity or temperature discrepancies so the vertical and horizontal temperature and humidity levels are the same. Achieving this effect requires the right number of properly sized fans, appropriately placed.
Given the number of factors involved in laying out an effective system for occupant comfort, this question is not easily answered without adequate information about the climate, type of conditioning if any, obstructions in the space, amount of process heat involved, and the presence of natural ventilation, to suggest a few. Fan manufacturers have trained experts who can help determine a space’s specific needs.
Numerous factors are involved in choosing an appropriate cooling system for a specific location. One factor is no more or less important than others, and you must weigh all of them.
Unlike small, high-speed fans that generate upward of 85 dBA, properly engineered industrial large-diameter, low-speed fans typically create sound levels of less than 55 dBA—the quiet end of the range for household dishwashers.
However, a fan’s decibel level does not tell the entire story. Clearly distinguishable tones (single frequencies) can cause a sound to seem louder than its actual dBA, thus causing significant annoyance even at theoretically acceptable dBA levels. Once a tonal noise has been heard, it is more easily recognized, even at lower sound levels. In other words, both sound quantity and sound quality should be considered before a fan is installed to prevent occupant noise complaints.
In addition to the high-pitched electrical noise sometimes caused by placing the fan’s variable frequency drive far from its motor, gear reducers and bearings can create tonal noises in the 400 to 2,000 Hz range that are problematic in sound-sensitive areas. While not as unpleasant as electrical noise, mechanical tonal noise can still be a significant source of occupant complaints. For sound-sensitive applications, it is recommended that fans with high-quality bearings and direct-drive motors (without gears) be used.
Energy usage depends on the size and number of fans, horsepower of the motors, hours of operation per week, and the local cost of electricity. With typical hours of operation during the summer months, a 12- to 24-ft. large-diameter, low-speed fan uses, on average, 7.1 to 11.6 kWh of energy on a daily basis, which is less than an air-conditioning system and more applicable in most warehouse facilities.
1. O Seppanen, WJ Fisk, and D. Faulkner, “Cost benefits analysis of the night-time ventilative cooling,” in proceedings from Healthy Buildings 2003 Conference, Singapore, 2003.