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With winter upon us (and a blast of arctic air set to bear down this weekend), facilities managers are again looking for ways to reduce their energy bills without sacrificing employees' comfort.
It’s a costly concern. According to the Commercial Buildings Energy Consumption Survey (CBECS), heating accounts for about 46% of energy use in warehouses and 36% of energy use in all nonresidential buildings. Luckily, there are numerous ways to reduce heater use and costs. Among the most efficient is the installation of a simple, cost-effective technology: ceiling fans.
Fans in winter? Yep. Fans are useful for more than just cooling – simple air movement can destratify spaces in winter and reduce heating costs by as much as 30%. What is destratification and how can it affect heating costs? Here are answers to those and a few other common questions:
What's the problem?
Heat rises. Without adequate airflow, different temperatures of air settle in layers, from the hottest at the ceiling to the coolest at the floor. This layering phenomenon is known as thermal stratification. Even the most efficient heaters can’t overcome the laws of physics, so some portion of the heat they generate will rise away from the workers who need it.
How does that affect heating bills?
Thermostats, which often mounted at floor level, register the cooler air there rather than the hot air at the ceiling. That means the heating system is forced to overdeliver in an effort to reach the desired temperature setting. What that means for heater use can be expressed in averages: If the thermostat registers 70 degrees at the floor but the air at the ceiling is 90 degrees, the average temperature of the space is 80 degrees. That’s equivalent to heating the building to 80 degrees when really all you want is 70 degrees.
Additionally, rising heat is wasted in a very literal sense, escaping through cracks, windows, vents, and straight through the ceiling without ever being felt by the workers who need it.
What types of buildings are most affected?
All buildings can suffer from stratification, but the problem is generally worse in facilities with high ceilings – factories, warehouses, and gymnasiums as well as older facilities with poor insulation and forced-air heat.
The taller the space, the wider the potential temperature gap between the floor and ceiling and the higher the average temperature in the space. Insulation comes into play because heat energy is easily transferred between the air and certain building materials. Rising heat more easily escapes from a metal ceiling that isn’t well-insulated, for example, which forces heaters to run even more to make up the difference. Facilities with large windows and doors are also at greater risk, as the cold from outside can easily creep in at ground level, further increasing the temperature gap between the floor and the ceiling.
How can I fix it?
You can remediate the problem trough destratification, which is simply the removal of thermal stratification. This is accomplished using air movement to equalize temperatures within a space. Fans push the hot air down, mixing it with the cooler air to create a uniform, facility-wide temperature closer to the actual thermostat setting. There will almost always be a small degree of stratification, but when fans are placed effectively, the temperature difference will be only 1°F to 2°F, rather than 10°F to 20°F without fans.
So, ceiling fans in winter?
Typically, the most efficient way to fight stratification in large spaces such as factories and warehouses is with overhead high-volume, low speed (HVLS) fans. HVLS fans use specially designed airfoils and their immense size, rather than speed, to move huge volumes of air. HVLS fans are among the most cost-effective destratification tool for large spaces, producing enough airflow to destratify up to 20,000 square feet per fan.
Should I reverse my HVLS fan?
No. The purpose of reversing fans is to prevent drafts, which can be uncomfortable in winter, by pulling cool air up instead of pushing warm air down. However, HVLS fans with infinite speed controls can be operated in the forward direction slowly enough to prevent drafts while still reducing stratification. Reversing fans is less energy-efficient and, in large spaces, much less effective. In a small living room, a reversed fan will send air up through the fan, out to the walls, and back down. In a large, open industrial space, the air might never reach the walls, and the reversed fan will simply stir the hot air around at the ceiling. Additionally, pushing that hot air upward can speed the rate of heat loss through the ceiling.
How can I test stratification at my facility?
The easiest way to test is by installing thermometers at the floor and the ceiling and calculating the temperature difference. (Note that infrared thermometers, or temperature guns, aren’t ideal for testing stratification, as they measure surface temperature rather than air temperature.) To estimate how much money can be saved without adjusting thermostats and monitoring bills for the whole winter season, search for energy-savings tools online.
How can I decide on a fan?
The same principles that apply to any major purchasing decision work for fans. Research the brands; read case studies; and talk to colleagues who use fans. Fan companies with thermal engineers and project managers on staff can offer custom recommendations on fan size and placement, because no two facilities are alike. In addition, check into warranties, installation services, and available discounts and rebates to find the best deal. Fan companies often offer rebates in winter.
Josh Kegley is a writer for Big Ass Solutions, the parent company of Big Ass Fans (www.bigassfans.com) and Big Ass Light (www.bigasslight.com). Based in Lexington, KY, Big Ass Solutions manufactures, sells and installs commercial and industrial fans as well as industrial-grade LEDs.