HVLS basics: Balancing the air temperature

Destratification creates more comfort and lower costs for plants throughout the entire year.


HVLS fans can better distribute air flow in high-ceiling plants and warehouses, creating a more balanced temperature at all levels of the plant. Courtesy: Rite-HiteLarge open workspaces are a hallmark of industrial and commercial facilities. Operations that include manufacturing, processing and warehousing need these wide-open areas for the specialized machinery and processes that allow them to be efficient. Unfortunately, the same floor plan that makes them efficient operationally also makes them inefficient from a heating and cooling standpoint.

Many plant managers attempt to address this problem by enhancing an existing system. For the most part, HVAC systems do an efficient job of providing heated or cooled air to specified areas of a building. However, while regular maintenance will keep an HVAC system running smoothly, it won't optimize HVAC operation as much as the addition of a high-volume, low-speed (HVLS) fan network. As one would assume, HVLS fans can play a significant role in helping to cool a facility. But even greater benefits can be seen during cold weather. Before looking at those benefits, though, let's first examine how HVLS fans keep working areas cool and operating at maximum efficiency.

Summer breeze feels nice

Worker comfort is no trivial matter. Studies have repeatedly shown that workers who are physically uncomfortable become distracted and are more prone to making mistakes. This is particularly true in cases of extreme discomfort, as when heat fatigue, heat stroke and other types of heat stress strike.

That's why HVLS fans are becoming increasingly common in industrial facilities across the nation. With or without air-conditioning, virtually any facility will benefit immensely from HVLS fans. In facilities that don't possess air conditioning, the benefits of HVLS fans are most noticeable.

Although smaller, traditional floor-mounted fans can be helpful in limited spaces, their high wind speed and noise levels may cause problems and they use a relatively high amount of electricity. In comparison, HVLS fans use relatively little energy and provide a gentle, quiet breeze that is very comforting to workers. This calm wind has profound effects on the perceived temperature for workers.

According to the U.S. Department of Health and Human Services paper, "Workers in Hot Environments," an air speed of two to three miles per hour creates an evaporative cooling sensation of seven to 11 degrees Fahrenheit. To put this in perspective, the effective temperature of an 84-degree warehouse environment can be dropped to 73 degrees by adding a fan moving air at three miles per hour. This cooling effect can make workers up to 35% more productive.

A large 24-foot diameter HVLS fan gently moves large volumes of air up to 22,000 square feet and replaces 10 to 20 floor fans. By mixing air, HVLS fans also help air-conditioning systems work more efficiently, allowing them to be operated at a set point up to five degrees higher.

Fans of winter

As counter-intuitive as it may seem, HVLS fans can be even more impactful during the cold weather months than in summer, especially in a large, cavernous facility.

Even in facilities with strong HVAC systems, warm air is going to rise. Thus, in tall warehouses there may be a significant temperature difference between the floor-level workspace and the ceiling. By continually mixing air through a process called destratification, HVLS fans can diminish this problem, helping facility managers to provide more comfortable working environments and even cut energy usage by up to 30%.

Warming up with destratification

During the heating season, there is often more than a 20-degree difference between the floor and ceiling at most manufacturing plants and warehouses as a result of warm air (light) rising and cold air (heavy) settling. Typically, the air temperature will be one-half to one degree warmer for every foot in height. Heating systems must work hard for extended periods of time to maintain the temperature near the floor, or at the thermostat set point, wasting precious energy and dollars. The charts in Figure 1 illustrates this concept.

Fig. 1: There can be more than a 20-degree difference between the floor and ceiling at most manufacturing plants and warehouses with no high-level air movement. Courtesy: Rite-Hite

HVLS ceiling fans mitigate the rising heat effect by gently moving the warm air near the ceiling back down toward the floor where it is needed. The air reaches the floor below the fan where it then moves horizontally a few feet above the floor. The air eventually rises to the ceiling where it is cycled downward again. This mixing effect creates a much more uniform air temperature, with perhaps a single degree difference from floor to ceiling. Facilities equipped with HVLS fans lower the burden on the heating system, reduce energy consumption and save money.

Conventional high-speed ceiling fans do not have this effect. Although they have been used to help circulate air for many years, they are ineffective in moving the warm air from ceiling to floor. By quickly spreading airflow away from the fan, little—if any—of that air reaches people working at the ground level. Thus, in facilities with traditional ceiling fans, the full benefits of the HVAC system rarely are realized on the floor.

Saving energy and money

Because HVLS fans run so efficiently, their return on initial investment often ranges from as quickly as six months to two years. However, this varies due to application variables.

As shown in Table 1, winter energy savings are substantial. Users can reduce their heating bills by 20 to 30 percent when using an HVLS fan to gently mix warm air from the ceiling with cooler air below.

Important aspects to contemplate

Some of the variables in these ROI calculations include obstructions such as pallet racks, machinery and product staging, personnel work areas, and overall building layout, to name a few. Larger diameter fans will move air further down rack aisles and over obstructions. Smaller diameter fans can be most effective in specific work areas, or where installation space is limited.

Fan suppliers can help configure an array of fans, determining the number, size and locations that provide the maximum benefit for the investment. They'll usually be able to provide installation when on-site resources are not available. While the basic concept is similar across all HVLS fan manufacturers, fan design and performance are important to consider, like the shape and number of blades, blade tilt, hub construction, blade-to-hub connection and safety features. The performance of different designs will vary in the uniformity of air movement directly below the fan, as well as the height and reach of air movement outward from the fan's diameter.

Valuable investment for any season

No matter the season or the temperature-controlled application, HVLS fans can provide numerous benefits. Not only will they enhance environmental control to help comfort workers and protect product, they do it by using less energy for less hassle than traditional high-speed floor fans. Capitalizing on the advantages of HVLS fans requires careful analysis of each application, as well as each HVLS fan design.

Andy Olson is product manager for Rite-Hite.

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