Fans for winter

HVLS fans gently move warm air from the ceiling toward the floor. PHOTO: RITE-HITE

Winter is almost here, so get ready to turn up the HVAC system and fans. That’s right: fans. As counter-intuitive as it may seem, high-volume, low-speed (HVLS) fans are even more important for temperature management during the cold weather months than in summer.

HVAC systems do an efficient job of providing heated or cooled air to specified areas of a building, but they don’t optimize airflow – and, as every grade schooler knows, warm air rises. Thus, there may be a significant temperature difference between floor-level and the ceiling in large, cavernous spaces. HVLS fans mitigate this problem by continuously mixing air through a process called destratification to provide more comfortable working environments while reducing energy use by as much as 30%.
During the heating season, there’s often a difference of more than 11 degrees C between the floor and ceiling in most plants and warehouses. Typically, the air temperature will be 0.6 degrees C warmer for every 0.3 metres in height. A heating system must work hard for extended periods to maintain the temperature near the floor or at the thermostat set point, wasting precious energy and dollars.

HVLS ceiling fans mitigate the rising heat effect by gently moving the warm air near the ceiling toward the floor where it’s needed. The air then moves horizontally a few feet above the floor and eventually rises to the ceiling where it’s cycled downward again. This mixing effect, known as destratification, creates a more uniform air temperature with perhaps a single 0.6 degree C difference from floor to ceiling. Conventional high-speed ceiling fans do not have this effect. By quickly spreading airflow away from the fan, little – if any – of that air reaches people working at the ground level.

Because HVLS fans are efficient, their return on initial investment often ranges from six months to two years. Payback varies according to a number of application variables, but winter energy savings are substantial. Users can reduce their heating bills by 20% to 30%.

Based on 22,000 square-foot building with 30-foot ceilings a 12 degree C set point and natural gas at $0.11 per cubic foot, winter energy savings in Edmonton are $3,620 and $2,485 in Toronto.

There are a number of factors to consider when deciding how and when to use HVLS fans. They include obstructions such as pallet racks, machinery and product staging; personnel work areas; and overall building layout. Larger diameter fans will move air further down rack aisles and over obstructions. Smaller diameter fans are most effective in specific work areas, or where installation space is limited.

Performance factors

Suppliers can help configure an array of fans and determine the number, size and locations that provide the maximum benefit for the investment. They also offer turnkey installation where on-site resources are not available. Fan design and performance are key considerations. There are significant differences between manufacturers, including 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.

Other important considerations include ease of installation, fan controls, local representative support, trial program availability and warranties.

HVLS fans are getting more attention as a practical way to improve air movement and enhance environmental control. Additionally, recent technical advancements make them more attractive. Some fans more than 7 metres in diameter provide maximum air circulation in expansive areas, while touchscreen control stations operate up to 18 fans at once. These types of fans are now recognized as a valuable supplement to help facility designers and engineers control energy costs, and improve employee comfort and productivity. But capitalizing on the advantages of these fans requires careful analysis of each application, and the most suitable fan design.

This is an edited version of an article provided by Rite-Hite, a manufacturer of industrial fans, dock equipment, industrial doors and safety barriers based in Milwaukee, Wis.

This article appears in the November/December issue of PLANT.