A number of independent studies reveal that a few HVLS fans can provide as much air movement in a given space as several high-speed fans. One such study, performed at UC Davis, determined that two 20-ft 1HP fans were as effective as twelve 3-ft high-speed fans at ventilating a 200-cow pen, while providing an 86% reduction in electrical consumption (Shultz, 1). This kind of efficient performance translates into any environment, not just commercial dairies.

Additionally, considering the sheer mechanics of moving air with conventional forced air units in something like a 200,000 sq. ft. warehouse with 30-ft ceilings is very revealing. In addition to the size (tonnage) of the unit required for such a large space, an enormous amount of ducting would be needed for merely adequate coverage. In addition several supplementary fans would be required to move the air nearly 30 feet to the floor and feed it back to the system. All this would create both high initial and high energy costs and make maintenance difficult and costly - all very good reasons why many people choose to go without any air-moving system. HVLS fans, on the other hand, are designed to move air in just this type of space without the huge up-front investment or the follow-on operating and maintenance costs. This makes them an excellent alternative or supplement to forced air units in large spaces.

HVLS plus HVAC

HVLS fans reduce thermal loads, electricity use, and mechanical heating and cooling times. Because HVLS fans circulate air so efficiently, they reduce the load of a building's HVAC system in many ways. In spaces with large, relatively open floor plans, air-conditioned air can be moved farther with less ductwork and even reduced tonnage. Heated air from radiant heaters can be circulated more efficiently with HVLS fans reducing or eliminating pooling, and increasing the efficiency of the heaters while potentially reducing the number of heaters required. Thanks to the destratifying effect (mixing of air in order to eliminate layers of air at different temperatures) of HVLS fans, thermostats can be adjusted to more energy-efficient settings. The same number of air exchanges - which means the same air quality - can be achieved with fewer ventilation fans due to the high volume of air moved by energy efficient HVLS fans.

Adding solar

In 2010, standalone solar-powered HVLS fans will become available. Energy operating costs of these models will approach zero. In addition to many applications in a range of building types, they could be well suited for facilities that require constant cooling or refrigeration. In cold storage or refrigerated rooms, they can continue to operate during power outages or intentional shutdowns during the hottest times of the day. This can reduce the chance of the product warming above unsatisfactory temperature levels due to stratification (the building up of layers of air at different temperatures.)

LEED® Credits

As of September 1, 2009, 45 states, 194 localities, 13 federal agencies or departments, 17 public school jurisdictions and 39 institutions of higher education have adopted various LEED initiatives and
requirement (www.usgbc.org/PublicPolicy/SearchPublicPolicies.aspx?PageID=1776). Since heating and cooling systems make up a large part of a building's energy use, HVLS fans can make a significant contribution to cutting those costs while increasing the effectiveness of the building's HVAC system. LEED v.3 categories where HVLS fans can contribute to prerequisites and points are: Energy and Atmosphere (35 possible points), Indoor Environmental Quality (15 possible points) and Innovation in Design (6 possible points.)

COOLING, HEATING AND VENTILATION

There are two major categories of HVLS fans: more efficient, lower horsepower (3/8 HP to 1 HP) models specifically designed to enhance the comfort of people, and higher horsepower (1½-2 HP) models best suited for extreme moisture or wet conditions and areas where some turbulence is acceptable.

Cooling

When used as a stand-alone cooling system, HVLS fans can provide a cooling effect equal to a reduction in temperature of up to 8 degrees F. within the fan's coverage area of up to 20,000 sq ft per 2HP 24-ft fan. (Report on Measurement, 3, see References)

More efficient, lower horsepower HVLS fans. 3/8HP to 1HP, often with six blades, 8-ft to 24-ft in diameter, deliver non-disruptive cooling that helps improve productivity and comfort of the work environment. AMCA testing (non-certified) shows that one manufacturer's 24-foot, 6-blade, 1HP HVLS fan produces 275,694 CFM. When installed at a height of 18-ft, as in the AMCA test, this is an effective coverage area of over 15,000 sq. ft., with an average calculated airspeed of only 609 ft/minute. By comparison, another manufacturer's 30-inch high speed 1HP fan delivers 12,000 CFM at an average calculated airspeed of 4,800 ft/minute. When used in conjunction with air conditioning or evaporative cooling systems, these lower-horsepower HVLS fans can efficiently circulate cooled air throughout the structure.

The Physics of Moving Air

Called a horizontal floor jet, the deep wall of horizontal moving air is relative to the diameter of a fan and, to a lesser degree, the speed of a fan. Once the floor jet reaches its potential, it migrates outward until it meets a side wall or other vertical surface. There it continues to entrain and circulate additional air. Under ideal conditions, an 8-ft fan produces a floor jet of air approximately 36 inches deep. A 24-ft fan produces a floor jet 108 inches deep. Image courtesy of MacroAir Technologies A large column of air ‘travels' farther than a small one. The friction between moving and stationary air occurs at the periphery of the moving column. The perimeter of a column varies directly with the diameter. And while the cross-sectional area varies with the square of the diameter, the large column has proportionately less periphery, and therefore, less ‘drag.' The air column from a 3-ft diameter fan has more than 6 times as much ‘friction interface' per cubic foot as the air column from a 20-ft fan. When the down column of air off a HVLS air circulating fan reaches the floor the air turns in the horizontal direction, following the floor, away from the column in all directions. The air flowing outward is called the ‘horizontal floor jet.' The height of the floor jet is determined by the diameter of the column of air. The larger the HVLS air circulating fan, the larger the column and the higher the floor jet.