HVLS - Big Fans

HVLS or High-Volume Low Speed Fans have taken an old idea and applied it in a new way to save energy while providing an effective cooling or heating solution in modern buildings.

Nearly everyone is familiar with the humble fan, a device that has been around for centuries that cools us when it’s hot. Since the advent of electric motors, powered fans have been used in myriads of applications from the most basic desk fan to highly evolved models used in large-scale air-conditioning systems.

Everybody knows that a cooling breeze on a hot day provides an improvement in comfort for human beings, but few people know why. When we perspire in still air, a moisture saturated layer forms close to the body preventing evaporation, the natural process of body cooling. Even gently moving air brakes up the saturated air layer allowing cooling evaporation to take place and we feel cooler. The solution to feeling too hot then is to move the air around but how to do that efficiently?

The basic principle of a fan is that energy is applied via a mechanical device; in this case the blades, to move air. Let’s examine the physics of air movement to understand why big slow-moving fans deliver the most air movement for the lowest input of energy. A larger volume of air ‘moves’ more efficiently than a smaller volume. Friction between moving and still air takes place at the boundary and because the larger volume has proportionally less surface area than a smaller one, there is less friction and therefore less energy required to sustain movement. In simple terms, one big fan is up to six times more efficient at moving air than an array of smaller fans. HVLS fans capitalize on this efficiency equation to deliver the greatest amount of air for the lowest amount of energy expended.

In this article I am focusing on the use of fans as applied to supporting human comfort in buildings and the energy efficiency improvements that can be derived when compared to conventional heating and cooling systems. In short, heating or cooling the air in buildings during summer and winter uses large amounts of energy. With larger buildings such as shopping malls, conditioning the air is the single biggest consumer of electrical energy above all else. In other buildings such as factories, the energy cost is so prohibitive as to prevent any form of heating or cooling being installed at all.

HVLS fans can produce a cooling effect of up to 6 degrees centigrade when installed in non-air-conditioned buildings. When used in conjunction with air conditioning in larger open buildings, thermostat settings can be increased in hot weather without reducing comfort, saving up to 15% in energy costs. In winter, thermostats can be turned down for similar savings as the big fans gently bring down warmer air which has risen to the ceiling through natural convection.