Thermal Comfort is a Breeze!


Hawaii’s perennially pleasant weather owes much to the steady trade winds that regularly caress the islands’ shores. For generations, builders and architects working in Hawaii and the Asia-Pacific region have utilized these winds to provide comfort by orienting structures to catch the airflow and direct the flow into building interiors.

Image: The Liljestrand House, Vladimir Ossipoff’s tropical modern masterpiece.

In Hawaii, where MKThink is working with the Hawaii Department of Education to make classrooms cooler, the trade winds are a major factor in thermal comfort. Many schools in the state were built with the trade winds in mind, oriented to catch the wind and fitted with jalousie windows to let in as much air as possible. When trade winds blow, schools configured in this way are generally comfortable with natural ventilation. But when trade winds are disrupted, thermal comfort can decline precipitously. El Niño conditions, which most recently occurred 2014-2016, disrupt trade winds.

Image: ©Asya Pereltsvaig

Unfortunately for places like Hawaii, the trade winds are changing. The frequent recurrences of El Niño conditions disrupt airflow over the Pacific Ocean and can diminish trade winds for an entire season. Additionally, urban development in Honolulu has given rise to the heat island effect—a bubble of warm air that disrupts the trade winds, causing them to blow over densely populated areas. Due to Honolulu’s rapid growth, many schools, which were originally located in low density communities, are now surrounded by urban development.

Image: ©Progressive Materials

For many, the reflex response to poor thermal comfort in schools is to install air conditioning. But in many parts of Hawaii, the solution is to create air movement through the schools. A new type of fan does just that. High Velocity Low Speed (HVLS) fans simulate the effect of the trade winds for a fraction of the energy required of air conditioning.

Image: Schlieren photography shows the layer of warm humid air that surrounds a body in still air.

Air movement cools the body by breaking up the zone of warm air that surrounds a person at rest. Traditional ceiling fans blow a turbulent column of relatively high speed air down towards occupants. Papers may be blown about directly underneath the fan while someone just feet away may feel little effect. In contrast, large diameter HVLS (High Volume, Low Speed) fans move a very wide column of air at lower speed. When this column of air encounters the ground, air spreads outwards, creating a sensation of air moving horizontally even for people not directly beneath the fan. The perceived effect of the fan more closely simulates the trade winds.

Image: HVLS fans create a steady flow of air across rooms much like the trade winds.

In Pacific sub-tropical climates like Hawaii’s, HVLS fans can improve thermal comfort by simulating or augmenting the trade winds without the energy intensive costs of air conditioning. Even in spite of increasingly volatile trade winds, naturally cooling buildings can still be a breeze!

Image: Essence is a fan made by Big Ass Fans, a premier manufacturer of HVLS fans.