Posted on: Monday, January 10, 2005

JAN TENBRUGGENCATE

By Jan TenBruggencate
Advertiser Science Writer

Architect Virginia Macdonald has one mission: to convince the world that you can cool a house in the tropics with proper design, and without air conditioning.

Macdonald is now retired, but she has designed and seen built dozens of homes, offices and other structures that use natural ventilation, insulation and other design features in such a way that instead of becoming hot boxes, they end up much cooler inside than outside.

The fundamental concept is that hot air rises. If you provide high vents so the rising air can exit the building and low-level inlets so cool air can enter from shaded areas under or alongside the house, then you not only have a cooler house, but you also have constant airflow.

Macdonald's own home on the Big Island won the American Institute of Architects' state award for passive solar design.

She is now preparing to publish a book on her designs that includes photographs and drawings of many of the buildings she has designed, explaining how she applied the ventilation principle in each.

The architect employs a variety of features, including floor vents, louvers low in walls, and vented fixed windows as ways to get air into a building. Air can get out through high louvers, vented skylights, eave vents and other structures.

"For effective passive solar ventilation, the building should act like a thermal chimney, always funneling the air upward through the structure," she writes.

Sometimes one or more skylights are designed into a structure to bring in enough sunlight to warm the air slightly, just to get the flow of air moving. She says a 10-degree temperature differential is what's needed to get the air flowing effectively.

In some homes in areas with regular winds, she may also design the breezes into the structure, using a combination of solar and wind-pressure ventilation to keep the home cool.

The system for moving air has multiple benefits for a homeowner, Macdonald said. It reduces mold. It cuts operating costs for cooling and dehumidification. It cuts energy use. Skylights reduce the need for electric lighting.

"There are only three things needed to make the system work: an intake area near ground level, where the air is always coolest; a light source to warm the air to create a 10-degree temperature differential; and vents in the upper reaches to let the warm air escape."

For more information, e-mail macdonald at vmandjm@aol.com.

If you have a question or concern about the Hawaiian environment, drop a note to Jan TenBruggencate at P.O. Box 524, Lihu'e, HI 96766, e-mail jant@honoluluadvertiser.com or call (808) 245-3074.