Smart design cools class without air conditioning
By Jan TenBruggencate
Advertiser Science Writer
One of the sun-baked portable classrooms at Wai'anae High School is considerably more comfortable than the others.
It's also quieter and less dusty. The interior is bathed in natural light from skylights overhead.
The unit has been retrofitted with a range of features that the Department of Education hopes will point the way for the future of the "temporary" buildings that are a common and often permanent component of crowded school campuses in Hawai'i.
Wai'anae High's Portable P-1 is not perfect, but it's a far better classroom than similar ones nearby, say those who have spent time in it.
Architect Virginia Macdonald, who consulted on the project at no fee, said many portable school buildings have the worst possible design for hot areas like Wai'anae. The sun beats on the flat roofs, heating up the interiors and forcing kids to open windows, which allows in dust and street noise. And it's so hot outside that the open windows don't do a lot of good.
"We have some classrooms out on the Wai'anae Coast where children are sitting in 95-degree temperatures trying to learn," Macdonald said.
Mainland studies show youngsters do better when classes are in a comfortable environment with good natural lighting, said Nick Nichols, a DOE facilities planner and chief of the design and evaluation section.
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Waianae High School students, from left, Jordan Kiyabu, Walter Tavares, Shannell Mahiai and Ahio Fangupo plant leafy shrubs that will provide cooler air under the building.
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The DOE issued a contract to Architecture Plus to try out features that might make the portables more comfortable without adding air conditioning. Problems with electric air conditioning include the initial cost of equipment and installation, high power bills, noise and stale air.
One idea was to insulate the structure. But by itself, insulation isn't enough in hot Wai'anae.
"Put a pizza in the oven and that pizza's going to bake, no matter how you insulate it," said Gary Kawakami, president of Architecture Plus.
The project had two parts, and design and construction over two phases came to $114,950, Nichols said. That's for a test project. Once officials figure out which features they want to include in future buildings, the cost per unit should come way down, he said.
One of the first parts of the Wai'anae P-1 project involved insulating the building's walls that face the sun, and then installing a second wall in front of that so there's an air space between them. The hot air behind the outer wall can escape rather than being trapped inside the building, and the actual wall is both insulated and shaded to limit the amount of heat that moves through it into the classroom.
It seemed like a good idea, but it didn't work very well in Wai'anae, Macdonald said.
"Wai'anae is the hottest place in which I have ever worked," she said. "It's hotter out there than we ever believed."
Several other features seemed to work better:
Skylights were installed. They have louvers around their edges to let hot air escape, and the upper surface is treated to allow light in but to reflect heat.
Solar-powered fans were installed. These are small fans powered by photovoltaic cells on the roof. Whenever the sun shines, the fans pump hot air out of the top of the building.
Floor vents were installed. As the solar fans pump air out the top, the vents allow cooler air from the shaded region under the building into the structure.
An insulated ceiling was installed below the roof, and the air space between the roof and the ceiling was vented.
Ceiling fans were installed, "creating moving air which cools the skin through evaporation," Macdonald said.
"When you're in a 95- to 100-degree environment, every little bit helps," Kawakami said.
Macdonald said officials of the Department of Accounting and General Services along with the architects and contractor Richard Hue sat in the building during the middle of a Wai'anae summer day with windows and doors closed. It was warm but comfortable, she said.
Tests in July, with the ceiling fans turned off, showed that ceiling temperatures in the unit were 20 degrees cooler than ceiling-height temperatures of nearby portable buildings. Desktop temperatures were 4 to 5 degrees cooler.
"It is expected that the ceiling fan effect will yield a perceptibly more comfortable environment," Macdonald said.
Macdonald, 83, now semi-retired, has been designing energy-efficient houses in Hawai'i for decades. She said she has never designed a building that required air conditioning. At the Wai'anae portable building, further improvement is quite possible, she said.
One plan is to plant naupaka, a native beach shrub with large leaves, around the perimeter of the building and to mist it with water. Then, air being pulled into the area under the building will be cooled as it passes over the moist leaves, and the air being sucked up into the classroom through floor vents will also be cooler, she said.
The misting equipment is in place. Macdonald said students are expected to take on the task of planting and caring for the naupaka, treating it and the entire classroom as a science project.
Nichols said he would like to experiment with skylights that bring indirect rather than direct sunlight into the building.
"I get the feeling that improvement can be continued," Kawakami said.
Even so, the existing improvements have brought average temperatures from the low 90s into the 80s.
"Anything in the 80s, we call the comfort zone," Macdonald said.
Reach Jan TenBruggencate at email@example.com or (808)245-3074.