August 26, 2002
Berkeley Lab Science Beat Berkeley Lab Science Beat
Toward cooler, quieter, energy-efficient portable classrooms
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Approximately two million children in California attend school in relocatable classrooms, also known as portables. Are these buildings as environmentally healthy and energy-efficient as they can be? Berkeley Lab scientists recently tested an experimental ventilation system that would improve indoor air quality in portable classrooms and use a third of the energy of current systems.

Relocatable classrooms in Modesto, California

Current HVAC systems are able to provide the 15 cubic feet per second of ventilation required in classrooms by law, but at a high energy cost, and only if the fan is turned on manually. Many portable classrooms are not being adequately ventilated, and there would be a significant impact on peak-hour energy use and the California power grid if current HVAC systems were operated continuously. A ventilation system tested by Environmental Energy Technologies Division researchers could solve those problems.

"Contrary to common belief," said Mike Apte, principal investigator, "you can design buildings that use less energy and address indoor air quality issues, if you do it right and are clever about it."

Clever ways to reduce energy consumption is one of the things EETD researchers do best. This work was done by Apte and his colleagues William Fisk, Alfred Hodgson, Richard Diamond, Dennis DiBartolomeo, Tosh Hotchi, Satish Kumar, Seung Min Lee, Shawna Liff, Leo Rainer, Marion Russell, Derek Shendell and Doug Sullivan. It was funded by the California Energy Commission. Also collaborating on the project were the Davis Energy Group, an innovator in heating and cooling technologies, two school districts, and AMS, Northern California's largest manufacturer of portable classrooms.

About one-third of all classrooms in the state are in portable buildings. This number continues to go up as California's population increases and school districts attempt to reduce class sizes. The classrooms have gained a reputation for bad indoor air quality, especially for high levels of volatile organic chemicals, or VOCs. The Berkeley Lab study set out to evaluate the benefits of an experimental building ventilation system and construction materials that emit fewer indoor pollutants.

The school districts -- hot Modesto and moderate Cupertino -- had each already decided to buy two new 24 foot by 40 foot classrooms. They agreed to have one standard classroom as a control, and one experimental classroom, finished with alternative low-emission carpets, wall panels and ceiling panels. Both standard and experimental buildings were constructed with energy-efficient lighting, windows, and insulation levels.

Each building also had two HVAC systems: a standard electric compressor-based air conditioner/heat pump, and an indirect-direct evaporative cooler, or IDEC. The standard heat pump is controlled by a thermostat and outdoor air is only supplied when the heat pump is either heating or cooling the air, or when the fan is turned on manually. Compared against newer heat-pump systems available on the market, many of these units have a relatively low seasonal energy efficiency ratio (SEER) rating, a measure of energy efficiency. They also have a reputation for being noisy.

The IDEC operates through the evaporation of water, but employs a heat exchanger to separate most of the water from the ventilation supply air. It provides continuous ventilation with fresh outside air, is much quieter, and uses up to 70 percent less energy than the standard HVAC. Apte and his colleagues also added a gas-hydronic heating system and an improved filtration system. The IDEC, developed by Davis Energy Group under contract from the California Energy Commission, is not currently commercially available for small buildings.

The four portables were delivered in August 2001. Air quality and comfort levels were monitored for nine weeks of hot weather in the fall and nine weeks of cold weather in the winter. The HVAC and the IDEC were operated on alternate weeks during the test periods. Researchers then compared the energy use and indoor environmental conditions for the two systems.

The researchers did not find that the building materials used gave off harmful levels of VOCs; the levels in both the standard and alternative-materials classrooms were very low. Apte says that although the control classrooms were furnished with standard available materials, other manufacturers could use different materials that have higher emissions.

When it comes to reducing volatile organic chemicals indoors, continuous ventilation appears to be more important that alternative building materials.  

What they did find is that continuous ventilation was a much more important factor for reducing indoor VOC levels than the alternative building materials that were selected.

Both the HVAC and the IDEC kept the classrooms heated and cooled, but the energy efficient classroom with the IDEC HVAC system required only 25 million btu/year, according to the DOE-2 computer model ?? about a third of the energy used by the currently sold standard portable with heat pump, which underventilates the classroom.

The IDEC also provided greatly improved ventilation when it was operating, during both the cooling and heating seasons, as measured by classroom carbon dioxide concentrations.

The study illustrated the added burden an inefficient ventilation system can place on teachers who, already busy with instructing, grading and maintaining order, often forgot or neglected to turn on the HVAC. Also, they found it difficult to teach over the noise of the standard HVAC at times and preferred to suffer in a hot, cold, or stuffy room rather than compete with the sound of the fan.

"Controlling the environment comes very low on the list of things a teacher has to do," said Apte.

Late in the study the researchers installed an occupant sensor that activated the ventilation system whenever there was someone in the building. That solution could help improve air quality and take the pressure off busy educators.

There is still more number crunching and modeling to be done on the collected data, but the researchers have big plans. Next steps include outreach to help schools make choices about equipment and materials, and collaboration with a number of groups developing better classrooms. Apte also wants to study health and productivity in classrooms, and work with HVAC manufacturers to find a way to retrofit existing buildings for continuous ventilation without increased energy usage.

This project is part of a larger plan to design high-performance portable classrooms that use less energy and provide a better indoor environment than models currently available.

"I think we can contribute a lot to that with what we've learned," said Apte.

Apte and his colleagues presented their research at the Indoor Air 2002 conference in Monterey this July.