|Better Air Quality and Energy Efficiency for Classrooms|
|Contact: Allan Chen, email@example.com|
As one element in the recently-concluded
High-Performance Commercial Buildings
Systems research program funded by the
California Energy Commission, researchers
in Lawrence Berkeley National Laboratory's Environmental Energy Technologies
Division (EETD) recently finished field-testing a "relocatable" classroom of their
own design, intended to save energy and provide good indoor air quality. This last in
a series of Science Beat articles on energy-efficient buildings looks at how energy costs
can be reduced and air quality can be improved in these ubiquitous structures.
On many school campuses throughout the U.S. portable structures are multiplying as school districts try to keep up with increasing student enrollments and requirements for class-size reduction. In California alone schools already use 85,000 relocatable classrooms, and the number is increasing at the rate of 4,000 to 10,000 structures per year.
In addition to the explosion in student enrollments, school districts also face the problem of operating and maintaining school facilities and paying the energy bill in the face of budget pressures. As in other buildings, indoor air and environmental quality can be a problem in schools for reasons ranging from incorrect design and operation of building equipment to improper maintenance.
Why classroom quality and efficiency matter
Energy-efficient structures can help school districts by lowering their energy bills, and structures designed with good air quality in mind help students and teachers stay healthy and sharp in the classroom. For these reasons scientists and school administrators asked whether relocatable classrooms (RCs) could be built that are both energy-efficient and provide good indoor air quality (IAQ) for their occupants.
"Some parents and teachers have expressed concerns about the air quality and HVAC system noise within RCs," says EETD's Michael G. Apte, the study's principal investigator, referring to the heating, ventilating, and air conditioning systems of the relocatable structures. "Inadequate ventilation can lead to higher concentrations of indoor pollutants, including occupant-generated carbon dioxide; materials used to manufacture and furnish RCs may emit organic air pollutants; and higher noise levels from the wall-mounted mechanical HVAC systems may impair the learning process."
To build an advanced, energy-efficient relocatable classroom, the EETD team worked with two school districts in California, a manufacturer of the classrooms, and a consultant partner, the Davis Energy Group. The team designed a classroom with two HVAC systems: a standard 10-SEER heat-pump air conditioner system (SEER stands for seasonal energy-efficiency rating), plus an energy-efficient hybrid system with an indirect/direct evaporative cooler (IDEC) and a natural-gas heating system. The study was designed to compare their performance by running the standard and advanced systems in the same classrooms on alternate weeks.
Evaporative cooling for quiet efficiency
An evaporative cooler works by using the evaporation of water to remove heat as the air passes across a heat exchanger, cooling outside air as it enters the building; an indirect-direct evaporative cooler consumes as much as 70 percent less cooling energy than a standard heat-pump system. And because it has a quieter fan and no compressor, an IDEC's noise output can be lower.
The research team's high-performance classroom design also uses other available energy-efficient construction materials and methods, including additional wall, floor, and ceiling insulation, a ceiling vapor barrier, "cool roof" reflective roof coating, low-emissivity window glazing, and energy-efficient fluorescent lighting.
The team located pairs of their classrooms at schools in two climatically distinct regions: the California Central Valley, whose climate is considered extreme, and the San Francisco Bay Area, which has a moderate climate. In the Central Valley the manufacturer placed two units at an elementary school in Modesto city schools; in the San Francisco Bay Area, two were placed at an elementary school in the Cupertino Unified School District.
During the 2001 to 2002 school year, third and fourth grade classes of 20 to 30 students, with one teacher each, occupied the test classrooms. During nine weeks of the 2001 cooling season (August to October) and nine weeks of the heating season (January to March 2002), the standard unit and the IDEC systems were switched weekly. The research team measured humidity, temperature, air velocity, sound level, indoor and outdoor carbon dioxide concentrations, particulate matter counts, volatile organic compound and formaldehyde concentrations, and energy use.
They found that average school-day indoor CO2 concentrations were higher when the standard system was turned on than when the IDEC system was operating. With the conventional system, CO2 concentration was 960 plus or minus 480 parts per million (average standard deviation). With IDEC, the concentration was 830 plus or minus 530 parts per million. The continuous ventilation provided by the IDEC was also better at reducing the average formaldehyde concentrations, as well as those of other targeted volatile organic compounds.
Thus the advanced IDEC system did a better job of keeping the classroom ventilated. But the way the systems were operated had a big impact on overall environmental quality.
"Teacher operation of the HVAC systems was not based solely on thermal demand," says Apte. "Teachers did not always turn on the system in the morning as instructed. When they didn't, the CO2 concentrations in the classrooms rose well above 1,000 parts per million, with peaks reaching almost 3,000 ppm, no matter what type of HVAC system was operating."
Noise data showed that standard system in unoccupied classrooms contributed up to 14 to 15 decibels and the IDEC system caused up to 7 to 8 decibels. Regardless of the HVAC system, however, when the classrooms were occupied the noise level averaged about 56 decibels most of it caused by the occupants.
Finally, the energy use of the IDEC system was considerably lower than that of the standard system. On average, the IDEC lowered cooling costs by about 50 percent and reduced heating costs about 30 percent, with more outside air provided for ventilation. Using the energy data gathered in this study, researchers did an energy simulation model for schools in the 16 climate zones of California. The resulting statewide average energy impacts per classroom included an 80 percent reduction in annual electricity use, more than 70 percent reductions in peak electricity requirements during both summer and winter, and an increase in natural-gas use for winter heating. Annual energy cost savings per classroom was calculated as $220.
"Clearly, RCs can be designed to be energy efficient and to provide students with a high-quality indoor learning environment," says Apte. The research team is now working with manufacturers to bring more energy-efficient RCs to the marketplace.
This study was conducted by Michael G. Apte, Dennis DiBartolomeo, Toshifumi Hotchi, Alfred T. Hodgson, Seung Min Lee, Derek G. Shendell, Douglas P. Sullivan, and William J. Fisk of Berkeley Lab; Shawna M. Liff of MIT, and Leo I. Rainer of the Davis Energy Group, Davis CA.