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BA-PIRC Partnership with
Pacific Northwest National Laboratory
Portland, OR

Record numbers of students, demands for smaller class size, shrinking budgets, and growing infrastructure costs are spurring demand for portable classrooms in America’s schools. Sixty-five percent of schools in the West report using portable classrooms; thirty-six percent nationwide do so. Over 180,000 students attend school in about 6000 portables in the Northwest. New portable classroom installations are increasing at a rate of 5 percent per year. Nationally, the use of portable classrooms is expected to grow throughout the century.

In the Northwest, the US Department of Energy’s Building America Industrialized Housing Partnership is exploring ways of making portable classrooms more efficient and better for learning. The Northwest state energy offices and Pacific Northwest National Laboratory, (PNNL) are using building science to examine energy consumption, lighting and ventilation to make these classrooms more comfortable and better value investments.

The Building America team studied both new, energy efficient portable classrooms in Oregon and Washington, and a retrofitted classroom (originally built in the 1970s) in Idaho. For all of the classrooms, team members installed monitoring equipment, collected data and performed tests to measure air leakage and indoor air quality. In the Oregon classroom, team members provided the school district with procurement specifications for a highly efficient classroom, including day lighting requirements. In the Idaho classroom, team members performed audits and monitored energy consumption pre- and post-retrofit to measure effectiveness. Washington team members also monitored a control classroom, built in 1985, to provide comparison data.

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Preliminary findings indicate that simple, low cost measures can do much to reduce energy costs and increase efficiency.

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 Key findings include:

  • Retrofitting energy saving measures to the Idaho classroom resulted in measured 35 percent energy savings.
  • T-8 lighting fixtures with electronic ballasts are cal-culated cost effective in both new and existing buildings.
  • In the field, it was observed that programmable thermostats do only part of the job if they cannot be turned off for holidays. If they can be programmed for automatic holiday shutdown, all the better.
  • A new classroom built to enhanced standards above Oregon code resulted in a measured 35 percent savings in comparison with a new unit built to existing code.
  • Field observations indicate that controlling HVAC equipment with volatile organic compound (VOC) sensors can be problematic, as VOCs tend to be off-gassed in the first year of the classroom’s occupancy.
  • Heating and ventilation controls that operate by measuring carbon dioxide were also not proven to be effective; however, more stable CO2 based controllers may be available in the future.
  • Additional high-efficiency operable windows, located on opposite walls, provide needed day lighting and ventilation.
  • Air leakage through T-bar ceilings can lead to substantial energy loss and inefficient ventilation. The new Washington classroom had over twice the air leakage - 19 ACH at 50 Pa than the control classroom - 9 ACH @ 50 Pa.
  • Commissioning the HVAC system is a critical component to efficient and healthy operation of the classroom, and should include air sealing of the marriage line and other leaks, balancing of the HVAC system, and proper thermostat programming.
  • Education of school district maintenance staff and teachers in the operation of the classroom’s HVAC system is an essential part of ensuring efficient system operation

The monitoring data from the Washington portable classrooms provides an excellent illustration of the importance of some of these findings. As seen in the adjacent graph, the new portable classroom consumed significantly more energy than the control classroom. This was attributable to two major factors:

  • Tests indicated twice the air leakage in the new classroom than in the control; additional tests indicate the predominant leakage path is through the T-bar ceiling.
  • Misunderstanding regarding the proper installation and commissioning of the HVAC system led to excessive operation of the exhaust fan during weekends, holidays and summer vacation. In addition, misunderstanding regarding the proper operation of the system led to comfort problems, resulting in the introduction of electric space heaters in the winter of 2001-2002.

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Future project work will include developing guidelines for the purchase, construction, set up, and operation of portable classrooms; preparing recommendations for low-emitting paints, furniture and flooring; and designing an advanced portable classroom that incorporates special roof sealing, natural day lighting, and renewable resources.

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