Relocatable classrooms (RCs) are becoming more common on school campuses. These structures, also known as modular or portable classrooms, offer education planners the flexibility and economy to meet the needs of growing student populations. They are especially popular in California schools, which have about 85,000 RCs, with the numbers increasing by thousands per year.
Because of their low cost and use as temporary buildings, RCs do pose concern to facilities planners, teachers and parents. Although this concern should not be relegated to RCs only, the rapid expansion of this part of the building stock has brought them attention.
Some parents and teachers have expressed concerns about the air quality and heating, ventilation and air conditioning (HVAC) system noise within RCs. 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 learning.
Standards require the HVAC system to be capable of providing adequate outdoor air ventilation because natural ventilation, which includes the operation of doors and windows, may be inadequate. The American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) Standard 62-1999 specifies a minimum ventilation rate of 15 cubic feet per minute per person in classrooms. Ventilation delivered at this rate typically will maintain indoor occupant-generated carbon dioxide at less than 1,000 parts per million (ppm). Although indoor carbon dioxide concentrations above 1,000 ppm are not expected to cause health risks, they imply that ventilation is insufficient, and therefore other pollutants may concentrate to levels of health concern.
All the elements
One method to improve energy efficiency and decrease levels of indoor pollutants is an indirect/direct evaporative cooler (see sidebar). In addition, a high-performance RC will use available energy-efficient construction materials and methods, including:
Wall, floor and ceiling insulation.
A ceiling vapor barrier.
A reflective roof coating.
Low-emissivity window glazing.
Efficient fluorescent lighting.
These technologies are readily available and can help improve air quality and energy efficiency when used in relocatable classrooms.
It also is important to ensure that staff and others who use the classrooms understand how to operate HVAC systems to maximize their effectiveness at keeping the air healthy. Often, the HVAC systems are not turned on in the morning as instructed. When the systems are off, the carbon dioxide concentrations in the classrooms can rise well above the 1,000 ppm maximum level required by ventilation rate standards, with peaks reaching almost 3,000 ppm. When a person opens a window without using the system, indoor carbon dioxide levels often can exceed 1,000 ppm. This suggested that windows alone could not provide adequate ventilation.
RCs can be designed to be energy-efficient and provide students with a high-quality indoor learning environment. By incorporating an awareness of energy efficiency and good indoor air and environmental quality into school facility planning and maintenance, classroom occupants can be ensured they have a healthy and efficient learning environment.
Apte, Shendell and Hodgson are researchers at Lawrence Berkeley National Laboratory's Environmental Energy Technologies Division, Calif.
Estimated number of relocatable classrooms (RCs) in California schools.
Minimum ventilation rate, in cubic feet per minute, per person in classrooms, according to ASHRAE standard 62-1999.
In parts per million, concentration of indoor occupant-generated carbon dioxide for sufficient ventilation.
When the HVAC systems are off, the carbon dioxide concentrations in the classrooms can rise well above this, in parts per million.
SIDEBAR: A case in point
Thanks to research performed with funding from the California Energy Commission, Lawrence Berkeley National Laboratory has identified some approaches to help improve energy efficiency, decrease levels of indoor pollutants, and ensure that HVAC systems in relocatable classrooms meet the ventilation standard.
Working with a manufacturer of RCs and a consultant partner, the laboratory designed an RC using an energy-efficient hybrid HVAC system incorporating an indirect/direct evaporative cooler (IDEC) and a conventional system. When the two systems were mounted side-by-side and tested on classrooms situated in pairs in California's Central Valley and the San Francisco Bay area, the laboratory found that the IDEC did a better job of ventilating than the conventional HVAC system.
The continuous ventilation with outside air from the IDEC system also kept indoor air pollutants, including formaldehyde and volatile organic compounds, low. The carbon dioxide levels in the IDEC-ventilated classroom were substantially lower — an important benefit of the continuous, adequate ventilation provided by this system. The appropriate use of low-emissions materials for RC construction also reduced the concentrations of volatile organic compounds, but supplying adequate ventilation was found to be a more effective control measure.
The average energy costs for operating the HVAC systems during the cooling and heating seasons were lower with the IDEC system than with the standard system. On average, with the IDEC system, there was more outside air for ventilation, cooling costs were about 50 percent lower, and heating costs about 30 percent lower.