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Indoor Air Quality in Schools (IAQ): The importance of Monitoring Carbon Dioxide Levels
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By David Sundersingh and David W. Bearg, PE, CIH

In the developed world, ninety percent or more of our lives are dependent on the indoor air quality in homes, workplaces, and vehicles. The technological advances made by the developed world have nearly eliminated the impact of the climate on humans, and we have created artificial climates that allow us to spend enormous amounts of time indoors. With artificial, mechanized climate control we can exist almost anywhere on earth, but we are subject to the indoor air quality we create.

Generally, the quality of the indoor air is directly linked to the quality of the outdoor air, which improves as one moves farther away from urban centers and closer to large amounts of vegetation. The natural process of photosynthesis in vegetation purifies the air , as carbon dioxide is consumed by plants and oxygen is released. Unfortunately, it is not practical to have enough indoor vegetation in our buildings to adequately purify the indoor air. Therefore, the air we breathe is too often found to be of inadequate quality and/or harmfully contaminated. Invisible to the naked eye, these contaminants include living and inanimate materials such as gases, fibers, dust, and microbes.

The Concern
Exposure to more than the maximum acceptable outdoor pollutant levels as established by the National Ambient Air Quality Standards (US EPA 1997) is of particular concern for children and the elderly. Children are at a greater risk in these environments because they breathe a larger volume of air than adults in relation to their body weight. The body burden of the harmful pollutants will be much higher for small children than for adults in similar environments. Pollutants are also more often present at a child’s breathing zone than at an adult’s breathing zone.

For most students across the United States, exposure to the classroom-learning environment occurs five days a week. Do we understand the impact of these issues on children’s health? Do we understand the relationship between air quality in learning environment and student performance? Can we empathize with the parents who may not understand the reasons for their child’s fatigue or headache? Children have no control over the environment in which they learn. We provide that to them. It is our responsibility to see that the indoor air quality of our learning environments is safe. It is imperative that all children have acceptable indoor air quality!

Air Pollutants Found in Schools
Typical air pollutants found in schools include: environmental tobacco smoke, formaldehyde, volatile organic compounds, nitrogen oxides, carbon monoxide, carbon dioxide, allergens, pathogens, radon, pesticides, lead, and dust.

  • Environmental tobacco smoke (ETS) is the combination of two forms of smoke from burning tobacco products: sidestream smoke, (smoke that is emitted between the puffs of a burning cigarette, pipe, or cigar), and mainstream smoke (the smoke that is exhaled by the smoker.)
  • Formaldehyde is released by sources such as particleboard, plywood, textiles, adhesives, foam insulation, and pressed wood furniture, cabinets and shelving.
  • Volatile organic compounds are released by sources such as commonly-used cleaners, personal care products, adhesives, paints, pesticides solvents, wood preservatives, furnishings, and copying machines.
  • Nitrogen oxide is released in the process of combustion, welding, and tobacco smoke.
  • Carbon monoxide is released during incomplete combustion or unvented gas, kerosene heaters, boilers, furnaces, auto, truck, and bus exhausts.
  • Carbon dioxide is released in all combustion processes and human metabolic processes.
  • Allergens and pathogens are released by humans, animals, the environment, draperies, carpet, dust collecting sources, cooling towers, dirty cooling coils, humidifiers, condensate drains, and ductwork, which can incubate bacteria and molds.
  • Radon is released by the earth around some buildings, well water, and even some masonry blocks.
  • Pesticides applied close to the building can be drawn indoors, polluting the indoor environment.
  • Dust is released from the soil, fleecy surfaces, and pollen, burning wood, oil, or burning coal (US EPA Tools for Schools Action Kit 1995).

Reasons For Poor Indoor Air Quality
Inadequate ventilation, inefficient filtration, and poor hygiene of air handling units are the most documented reasons for poor indoor air quality. This article discusses only the scope of inadequate ventilation to emphasize some inadequacies in the present framework of codes and practices. These inadequacies are detrimental to delivering good indoor air quality, especially in schools. The American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) recommends Standard 62-1999 Ventilation for Acceptable Indoor Air Quality (1999b), as follows:

In reviewing these values, the question arises as to why the recommended minimum ventilation rates are less for classrooms than they are for office spaces? Perhaps, though, an even more important question is, “How many schools have been monitored to determine the actual amount of outdoor air for ventilation being provided?” Just as doubling this ventilation rate has been shown to increase office productivity by reducing short-term absenteeism (Risk of Sick Leave Associated with Outdoor Air Supply Rate, Humidification, and Occupant Complaints; Milton, Glencross & Walters; Indoor Air 2000; 10: 212-221), the question arises as to whether this effect would occur in the classroom as well. Unfortunately, the determination of the actual ventilation rate is not yet a standard procedure in the commissioning of schools. The tide is turning in at least one district, Boston Public Schools, where monitoring is being performed to document the amount of ventilation provided.

Case Study
The following study was done as part of the product demonstration in the Exhibit Hall of the Austin Convention Center during the USGBC 2002 Green Building Conference & Expo. The carbon dioxide monitoring was performed in accordance with the sampling guidelines of ASTM D6245, Standard Guide for Using Indoor Carbon Dioxide Concentrations to Evaluate Indoor Air Quality And Ventilation. Results of this study will be useful for projects in which CO2 monitoring is being considered.. The summary of the findings are listed below:

The monitoring of CO2 concentrations at seven floor-level locations in the Exhibit Hall during the Green Building Conference yielded the following key results:

  1. During the Opening Reception in the Exhibit Hall from 5:00 to 8:00 p.m. on Tuesday, November 12, 2002, the CO2 monitoring values indicated that the amount of ventilation provided to occupants was only 8 cubic feet per minute (CFM) per person or less. This amount is only about half of the minimum of 15 CFM per person recommended in ASHRAE Standard 62-1999, Ventilation for Acceptable Indoor Air Quality.
  2. The next morning, the details of this ventilation deficiency were communicated verbally to the operators of the building’s HVAC system, and at noon they increased the opening of the outdoor air dampers to provide more ventilation in the Exhibit Hall.
  3. AIRxpert’s continual monitoring of CO2 in the Exhibit Hall documented that the new damper position resulted in a significant increase in the ventilation rate at the breathing zone. For the duration of the Conference, USGBC attendees enjoyed a healthier and more productive environment in terms of the amount of ventilation provided.
  4. In regard to the LEED certification process, these results call into question the wording of IEQ Credit 1 of LEED 2.1. The section titled “Potential Technologies & Strategies” mentions, without elaboration, the integration of CO2 sensors with the Building Automation System (BAS). Fourteen of the Exhibit Hall’s air handlers are equipped with CO2 sensors in the return air streams, and yet adequate ventilation was not being provided at the breathing zone. As this study indicates, the Exhibit Hall’s CO2 monitoring system was not living up to its potential of being a commissioning tool to help those in charge of the building learn how to operate the HVAC systems through the benefit of feedback on their actions. By suggesting that CO2 sensors be integrated with the BAS, LEED 2.1 invites confusion between monitoring for diagnostic purposes and monitoring for energy conservation. These are two very different priorities, and they could, perhaps, be understood if a separate credit for CO2 monitoring were added in the Energy Section for Demand Controlled Ventilation (DCV) purposes.

According to IEQ Credit 1 of LEED 2.1, the CO2 monitors in the return air stream above the Exhibit Hall could ostensibly qualify for a LEED Point, even though they fail to achieve the intended amount of ventilation in the breathing zone in the space they serve. This suggests that an effort needs to be made in the ongoing revisions to LEED to clarify this distinction between the two uses of CO2 monitoring.

A related issue is that the CO2 monitors installed in the return air streams may be registering short-circuiting of the supply air that is circulating near the ceiling in this tall Exhibit Hall. If so, the diluted CO2 concentrations measured by these sensors would be incorrectly signaling that the intended ventilation at the breathing zone was being achieved. This situation suggests that, maybe, the LEED Credit for CO2 monitoring should include more specific guidance as to the appropriate number and location CO2 sampling points. (Note that ASTM D 6245-98 recommends against sampling in the return air stream for just these reason.).

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March 2nd, 2006

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