Implications for Good Ventilation Practices
A substantial body of scientific evidence suggests that providing ventilation rates, at or above the minimum rates prescribed in current U.S. building codes, is a priority in order to maintain occupant health, and work and school performance. Therefore, careful attention to ventilation system design features, operational practices, and maintenance practices that affect building ventilation rates is advisable. Practical suggestions pertaining to building ventilation are provided in this section. The suggestions rely heavily on engineering-based judgments about the ventilation designs and practices needed to maintain adequate ventilation rates. Due to the reliance on expert engineering judgments, the suggested measures are not always fully proven by scientific research to provide health benefits.
- When possible, given a building's design, maintain building ventilation rates at or above the minimum rates specified in current applicable codes and professional standards [36, 48].
- Periodic or continuous monitoring of outdoor air intake flow rates  or indoor and outdoor carbon dioxide concentrations is recommended to assure that the amount of ventilation actually delivered is consistent with the design and operational intent. The outdoor air intake system should be designed  so that reasonably accurate measurements of intake flow rates are possible. The typical reliance solely on the building design and occasional air balancing to maintain desired ventilation rates is not recommended because available data indicate that building and building subspace ventilation rates, in practice, are very often well below or above code requirements and professional standards .
- Commissioning, periodic re-commissioning, and maintenance of building ventilation systems are recommended to assure that the desired ventilation rates are maintained. To enable commissioning, adequate access must be provided to air handler components for measurements and maintenance. The commonly reported ventilation equipment failures and control system problems, particularly in commercial buildings, point to the need for this ongoing commissioning and maintenance.
- Post occupancy evaluations (POEs) are assessments, often in the form of a survey, to determine how well the building is meeting the needs of occupants (see http://www.wbdg.org/resources/fpe.php). A POE that assesses satisfaction with IAQ, for example with indoor odors, may provide indirect evidence regarding the adequacy of building ventilation.
- Mechanical ventilation is often needed in new homes, which often have low leakage building envelopes . Analyses of data on the air tightness of new homes and data on window opening behaviors indicate that infiltration and natural ventilation in many of these homes are not sufficient to meet the ventilation requirements in industry standards and codes .
- Use of technologies and practices to increase ventilation rates above the minimum values in industry standards and codes, without substantial increases in energy use or cost, is recommended when practical options are available. Examples of such technologies and practices include the following:
- In commercial buildings, outdoor air economizers , (http://www.peci.org/ftguide/ftg/index.htm) increase time-average ventilation rates well above the code minimum rates, while simultaneously saving energy. The projected economic benefits of the improved health exceed, and add to, the energy cost savings from economizer utilization . During hot humid weather, controls are needed to prevent economizers from providing large amounts of humid air to a building.
- Heat Recovery Ventilation (HRV) or Energy Recovery Ventilation (ERV) systems reduce ventilation-related energy use by transferring heat or heat plus water vapor between the inlet and exhaust air streams. In some applications, HRV and ERV systems should be equipped with a bypass feature that enables free-cooling with outdoor air, when this free cooling is economically more advantageous than heat/energy recovery.
- More energy efficient HVAC systems can be used to reduce the amount of heating and cooling energy needed to thermally condition the ventilation air provided to a building. For example, evaporative cooling systems provide very high ventilation rates with low cooling energy costs in some climatic applications; however, these evaporative cooling systems must be designed and maintained to reduce the risk of related dampness and microbial exposure problems.
- Utilize local exhaust ventilation at localized sources of indoor air pollutants and moisture generation, such as in copy rooms, kitchens and bathrooms.
- Increase ventilation rates during, and for a period after painting, cleaning, waxing floors, or similar pollutant generating activities. Whenever possible these pollutant-generating activities should be performed when the building is as unoccupied as possible. The most effective option is often to add exhaust ventilation or increase the existing rate of mechanical exhaust ventilation from the space containing the pollutant source . For example, when a room is being painted, a box fan can be used to blow air from this room to outdoors through an open door or window. To reduce exposures to occupants located elsewhere in the building, interior doors of the space containing the pollutant sources should be closed. When exhaust ventilation is impractical, the ventilation rate in the space containing the pollutant source, or the ventilation rate throughout the building, should be increased by adjusting the outdoor air flow rates in existing mechanical ventilation systems or opening doors and windows.
- Locate the outdoor air intakes of mechanical ventilation systems away from sources of pollutants such as sanitary vents, combustion vents, garbage dumpsters, outdoor smoking areas, parking garages, and idling vehicles.
- In hot humid climates, the ventilation air can be a large source of water vapor. Thus, in these climates, dehumidification systems must be able to remove sufficient moisture to prevent high levels of indoor humidity during peak and off-peak thermal load conditions.
- Reducing the sources of indoor pollutants, for example through selection of low emitting building materials, furnishings, and consumable supplies and frequent changing of filters, diminishes the amount of ventilation needed to maintain low indoor pollutant concentrations. Pollutant source control often does not affect building energy use, while increasing the ventilation rate increases energy consumption.