Implications for Good Building Practices
The scientific evidence reviewed suggests that maintaining indoor temperatures near the center of the comfort zone and providing higher ventilation rates will often increase work performance and bring financial benefits. Practical suggestions pertaining to building temperature control and ventilation are provided in this section. The suggestions rely heavily on expert engineering-based judgments, consequently, the suggested measures are not always fully proven by scientific research to increase work performance.
Indoor Temperature Control
Although the design and operational intent is to maintain temperatures near the center of comfort zone in nearly all thermally conditioned commercial buildings, in practice temperatures are often significantly above the estimated 22 °C optimum for productivity. In the EPA's Building Assessment Survey and Evaluation (BASE) study of 100 representative U.S. office buildings, 33% of the indoor measurements sites located at a height of 1.2 or 1.7 m above the floor had a workday maximum temperature at least 2.8 °C above 22 °C, and 72% of these sites had a workday maximum temperature at least 1.7 °C above 22 °C. Temperatures well below this estimated optimum were rare — only 1.4% of sites had a workday minimum temperature below 18.3 °C. In a European survey of 56 office buildings , time average temperatures in four of nine countries exceeded 23 °C.
Good standard engineering practices are the key to good indoor temperature control. These practices include the following:
- Heating and air conditioning systems must have sufficient capacity and be maintained to meet heating and cooling loads.
- Large sections of a building should not be treated as a single thermal zone with temperatures controlled by a single thermostat, as this practice can often result in temperature control problems.
- Thermostats must be accurately calibrated.
- Airflow to various sections of a building must be adjusted (balanced) as needed to maintain desired temperatures.
- Temperature control systems must be commissioned and maintained.
Providing Adequate Building Ventilation
- 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 [45, 46].
- Periodic or continuous monitoring of outdoor air intake flow rates in air handling units  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 [47, 48] 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 common anecdotal reports of ventilation equipment failures and control system problems, particularly in commercial buildings, point to the need for this ongoing commissioning and maintenance.
- While not frequently performed, consider post occupancy evaluations (POEs) which 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. As discussed above, in some studies higher levels of satisfaction with air quality have been correlated improved work performance.
- 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 performance can be several fold larger than 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. Based on the limited information available, reductions in some types of indoor pollutant sources will help to maintain high productivity without high building ventilation rates. Pollutant source control often does not affect building energy use, while increasing the ventilation rate increases energy consumption.