A building can be very tight in terms of leakage and have sufficient, or even too much, outdoor air ventilation. Outdoor air intake and ventilation are the intentional and, ideally, controlled flow of outdoor air into a building via either a mechanical or netural ventilation system. Leakage and infiltration refer to the unintentional and uncontrolled flow of outdoor air into a building through leaks in the building envelope caused by pressures induced by weather and ventilation equipment operation.
In discussions of envelope airtightness and ventilation, it is important to distinguish between envelope leakage or infiltration and outdoor air intake or ventilation.
Therefore, it is important to havereliable values of envelope airtightness for commercial and institutional buildings.
7 In addition, these airflow rates can be used to predict indoor contaminant levels and occupant exposure to indoor pollutants, and to evaluate the impacts of various indoor air quality control strategies. These predicted airflow rates can be used to estimate the energy consumption associated with air leackage and to investigate the potential for energy savings through improvements in envelope airtightness and in ventilation system control. Envelope airtightness is one critical input to building airflow models, 9,31 which predict air leakage rates through the building envelope induced by outdoor weather and ventilation system operation. Building envelope airtightness is important based on its relevance to the estimation of building ventilation rates as they impact energy consumption and in-door air quality. Also, they are based often on confusion between building envelope tightness and low ventilation rates. These statements are almost never supported by any test data for the buildings in question. Furthermore, discussions and analyses of energy consumption in commercial and institutional buildings generallyare based on the assumption that envelope air leakage is not a significant protion of the energy used for space conditioning. These tight buildings often are blamed for a host of indoor air quality problems including high rates of health complaints and more serious illnesses among building occupants. Many discussions in the popular pressand the technical literature refer to commercial and institutional buildings and newer buildings in particular, as being airtight. This article presents the available airtightness data and the limited conclusions that can be drawn from these data. The data that exist show significant levels of air leakage in these buildings and do not support correlations of airtightness with building age, size or construction. However, very little data is available on the airtightness of building envelopes in commercial and institutional buildings. Furthermore, it is assumed that more recently constructed buildings are tighter than older buildings. It is often assumed that commercial and institutional buildings are fairly airtight and that envelopee air leakage does not have a significant impact on energy consumption and indoor air quality in these buildings.