ReviewReview of research on air-conditioning systems and indoor air quality control for human healthRecherches sur les systèmes de conditionnement d’air et la qualité de l’air intérieur dans le cadre de la santé humaine : tour d’horizon
Introduction
Air-conditioning systems have been used in many parts of the world. The purpose of most systems is to provide thermal comfort and an acceptable indoor air quality (IAQ) for occupants. With the improvement of standard of living, occupants require more and more comfortable and healthful indoor environment. People spend 80−90% of their time indoors, and indoor environment has important effects on human health and work efficiency. The factors affecting indoor environment mainly include temperature, humidity, air exchange rate, air movement, ventilation, particle pollutants, biological pollutants, and gaseous pollutants (Graudenz et al., 2005). By analyzing recent studies, Seppanen and Fisk (2002) found that there was an increase in prevalence of sick building syndrome (SBS) between 30% and 200% in the buildings with air-conditioning systems when compared with natural ventilation systems. Death caused by Legionnaires' disease even occurred in air-conditioned buildings. In addition, SARS occurred in 2003. All of these events are a warning for indoor environment problems related to AC systems. It is fair to say that indoor environment problems still exist in many air-conditioned and mechanically ventilated buildings, even though existing standards may be met.
One of the consequences of the worldwide energy crisis in 1970s is the public recognition of the importance of energy saving. The buildings built since then are more airtight and use a great deal of insulation materials to minimize the loss of energy through the building envelope. Fresh air is reduced in air-conditioning systems in order to reduce the energy consumption. Meanwhile, synthetic materials and chemical products (e.g., building materials and decorating materials) have widely been used indoors. The combination of low ventilation rates and the presence of numerous synthetic chemicals results in elevated concentrations of indoor particle pollutants and volatile organic compounds (VOCs) (e.g., benzene, toluene, and formaldehyde). This is deemed to be a major contributing factor to compound hypersensitiveness (Wang et al., 2004a).
However, it is exciting that some comfortable and healthy air-conditioning systems were proposed in the past few years. In order to control the concentration level of indoor pollutants and to improve IAQ, many researchers have investigated the control methods of IAQ. In this paper, recent research will be reviewed on air-conditioning systems and indoor air quality control for human health.
Section snippets
Indoor air environment
Indoor air environments must meet the requirement of thermal comfort and IAQ. Thermal comfort is affected by many factors, which mainly include air temperature, air humidity, air velocity, mean radiant temperature, human clothing, and activity levels. The wide use of air conditioning helps to improve thermal comfort, but health problems associated with poor IAQ appear more frequently (e.g., SBS) (Niu, 2004). Many experts believe that IAQ may be the most important and relatively overlooked
Air-conditioning systems
Many kinds of AC systems are used to improve indoor thermal comfort and IAQ. Recent research is focused on dedicated outdoor air system (DOAS), independent control of temperature and humidity system (ICTHS), and cooling ceiling and displacement ventilation systems (CC/DV).
Control of IAQ
In order to provide a comfortable and healthy indoor air environment, measures must be adopted to control the concentration level of indoor pollutants and improve IAQ. The current methods mainly include control of pollution sources, ventilation and indoor air purification. The recent research on ventilation has been described in Section 3.
Conclusions and future work
A comfortable and healthy indoor air environment is favorable to occupants. In recent years, indoor thermal comfort has been improved greatly due to the development of air-conditioning systems. However, health problems related to poor IAQ appear more frequently, and it is the indoor pollutants that lead to poor IAQ. Many researchers have widely investigated the composition of indoor pollutants, sources, physical and chemical characteristics, and effects on human health. However, a given symptom
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