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INTRODUCTION

Due to deficiencies in natural ventilation or air exchange in the indoor environment of buildings, mechanical ventilation equipment may be installed to maintain quality standards, and health and comfort levels of the indoor air. However, when excessive indoor related materials or chemical-based products are present in the indoor environment, harmful chemical substances may be produced (Chiang, 2006), including volatile organic compounds (VOCs) from solvent-based paint and formaldehyde from wooden or other construction materials. These substances are just two indoor factors that may affect human health.

A common pollutant of the indoor environment is Volatile organic compounds (VOCs) and formaldehyde (Zhang, 2007), which may originate from smoking by building occupants and/or from construction or related materials. In studies of the relationships between temperature, relative humidity (RH), and formaldehyde concentration indoors, it has been reported that formaldehyde can be removed by photocatalysts (Yang, 2007). However, Matthews et al. (Matthews, 1986) showed a seasonal pattern, with formaldehyde concentrations in summer 6-9 times higher than in winter. Yu et al. (2006) studied air change rates (ACR), RH, and photocatalytic filters in a simplified heating ventilation air-conditioning (HVAC) system. Their results showed that first-order decay of toluene and formaldehyde ranged from 0.381 to 1.01 h-1 under different total ACR, from 0.34 to 0.433 h-1 under different RH, and from 0.381 to 0.433 h-1 for different photocatalytic filters. However, increasing outdoor airflow rate increased the cooling load of the HVAC system (Amal, 2001). In order to effectively solve the above problem, it is possible to increase purification equipments of indoor is needed, as to reduce the volume of external air induction, and then to save energy and enhance indoor air quality.