Proceedings of BS2015: 14th Conference of International Building Performance Simulation Association, Hyderabad, India, Dec. 7-9, 2015.
EFFECT OF WINDOW FILTRATION VENTILATOR ON INDOOR THERMAL COMFORT AND AIR QUALITY
Jiayu Li1 , Yuefei Hou1 , Junjie Liu*1
1Tianjin Key Laboratory of Indoor Air Environmental Quality control, School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China.
Providing an adequate quantity of fresh, clean air to occupied areas of residential and public buildings is necessary for diluting indoor CO2, airborne particles and other gas pollutant, especially for overpopulated buildings like school. The window filtration ventilator is a new idea which replacing one part of the window frame by a ventilator with filter, and it is considered suitable to improve on air quality in the classroom. However, the practical use of the new kind of ventilator in an actual room is still needed to be verified. This paper aimed at investigating thermal comfort and air quality in rooms by both experimental and numerical methods, both before and after window filtration ventilator had been installed.
Indoor air quality influences the people’s health and thermal comfort, because about 85% of the lifetime of a person are in the indoor environment (Klepeis et al. 2001). Providing an adequate quantity of fresh air to occupied areas are necessary for dilution of indoor CO2, airborne particles and other gas pollutant (Awbi 2003). However, the outdoor air quality becoming worse and worse in recent years (van Donkelaar et al. 2010), especially in developing countries. Moreover, many articles indicated that outdoor particles contribute to indoor particle pollution significantly (Abt et al. 2000; Kopperud et al. 2004; Turpin et al. 2007; Chen and Zhao 2011). For classrooms, inadequate ventilation was considered the main cause of health symptoms (Clements-Croome et al. 2008, Bakó-Biró et al. 2012) In order to cope with this situation, supplying purified fresh air is needed instead of simply delivering outdoor air into the room without any control. The window filtration ventilator is a brand new ventilation device which replacing one part of the window by a mechanical ventilator. Fig 1 showed the design sketch and the original designed model. The ventilator is the positive pressure source in positive pressure fresh air supply system, which is designed to have the air filtration capability.
To evaluate the thermal comfort in the room, air velocity and temperature was the most influencing parameters (Fanger 1970). To evaluate the air quality, the concentration of CO2, local mean age (LMA) and local mean residual lifetime (LMR) were involved in the analysis. As shown in Figure 2, LMA and LMR are defined based on the concept of “age of air” (Sandberg 1981), which were to examine ventilation efficiency. As air can reach the point through various paths, the mean value of the ages at the point is called the local mean age (LMA) of the air at P. Likewise, the length of time required for the contaminant located at P to reach an exhaust is called the residual lifetime of the contaminant at P. The mean value through various paths is the local mean residual lifetime (LMR).
Currently, these parameters mentioned above are typically obtained by two main methods: experimental measurements and numerical simulations, predominantly computational fluid dynamics (CFD) simulations. Since Nielsen 1974, who was the first one to apply CFD to room airflow prediction, applications of CFD for airflow predictions in enclosed spaces have become popular (Chen 2009). Compared with experimental study, CFD simulation is less expensive and more efficient. However, since the turbulence models in CFD used approximations, the simulation results may contain uncertainties. Therefore, the CFD results need to be validated by corresponding experimental data before CFD can be used for further studies. (Chen and Srebric 2002) In this study, the research object is a typical classroom of a primary school in Beijing, China. The window filtration ventilator is considered to supply purified fresh air into the classroom. Before the large scale application of the ventilator, its effects on thermal comfort and air quality must be investigated in advance, especially in winter, which probably have bigger thermal comfort risk using the new kind of ventilator.
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