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Verification of dC(1) parameter for measuring the effectiveness of a personalized ventilation system.

Article Excerpt
INTRODUCTION

Indoor air quality and the importance of providing a healthy and comfortable indoor environment for occupants have been drawing more and more attention (Butala et al. 2001a). Most areas within buildings space in which fresh air is normally supplied by mixing ventilation or displacement ventilation systems can be polluted by various indoor air contaminants before the air is inhaled by the occupants. People have also become more aware of sick building syndrome (SBS) (USEPA 1991) and building-related health complaints, which represent significant health problems, such as headaches, allergies, and fatigue.

The main cause of SBS is a poorly ventilated working area (WHO 1984), which depends on several influencing parameters, such as the type of ventilation and HVAC system, the hygienic quality of the inlet air, and classical physical factors in the environment. The parameters interact to influence people's health conditions and feeling. SBS has a significant economic impact that is manifested in decreased productivity and absence from work, as well as the consequently higher health care costs of employees (USEPA 1989; Wargocki et al. 1999, 2000).

On this basis, a new approach based on the philosophy of excellence for future air-conditioned environments was proposed by Fanger (2001). He suggested narrowing the air-conditioned space from the whole room space to the local space within the occupants' breathing zone, and proposed a novel personalized air (PA) system that would gently serve a small amount of cool, clean air close to or directly into the breathing zone of each individual without causing a draft.

Based on studies carried out in Slovenia (Butala et al. 2001a, 2001b, 2002; Muhic and Butala 2002, 2004; Butala and Novak 1997), conclusions similar to Fanger's proposal were presented (Muhic and Butala 2006). There is a need for more qualitative ventilation or air-conditioning systems for workplaces. New systems with a personalized inlet of fresh air will allow local regulation of key indoor environment parameters. This concept of a properly designed personalized ventilation system makes it possible to achieve high local ventilation efficiency with a very small fresh airflow rate and satisfactory thermal comfort parameters for each occupant.

Researchers of the personalized ventilation applications evaluated performances of different air terminal devices under many operating regimes in terms of flow rate, temperature of personalized air, and space air temperature, using an index named the "personal exposure effectiveness" (Melikov et al. 2002; Naiping and Kianlei 2004; Niu et al. 2007; Sekhar et al. 2005). Proper design and orientation of an air terminal device and the temperature of personalized air have a great impact on achieving very high rates of personal air in inhaled air (Bolashikov et al. 2003), and the most critical factor in improving the efficiency of personal air distribution is the location of an air terminal device (Kaczmarczyk et al. 2006; Jeong 2003; Faulkner et al. 2004). However, it was also found that in some special cases personalized ventilation did not ensure better inhaled air quality due to the influence of the location of pollutant sources and the background air-conditioning system (Cermak and Melikov 2003; Melikov et al. 2003). The results showed that personalized ventilation will always be able to improve the inhaled air quality in spaces with a mixing ventilation concept, but that the improvement in rooms with displacement ventilation still depends on the ventilation efficiency of the personalized ventilation system and its ability to promote mixing. In such cases, personalized ventilation can strengthen the contaminant transport in the breathing zone so that there is a higher risk of personal exposure observed (Cermak et al. 2006). This is the reason why ventilation efficiency of the personalized ventilation system is an important and influential parameter that must be measured and calculated for the assessment of system operation.

In our previous studies of personalized ventilation effectiveness, a new index of relative decrease of tracer gas concentration in the first minute of system operation dC(1) was defined (Muhic and Butala 2006; Muhic 2004). The parameter dC(1) can be used for direct measurement of ventilation efficiency in a shorter time. On the basis of dC(1) measurements, the computational fluid dynamics (CFD) simulations using the same boundary conditions were carried out, which have successfully verified the results of dC(1) measurements. This...

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