Hospitals are the places where the sick and the weakened are accepted to be cured and to recover. The medical staff, as well as the visitors and the patients in hospitals are experiencing elevated risk from getting infected with airborne infectious disease from contagious patients. Mechanical ventilation is one of the factors that may affect the spread of airborne pathogens, and lead to Hospital Acquired Infections (HAI) in hospitals (van der Wel et al. 1996, Menzies et al. 2000, Qian et al. 2006, Li et al. 2007). The ventilation in the hospital facility may fail to successfully and fully evacuate the pathogens from the air and even may increase further their spreading within the building envelope and thus contaminate more people (Li et al. 2007). Therefore good ventilation design plays an important role for controlling the spread of airborne diseases in hospitals (Streifel 1999, Kaushal et al. 2004, Beggs et al. 2008).