A system (100) for conditioning and sterilizing air in an enclosure having protected environment is disclosed. The system (100) is ductless and 5 operates at a positive pressure. The system (100) comprises a lower first chamber and an upper second chamber, where an ozone-producing UV lamp is positioned in the first chamber for purifying and sterilizing the air. The system (100) eliminates bacteria, dust, microbes, fungi, virus, etc., from the air, while conditioning the air to provide optimum temperature and relative 0 humidity in the enclosure. The system (100) is adapted to reduce the particulate matter count up to Class 10.