Abstract: The present invention provides an air conditioning system including an outdoor unit, an indoor unit, and air supply and air discharge duct. The outdoor unit includes a compressor and an outdoor heat exchanger, and the indoor unit in a ceiling includes an indoor heat exchanger, a fan, guide means, and a preheat exchanger. The indoor heat exchanger has a space therein in communication with a room, and the fan is in the space for drawing air and discharging through the indoor heat exchanger. The guide means is provided on an underside of the indoor heat exchanger, for guiding the external air to the room through the fan, and the room air to an outside of the room. The preheat exchanger is arranged adjacent to, and in communication with the guide means, for indirect heat exchange of the external air and room air passing therethrough.

Abstract: There is provided an air conditioning system and method for operating an air conditioner according to a user's physical response to external conditions. The air conditioning system includes: an indoor environment sensing unit/a personal characteristic value reception unit for measuring an indoor environment and the user's physical status so as to obtain information used to operate an air conditioner; a control unit including at least a microprocessor, for finding out personal characteristic values which are used to evaluate the user's physical status on the basis of information inputted from the personal characteristic value reception unit; and a driving unit controlled by the control unit, for promptly enhancing the user's physical status.