This paper puts forward a new way in air_conditioning,which combines the fresh_air supply unit and such floor radiation system for the dehumidication and cooling in summer or heating in winter. By analyzing its advantages and limitations, it is found that this so called Cooling/Heating Floor AC System can improve the IAQ of residential building while keep high efficiency quality. It is also recommended that an methodology for the HVAC system designing,which will ensure the reduction of energy cost of users.