Outside air is cooled and dehumidified by a pre-cooler to pass through an adsorption zone of a carbon dioxide adsorbing rotor, producing air having a low carbon dioxide concentration which is cooled by an intercooler. The air that has passed through the intercooler is passed through an adsorption zone of a moisture adsorption rotor and then supplied to a low humidity working chamber. Return air from the low humidity working chamber may be mixed with the air leaving the pre-cooler. A part of the air which passed through the intercooler is branched to pass through a purge zone of the moisture adsorption rotor before being sent to a regeneration zone of the humidity adsorption rotor. Air that passed through the regeneration zone of the humidity adsorption rotor is mixed with outside air and then passed through a regeneration zone of the carbon dioxide adsorption rotor before being exhausted.

The AHU includes an air dehumidifying (AD) flow path, an air regeneration (AR) flow path, a first desiccant wheel and a second desiccant wheel each in the AD flow path and the AR flow path, a first cooler heat exchanger in the AD flow path, a second cooler in the AD flow path, and a heater disposed in the AR flow path. An HVACR system includes the AHU and a chiller configured to supply chiller liquid to the first cooler heat exchanger and the second cooler heat exchanger in the AHU. A method of conditioning air in an HVACR system includes directing air through the air dehumidifying (AD) flow path and directing air through an air regeneration (AR) flow path to regenerate the desiccant in a first desiccant wheel and the desiccant in a second desiccant wheel.