Abstract: An open-cycle air-conditioning apparatus including a rotatable heat exchanger wheel, a rotatable moisture transfer wheel, evaporative elements, and heating means disposed between the heat exchanger wheel and the transfer wheel wherein both wheels are constructed of spaced alternate layers of material mounted on a hub with means for forming a plurality of axial passages in the area between the layers. The moisture transfer wheel has an absorbent material alternating with a rigid polymeric material and the heat exchanger has rigid material of a low thermal conductivity, such as a rigid polymer forming both layers. In each instance, axial passages exist between the layers. Both wheels have outer semi-rigid rims and a plurality of rigid spokes secured to and extending radially from the hub, through the material and the rim for structurally strengthening the wheels and terminating in a threaded end with a cooperating nut for truing the wheel through adjustment of the nuts.