This invention relates in general to air exchange systems and, in particular, to an improved energy recovery ventilator, a cross flow plate core associated therewith and a method of conditioning air for a building. In one aspect, the invention provides a cross flow plate core comprising: a left hand wafer comprising a left hand spacer with a first of a plurality of membranes bonded thereto, the left hand spacer comprising a plurality of parallel curvilinear rails which form channels for receiving a first stream of air; and a right hand wafer comprising a right hand spacer with a second of the plurality of membranes bonded thereto, the right hand spacer comprising a plurality of parallel curvilinear rails which form channels for receiving a second stream of air, wherein the left hand spacer of the left hand wafer is bonded to the top of the membrane of the right hand wafer.