An apparatus for conditioning an inlet air stream. A first stage is provided with a dehumidifier cooling an air stream input by absorption of water vapor from the input air stream. A second stage is provided with an indirect evaporative cooler to receive a cooled portion of the input air stream and sensibly cool the received portion of the input air stream to a temperature range near the dew point temperature. A first portion of the sensibly cooled air stream is exhausted to a cooled space while a second portion is directed to a wet side of the indirect evaporative cooler and receives heat to sensibly cool the input air stream. A flow channel for the second portion of the sensibly cooled air stream in the indirect evaporative cooler is defined by a surface of a separation wall covered with wicking material acting to wick a stream of liquid coolant.
 The United States Government has rights in this invention under Contract No. DE-AC36-08G028308 between the United States Department of Energy and the Alliance for Sustainable Energy, LLC, the Manager and Operator of the National Renewable Energy Laboratory.