A multi-stage down-draft evaporative cool tower (DECT) was developed as an improvement to a previously developed single-stage design. The new tower incorporates a secondary air inlet, added to reduce the water consumption required to produce a desired cooling output in a tower of given maximum cross-section and primary inlet geometry. The secondary air, which may be drawn from the interior space being chilled, is cooled by evaporation in the lower section of the tower. This paper reports on the results of experiments conducted to establish the aerodynamic performance of the design prior to installation of a water spraying system. Design of the water spraying system and experiments on cooling performance are discussed in a companion paper. (C) 2007 Elsevier Ltd. All rights reserved.