For selection of cooling towers (to select which tower from a particular manufacturer will give the capacity required for an specific application) you can use a selection program from the manufacturer, or just select the tower using their techincal brochure and the tables you will found there. However if what you need is to calculate a cooling tower, then you can use a set of software programs published by Mr. Marcel R. Lefevre called MRL, you will need several programs depending on what you need to calculate, for example the IDXF program will calculate a cross flow tower, the PC program will plot the performance of the tower, the KHAL will calculate the tower's capability, etc. You can contact Mr. Marcel R. Lefevre at mr_cooling_tower@compuserve.com Mr. Lefevre is an old mechanical engineer with many years of experience in thermodynamics and cooling tower design, the programs where writen long time ago and they work in DOS environment, but they are the only ones that are not private use of the engineering department of a cooling tower manufacturer. in fact many manufacturers utilize Mr. Lefevre programs to calculate large field erected towers. Hope this will help