Indirect-contact towers require a closed-circuit heat exchanger (usually tubular serpentine coil bundles) that is exposed to air/water cascades similar to the fill of a cooling tower. Some types include supplemental film or splash fill sections to augment the external heat exchange surface area for instance, air flows down over the coil, parallel to the recirculating water, and exits horizontally into the fan plenum. Recirculating water then flows over cooling tower fill, where it is further cooled by a second air stream before being reintroduced over the coil.
Coil Shed Towers (Mechanical Draft). Coil shed towers usually consist of isolated coil sections (non ventilated) located beneath a conventional cooling tower. Counter flow and cross-flow types are available with either forced- or induced-draft fan arrangements. Redistribution water pans, located at the tower’s base, feed cooled water by gravity flow to the tubular heat exchange bundles (coils). These units are similar in function to closed-circuit fluid coolers, except that supplemental fill is always required, and the air stream is directed only through the fill regions of the tower. Typically, these units are arranged as field-erected, multi fan cell towers and are used primarily in industrial process cooling.