Abstract: A method of operating recuperative heat exchange means in the supply and exhaust ducts of a ventilation installation exposed to sub-freezing atmospheric condition so that the heat exchanger in the exhaust duct is allowed to ice up and is periodically defrosted. The method operates to control the temperature in the spent-air heat exchanger in various ways, including raising the input temperature of the the exchange medium to reduce the cooling effect on the spent air, or by reducing the flow of heat exchange medium to achieve the same result.

Abstract: A contact body comprising a sheet of material adapted to be positioned upright on edge within a cooling tower along with a plurality of similar bodies. Water is caused to flow downwardly upon the surfaces of said body, in the preferred embodiment countercurrent to the flow of air through the tower. A fine surface structure on the body consists of corrugations or folds disposed at an angle to the vertical between 65.degree. and 88.degree.. The corrugations have a wave length below 12 mm and an amplitude between 1 and 5 mm. The corrugations are arranged in fields whose angles of inclination alternate successively between positive and negative inclination. The fields may range between 20 and 50 mm and alternate along the vertical extent of the body. They may also alternate along the horizontal extent of the body. Integral spacer elements are pressed out of the body to position adjacent vertical bodies in spaced, generally parallel arrangement.