Wet walls are a type of evaporative cooling system. In general, they are more cost-effective to install and operate than air conditioning. Wet walls consist of an array of evaporative cooling pads through which water is circulated using a pump. On the opposite wall, there are cooling fans that draw air through the wet wall, cooling it by means of the evaporation of water from the pads. The wetwall should be on the side of the building facing the prevailing wind.

Wet walls are widely used for agricultural applications, particularly greenhouses and poultry farming. They are not ideal where a near-uniform temperature is required throughout the affected space, since the cooling effect is much more pronounced near the wet wall and drops off towards the other end of the installation. This happens because the air is heated by solar radiation and objects in the environment as it passes through the space. An entire side of the building should be occupied by the pads, as breaks in the continuity of the wet wall cause large hot spots in the building. Roof design and the layout of objects in the building should be taken into account to maximize the system’s efficiency. The cooling effect will also be more pronounced when the humidity of the outside air is relatively low. As with other temperature control systems, every possible effort should be taken to prevent the entry of outside air (other than through the wet wall).

The pads can become clogged with mineral deposits or other impurities in the water. In some cases, algae may also be a problem and can markedly reduce the lifespan of the pad. Insufficient pad area is a common reason for sub-optimal performance of wet walls. The reduced surface area not only reduces cooling efficiency but leads to reduced air flow and thus poor ventilation and a lower wind-chill effect. Poorly designed water delivery systems lead to dry spaces on the pads and are another cause of reduced cooling efficiency. Good quality pads and well-installed systems help to prevent these problems. The pads should be covered with a water film, but not a sheet of water that may lead to lower airflow.