A new type of surface cooling system

The chilled water wall is a comfortable form of air conditioning which also effectively reduces humidity in rooms. Here it is used with a green wall in an office landscape.

Air conditioning systems in buildings ensure a defined indoor climate as far as temperature, humidity and air quality are concerned. However, dry and cold air is often blown into the room, which has negative effects. Users frequently complain about draughts and the noise generated by air conditioning systems. In hot, humid countries, rooms also tend to be cooled too much because the air conditioning system is set to reduce the level of humidity rather than control the ambient temperature.

As an alternative to air-conditioning units, large-surface cooling elements such as chilled ceilings have become established on the market. Their advantage and efficiency lie in their dual effect: they not only cool the air as it moves over the surface but also form a sink for the long-wave radiation emitted from people and objects in the room. In addition, they are silent and do not cause annoying draughts. However, a major drawback is their limited cooling capacity.

The temperature on the surface of a chilled ceiling must be kept at a certain level above the dew point of the indoor air in order to prevent mold from growing. This means that surface humidity should be kept slightly below 80 percent relative humidity, which in turn limits the cooling effect of the element. Chilled ceilings are also not suitable for reducing humidity in rooms because the moisture contained in the air may not be allowed to condense.

With the development of the chilled water wall, the researchers at the Fraunhofer Institute for Building Physics IBP have succeeded in combining the advantages of different systems, while at the same time eliminating the disadvantages of air-conditioning units and also circumventing the limiting factors of conventional surface cooling systems.

Cooled water circulates in a vertical wall component in the room, forming an even film of liquid on the surface. Alternatively, the surface can be cooled by a secondary cooling circuit. As with any active air conditioning system, the temperature of the cooling liquid is controlled by a cooling unit outside the room. In contrast to chilled ceilings, the chilled water wall can even reach temperatures below the dew point without any problem.

The large temperature difference between the air in the room and the water ensures efficient cooling while dehumidifying the air at the same time.

If the temperature of the water film is below the dew point temperature of the room air, the moisture in the indoor air condenses on the water film and is discharged with it into a collecting basin. Excess water is drained off via an overflow and can be collected for reuse if required. Due to the long-wave radiation exchange with the cooled surface of the chilled water wall and the reduced level of humidity, air temperatures in the room are perceived as pleasant even if they are a few degrees above the normal comfort range. This makes the air conditioning system efficient and results in energy savings.

One of the biggest advantages of the chilled water wall is the possibility of zonal air conditioning. This means that it is possible to condition the air only in certain areas in a room, such as where people are present, and not to treat the air in the remaining areas. This enables huge energy savings in production halls or high entrance halls, for example.

The chilled water wall can also be used as a cooling oasis in non-air-conditioned buildings. In the vicinity of the chilled water film, the user can recover from the summer heat. Such areas can also serve to increase the attractiveness of department stores, fitness centers, water parks and other leisure facilities.

Moreover, the chilled water wall is well suited as a supplement to surface cooling systems such as heating systems that are used for cooling purposes.