Adiabatic Cooling
Adiabatic cooling is a passive measure to ensure thermal comfort in summer. The lack of a refrigerant circuit labels this system as a passive one.
For water to evaporate, energy is required, which is extracted from the air in the form of heat during adiabatic cooling. Thus, by adding water, the temperature of the air can be lowered. This effect is comprehensibly shown in a psychrometric diagram.
The blue dot represents an exemplary summer situation. The outside air measures 29 °C and a humidity of 45 %. If only water is supplied to the system, the absolute as well as the relative humidity increases. Since the energy content of the system remains the same, the temperature decreases along the enthalpy curve. To continue to ensure comfort, only enough water is added to achieve a maximum relative humidity of 65 %. Thus, in the example described, the situation marked in orange measures 25.3 °C. If there is no need to ensure comfort, the air can be cooled down to the dew point temperature (100 % relative humidity), which is in this case 21 °C.
Exactly this principle of adiabatic cooling is also used in the demonstration unit. For this purpose, Mylar threads are stretched in front of the windows along which water can run down. The water is collected in a tank at the bottom and pumped back up into a second tank. When the window is opened, the outside air flows past the threads, is humidified and cools down. In this way, hygienic air exchange or even increased ventilation can be ensured even at higher outside air temperatures without the need for active preconditioning. If there is a risk of humidification beyond the comfort point, the window can be closed again.
The effect of adiabatic cooling in the demonstration unit was tested using a building simulation. The blue curve shows the outdoor temperature curve of an exemplary summer week in Wuppertal. In comparison, the adiabatically cooled outdoor air during the day is illustrated in orange. The maximum difference in air temperature is almost 6 K.
To make the principle of adiabatic cooling more tangible, there are also Dry Mist Fans in the outdoor area of the demonstration unit installed. These spray fine mist. The combination of air movement and small water droplets makes it particularly easy for the water to evaporate and thus efficiently cool the air.
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