Adiabatic cooling refers to a thermodynamic process in which a system does not exchange heat with its surroundings. In HVAC engineering, the principle is primarily used for adiabatic cooling: water evaporates in an air stream. The energy required for evaporation comes from the air itself, which cools as a result. The heat does not disappear; it is merely transferred into the water vapor that forms. Because no heat is supplied or removed from outside, this is referred to as an adiabatic process. The air temperature drops without necessarily having to use a conventional, energy-intensive vapor-compression chiller.
In data centers, adiabatic cooling can therefore help reduce the energy required for air conditioning. At the same time, the process requires water. To assess efficiency, both the PUE value (Power Usage Effectiveness) and the WUE (Water Usage Effectiveness) should therefore be considered.
In adiabatic cooling, water is introduced into an air stream and evaporates. This phase change requires energy. That energy is drawn from the air in the form of heat, causing the air to cool.
A simple example: on a hot, dry day, outside air can be cooled significantly by water evaporation before it is used to air-condition a building or data center.
How strong the cooling effect is depends, among other factors, on the temperature and humidity of the outside air. The drier the air, the more water it can absorb and the greater the potential of evaporative cooling. The physical limit is the so-called wet-bulb temperature: the air cannot be cooled any further by evaporation alone. In humid weather, it is close to the air temperature, so the cooling effect is then low.
In principle, a distinction is made between two methods:
Direct adiabatic cooling:
The water evaporates directly in the air stream. This lowers the temperature, but the humidity increases at the same time.
Indirect adiabatic cooling:
Evaporation takes place in a separate air stream, which cools as a result. The supply air then transfers heat to this cooled air stream via a heat exchanger. As a result, the air that reaches the IT area does not come into direct contact with the evaporated water, and its humidity remains unchanged.
Controlled airflow is particularly important for data centers, as temperature and humidity must be kept within defined operating ranges. For this reason, the indirect variant is often used there.
The key advantage of adiabatic cooling is its comparatively low electrical energy demand. Under suitable climatic conditions, it can reduce or temporarily replace mechanical cooling.
This can:
Especially in combination with free cooling, adiabatic cooling can be a way to extend the periods during which energy-intensive mechanical cooling can be avoided.
However, lower electricity consumption has a second side: water is required for evaporation.
For this reason, a data center’s efficiency should not be assessed solely on the basis of the PUE value. In addition, Water Usage Effectiveness (WUE) is relevant. It indicates how much water is consumed in relation to the energy consumption of the IT systems, stated in liters per kilowatt-hour (l/kWh).
Evaporative cooling can therefore have a positive effect on PUE, while at the same time worsening the WUE value.
For a holistic assessment of a data center, energy and water efficiency must therefore be considered together.
Whether adiabatic cooling is sustainable cannot be answered in general terms. The method can significantly reduce the electrical energy required for cooling. At the same time, evaporation results in water consumption.
Key factors include:
Especially against the backdrop of increasing water scarcity, metrics such as WUE are becoming increasingly important alongside energy efficiency.
Modern data centers can use different cooling concepts or combine them. In addition to adiabatic systems, for example, direct and indirect free cooling, classic precision air conditioning, and increasingly liquid cooling are used.
Which technology makes sense depends, among other factors, on IT power density, the climatic conditions, and the requirements for energy and resource efficiency.
Liquid cooling is becoming particularly important for high-density and AI infrastructures, as air reaches its physical limits at very high power densities per rack. The new firstcolo data center FRA7 in Rosbach, for example, is designed for high power densities and modern liquid cooling.
Do you have more questions? You can find answers in our glossary.
In adiabatic cooling, water evaporates and draws heat from the surrounding air. This lowers the air temperature.
Adiabatic cooling can reduce the electrical energy required for air conditioning and thus contribute to a lower PUE value.
Free cooling uses low outside temperatures to remove heat from the data center. Adiabatic cooling additionally uses the evaporative effect of water to lower the air temperature. Both methods can also be combined.
