Evaporative cooling: cooling the air with water

Evaporative cooling

Water needs energy to evaporate. This phenomenon is exploited in air-conditioning where, in the absence of an external energy source, the moisture (water) in the air absorbs the energy needed to evaporate from its surrounding environment. Specifically, 2501 kJ for each kilogram of evaporated water. As a consequence, the air is cooled.

It can be said that evaporation of water converts the sensible heat of the air (temperature) into latent heat (humidity). This type of cooling is referred to in literature as "evaporative cooling" or adiabatic cooling.

In all these applications,
the essential principle is always the same:
water evaporates and cools the environment.

In ancient Persia, palace courtyards were cooled by fountains with jets of water that provided permanent humidification and thus cooled the air. Excavations in Italy, Spain and Egypt show the importance of this air-conditioning technique in ancient times.

disegno antico


Very low energy consumption means evaporative cooling systems are environmentally-friendly, energy saving solutions: 100 kg/h of evaporated water absorbs around 69 kW of heat from the air, for a power consumption of less than 1 kW!

Direct evaporative cooling (DEC), involves cooling and humidifying the fresh air intake on an AHU. This technology is very efficient, especially when the outside air is hot and dry.

If outside humidity is already high, on the other hand indirect evaporative cooling (IEC). technology can be used. This technique exploits an adiabatic humidifier to cool the exhaust air via a plate heat exchanger or run-round coil, without affecting its humidity.


The investment
can be repaid very quickly.

Equipping an AHU with a DEC and/or IEC system means significant savings in running costs, and allows the cooling coil and the chiller capacity to be sized smaller.

Lazzarin, R., Nalini, L., Air humidification, CAREL 2004


Carel supplies a vast choice of solutions, with a wide range of flow-rates, features and operating modes, both for installation in air ducts and to cool/humidify directly in air-conditioned spaces.
These are sophisticated, high-efficiency and highly versatile systems that cover a vast variety of applications: improving comfort in hotels, offices and hospitals; temperature and humidity control in industrial applications, to both improve worker comfort and ensure stability of the production process, especially in industries where the machinery produces large amounts of heat, such as textiles, timber and tobacco processing, electronics; or to create outdoor cooling systems for large spaces.

Evaporative cooling techniques can be easily integrated into existing systems, and can bring the following benefits:

  • lower upfront investment costs;
  • substantial energy savings: less energy needed for cooling;
  • reduction in peak electricity demand and consequently greater energy independence;
  • no chlorofluorocarbons used;
  • smaller ducts and lower capacity (kW) of cooling equipment;
  • lower CO2 and other emissions; low running costs throughout the appliance's life cycle.