The basic principle of Handlair make Air cooling unit / Air washer unit / Evaporative cooling unit is that the air cools through the evaporation of water. Evaporative cooling works by exploiting water's large enthalpy of vaporization. The temperature of dry air can be dropped significantly through the phase transition of liquid water to water vapor (evaporation). The cooling potential for evaporative cooling is dependent on the wet-bulb depression, the difference between dry-bulb temperature and wet-bulb temperature.

The fresh, filtered air is made to pass through specially designed honeycomb structure of cellulose paper fills media, which has water absorbing properties. The air when passes through the fill media, absorbs the water and loses heat in the process. This makes air cool, which when supplied to the work area, provides comfortable conditions inside the work area. These units are available with capacity varying from 2500 cu.mtr per hour to 2,00,000 cu.mtr/hr with combinations of single and multiple blowers. Air cooling units are also manufactured with spray type cooling sections, as per customer requirements. The unit chamber is normally fabricated with standard G.P. Sheet and powder coated for longer life. These are available in single skin as well as in double skin construction, and also available in stainless steel construction.