For every kg of water evaporated from a cold water humidifier, 0.68kW of cooling is provided to the atmosphere. As cold water humidifiers can operate on as little as 0.5kW while delivering hundreds of litres of water per hour, their potential for low cost cooling is great.

Traditional compressor driven air conditioning systems have relatively high energy requirements. Evaporative cooling can't always replace the need for compressor driven cooling as it's effectiveness depends on the conditions of the supply air. However, it can offer a low cost alternative and significantly reduce the load on chillers when conditions allow.

It is particularly effective when used alongside free air cooling systems, which use high volumes of outside fresh air to cool an internal atmosphere, such as those used in modern data centres.

There are two types of evaporative cooling using cold water humidifiers – direct and indirect. Direct evaporative cooling sees the humidifier providing moisture to the incoming air, increasing its humidity while decreasing its temperature.

Indirect evaporative cooling is when the humidifier operates on the exhaust air. Before being expelled, the air is humidified and cooled, then passed through a heat recovery unit to transfer the cool thermal energy to the incoming air. This cools the incoming air without adding any additional moisture.

Direct Evaporative Cooling

Supply air is cooled and humidified.

Type of Evaporative Coolers

The main types of cold water humidifiers used in evaporative cooling systems are either spray or evaporative humidifiers.

Spray humidifiers can deliver cooling either directly to a room's atmosphere or as part of an air handling system. They include compressed air and water spray humidifiers such as the JetSpray or high pressure spray humidifiers, such as the Condair FF2.

Evaporative humidifiers, such as the HumEvap MC3 , are located inside a duct or AHU.

In-Direct Evaporative Cooling