Evaporative Cooling Systems and Processes Explained

Evaporative cooling is the process of liquid water evaporating from a surface, resulting in a decrease in the surface's temperature.

A device that cools air through the evaporation of water is an evaporative cooling system and differs from typical air-conditioning systems that generally use vapour-compression or absorption-refrigeration cycles, where the water absorbs relatively more heat in order to evaporate. In contrast, evaporative cooling uses less energy, and the temperature of dry air can be significantly and more efficiently decreased. The evaporative cooling process offers the added benefit of conditioning the air with more moisture for the comfort of building occupants in extremely dry climates.

Direct Evaporative Cooling

Direct evaporative cooling uses latent heat of evaporation to convert water into water vapour in order to lower the temperature and increase the humidity of the air. In this process, there is no change in the energy in the air; warm, dry air is converted into cool, moist air using the heat present in the outside air. The water evaporates directly into the air stream, thus reducing air temperature while humidifying the air.

Indirect Evaporative Cooling

Indirect evaporative cooling uses direct evaporative cooling in addition to a heat exchanger to remove heat from the supply air. The cooled, moist air never comes into direct contact with the conditioned supply air. The stream is released outside or used to cool other external devices. Indirect cooling is an effective strategy for climates that are hot and humid, where one cannot afford to increase the moisture content of the supply air due to indoor air quality. Essentially, the primary air is sensibly cooled in a heat exchanger, while the secondary air removes heat from the primary air as generated vapour.

Indirect Direct Evaporative Cooling

With Indirect Direct evaporative cooling systems, the primary air stream is first cooled with indirect evaporative cooling and then cooled again using direct evaporative cooling. Warm air is indirectly pre-cooled inside a heat exchanger that is cooled by evaporation on the outside; this pre-cooled air is then passed through a water-soaked pad that picks up humidity as it cools. Since the air supply is pre-cooled, less humidity is transferred before reaching the desired cooling temperatures. To reduce the temperature below the wet-bulb limit and/or increase the overall efficiency, direct or indirect cooling is combined with vapour-compression or absorption air-conditioning.

One such Indirect Direct evaporative cooling system is the HMX-Ambiator manufactured by Hmx. HMX evaporating cooling is used for cooling large spaces for process requirements and/or to maintain a comfortable environment for workers in a variety of industries. It uses a revolutionary two-stage process to cool air: Indirect Evaporative Cooling followed by Direct Evaporative Cooling allows the HMX-Ambiator to dispense air-cooled to below the collective atmospheric wet-bulb temperature.

Its applications include industrial and commercial ventilation and cooling, and the advantages are positive pressure, a dust-free environment, lower energy consumption, and 100% fresh, clean, cool air. It is eco-friendly and prevents solvent evaporation under controlled temperature conditions.