In terms of raw energy efficiency and the ability to provide precise cooling under fluctuating load conditions, recirculating evaporative cooling water systems with chillers or heat pumps are the most efficient way to remove heat from a process or building air. However, adiabatic cooling systems can be a good fit with an overall lower cost for heat removal in some climates and applications.

What are Adiabatic Cooling Systems?
Adiabatic cooling systems remove heat by evaporating water in a stream of warm, dry (low humidity) air. In the process of going from a liquid to a gas, the evaporated water simultaneously humidifies and cools the air stream to within a few degrees of the wet bulb temperature. 

Cooling systems that employ adiabatic cooling can have a wide variety of names and configurations, but will generally fall into one of three categories:

1. Direct Evaporative Coolers (also called swamp coolers) blow dry air through a water spray or water-soaked media pad. As the dry air passes through the spray or wetted pad, the evaporated water both cools and humidifies the air stream. This process is termed Direct Adiabatic Cooling.

2. Indirect Evaporative Coolers function very similarly to direct evaporative units except the air stream being cooled is separated from the outside air stream by a heat exchanger. This allows the air stream to be cooled without increasing the humidity. This process is termed Indirect Adiabatic Cooling.

3. Adiabatic Cooling Towers are air-cooled fluid coolers or refrigerant condensers that can employ adiabatic cooling as needed when the outside air temperature becomes too warm for efficient heat removal. They operate like a standard air-cooled fluid cooler or condenser when outside air temperatures are low. When the air temperature becomes too warm, they switch to adiabatic mode with water evaporated into the inlet air stream to lower its temperature and provide additional cooling. Unlike traditional recirculating cooling towers, adiabatic cooling towers only use water during the hottest part of the day and year. In some applications, annual water usage may be reduced up to 80%.

Where are Adiabatic Cooling Systems a Good Fit?
Adiabatic cooling systems can be a good technical and economic fit in hot, dry climates, especially where water supplies are scarce and costs are high. They can also be a good match where outside air temperatures are cool enough for most of the year for air-cooled fluid coolers or refrigerant condensers to operate efficiently.

The data center industry has employed adiabatic cooling technology on the air side for air handlers for years. With the development of new adiabatic designs applied to fluid coolers and refrigerant condensers and the increasing scarcity of water, adiabatic cooling systems are seeing wider use across a range of industries and applications.

Water Treatment Requirements
There may be two separate water systems in an adiabatic cooling tower: a water system for humidifying and cooling the inlet air stream and a recirculating closed loop. 

Eliminating the recirculating cooling tower from the cooling equation greatly simplifies water treatment. The closed loop portion of an adiabatic system should be treated with corrosion inhibitors appropriate for the water quality and system metallurgy. Don’t forget that glycol may be required for freeze protection in cold climates.

To create a high surface area for the water to cool quickly and totally evaporate in the air stream, adiabatic cooling systems typically use wetted humidification pads or misting spray nozzles. If the makeup water to the cooling pads or spray nozzles has significant hardness, softening may be necessary to help prevent the build-up of mineral deposits that will reduce cooling efficiency. Cooling media pads should be maintained and replaced according to the manufacturer’s specifications. Where misting spray nozzles are used, deionized water may be specified if adiabatic cooling will be employed more than a certain number of hours annually.

Adiabatic designs that employ a sump or basin to recirculate the spray water may also require bleed control equipment, a scale/corrosion inhibitor, and biocide additions. Although adiabatic cooling system designs may be less prone to Legionella amplification and transmission than a standard cooling tower systems, the spray water system can generate aerosols that present Legionella concerns. All water treatment chemicals should conform to manufacturer specifications and regulatory requirements.

In many geographies and applications, adiabatic cooling systems can be a good fit. Although routine preventative maintenance is required for the cooling pads or spray system, the overall water treatment requirements are greatly reduced.

For more information on treating adiabatic cooling systems or for help determining if your facility is a good fit, contact Chem-Aqua today!

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