Evaporative condensers are frequently used to reject heat from mechanical refrigeration systems. The evaporative condenser is essentially a combination of a water-cooled condenser and an air-cooled condenser, utilizing the principal of heat rejection by the evaporation of water into an airstream travelling across the condensing coil.
Evaporative condensers offer important cost-saving benefits for most refrigeration and air-conditioning systems. They eliminate the problems of pumping and treating large quantities of water associated with water-cooled systems.
They require substantially less fan horsepower than air-cooled condensers of comparable capacity and cost. Most importantly, systems utilizing evaporative condensers can be designed for a lower condensing temperature resulting in lower compressor energy input, at a lower first cost, than systems utilizing conventional air-cooled or water-cooled condensers.
Evaporative condensers are used primarily in the refrigeration industry. The unit is fitted with a closed circuit coil instead of an open fill media. The refrigerant vapor to be condensed is circulated through a condensing coil, which is continually wetted on the outside by a recirculating water system. Air is simultaneously blown upward over the coil, causing a small portion of the recirculated water to evaporate. This evaporation removes heat from the coil, cooling and condensing the vapor in the coil.
Evaporative condensers offer energy savings by providing lower system power consumption than conventional air-cooled and water cooled condensing systems.
Evaporative Condenser Compared to Air Cooled Systems
Evaporative condenser capacity is a function of ambient wet bulb temperature while air-cooled condenser capacity is a function of ambient dry bulb temperature. Since design wet bulb temperatures, system condensing temperatures using evaporative condensers can be 8°to 12°C lower than design dry bulb temperatures, system condensing temperatures using evaporative condensers can be 8° to 12°C less, resulting in compressor and system power savings of up to 30%.
Evaporative Condenser Compared to Shell and Tube Condenser/Cooling Tower Systems
The evaporative condensers rejects heat directly to the ambient air in one step of heat transfer. In the shell-and-tube condenser/cooling tower system, heat must be first transferred to the cooling water by the condenser, and then to the atmosphere by the cooling tower. The single heat transfer stop in evaporative condensers provides lower condensing temperatures and compressor power savings of up to 15%.