We’re facing today the topic of dry cooling, and in particular of self draining dry cooling. First of all, a dry cooler is an air/water exchanger that employs ambient air as cooling media to cool down the temperature of water. Compared to an evaporative cooling tower, a dry cooler offers simple installation, easy management and employs water in closed circuit, never in direct contact with external ambient air. The fluid to be cooled is indeed circulating in pipes, while the exchanger has a fin pack, often with copper pipes and aluminium fins but it’s also possibile to have stainless steel pipes and aluminium fins or both pipes and fins in carbon steel, depending on the kind of application and type of fluid to be cooled (water, water glicol, hydraulic oil, diathermic oil for example).
A dry cooler is in addition a quite economic solution, due to the fact that the only energy consumption is related to the fans ensuring the air flow.
A dry cooling solution has some limits, strictly related to the external ambient air employed to cool down the fluid. During the summer, the outlet temperature of the water can be indeed at maximum 5-10° C higher than the temperature of ambient air.
On the other hand, during the winter, when air temperature goes below 0° C, the risk is that the water inside the pipes can freeze, with severe damages to the plant with breakage of pipes. In this case there are two solutions: if the requirement of the process allows it, is it possibile to employ water glicol, preventing the freezing, otherwise the solution is represented by self draining dry coolers. In this kind of dry cooler the water inside the pipes is automatically and completely drained out of the exchanger, thanks to a sloped exchange pack and to a special pipe battery with valves for the complete discharge of the water.
At last, dry coolers have significantly increased their energy efficiency thanks to developments in the technology of fans, using EC motor fans that during the different seasons provide the proper adjustment of the functioning speed to the weather conditions and to the effective needs of the plant, reducing energy consumption at the minimum required.