A closed loop water system, also known as a closed recirculating circuit, is an engineered network designed for efficient thermal control in industrial applications. Unlike open systems, the circulating fluid in a closed loop remains isolated from the atmosphere, thereby minimizing evaporation, contamination, and oxygen pressure. Water (or a water-glycol mixture, depending on process requirements) is continuously pumped through heat-generating equipment, where it absorbs process heat, and is subsequently cooled before being reintroduced into the system. This cyclic operation significantly reduces make-up water demand and optimizes resource utilization.

The thermal load in closed systems is typically rejected through a plate-and-frame or shell-and-tube heat exchanger, where energy is transferred to an auxiliary open loop, which then dissipates it to the atmosphere via cooling towers or other heat rejection devices. By isolating the fluid process, closed loop systems mitigate scaling, corrosion, and fouling potential, thereby extending equipment service life and maintaining stable heat transfer performance. These systems are integral to sustainable water management strategies in power generation, chemical processing, HVAC, and heavy industries, where reliability, efficiency, and conservation are critical operational drivers.