In closed recirculating systems, heat is transferred to the cooling water from the hot process and then it is transferred out of the cooling water by conduction in another piece of heat transfer equipment. No water is evaporated or concentrated. A system is considered "closed" when it is designed to be filled with water once and then run continuously for long periods of time without any significant amount of make-up water added. In closed cooling systems, the heat is usually dissipated by an auxiliary open cooling loop or forced air that passes over tubes containing the closed system water (as in a Fin-Fan Cooler).