In a closed system, water forms a closed loop for water conservation and energy saving when it flows through the coils, chillers, boilers, heaters, or other heat exchangers and water is not exposed to the atmosphere. Corrosion is a destructive process caused by a chemical or electrochemical reaction on metal or alloy. In water systems, dissolved impurities cause corrosion and scale and the growth of microbiologicals like algae, bacteria, and fungi. The chillers and boilers in a central plant are often located in the basement, machinery room, or on the rooftop of the building. Generally, a fairly constant-volume water flow is required in the evaporator to protect it from freezing at part load. Chilled water and hot water distribution pipes are often mounted in underground accessible tunnels or trenches. Many retrofits of campus-type chilled water systems required an existing refrigeration plant(s) and a new developed plant(s) connected to the same plant-distribution-building loop.