There are two general types of recirculating loops: An open recirculating loop (cooling tower), and a closed loop (or semi-closed loop). A closed loop is a recirculating water loop that is not exposed to outside air and is under pressure. Typically closed loops are used in glycol systems, chilled water systems or hot water systems. They are susceptible to low pH and highly corrosive conditions which is why chemically treating them is imperative in order to maintain the longevity of the piping system. Semi-closed loops are often more challenging to treat as they are exposed to the outside elements. Water treatment of a semi-closed loop is commonly centered around microbiological control, in addition to scale/corrosion control.
It is important to collect and analyze the water in these systems to check for microbiological growth and corrosion. Click here to see how to analyze a water sample from a closed or semi-closed loop.