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Monitoring. 

Closed-loop systems should be monitored weekly for mild-steel inhibitor or tracer concentrations and conductivity. Ideally, the makeup water volume should be metered and recorded weekly. If the system has leaks, copper-corrosion inhibitor and aerobic bacteria monitoring should be conducted weekly.

Monthly monitoring parameters include copper-corrosion inhibitor concentration, anaerobic bacteria count and pH. Anaerobic bacteria includes sulfate reducers, iron reducers and nitrate reducers. Samples should be taken at the circulation pump discharge.

If the surge tank is exposed to the atmosphere, then the frequency of bacteria monitoring should be increased to a weekly schedule. Also, the corrosion-control program should be designed to protect the system from dissolved oxygen corrosion. If the makeup rate for water and chemicals is high (>5% of water volume), then the system chemical treatment should be changed to accommodate the increased risk of microbiological-related fouling and corrosion.

The corrosion rate should be directly measured using corrosion coupons on a quarterly basis. The maximum corrosion rate should be 0.5 mils/yr (0.5 mpy) (0.013 mm/y) for mild steel, and 0.1 mpy (0.0025 mm/y) for copper.

Corrosion coupons can be installed in a rack that receives water on the supply side or by using a specially designed holder that is installed directly into the return line (stab-in type). Often the rack is installed across the supply and return lines of the chilled water system to ensure adequate pressure drop and flow through the rack. All racks should use flow-control orifice valves to regulate flow. Coupons should be visually examined prior to cleaning and photographed before and after cleaning. If comfort systems are operated on a seasonal basis, they will require additional chemical treatment when idled. Idled systems should be circulated once per week for several hours.