Application Note - Remote monitoring of commercial heating and cooling systems

Hot and cold water systems today are part of every kind of building. The media used as heat or cold transfer liquids is typically untreated water or inhibited water, depending on the application. In order to convey the liquid, different piping materials can be used, such as steel or copper. In addition, aluminium and brass are found in components such as valves and heat exchangers. The presence of high levels of oxygen is known to be a major contributory factor to the corrosion of metals, particularly iron and steel, in commercial heating and cooling systems. Corrosion eventually leads to failures of the system, resulting in costly remedial work, like cleaning or flushing of systems, or replacement of part or all of the system.

For example, failure of pipework in a hospital may lead to closure of wards or cancellation of operations. These types of shutdowns can be prevented by monitoring the dissolved oxygen content and conductivity of the liquid in the system. Increased levels of dissolved oxygen indicate that oxygen has entered the system through a possible leak, poor installation, or maintenance. The use of a simultaneous conductivity measurement allows for the determination of corrosion inhibitor concentrations. Since insufficient inhibitor can lead to corrosion, and too much is a costly waste, correct concentration levels should be maintained at all times.

Midland Corrosion Services has developed a remotely managed service using a GPRS-enabled data logger to capture data and send it over the mobile network to a central database and web server. The data can be viewed, trends can be identified and when readings exceed critical levels, an alarm can be set. The data is collected using Hamilton Arc sensors: VisiFerm DO for dissolved oxygen and Conducell 4USF for conductivity.

Every installation is somewhat unique, however, it is necessary to install the sensors where they will be exposed to the water circulating around the main system. For practical reasons, it is often best to locate the sensors and instrumentation in the main plant room. In case of Addenbrooke's Hospital, each building has its own plant room. In large buildings, it is often desirable to measure the conditions within the heating system a long way from the plant room so that local variations can be monitored. For this reason, Midland Corrosion Services also utilizes smaller data loggers as satellite monitoring systems.

Author

Steve Munn

Project Director, Midland Corrosion Services, Stancliffe House