MASS FLOW METERS FOR COMPRESSED AIR SYSTEMS
Managing Leaks in Compressed Air Systems with Thermal Mass Flow Technology
Compressed air within a manufacturing facility has become quite high over the last decade, and so has the expense in operating them. Compressed air systems are found throughout industry and are often the largest end-use of electricity in a manufacturing plant. Compressed air leaks can be a significant source of wasted energy and should be addressed through the application of a thermal mass flow meter to monitor the out flow of compressed air to the upstream value.
The fact of the matter is, compressed air is not free and it’s becoming a financial burden to a company’s operating expenditures. It is now even more important as a means of reducing costs for companies to monitor their compressed air usage, identify the leak points within the air system, and replacing older equipment with newer items. Why is it so important to monitor the air flow rate in compressors? There have been extensive studies done over the years on plant wide operating costs for virtually any type of industry, and most facilities had 70 to 80% of their expenditures in electricity fees. The major contributor to this excessive electricity draw are the air compressors. The actions required though to reduce excess electricity usage and provide for a more efficient compressor throughput is to monitor the flow rate and optimize the compressor’s efficiency more.
Older compressor systems within facilities can operate very inefficiently, and through audits performed by air system compressor technicians, it is usually found that replacement of the compressor needs to happen. Some of these system management companies have stated that replacement of a new compressor system can provide a short term payback and results in monetary savings of up $35,000 per year with the elimination of air leaks.
After wide applicability on compressed air applications, thermal mass flow technology has distinct advantages that make it a much more effective technology versus other technologies. The technology lends itself to having a high turndown ratio and uses a single probe design for insertion into the customer’s piping arrangement. Accuracies down to + 0.5% of full scale and an even better on repeatability makes this technology shine over other measurement techniques. Now with the wide turndown ratio of 100:1 and even higher using thermal mass flow technology, the measurement range from very low velocities to higher flows can be measured with no problems. It is at the lower velocities where compressed air equipment begins to become weak and leakage starts to be seen here.
An air flow technology commonly applied in this compressed air systems is the orifice plate technique. The orifice plate design utilizes a differential pressure transmitter and with the low velocities requiring detection, the system cannot discern the flow velocities at the low flows. Additionally, orifice plate designs have to be compensated for changes in pressure and temperature in order to calculate mass flow rate unlike with thermal mass flow meters. The orifice meter typically produces error in flow measurements as much as 5 to 9% especially when you have changing pressure or temperature in the application. With inaccuracies of the flow measurement, the compressed air system may show a leakage of air from the outlet of the compressor to some changed value further downstream. This change seen by the “flow meter” may prove to be false information, so it’s important to use a technology like thermal mass flow that can measure with pin point accuracy throughout a wide flow range and not be affected by temperature and pressure swings.