Waste heat usage
If one is designing a compressed air system, it is worthwhile investigating the possibility of using some part of the 81% for other purposes such as space heating, for hot washing water or, if the factory can use it, for processing. Paint drying, paper drying and baking ovens are possible applications that could use some of the waste heat. It is quite possible to produce hot water at a temperature of 90°C. This subject is discussed in detail later. It has been calculated that 10% of all electrical power used in industry produces compressed air; the opportunity of using 80% of that for heating presents a considerable challenge to the designer.
The subject of Compressor Control has been dealt with previously. Maximum efficiency in the control system will ensure that power is not wasted. A compressor that runs partially or totally unloaded for any appreciable time may consume up to 75% of its full load power because of the minimum power needs of the compressor, the lower power factor and reduced motor efficiency. It is worthwhile incorporating an automatic control system that stops the compressor when it no longer needs to provide air. For installations where there are wide fluctuations in demand, the use of several smaller compressors connected to a multi-set control enables the shutdown of one or more units when demand for air is low, significantly reducing the power consumption.