COMPRESSORS PETplanet Insider Vol. 26 No. 05/25 www.petpla.net 28 Heat recovery saves money and benefi ts the environment Sustainable savings based on an article by Daniela Koehler, Press Officer at Kaeser Kompressoren Compressors and the compressed air they generate are used in a multitude of industrial applications. However, the fact that compressor exhaust heat can be harnessed often remains forgotten. Up to 96% of the drive energy supplied to a compressor is available for reuse. Heat recovery not only saves energy and costs, but also reduces the operator’s CO2 footprint. Fully 100% of the drive energy supplied to a compressor is converted into heat. Both air- and fluid-cooled rotary screw compressors are exceptionally well-suited to comprehensive recovery and reuse of this energy; around 76% of their energy input remains as heat in the cooling fluid and is removed in the fluid cooler. A further 15% can be recovered as heat via the compressed air aftercooler. Up to 5% of the heat produced is emitted by the electric motor – with targeted cooling, fully enclosed rotary screw compressors can even recover this energy as well. Only 2% of the total energy input is lost as heat radiation, whilst a further 2% remains as heat in the compressed air. Of course, this heat could simply be conveyed away. However, there are plenty of ways to make use of this readily available energy source that occurs as a by-product of the compression process. The simplest and most efficient method is to use the compressor exhaust heat directly, e.g. for heating adjoining rooms or spaces. Here, instead of discharging hot air from the compressed air station outside, an air ducting system directs it to neighbouring warehouses or workshops. When no hot air is required, the heated exhaust air is simply conveyed outdoors by means of a flap or louvre. A thermostatically controlled louvre enables hot air to be provided as and when required in order to maintain a constant temperature. In addition to providing full or supplementary heating for operating spaces, hot compressor exhaust air can be used to support applications such as drying processes, generating hot air curtains or preheating burner air for heating systems. The corresponding investment costs can often be amortised within a period of one year. Compressor exhaust heat can also be used to supply existing hot water heating and service water systems; depending on the available storage capacity, water temperatures of 70 °C and even higher can be generated. There are several ways to achieve this. The most cost-effective method is to use a plate-type heat exchanger integrated into the compressor, which is connected to the compressor cooling fluid circuit and transfers energy from the heated cooling fluid to the water that requires heating. Depending on whether the hot water is required for particularly sensitive production or cleaning processes, for showering and washing, or for general heating systems, special safety heat exchangers or conventional plate-type heat exchangers may be used. These enable 70-80% of the installed compressor output to be used for heating purposes without the need for any additional expenditure on energy. This variant of heat recovery is also possible with primary water-cooled rotary screw compressors. Heat recovery is principally worthwhile when the compressors in question feature a power output of at least 5.5 kW. Establishing actual requirement Since very few operators know their exact air demand, Kaeser recommends conducting a compressed air audit before installing a compressor system. Performed swiftly and seamlessly using state-of-theart analysis tools such as the ADA/ KESS (Air Demand Analysis/Kaeser Energy Saving System), this audit can determine the precise demand data for a project, says the company. The web-based system transmits measured data and system data for the audited station, and provides an initial report for the operator. These data can then be transferred to the KESS system and subsequently used to determine the planning steps for the air station operator, as well as the investment costs and potential COMPRESSORS Compressed air station with air ducts for heat recovery. The ducts convey hot air to neighbouring spaces.
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