Energy-efficient thanks to heat recovery

Up to 96% of the compressor drive energy is available for heat recovery. This saves energy and costs and reduces the_{CO2 footprint}.

All of the drive energy supplied to a compressor is converted into heat. Air-cooled and fluid-cooled screw compressors are ideally suited to recovering and further utilizing this energy as much as possible. With them, around 76 % of the energy used is found as heat in the cooling fluid and is extracted from it in the fluid cooler. A further 15 % of this energy can be recovered as heat via the compressed air aftercooler. The electric motor gives off up to 5 % in the form of heat. Fully encapsulated screw compressors make it possible to recover even this proportion of energy with targeted cooling. This means that up to 96 % of the originally supplied drive energy is available for secondary use. Only around 2 % is lost through heat radiation and a further 2 % remains as heat in the compressed air.

Of course, the heat can simply be dissipated. However, there are other ways of using this existing energy source. The simplest and most efficient way is to use the cooling air heated by the compressor directly. For example, as heating air for adjoining rooms. An air duct system directs the warm air from the compressed air station into neighboring warehouses or workshops instead of discharging it outside. If there is no need for heating air, the heated exhaust air is directed outside by simply moving a swing flap or louvre. A thermostatically regulated louvre control allows the warm air to be precisely dosed and constant temperatures to be achieved.

Investments quickly amortized

In addition to full or additional heating for operating rooms, the warm exhaust air from the compressor can also be used, for example, to support drying processes, to set up warm air locks or to preheat the burner air of heating systems. The corresponding investments often pay for themselves within just one year.

In addition, the compressor waste heat can also be fed into existing hot water heating systems and domestic hot water systems. Depending on the intended storage capacity, water temperatures of 70 °C and more can be generated. The most cost-effective way to do this is with a plate heat exchanger that is integrated into the compressor. It is connected to the cooling fluid circuit of the compressor and transfers the energy from the heated cooling fluid to the water to be heated. Depending on whether the hot water is to be used for very sensitive production and cleaning processes, as shower and washing water or for heating purposes, special safety heat exchangers or standard plate heat exchangers are used. In this way, around 70 to 80 % of the installed compressor output can be used for heat recovery without additional energy input. This variant of heat recovery is also possible with primary water-cooled screw compressors. In general, the use of heat recovery methods makes sense if the compressors required for compressed air generation have an output of at least 5.5 kW.

Determine the real need

Before installing a compressed air system, it is advisable to carry out a compressed air audit. This is because very few operators know their exact compressed air requirements. This audit, which can be carried out quickly and easily using modern analysis tools such as the ADA/KESS (Analysis of Compressed Air Utilization/Kaeser Energy Saving System Service), determines the exact demand data for a project. The web-based system not only transports the measurement data, but also the system data of the audited station and quickly provides the operator with a report for initial information. The data can then be transferred to the KESS system, for example. This is used to determine planning steps for the operator of the compressed air station as well as the investment costs and potential energy savings. In the event of a completely new installation, optimum solutions are offered from the outset. Independent comparisons of different system variants are possible so that the most economical one can be selected. In the case of building services, it is advisable to carry out a heat audit at the same time as this compressed air audit in order to determine the development of the heat balance in parallel with the air consumption.

In addition to the characteristic data for compressed air, the data for heat should also be requested. Once these are known, it is possible to determine what percentage of the waste heat from the compressors can be used for the project's normal heating requirements. This can be used to calculate how large the storage tanks need to be and how high the temperature levels are. In the optimum case, 96 % can be used.