COMPRESSORS PETplanet Insider Vol. 26 No. 05/25 www.petpla.net 29 for energy savings. In the case of a completely new installation, optimised solutions are devised and suggested from the outset so that the operator can compare independently between different system variants and select the most cost-efficient choice. Where building management systems are used, it is recommended to conduct a thermal audit in conjunction with the compressed air audit so that the heat balance can be determined in parallel with the air consumption. This allows thermal data such as temperature flow and return to be investigated in addition to compressed air data such as volume, pressure and required air quality. Once these details are established, it can be determined what percentage of the compressor exhaust heat can be absorbed into the normal heat requirement of the project. This in turn allows the size of the storage vessel and the required temperature to be calculated. In the best-case scenario, 96% of the heat output can be used. A few points must be taken into account when planning or optimising a compressed air station. For example, compressors and heating systems should not be placed in the same room, since optimal use of these requires different room climate conditions and the compressor must not be permitted to draw in dangerous admixtures. The compressor room needs to be well ventilated; the room for the heating system does not. In an ideal world, the two rooms would be separate but situated near to one another, so that the ducting route between compressors and heating system can be as short as possible. Even when the two systems are positioned apart, the heat from the compressors can be used to heat the burner intake air for the heating system. Since the volume of accumulating heat and the heat requirement are rarely identical, it is important to ensure that there is sufficient thermal storage potential in the form of large vessels. This guarantees optimum supply when generation and consumption volumes differ, as happens in the case of a house equipped with solar heating, where it also necessary to install a means of thermal storage so that hot water is still available when the sun is not shining. Heated compressor cooling air can be used for simple and effective heating of neighbouring spaces via air ducting. Virtually the full amount of energy supplied for compressed air generation can be used for heat recovery. Air- or water-cooled compressors Once the design has been decided, it is vital to select the correct compressors. In general, two different cooling methods are available for compressors: air cooling and water cooling. As already mentioned, in the case of the former, air ducts with thermostatically controlled flaps convey the hot exhaust air directly from the compressors to the neighbouring operating spaces, in order to provide heating for example. To minimise heat losses, the distance the exhaust air needs to travel from the compressor to the point of use should not be too great. According to Kaeser, air-cooled rotary screw compressors, available with up to 315 kW of power, can offer significant heat recovery potential — an investment that typically pays off quickly, with costs often amortised within a year. Systems equipped with additional hot water heat recovery can supply water at temperatures up to 70 °C throughout the year, and even higher if needed. However, since these systems have an impact on compressor power consumption, it should be checked beforehand that their use is justifiable from a cost-efficiency point of view. In the case of water-cooled compressors, the user-end requirements and cooling water costs also play an important role; in principle, however, heat recovery as described above can also be achieved here by means of a second connected circuit. www.kaeser.com
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