Dissolved nutrients were still present in the wastewater from the treatment plant , and these can form a bio-film in pipes and equipment. This can impede the water flow and the performance of the heat pump over time. The heat exchangers were particularly at risk. Chemical cleaning was not possible because there was a risk that chemical residues could end up in Lake Constance together with the return water. The new heat pump system was supposed to not only run smoothly but also much more efficiently than the previous one. Our challenge was to develop a sustainable solution. 

The heat exchangers are equipped with a conventional particle filter and they are also operated with increased flow velocities. This makes it difficult for microorganisms to attach themselves to the surface of the pipe. In addition, regular backwashing is carried out in order to dissolve any bio-films that form and to flush them out. Intelligent machine management optimises the energy efficiency of the heat pump. This means that the machine is operated at the lowest condensation temperature at all times. In addition, all pumps are controlled in such a way that they always deliver only the amount of water required for the current heat pump output.