Installation of an ultrafiltration plant in a multi-family house to reduce the hot-water temperature and energy demand: A case study in Germany

Abstract

Hot-water generation complicates energy efficiency and emission reduction efforts in buildings. High water temperatures are designated for thermal disinfection to prevent human harm from pathogenic microorganisms. Therefore, almost 200 Mt CO2 are annually emitted in the US, Germany and Canada. Heat pumps can replace fossil energies. However, lower temperatures are required to enhance efficiencies.In this case study, the hot-water temperature of the drinking-water installation of a retrofitted multi-family house was decreased by 5 °C to 50 °C. For physical separation of microorganisms, an ultrafiltration plant was installed in the hot-water circulation. To control hygienic safety, microbiological conditions were assessed by laboratory methods such as the cultivation of Legionella spp. and counting of total cells using flow cytometry. The filtrated hot-water was constantly Legionella-free. The cleaning effect of ultrafiltration was 91.15%. Cold-water was not filtrated so that contaminations occurred. As cold- and hot-water pipes (including circulation) are embedded in the same riser strands, temperature transfer occurred promoting bacterial growth. An energy demand calculation revealed that heat losses of the distribution network accounted for 55.25% of the total heat quantity required for hot-water generation. The actual heat up process of water and storage losses constituted 42.74% or 2.01%. Lowering the water temperature by 5 °C saved 7355 kWh yr−1 (equiv. to 1.77 t CO2e yr−1) in this multi-family house. Extrapolation of this case building results in a saving potential of 7.78–14.50 TWh yr−1 (equiv. to 1.87–3.48 Mt CO2e yr−1) in Germany alone, if the energy source is natural gas.