Decentralized heat recovery from domestic waste water; Decentralized wastewater heat recovery to increase energy efficiency in buildings
Decentralized heat recovery from domestic waste water: 06/2010 to 10/2011
Decentralized wastewater heat recovery to increase energy efficiency in buildings:
12/2011 to 05/2013
Federal Ministry of Transport, Building and Urban Development (BMVBS)
As part of the research project, a detailed metrological analysis served to assess the potential of wastewater as a power source – based on measurements of the consumption of cold drinking water as well as the wastewater temperatures in two student dormitories (246 and 209 inhabitants), a hotel (150 rooms) and a hospital (348 beds). The amount of drinking water was also considered as an estimate for the amount of wastewater.
The aim of the accompanying monitoring was to identify representative hydrographs regarding wastewater temperature and passage for different types of buildings and usage patterns, in order to identify the energetic potential of wastewater streams.
All observed hydrographs show a pronounced water consumption peak in the mornings. For residential usage patterns and for the hotel, there is another water consumption peak in the evenings, but less pronounced. Throughout the day, the residential usage pattern reaches the average daily water consumption amount per capita that was published by the Federal Statistical Office. In the hotel, the consumption amounts are even higher. With average temperatures of 23 to 26 °C, wastewater exhibits a higher temperature level that other renewable energy sources. Thus, wastewater can be seen as an ideal heat source for a heat pump.
An analysis concept was developed in the scope of the research project, allowing for an energetic assessment of heat recovery from wastewater. The results show high performance coefficients for the heat pumps, which – extrapolated to one year – result in seasonal performance factors (SPF) of 3.0 to 4.7. With an average of 10 K, the cooling effect due to the heat pumps is fairly moderate, so it is to be assumed that the downstream wastewater treatment will not be impaired. Due to the nutrient richness of wastewater, biofilm formation is to be expected for sewage-side heat exchangers. The resulting insulating effect causes a significant reduction of the heat passage from the wastewater to the heat transfer medium. Here, methods to reduce biofilm formation, for example by automated cleaning methods, are critical with regard to the system’s efficiency.