Energy Transition through Surface and Sewage Water

Published on December 28, 2019

Introduction

Municipalities in the Netherlands are getting more control and responsibility over the energy transition of the country. This transition demands eventual disposal of fossil fuel-based energy systems which have a massive effect on the heating demand of the built environment. As alternatives, the focus of this study is on thermal energy from waste water (WW) and surface water (SW). Even though some studies have already shown the national and local energy potential of WW and SW, for a lot of local policymakers, the energy potential and how and where it can be applied in their community is unclear. This study explored current methods of extraction, storage and distribution of thermal energy from WW and SW and how and where it can be applied in a local region (the municipality of Breda). Key performance indicators (KPI) for the systems are the location, flow rates, volume, recharge capability and the possible temperature change of the water. Other than that, the possibility of seasonal energy storage, the current energy label and waters with botulism and/or algae problems also have an impact on the application of the system

Result

The monthly heating/cooling demand of the neighborhoods within the municipality and the energy that can be supplied by different energy sources has been calculated. This has been done not only for the current situation, but also for future scenarios, see Figure 1, where it is calculated for the whole municipality of Breda. The energy demand is calculated using gas data and degree days to make an estimation over the year. The potential supplied energy is calculated by using monthly averaged flows and temperatures based on measured data. Furthermore, by calculating the coefficient of performance (COP) values, averaged inlet temperatures and efficiency factors for the heat pump and the district heating network. Using these results and the other KPI’s potency maps have been made, showing which areas one could look at to implement these technologies; see Figure 2.

Figure 1. Average monthly demand for the whole municipality of Breda and heating energy supply from a SF and a WW point.

Figure 2: Potency map for waste water (left) and surface water (right).

Conclusion

The results show that currently, based on averaged values, around 41% of the heating demand for residential buildings can be supplied with energy coming from river water (surface water) and that in the future, when the houses are more energy efficient, it could be 69%. The water temperature has to be at least 12°C to enable the use of SW sources, which implies that the energy supply for SW is limited to summer months. For WW, the energy supply is probably lower with a current value of 25% and future values of 44%. The WW sources are, however, more stable. With more energy efficient housing the heating demand will go down and the cooling demand will go up. This cooling demand can also be supplied by using the WW or SW. However, a separate network will have to be made as the houses need heating at the same time as cooling

Limitations

There are limitations and matters for discussion to this method and the results. The method is more of an indication than an actual prediction. The river water (SW) potential seems quite high, as at the moment the whole river is used for the calculation. In reality, it is likely that this percentage is a tenfold lesser as the intake pump or heat exchanger will only use a small part of the river. Also, averaged values were used for the calculation and for some years the amount of energy may be more than for others, which means that some sort of storage or secondary energy source is necessary. In the future, the WW potential can go down, as household equipment and manufacturing processes become more efficient causing lower water temperatures and lesser water to be used. Also, to be able to efficiently make use of the LT energy sources, buildings have to be fitted with LT-radiators. It is considered that this is only possible with a building that has at least an insulation level corresponding to label B. In the short term, new neighbourhoods can make use of these energy sources, whereas in the future, it will be easier to make use of these sources for all neighborhoods as more houses become energy efficient. Although the study is a preliminary analysis and a follow up study is needed, the results, methods and gathered information can be used by water boards and municipalities in their energy policies and can be compared with other energy sources to identify the most sustainable strategies.