Investigating the interactions of decentralized and centralized wastewater heat recovery systems

Abstract

In the urban water cycle there are different sources for extracting energy. In addition to potential and chemical energy in the wastewater, thermal energy can also be recovered. Heat can be recovered from the wastewater with heat exchangers that are located decentralized and/or centralized at several locations throughout the system. It can be recovered directly at the source (e.g. in the showers and bathrooms), at building block level (e.g. warm water tanks collecting all grey water), in sewers or at the wastewater treatment plant. However, an uncoordinated installation of systems on such different levels can lead to competing technologies. To investigate these interactions, a modelling environment is set up, tested and calibrated based on continuous sewer temperature and flow measurements. With that approach different heat recovery scenarios on a household level (decentralized) and of in-sewer heat recovery (centralized) are investigated. A maximum performance drop of 40% for a centralized energy recovery system was estimated when all bathrooms are equipped with decentralized recovery systems. Therefore, the proposed modelling approach is suitable for testing different future conditions and to identify robust strategies for heat recovery systems from wastewater.

In-building heat recovery mitigates adverse temperature effects on biological wastewater treatment: a network-scale analysis of thermal-hydraulics in sewers

“…no evaporation or heat losses). However, a side study using the empirical heat loss model developed by Wong et al (2010) and used in other studies (Sitzenfrei et al 2017)showed no significant reduction in the morning peak temperature, indicating that in-shower processes are not major drivers of morning-peak discrepancy. Further details are available in the SI (Figure S3).…”

“…These results tend to disagree with thescarceliterature on the topic. Sitzenfrei et al (2017) for instance, report a maximum temperature decrease of 1.2 -1.3 K in the sewer network downstream. In this regard, we discuss important perspectives to challenge and explain our conclusion in the sections below.…”

“…However, the systemic implications of these technologies, both on WRRF processes and the performance of centralized heat recovery systems located downstream in the sewer network, are still unclear. Sitzenfrei et al (2017), for instance, have warned that in-building heat recovery systems may lead to significant competition with sewer-level heat recovery, reducing the potential of the latter technology. Because the implementation of in-building heat recovery technologies can hardly be regulatedbeing located in private buildingsthey emphasize that robust strategies are required for the efficient management of heat recovery along the urban water cycle.…”

Modelling the potential for multi-location in-sewer heat recovery at a city scale under different seasonal scenarios

“…The model developed by Dürrenmatt and Wanner (2008), named TEMPEST, was the first capable of predicting wastewater temperature in successive sewer pipes. Published studies have shown that TEMPEST was implemented in a single string of sewer pipes; 1.85km long (Dürrenmatt and Wanner, 2014) and 3km long (Sitzenfrei et al, 2017). The TEMPEST model was calibrated using a dataset collected over a 5 week period from 14 th February to 22 nd March 2008.…”

Participation as a Key Aspect for Establishing Wastewater as a Source of Renewable Energy

“…Dürrenmatt and Wanner [15], Abdel-Aal et al [16], and Elias-Maxil et al [17] introduce different mathematical models for predicting the impact of wastewater heat extraction on the inflow temperature at wastewater treatment plants. Sitzenfrei et al [18] apply one of these models to investigate the interactions of decentralised (in-house) and centralised (in-sewer) wastewater heat recovery. Abdel-Aal et al [19] use another model to estimate the potential for multi-location in-sewer heat recovery at a city scale level.…”