Département Gestion des eaux urbaines

Future climatic, demographic, technological, urban and socio-economic challenges call for more flexible and sustainable wastewater infrastructure systems. Exploratory modelling can help to investigate the consequences of these developments on the infrastructure. In order to explore large numbers of adaptation strategies, we need to re-balance the degree of realism of sewer network and ability to reflect key performance characteristics against the model's parsimony and computational efficiency. We present a spatially explicit algorithm for creating sanitary sewer networks that realistically represent key characteristics of a real system. Basic topographic, demographic and urban characteristics are abstracted into a squared grid of 'Blocks' which are the foundation for the sewer network's topology delineation. We compare three different pipe dimensioning approaches and found a good balance between detail and computational efficiency. With a basic hydraulic performance assessment, we demonstrate that we attain a computationally efficient and high-fidelity wastewater sewer network with adequate hydraulic performance. A spatial resolution of 250 m Block size in combination with a sequential Pipe-by-Pipe (PBP) design algorithm provides a sound trade-off between computational time and fidelity of relevant structural and hydraulic properties for exploratory modelling. We can generate a simplified sewer network (both topology and hydraulic design) in 18 s using PBP, versus 36 min using a highly detailed model or 1 s using a highly abstract model. Moreover, this simplification can cut up to 1/10^th to 1/50^th the computational time for the hydraulic simulations depending on the routing method implemented. We anticipate our model to be a starting point for sophisticated exploratory modelling into possible infrastructure adaptation measures of topological and loading changes of sewer systems for long-term planning.

In the effort to de-carbonize the building stock, heat pumps are increasingly utilized in Switzerland, with 70% of the fast-growing heat pump market using ambient air as heat source. Inexpensive and easy to implement, these heat pumps are, however, less efficient than their ground- or water-source counterparts. In this modeling study, we aim at increasing the efficiency of air-source heat pumps using domestic greywater-contained heat. We assess the performance improvement relative to standard heat pump configurations across various climates, seasons, building envelopes, and domestic hot water consumption patterns. The results show that the annually-averaged coefficient of performance improves by 4.1% on average - ranging from 0.6% to 7.5%. This efficiency gain translates on average to 1.8 kWh/week of compressor electricity savings. Although attractive due to its simplicity, the proposed open-loop configuration - preheating of an external heat source - only leads to moderate performance improvement of air-source heat pumps. Based on these results, we extensively discuss and compare alternative system configurations and identify several fundamental differences in the heat recovery dynamics of each configuration. We show that closed-loop systems - using greywater as direct heat source - show the largest performance improvement potential, although being more expensive and complex to implement.

Schwammstadt, grüne Infrastruktur, WSUD, LID, SuDS – für das Konzept, den Wasserhaushalt in der Stadt naturnaher zu gestalten, gibt es viele Namen. All diese Ansätze versprechen verschiedenste naturnahe Servicefunktionen, die für die Adaptation unserer Städte an den Klimawandel eine zentrale Rolle spielen. Dieser Artikel geht der Frage nach, was wir über die Wirkung für die Hitzereduktion solcher «blau-grüner Infrastrukturen» wissen, wie wir diese quantifizieren und effektiv planen können.

Abflussregelungen können oft kostengünstige Massnahmen sein, um den Gewässerschutz bei Regenwetter durch die bessere Auslastung der vorhandenen Infrastruktur zu verbessern. In Zukunft könnte die tatsächliche Leistung von Abflussregelungen mit Betriebsdaten und statistischen Methoden beurteilt werden. Eine verlässliche messdatenbasierte Leistungsanalyse von Regelungssystemen muss Variabilität und Unsicherheiten in den Messdaten berücksichtigen. Der «Potential Outcome»-Ansatz und flexible Regressionsmethoden, wie z. B. Random Forest, scheinen vielversprechende Lösungen zu sein, um den Effekt einer Abflussregelung zu schätzen.