Port-Hamiltonian Modeling of Hydraulics in 4th Generation District Heating Networks

In this paper, we use elements of graph theory and port-Hamiltonian systems to develop a modular dynamic model describing the hydraulic behavior of 4th generation district heating networks. In contrast with earlier generation networks with a single or few heat sources and pumps, newer installations will prominently feature distributed heat generation units, bringing about a number of challenges for the control and stable operation of these systems, e.g., flow reversals and interactions among pumps controllers, which may lead to severe oscillations. We focus thus on flexible system setups with an arbitrary number of distributed heat sources and end-users interconnected through a meshed, multi-layer distribution network of pipes. Moreover, differently from related works on the topic, we incorporate dynamic models for the pumps in the system and explicitly account for the presence of pressure holding units. By inferring suitable (power-preserving) interconnection ports, we provide a number of claims about the passivity properties of the overall, interconnected system, which proves to be highly beneficial in the design of decentralized control schemes and stability analyses

Land, Water, Infrastructure And People: Considerations Of Planning For Distributed Stormwater Management Systems

When urbanization occurs, the removal of vegetation, compaction of soil and construction of impervious surfaces—roofs, asphalt, and concrete—and drainage infrastructure result in drastic changes to the natural hydrological cycle. Stormwater runoff occurs when rain does not infiltrate into soil. Instead it ponds at the surface and forms shallow channels of overland flow. The result is increased peak flows and pollutant loads, eroded streambanks, and decreased biodiversity in aquatic habitat. In urban areas, runoff is typically directed into catch basins and underground pipe systems to prevent flooding, however such systems are also failing to meet modern environmental goals. Green infrastructure is the widely evocative idea that development practices and stormwater management infrastructure can do better to mimic the natural hydrological conditions through distributed vegetation and source control measures that prevent runoff from being produced in the first place. This dissertation uses statistics and high-resolution, coupled surface-subsurface hydrologic simulation (ParFlow.CLM) to examine three understudied aspects of green infrastructure planning. First, I examine how development characteristics affect the runoff response in urban catchments. I find that instead of focusing on site imperviousness, planners should aim to preserve the ecosystem functions of infiltration and evapotranspiration that are lost even with low density development. Second, I look at how the spatial configuration of green infrastructure at the neighborhood scale affects runoff generation. While spatial configuration of green infrastructure does result in statistically significant differences in performance, such differences are not likely to be detectable above noise levels present in empirical monitoring data. In this study, there was no evidence of reduced hydrological effectiveness for green infrastructure located at sag points in the topography. Lastly, using six years of empirical data from a voluntary residential green infrastructure program, I show how the spread of green infrastructure depends on the demographic and physical characteristics of neighborhoods as well as spatially-dependent social processes (such as the spread of information). This dissertation advances the science of green infrastructure planning at multiple scales and in multiple sectors to improve the practice of urban water resource management and sustainable development

Control of flow networks with constraints and optimality conditions

Meer dan 40% van de totale energieconsumptie wordt gebruikt voor gebouwverwarming terwijl het grootste gedeelte wordt gegenereerd door fossiele brandstoffen. Gelukkig is er een verschuiving naar meer hernieuwbare bronnen zoals geothermie, restwarmte en warmtepompen. Echter, de productie van deze bronnen kan fluctueren en bevind zich vaak niet op dezelfde locatie als de vraag. Om deze redenen kan een warmtenetwerk met opslagmogelijkheden gebruikt worden voor het transport en garantie van aflevering. Een nadeel is dat een deel van de warmte verloren gaat in de pijpen. Deze verliezen kunnen kleiner gemaakt worden door de pijpen te verkleinen maar heeft als gevolg dat de wrijving in de pijpen toeneemt. Om dit op te lossen kunnen meerdere pompen geïnstalleerd worden.Door de extra pompen en de toevoeging van meerder producenten die niet noodzakelijk worden beheerd door één partij, volgt het dat de volgende generatie van warmtenetten nieuwe regeltechnische strategieën nodig hebben. In dit proefschrift ontwerpen en analyseren we zulke strategieën om de productie optimaal te coördineren en de opslagniveaus te reguleren zodanig dat de warmtelevering gegarandeerd kan worden. Om schaalbaarheid te garanderen, een ‘single point of failure’ te voorkomen en informatie-uitwisseling te minimaliseren stellen we een gedistribueerd mechanisme voor dat een peer-to-peer communicatienetwerk gebruikt. We ontwerpen ook regelaars die de druk in de netwerken met meerdere pompen reguleert. Omdat deze pompen vaak alleen een positieve druk kunnen leveren zorgen we er voor dat aan deze voorwaarde wordt voldaan.More than 40% of the total consumed energy is used for space heating and most of it is generated form fossil fuels. Fortunately there is a shift towards more sustainable sources such as geothermal energy, waste heat and heat pumps. However the supply of these heat sources can be intermittent and is often not co-located with the demand. For this reason a district heating network with storage capabilities can be used for the transportation and security of delivery. A downside is that some heat dispersion occurs in the transportation pipes. This dispersion can be lowered when smaller pipes are used, but this increases the friction in the pipes. To overcome this, the number of pumps in these networks can be increased.Due to the extra pumps and the introduction of multiple producers that are not nessecarily owned by the same entity it follows that the next generation of heat networks require new control strategies in which communication is crucial. In this thesis we design and analyze such control strategies to optimally coordinate the generation and regulate the storage levels such that the heat supply can be guaranteed. In order to guarantee scalability, avoid a single point of failure and minimize the information that companies need to share, we suggest a distributed mechanism that uses a peer-to-peer communication network. We also design controllers that can regulate the pressure in a network with multiple pumps. As these pumps can often only generate positive pressures we guarantee that this constraint is satisfied