Énergie

One third of the global carbon emissions are emitted by the building sector. Over the last decades, space heating loads have decreased in modern buildings, and domestic hot water (DHW) is now oftentimes the largest energy consumer in the household. We developed the WaterHub modeling framework to assess the potential of technologies or measures targeting DHW energy demand. The framework combines process-based technological models and stochastic water demand modeling in a modular way to allow for holistic simulations of complex DHW systems. In two rigorous tests of the modeling framework, we demonstrated the importance of water consumption dynamics in the modeling of DHW systems, showing that static modeling leads to underestimated heat losses and wrong energy consumption predictions. In an exemplary case study, we identified and quantified the synergistic interactions between water boiler temperatures and a drain water heat recovery device, demonstrating the strength of this methodology for optimizing strategies targeting DHW systems. With its modular structure, this open-source modeling framework can be extended to include any DHW-related technology, providing a useful common platform for collaboration between technology developers and water experts.

Carbon lock-in hampers the realisation of sustainable energy systems. It occurs when carbon-intensive technologies, markets and institutions co-evolve and become wedded to historical trajectories despite environmentally superior technologies being available. Multiple material and non-material causes are discussed in literature on socio-technical or energy transitions and carbon lock-in. However, these are yet to be synthesised into a comprehensive framework to guide the empirical identification of lock-in factors. Also, empirical understanding into how various causes of lock-in can interact is limited. To deepen understanding into the various types of socio-technical lock-in affecting energy transitions, we develop an encompassing analytical framework accounting for material, human, non-material and exogenous factors. In addition to carbon lock-in and path dependency, we synthesise diverse literature encompassing sustainability transitions, energy policy, innovation and firm management, economics and political economy. The resultant framework provides a finer-grained and more comprehensive understanding of lock-in than previous studies. Using Japan as a case study, we then apply this framework with two questions in mind: (i) What factors are contributing to the perpetuation of coal power in Japan? and ii) What opportunities emerge to overcome these? The empirical analysis is informed by triangulated data involving 46 semi-structured interviews and diverse documents. Our findings reveal a wide array of interacting factors that contribute to the perpetuation of coal-power in Japan and several emerging opportunities to tackle these. They also demonstrate our framework's utility as a heuristic that scholars could apply to other cases to increase empirical understanding into the multiple causes of socio-technical lock-in.

In lakes, large amounts of methane are produced in anoxic sediments. Methane-oxidizing bacteria effectively convert this potent greenhouse gas into biomass and carbon dioxide. These bacteria are present throughout the water column, where methane concentrations can range from nanomolar to millimolar. In this study, we tested the hypothesis that methanotroph assemblages in a seasonally stratified freshwater lake are adapted to the contrasting methane concentrations in the epi- and hypolimnion. We further hypothesized that lake overturn would change the apparent methane oxidation kinetics as more methane becomes available in the epilimnion. In addition to the change in the methane oxidation kinetics, we investigated changes in the transcription of genes encoding methane monooxygenase, the enzyme responsible for the first step of methane oxidation, with metatranscriptomics. Using laboratory incubations of the natural microbial communities, we show that the half-saturation constant (K_m) for methane - the methane concentration at which half the maximum methane oxidation rate is reached - was 20 times higher in the hypolimnion than in the epilimnion during stable stratification. During lake overturn, however, the kinetic constants in the epi- and hypolimnion converged along with a change in the transcriptionally active methanotroph assemblage. Conventional particulate methane monooxygenase appeared to be responsible for methane oxidation under different methane concentrations. Our results suggest that methane availability is one important factor for creating niches for methanotroph assemblages with well-adapted methane oxidation kinetics. This rapid selection and succession of adapted lacustrine methanotroph assemblages allowed the previously reported high removal efficiency of methane transported to the epilimnion to be maintained – even under rapidly changing conditions during lake overturn. Consequently, only a small fraction of methane stored in the anoxic hypolimnion is emitted to the atmosphere.