Ce travail a été réalisé en collaboration avec EDF R&D, dans le cadre d’une convention CIFRE-ANRT, l’objectif étant d’améliorer le coefficient de performance de pompes à chaleur thermoélectriques (PACTEs) pour des "Bâtiments Basse Consommation". Les PACTEs présentent de nombreux avantages environnementaux, le désavantage étant leur faible performance. Ainsi l'objectif de ce travail a été d'examiner la possibilité d'améliorer, par nanostructuration les performances des semi-conducteurs utilisés dans les modules thermoélectriques des PACTEs. Nos travaux se sont concentrés sur les solutions solides à base de Sb2-xBixTe3, celles-ci étant, selon l’état-de-l’art, les plus performantes pour l’application visée. La nanostructuration a été réalisée par la technique de trempe sur roue (technique de refroidissement rapide de liquides) de matériaux synthétisés auparavant à l'état liquide dans des tubes en quartz. Les moyens de caractérisation (DRX, MEB, MET, METHR) ont permis de corréler les changements structurels avec la variation des propriétés thermiques et électriques (le pouvoir thermoélectrique, la résistivité électrique, l'effet de Hall, la conductivité thermique) mesurées sur de larges gammes de température (5-460 K). L'influence favorable de la nanostructuration par la diminution de conductivité thermique a été prouvée. Nous avons montré la forte dépendance des propriétés thermoélectriques des matériaux étudiés avec la concentration de défauts et la stœchiométrie. Le dopage avec du Te a été examiné comme une possibilité de contrôler le niveau de la concentration des porteurs de charge. L'idée de créer des niveaux d'impuretés résonantes par un dopage au Sn s’est montrée infructueuse, vraisemblablement en raison de la structure de bande complexe du composé ternaire. Néanmoins, des valeurs du facteur de mérite adimensionel ZT de près de 1,2 ont été obtenues pendant ce travail / This work results from the collaboration between IJL and EDF R&D performed under a CIFRE-ANRT convention, in order to improve the coefficient of performance of thermoelectric heat pumps (THPs). THPs attracted attention of EDF due to its numerous environmental advantages, but the main drawback remains its low performance. The objective of our work was thus to investigate the possibility to enhance the performance of the semiconductors used in the thermoelectric modules of the THPs, by nanostructuration. The research was concentrated on the Sb2-xBixTe3-based solid solutions, the most effective materials for the application sought. The nanostructuration was performed by applying the melt-spinning technique (rapid quenching from a melt on a water-cooled cupper wheel) to the material synthesised beforehand from liquid state in quartz tubes. The means of characterisation (XRD, SEM, TEM, HRTEM) gave the possibility to correlate the structural changes with the variation of the thermal and electrical properties (thermoelectric power, electrical resistivity, Hall effect, thermal conductivity) measured over a wide temperature range (5-460 K). The favourable influence of nanostructuration through the decreasing of thermal conductivity was proved. A high dependence of the thermoelectric efficiency of the studied materials on the concentration of defects and stoichiometry is shown. Doping with Te was investigated as a possibility to control the resulting level of the charge carrier concentration. The idea of creating resonant impurity levels by Sn-doping was shown to be non-conclusive presumably due to the complex band structure of the ternary compounds. Nevertheless, relatively high values of the dimensionless TE figure of merit, close to 1.2, were obtained during this work

The main outcome of this research is the development of a Probabilistic Impact Assessment methodology to comprehensively understand the effects of low carbon technologies (LCTs) in low voltage (LV) distribution networks and the potential solutions available to increase their adoption. The adoption of LCTs by domestic customers is an alternative to decreasing carbon emissions. Given that these customers are connected to LV distribution networks, these assets are likely to face the first impacts of LCTs. Thus, to quantify these problems a Monte Carlo-based Probabilistic Impact Assessment methodology is proposed in this Thesis. This methodology embeds the uncertainties related to four LCTs (PV, EHPs, µCHP and EVs). Penetration levels as a percentage of houses with a particular LCT, ranging from 0 to 100% in steps of 10%, are investigated. Five minute time-series profiles and three-phase four-wire LV networks are adopted. Performance metrics related to voltage and congestion are computed for each of the 100 simulations per penetration level. Given the probabilistic nature of the approach, results can be used by decision makers to determine the occurrence of problems according to an acceptable probability of technical issues. To implement the proposed methodology, electrical models of real LV networks and high resolution profiles for loads and LCTs are also developed. Due to the historic passive nature of LV circuits, many Distribution Network Operators (DNOs) have no model for them. In most cases, the information is limited to Geographic Information Systems (GIS) typically produced for asset management purposes and sometimes with connectivity issues. Hence, this Thesis develops a methodology to transform GIS data into suitable computer-based models. In addition, thousands of residential load, PV, µCHP, EHP and EV profiles are created. These daily profiles have a resolution of five minutes. To understand the average behaviour of LCTs and their relationship with load profiles, the average peak demand is calculated for different numbers of loads with and without each LCT.The Probabilistic Impact Assessment methodology is applied over 25 UK LV networks (i.e., 128 feeders) for the four LCTs under analysis. Findings show that about half of the studied feeders are capable of having 100% of the houses with a given LCT. A regression analysis is carried out per LCT, to identify the relationships between the first occurrence of problems and key feeder parameters (length, number of customers, etc.). These results can be translated into lookup tables that can help DNOs produce preliminary and quick estimates of the LCT impacts on a particular feeder without performing detailed studies. To increase the adoption of LCTs in the feeders with problems, four solutions are investigated: feeder reinforcement, three-phase connection of LCTs, loop connection of LV feeders and implementation of OLTCs (on-load tap changers) in LV networks. All these solutions are embedded in the Probabilistic Impact Assessment. The technical and economic benefits of each of the solutions are quantified for the 25 networks implemented.

Air source heat pumps coupled with a photovoltaic system is onefeasible technology to reduce the emissions from the building sector.These systems usually have an auxiliary heating device that is able tocover the whole heat demand on its own. Because of this, often faultsof the system go unnoticed by the user for long periods of time,decreasing the benefits of having a renewable energy electricitysource. Measuring just the solar energy yield is not sufficient, asfaults in the other parts of the system outside the solar loop caninfluence the contribution of the solar panels. Hence, it is the goalto study the overall system performance with faulty conditions in boththe photovoltaics system and the heat pump. In this paper, a detailedreview of common PV faults and detection and inspection methods isgiven in order to perform a simulation of a PV solar assisted heat pumpsystem (PV-SAHP) in study at the Catalonia Institute for EnergyResearch (IREC). The simulation model is developed with TRNSYS and thepvlib Python package. The power curves and the energy yield obtainedprovide an outline on the performance of the system when the heat pumpand the photovoltaic system are operating in faulty and non-faultyconditions. The results show the electrical energy exchange with thegrid, the self-consumed energy and how the overall system efficiency isaffected by faulty operating conditions. The economic assessment withthe NPV criteria highlights the benefits of having a defect-freephotovoltaic system.

This master`s thesis deals with low-temperature heating that employs a heat pump. The introduction gives reasons for utilization of the renewable heat sources for heating. The next part focuses on a practical application of renewables on the heating of a family house. It covers a detailed description of the building and the designed heating system which includes: the calculation of thermal losses, design of the low-temperature boiler, heat pump, safety devices, heating elements, sizing and control of the system. The last part is devoted to the assessment of the system performance.

The aim of this thesis is to increase the understanding of small-scale green energy technology development. In the transition towards a fossil free energy system, heat pumps are a low emission heating alternative. Contrary to other types of new small-scale green energy technology such as solar cells and electric vehicles, heat pumps are established on the Swedish market, with more than half the share of single family buildings. This makes it possible to study an example of a mature technology, and that knowledge could be used in the development and deployment of other technologies with similar small-scale green characteristics. The type of heat pump technology studied is ground source heat pumps, and their development is explored from an economic and performance perspective, using the concept of learning. Learning tracks how a product develops for each doubling of units produced. The results show that the efficiency has increased by a learning rate of 2.8 %. When the effects of a low-temperature heating system is included, the learning rate is even higher, 5.8 %. The efficiency improvement is mainly due to new and more expensive components, which has resulted in a price increase. Even if the price slightly decreased until 2008, it has increased with 29 % since. Nevertheless, the ground source heat pump is profitable compared to several other heating technologies. The most important factors underpinning the development are regulations, competition among manufacturers and research.

The overall objective of this thesis is to develop methods for fault detection and diagnosis for ground source heat pumps that can be used by servicemen to assist them to accurately detect and diagnose faults during the operation of the heat pump. The aim of this thesis is focused to develop two fault detection and diagnosis methods, sensitivity ratio and data-driven using principle component analysis. For the sensitivity ratio method model, two semi-empirical models for heat pump unit were built to simulate fault free and faulty conditions in the heat pump. Both models have been cross-validated by fault free experimental data. The fault free model is used as a reference. Then, fault trend analysis is performed in order to select a pair of uniquely sensitive and insensitive parameters to calculate the sensitivity ratio for each fault. When a sensitivity ratio value for a certain fault drops below a predefined value, that fault is diagnosed and an alarm message with that fault appears. The simulated faults data is used to test the model and the model successfully detected and diagnosed the faults types that were tested for different operation conditions. In the second method, principle component analysis is used to drive linear correlations of the original variables and calculate the principle components to reduce the dimensionality of the system. Then simple clustering technique is used for operation conditions classification and fault detection and diagnosis process. Each fault is represented by four clusters connected with three lines where each cluster represents different fault intensity level. The fault detection is performed by measuring the shortest orthogonal distance between the test point and the lines connecting the faults’ clusters. Simulated fault free and faulty data are used to train the model. Then, a new set of simulated faults data is used to test the model and the model successfully detected and diagnosed all faults type and intensity level of the tested faults for different operation conditions. Both models used simple seven temperature measurements, two pressure measurements (from which the condensation and evaporation temperatures are calculated) and the electrical power, as an input to the fault detection and diagnosis model. This is to reduce the cost and make it more convenient to implement. Finally, for each models, a user friendly graphical user interface is built to facilitate the model operation by the serviceman.

The Ground Source Heat Pump systems (GSHP) are an emerging technology used to exchange heat with the ground through the use of some buried heat exchangers. The thermal response of a borehole field can be characterized by its g-function. It is a non-dimensional temperature response factor, which can be calculated using either numerical or analytical solutions. Eskilson developed the first study made for the calculation of these g-functionts. Lamarche and Beauchamp proposed another analytical approach based on the Finite Line Source (FLS). Generally, both solutions present similar results with some small differences. They could be attributed to the boundary condition performed in both researches: the FLS solution considers uniform heat flux along the borehole wall in all the heat exchangers, while Eskilson’s model defines as a condition, uniform temperature at the borehole wall within all the pipes in the field. In this Master of Science Thesis, the temperature response factors (g-functions) of a 6x6 borehole field with 36 heat exchangers (BHE) arranged in a squared configuration are obtained from new numerical models, mainly based on the use of a highly conductive material composing the BHE. For this purpose, a commercial software called Comsol Multyphisics© is employed. The aim of this thesis is to get larger knowledge in generating the g-function in relation to the boundary condition performed in the model trying to reach better approximations to the reality. Some strategies with respect to the geometry, size of the model and mesh are performed to reduce the computing time. The influence of the geothermal heat flux and the influence of the highly conductive material (HCM) composing the BHEs are also studied in our model. Going further, the thermal behavior of the ground is also studied by imposing variable heating and cooling loads during seasonal periods over a time of 25 years. Finally, the g-functions obtained from our numerical models are compared to the one generated with the commercial software, Earth Energy Design (EED), which represents the numerical solution proposed by Eskilson, and the one generated with FLS approach. The results may explain in a closer approximation to the reality the thermal response for large borehole fields.

4th generation district heating (4GDH) and varying the indoor temperature to store heat are both important concepts that can make it easier to implement more renewable energy and reduce costs of heating. This study looks at these concepts from a customer perspective using one building and looking at how energy can be stored and the performance of 4GDH. Low temperature heat sources from industry, supermarkets, and datacentres are used in combination with heat from a combined heat and power plant to get the required heating. A heat pump has also been modelled as a part of the 4GDH structure. In addition to looking at heat storage in 4GDH a scenario with direct electric heating has also been evaluated. In conclusion 4GDH has lower operating costs than 3rd generation district heating, but it is not worth varying the indoor temperature to store energy when using 4GDH. It is, however, profitable to vary indoor temperature if direct electric heating is used.

This dissertation combines methods from engineering, operations research, and economics to analyze how emerging residential energy technologies can be effectively used to reduce both energy costs and carbon emissions. Our most important finding is that air-source heat pumps can be used to reduce both energy costs and carbon emissions in four out of the five major climate regions studied, but that electric retail rate reform is needed to provide customers with appropriate incentives. In cold climates, it may be advantageous to use heat pumps in tandem with fossil fuel-powered furnaces; in warmer regions, furnaces can be cost-effectively abandoned altogether. We do not find that distributed rooftop solar panels or distributed battery storage are effective tools for reducing the cost of energy services. Rather, in our simulations, customers adopt these technologies in response to poor price signaling by electric utilities. By reforming electric retail rates so that the prices paid by consumers better reflect the cost of energy services, utilities can promote the adoption of technologies that reduce both aggregate costs and carbon emissions.

The road to energy-efficient housing is not without cracks and potholes. Many building stakeholders have pointed to the discrepancies that exist between simulated and measured efficiency results, where some have called it a post-occupancy gap, others have called it an energy efficiency information gap. The research presented in this thesis addresses that gap by detailing the results of two exploratory case studies of affordable housing projects in Virginia across three manuscripts. The data utilized in the first manuscript includes measured data collected at the second level through the NEXI energy monitoring and feedback device, wherein we used descriptive statistics to investigate the impact of temperature on energy use over different timeframes. We had anticipated our findings may not all be consistent with previously existing studies. We found this to be true in many cases, but we also discovered interesting contradictions to our assumptions. This study thereby investigates the gap in energy performance within net-zero buildings and contributes to the existing body of literature by presenting the findings of this unique study. The data utilized in Manuscript 2 and Manuscript 3 was utility data, which was reported as end-of-use monthly consumption values. We were able to investigate the impact of 3 different HVAC systems energy use by evaluating the energy and cost performance before and after the installation of newer, more efficient systems. We found that although all systems were performing below anticipated standards, the one-stage system outperformed in terms of efficiency, and the second-stage system outperformed in terms of cost. The findings in these studies emphasize the importance of energy education for residents to achieve greater efficiency gains. / Master of Science / Humans are complex beings; hence the buildings they inhabit are complex systems. While breakthroughs in simulating, designing, and constructing high-performance buildings as well as advanced energy use technologies have been promising, many have fallen short of their ambitious goals primarily due to the complexity of building occupant behavior. Achieving energy efficiency requires thorough research before design and construction, the use of advanced technologies, and the incorporation of behavior-driven energy use dynamics. Furthermore, with the breadth of literature to support the delivery of individualized energy information in real-time to residents comes the opportunity to investigate further the impact of advanced technologies in high performing buildings that have fallen short of their optimistic design goals. This thesis consists of three manuscripts, which describe two exploratory case studies of high-performance residential homes in Virginia's affordable housing sector. The first manuscript, a journal paper, investigates the individual HVAC energy use of six senior residents, wherein we explore the interplay between temperature, energy use, and age across different timeframes. We find that, across different timeframes, energy use for senior citizens remains relatively consistent in high-performance homes. The second and third manuscripts are conference papers, which have been presented on and published in the respective conference proceedings. We quantitively investigated the energy performance of energy-efficient HVAC systems and compared predicted results and measured results. In conclusion, we hope to contribute to the body of literature, which investigates shortcomings in achieving energy-efficiency within high-performance homes.