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Large-scale heat pumps can contribute towards the decarbonisation of district heating systems and industrial processes. Unidentified faults can have a negative impact on the availability, performance and maintenance costs of heat pump systems. This study provides a description of faults related to the operation of 53 heat pumps based on a vapour compression cycle. Faults were characterized according to potential causes, mitigation or prevention implications as well as detection and diagnosis methods. Faults in the compressor, evaporator and source heat exchanger were more recurrent than in other components of large-scale heat pumps. Overall, the most common faults were fouling of heat exchangers and refrigerant leakage. Faults related to negative impacts like system shutdown, performance reduction and release of refrigerant into the environment, were mainly described to be originated in the compressor. Several directions for future research were identified, which included developing specific fault detection and diagnosis methods for large-scale heat pump applications, proposing methods to detect and diagnose multiple and simultaneous faults, and integrating performance degradation monitoring with fault detection and diagnosis.

[ENG] With the aim of reducing costs and weight and increasing thermal efficiency of parabolic dish collectors (PDCs), a modified cavity receiver for a PDC is proposed and analysed. The application is generation of steam at 150 _C in an industrial pilot plant of thermal treatment. The diameter of the PDC is 4:5m. The proposed cavity receiver does not use molten salts due to the maze-like design of its interior. The performance in the absorption of solar radiation of the proposed cavity receiver is studied with a ray-tracing model. It is found that there is a range of positions where the amount of absorbed radiation does not significantly change. Energy losses by natural and forced convection are studied by using a CFD model. Two correlations for natural and forced convection are developed and it is found that the use of a window can help to suppress convection. The interior is analysed with a CFD model for different HTF mass flow rates. An accurate distribution of radiation in the walls is applied, computed by a ray-tracing model for a fixed EDNI. It is found that the proposed cavity receiver has some zones of low flow speed which produce peaks of high temperature. The thermal performance over a typical meteorological year (TMY) of the PDC is studied for three different receivers: the proposed cavity receiver (OCR), an equivalent flat-plate receiver (FPR), and the proposed cavity receiver with a window (CCR). The results show that in comparison with the thermal efficiency of the FPR, the OCR gives an improvement of 5%-7%, but the CCR gives a significant improvement of 17%-20%. And, in addition, the temperatures reached by the FPR are significantly higher than the ones reached by the OCR and the CCR. By itself, this may be a rejecting factor for FPR in practice (like in the case considered in this work where the limit temperature of the HFT is 350 _C). Finally, a solar plant is designed for convenient use of the energy collected at the PDC in the cogeneration of steam at 150 _C in an industrial pilot plant for thermal treatment. The system integration is done at boilers. For the cogeneration, a solar boiler is used in parallel with an existing electrical boiler. The two boilers are connected to the steam main of the pilot plant. The plant is regulated to met a constant demand of steam. A lumped-element model of the solar and industrial pilot plants is used to estimate the performance on two selected days of the TMY. It is found that the solar boiler supplies part of the steam demand when there is solar energy available. In particular, the mass flow rate of steam meets the required demand and it is the sum of steam generated at the electrical and solar boilers. [SPA] Con el objetivo de reducir costes y peso e incrementar la eficiencia térmica de los colectores de disco parabólico (PDC, por sus siglas en inglés), se propone y analiza un receptor de cavidad modificado. El PDC tiene un diámetro de 4:5m. El PDC se aplica en una planta piloto de tratamiento térmico industrial para generar vapor a una temperatura de 150 _C. El receptor de cavidad propuesto no usa sales fundentes debido al diseño de laberinto del interior de la cavidad. El rendimiento en la absorción de la radiación solar del receptor de cavidad propuesto se estudia con un modelo de trazado de rayos. Se encuentra que el receptor puede ser desplazado en un intervalo alrededor del foco de la parábola sin que varíe prácticamente la radiación absorbida. Se analiza el interior de la cavidad con un modelo CFD para diferentes situaciones de velocidad de flujo másico del fluido caloportador (HTF, por sus siglas en inglés) y para una temperatura fija de 150 _C. Se usa una distribución precisa del flujo de radiación en las paredes, calculada en análisis previos para un EDNI dado. Se encuentra que el receptor de cavidad propuesto tiene zonas de baja velocidad del HTF, lo que genera picos de alta temperatura. El rendimiento térmico del PDC durante un año meteorológico típico (TMY, por sus siglas en inglés) se estudia para tres receptores diferentes: el receptor de cavidad propuesto (OCR), un receptor plano equivalente (FPR), y el receptor de cavidad propuesto con una cubierta de cristal (CCR). Para calcular la eficiencia térmica media anual, se desarrolla un modelo compartimental del sistema. Los resultados muestran que, en comparación con el FPR, el OCR da una mejora de 5%-7%, pero el CCR da una mejora significativa de 17%-20%. Y, además, las temperaturas alcanzadas por el FPR son significativamente más altas que la alcanzadas por el OCR y el CCR. Por sí mismo, esto puede ser un factor de rechazo del FPR en la práctica (como en el caso considerado en este trabajo donde el límite de temperatura del HTF es 350 _C). Finalmente, se diseña una planta solar simple para el uso de la energía solar obtenida en el PDC en la cogeneración de vapor a 150 _C en una planta piloto industrial de tratamiento térmico. La integración de sistemas se hace en las calderas. Para la cogeneración, se usa una caldera solar en paralelo con la caldera eléctrica existente. Las dos calderas se conectan a la línea principal de vapor de la planta. La planta se regula para satisfacer una demanda constante de vapor. Un modelo compartimental de la planta solar y de la planta piloto se usa para estimar el rendimiento durante dos días seleccionados del TMY. Se encuentra que la caldera solar suministra parte del vapor que se demanda cuando hay energía solar disponible. En particular, el flujo de vapor suministrado se mantiene constante en el nivel requerido y es la suma de los vapores generados en las calderas eléctrica y solar. Escuela Internacional de Doctorado de la Universidad Politécnica de Cartagena Universidad Politécnica de Cartagena Programa de Doctorado en Energías Renovables y Eficiencia Energética

Molten-salt reactors (MSRs) can provide inexpensive industrial process heating in addition to generating electricity. In most cases, this can be best accomplished by design simplification, which results in improvements to MSR’s already existing and inherently strong safety characteristics. This is just one of a number of possible future scenarios that will influence the way in which MSR technology can develop and become marketable. The emphasis in this paper is to develop a reactor with application to the widest possible range of industries. This paper concentrates on the need to develop the inherent safety characteristics of the single fluid thermal reactor with the expectation that sufficient reliability and safety will be achieved in design so that these power generators will eventually be accepted for close integration into the fabric of modern society. It seems inevitable that the required licensing procedures needed for MSRs will vary considerably depending on their type because different designs vary so much. Those used for low-temperature process heat in addition to power generation require much less demanding regulatory procedures than those operating at higher temperatures. This is largely because long-term corrosion is more problematic at higher temperatures and present-day construction materials limit the development of MSRs from reaching their full potential. With appropriate experience with operating early designs of MSRs it is reasonable to expect that lower temperature versions will become certifiable for use in close proximity to a large range of human activities. Ultimately these reactors will be controllable remotely without the local attendance of technical staff.