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The purpose of a heat pump is to control the temperature of an enclosed space. This is done by using heat exchange with a heat source, for example water, air, or ground. In the air source heat pump that has been studied during this master thesis, a refrigerant exchanges heat with the outdoor air and with a water distribution system. The heat pump is controlled through the circuit containing the refrigerant and it is therefore crucial that this circuit is functional. To ensure this, a diagnosis system has been created, to be able to detect and isolate sensor errors. The diagnosis system is based on mathematical models of the refrigerant circuit with its main components: a compressor, an expansion valve, a plate heat exchanger, an air heat exchanger, and a four-way valve. Data has been collected from temperature- and pressure sensors on an air source heat pump. The data has then been divided into data for model estimation and data for model validation. The models are used to create test quantities, which in turn are used by a diagnosis algorithm to determine whether an error has occurred or not. There are nine temperature sensors and two pressure sensors on the studied air source heat pump. Four fault modes have been investigated for each sensor: Stuck, Offset, Short circuit and Open circuit. The designed diagnosis system is able to detect all of the investigated error modes and isolate 40 out of 44 single errors. However, there is room for improvement by constructing more test quantities to detect errors and decouple more fault modes. To further develop the diagnosis system, the existing models can be improved and new models can be created.

The global growth in electricity consumption and the shortcomings of renewable electricity generation technologies are some of the reasons why it is still relevant to evaluate the performance of power conversion technologies that are used in fossil fuel power stations. The power conversion technology that is widely used in fossil fuel power stations is the Rankine cycle. The goal of this study was to determine if the efficiency of a typical Rankine cycle can be improved by adding a heat pump as a bottoming cycle. Three simulation models were developed to perform this evaluation. The first is a simulation model of a Rankine cycle. A quite detailed Rankine cycle configuration was evaluated. The simulation model was used to determine the heating requirements of the heat pump cycle as well as its operating temperature ranges. The efficiency of this Rankine cycle was calculated as 43.05 %. A basic vapour compression cycle configuration was selected as the heat pump of the combined cycle. A simulation model of the vapour compression cycle and the interfaces with the Rankine cycle was developed as the second simulation model. Working fluids that are typically used in vapour compression cycles cannot be used for this application, due to temperature limitations. The vapour compression cycle’s simulation model was therefore also used to calculate the coefficient of performance (COP) for various working fluids in order to select a suitable working fluid. The best cycle COP (3.015 heating) was obtained with ethanol as working fluid. These simulation models were combined to form the simulation model of the Rankine-heat pump combined cycle. This model was used to evaluate the performance of the combined cycle for two different compressor power sources. This study showed that the concept of using steam turbine or electrical power to drive a compressor driven vapour compression cycle in the configuration proposed here does not improve the overall efficiency of the cycle. The reasons for this were discovered and warrant future investigation. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.

The global growth in electricity consumption and the shortcomings of renewable electricity generation technologies are some of the reasons why it is still relevant to evaluate the performance of power conversion technologies that are used in fossil fuel power stations. The power conversion technology that is widely used in fossil fuel power stations is the Rankine cycle. The goal of this study was to determine if the efficiency of a typical Rankine cycle can be improved by adding a heat pump as a bottoming cycle. Three simulation models were developed to perform this evaluation. The first is a simulation model of a Rankine cycle. A quite detailed Rankine cycle configuration was evaluated. The simulation model was used to determine the heating requirements of the heat pump cycle as well as its operating temperature ranges. The efficiency of this Rankine cycle was calculated as 43.05 %. A basic vapour compression cycle configuration was selected as the heat pump of the combined cycle. A simulation model of the vapour compression cycle and the interfaces with the Rankine cycle was developed as the second simulation model. Working fluids that are typically used in vapour compression cycles cannot be used for this application, due to temperature limitations. The vapour compression cycle’s simulation model was therefore also used to calculate the coefficient of performance (COP) for various working fluids in order to select a suitable working fluid. The best cycle COP (3.015 heating) was obtained with ethanol as working fluid. These simulation models were combined to form the simulation model of the Rankine-heat pump combined cycle. This model was used to evaluate the performance of the combined cycle for two different compressor power sources. This study showed that the concept of using steam turbine or electrical power to drive a compressor driven vapour compression cycle in the configuration proposed here does not improve the overall efficiency of the cycle. The reasons for this were discovered and warrant future investigation. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.

Yes / Owing to the high specific energy consumption associated with thermal desalination technologies such as Multi Effect Distillation (MED), there is a wide interest to develop a cost-effective desalination technology. This study focuses on improving the operational, economic, and environmental perspectives of hybrid MED-TVC (thermal vapour compression) process via optimisation. Application of particle swarm optimisation (PSO) in several engineering disciplines have been noted but its potential has not been exploited fully in desalination technologies especially MED-TVC in the past. A multi-objective non-linear optimisation framework based on PSO is constructed here. Two of our earlier models have been used to predict the key process performance and cost indicators. The models are embedded within the PSO optimisation algorithm to develop a new hybrid optimisation model which minimises the total freshwater production cost, total specific energy consumption and brine flow rate while maintaining a fixed freshwater production for a given number of effects and seawater conditions. The steam flow rate and temperature are considered as control variables of the optimisation problem to achieve the objective function. The PSO has successfully achieved the optimum indexes for the hybrid MED-TVC process for a wide range of number of effects. It also shows a maximum reduction of freshwater production cost by 36.5%, a maximum energy saving by 32.1% and a maximum reduction of brine flow rate by 38.3%, while maintaining the productivity of freshwater.

Se ha desarrollado y construido una infraestructura experimental orientada a la validación de modelos de intercambiadores compactos de aletas y tubos y sistemas de refrigeración con sobrealimentación de líquido. El objetivo ha sido la obtención de datos experimentales fiables, con condiciones geométricas y de contorno exactamente definidas, para poder compararlos inequívocamente con resultados de simulaciones numéricas. Se presentan los modelos matemáticos, objetivo de la validación, y una descripción detallada del circuito de aire, del refrigerante líquido, y del refrigerante de cambio de fase, que integran la infraestructura.Estos tres circuitos están encargados de asegurar condiciones estables y controladas para los prototipos ensayados y para el sistema de refrigeración con sobrealimentación de líquido, en un amplio rango de temperaturas, flujos másicos y potencias. El diseño permite el ensayo de prototipos de intercambiadores de calor con diferentes geometrías y dimensiones. Se presentan detalladamente los instrumentos de medida con sus precisiones, montaje, se describen también los componentes y los parámetros de la unidad de adquisición de datos.Especial atención se ha dedicado a la calibración de los instrumentos de medida como parte esencial del proceso de preparación de los ensayos. Se describe el proceso de estimación de las incertidumbres sistemáticas de los sensores calibrados. Se expone en detalle la formulación y la metodología adoptada para el análisis de incertidumbre de los resultados experimentales.El procesamiento y el análisis de los datos experimentales se ha realizado en forma automática con un código computacional especialmente desarrollado, encargado de calcular los resultados a partir de las variablas medidas, de llevar a cabo el análisis de incertidumbres detallado, y de comparar los resultados numéricos y experimentales.Se presentan resultados experimentales obtenidos con la infraestructura experimental desarrollada. Se presentan estudios detallados de intercambiadores de calor compactos en condiciones de enfriamiento de aire, utilizando refrigerante líquido y de cambio de fase. Se presentan también resultados del estudio experimental del sistema de refrigeración con sobrealimentación de líquido. Los resultados han sido comprobados y verificados a través de balances energéticos en todos los componentes, donde la misma magnitud física ha sido evaluada de mediciones independientes. Con el objetivo de permitir el uso mas general de los resultados experimentales se presentan también los datos crudos de las variables medidas durante los ensayos.Se ha propuesto una metodología de validación para el modelo de intercambiadores compactos, basada en comparaciones sistemáticas de resultados numéricos y experimentales. Estas comparaciones han sido analizadas en términos estadísticos con el objetivo de cuantificar las diferencias observadas y dar una evaluación global de las prestaciones del modelo numérico en las condiciones ensayadas. La metodología propuesta para la validación del modelo de intercambiadores compactos puede ser utilizada como base para metodologías de validación en general. / Experimental infrastructures intended for validation of compact heat exchanger models, and models of liquid overfeed refrigeration systems have been developed and constructed. The aim has been the obtaining of reliable experimental data from tests at exactly defined geometrical and boundary conditions, permitting the unequivocal comparisons with numerical simulation results. The mathematical models are presented and detailed description of the airhandling, the liquid refrigerant, and phase-changing refrigerant circuits integrating the experimental infrastructure is given.These three circuits are encharged to provide stable controlled conditions for the tested prototypes and the liquid overfeed system in the desired range of temperatures, fluid flows, and capacities. The design permits the accommodation of heat exchanger prototypes with different geometry and sizes.Detailed overview of the measuring instruments is presented, with their accuracies and mounting, and the components and parameters of the data acquisition system are described.Special attention has been paid to the calibration of the measuring instruments as an essential part of the test preparation. The process of estimation of the systematic uncertainties in the calibrated sensors measurements is described. The formulation and the methodology adopted for the uncertainty analysis of the experimental results is exposed in detail.The experimental data processing and analysis has been performed automatically with a specially developed program encharged with the calculation of the experimental results from the measured variables, the detailed uncertainty analysis, and the numerical to experimental results comparisons.Experimental results obtained with the developed infrastructure are presented. Detailed studies of compact heat exchangers under cooling conditions, using liquid and phase-changing refrigerants, are performed and presented. Results from the experimental studies of the liquid overfeed refrigeration system are also presented. The results have been checked and verified through energy balance checks for all the components where measurements of the same physical magnitude can be contrasted with independent measurements. In order to give more general use of the obtained experimental data, the raw measured variables during the tests are also presented.An experimental validation methodology for the compact heat exchanger model has been proposed, based on systematic comparisons between numerical and experimental results. The comparisons have been analysed in statistical terms in order to quantify the observed differences and to give global evaluation of the numerical model performance in the tested conditions. The methodology proposed for validation of the heat exchanger model can be used as a basis for validation methodology for numerical models in general.

Improving the climate system of cars is important since it is the largest auxiliary load in a standard vehicle with an increase of fuel consumption by up to 20%. In Electric Vehicles (EV) the range of the car is more limited than in a fossil fueled car; furthermore there is a limited waste heat available from the EV, approximately 2-3kW at 40oC for heating and defogging in winter. The goals of this report have been part of an existing European project (ICE) where the climate system of an electric minibus is being investigated. The specific objectives of this project were to develop a radiation model and integrate it in the existing thermal model of the cabin, validating the new model with existing experimental data, including the thermal model in the overall model of the complete vehicle and to use the existing AC-model to optimize the control with the aim of decreasing the energy consumption maintaining thermal comfort inside the cabin. The radiation model uses total radiation on a horizontal surface in order to calculate the radiation hitting the different parts of the car body and windows, finally the total radiative power entering the minibus is calculated. After including these calculations into the thermal model it could be seen that the results from the model in terms of cabin temperatures fit the experimental values surprisingly well. The control of the AC-system was optimized for a hot and sunny summer day in Italy which resulted in the AC-system working very hard following that the best control strategy was to reduce only the speed of the compressor in order to save energy. Calculations show that in the Normal European Driving Cycle (NEDC) the potential energy savings of following this control strategy can result in an energy saving of the AC-system by up to 27% compared to an unregulated case, with a maintained thermal comfort resulting in 4,2% increase in autonomy.