This research investigates the potential of a solar powered cooling system for single family houses in Pakistan. The system comprises water heating evacuated tube solar collectors, a hot water storage tank, and an absorption chiller. A literature review was carried out covering: • Energy situation, climate, and renewable energy potential in Pakistan; • Energy and thermal comfort in buildings, particularly for hot climates; • Solar collectors and solar cooling systems, particularly for hot climates; • Dynamic thermal simulation and weather data for solar energy systems and buildings. It was found that Pakistan is short of energy and that there is a great need to cool buildings. Renewable energy cooling systems are, therefore, of interest. The system described above was selected, as it was found that solar energy is abundant in Pakistan when cooling is required; thermal systems can be more economical than photovoltaics for hot climates and suitable components (collectors, absorption chillers, etc.) are commercially available. The TRNSYS dynamic thermal simulation program was selected as the main research tool, as it has been tested for solar energy and building applications by many researchers and suitable experimental facilities were not available. A simple typical building in Pakistan with a solar cooling system was simulated. Optimum values for key parameters were found by repeated simulations. It was concluded that the system would be able to provide cooling when required without an auxiliary heat source, and that an evacuated tube collector with a gross area of 12 m2, a collector flow rate of 165 kg/h, and a storage tank volume of 2 m3 would provide satisfactory performance for a 3.52 kW absorption chiller integrated with 42m3 single room. The results were in good agreement with published results from other researchers. Sensitivity analysis was carried out for the collector area, collector flow rate and storage tank size. It was found that varying the collector area had the largest effect on system performance, followed by varying the storage tank volume. Varying the collector flow rate had the smallest effect. It is recommended that solar cooling systems should be considered for Pakistan, and that further research should be carried out into reducing building cooling loads, using surplus heat for other loads, improving the performance of the proposed solar cooling system, and comparing it with other systems such as photovoltaics.

This thesis studies the use of night ventilation as a passive cooling strategy for a traditional courtyard house in a hot dry climate. This was done by CFD simulation of the house and its surroundings, using weather data for Baghdad. The simulation was done for a large number of scenarios in which each represented a change in one of the house elements, such as courtyard and room dimensions, and in some cases included modern technologies such as a ceiling fan. The thesis suggests that performance should be calculated with the aid of a "Night Time Effectiveness Ratio" (NTER) and time constants. The findings show that building elements can change the performance to various degrees, that the airflow patterns inside the rooms change from day to night, and that the thermal conditions during the day depend more on the intensity of solar radiation than other factors. The results show that a courtyard house can ensure the thermal comfort for its residents. However, it needs some assistance from new techniques such as fans to keep the air quality inside the house within acceptable limits. The values for NTER from initial simulations are around ten, which indicate that night ventilation is not enough for cooling the building. However, the values drop to less than one by using a small and narrow courtyard with a two-level house and a gallery around the courtyard. Also, it is necessary to have a connection between the courtyard and alleyway at ground level in the night only and to cover the courtyard during the day. The windows have the largest role in deciding the performance of night ventilation. Ideally they should be small and tall, or preferably a pair of windows separated by a vertical distance and kept closed during the day. The effects of room dimension are clearer in affecting the thermal comfort more than improving the performance of night ventilation. The research also examines the indoor air quality and suggests ways to improve it. Some of the ways are traditional like the use of a wind catcher in ventilating the courtyard and the basement, and others are more modern like using an exhaust fan. Furthermore, it suggests an algorithm to control these ways and to introduce only a limited quantity of fresh air to avoid excessive warming. Suggestions for future work are given, including tests for more elements in the courtyard house and for longer duration runs. It would also be helpful to study the use of latent heat storage (e.g. phase change material) as an additional effective thermal mass.

Étude d'un système innovant magnétothermique pour le chauffage et la climatisation sans gaz à effet de serre : application à un véhicule électrique.Ce travail de thèse est destiné à l'étude d'un système de climatisation et de chauffage basé sur la réfrigération magnétique. L'étude de ce système basé sur l'effet magnétocalorique (EMC)est structurée en deux parties: la première représente l'état de l'art, c'est-à-dire une analyse bibliographique des principaux systèmes de climatisation existants, des différentes études relatives à la modélisation numérique des systèmes de réfrigération magnétique, et les études ·les plus récentes concernant l'écoulement et le transfert thermique dans les microcanaux constituants la matrice du régénérateur magnétocalorique actif étudié dans cette thèse. Ensuite la deuxième partie comporte l'étude du coefficient de transfert thermique h entre le régénérateur solide et le fluide caloporteur, et la simulation du comportement d'un cycle AMR. Un modèle numérique est développé pour chacune des études. Le premier modèle permet de calculer le coefficient de transfert convectif h et d'évaluer l'influence sur ce même coefficient de la hauteur des canaux Hc et de la vitesse du fluide Vf, en considérant deux types de canaux: canaux à parois lisses et canaux à parois rugueuses. Ainsi l'effet de la rugosité de surface des matériaux sur l'écoulement et le transfert thermique est déterminé, et l'augmentation résultante de h est évaluée. Dans cette même partie une approche de dimensionnement du système de climatisation basé sur un cycle AMR est proposée pour application à la climatisation d'un véhicule électrique. Enfin ce travail est conclu par une synthèse comprenant les contributions de ce travail, ses limites, et les perspectives qui en découlent. / This work is intended for the study of an air conditioning system and heating based on themagnetic refrigeration. The study of this system based on the magnetocaloric effect (MCE) ismade in two parts: the first one represents the state of the art, that is a bibliographical analysis of the main existing air conditioning systems, the various studies relative to the numerical modelling of the magnetic refrigeration systems, and the most recent studies concerning fluid flow and heat transfer in the microchannels which constitute the matrix of the active magnetic regenerator studied in this work. Then the second part contains the study of the heat transfer coefficient h, between the solid regenerator and the coolant, and the simulation of the behaviour of an Active Magnetic Regeneration cycle. A numerical mode! is developed for each of the studies. The first one enables to calculate the convective heat transfer coefficient and to estimate the influence of the charmels height Hc and the fluid velocity Vf on the heat transfer coefficient.Two types of charmels are considered: charmels with smooth walls and charmels with rough walls. So the effect of the surface roughness of the magnetocaloric material on the fluid flow and the heat transfer is determined, and the resulting increase of h is estimated. An approach of sizing the air conditioning system based on a cycle AMR is proposed for an application in theair conditioning of a battery-driven vehicle. Finally this work is concluded by a synthesis including the contributions of this work, its limits, and the perspectives which ensue from it.

Wards occupy significant proportions of hospital floor areas and due to their constant use, represent a worthwhile focus of study. Single-bed wards are specifically of interest owing to the isolation aspect they bring to infection control, including airborne pathogens, but threats posed by airborne pandemics and family-involvement in hospital care means cross-infection is still a potential problem. In its natural mode, ventilation driven by combined wind and buoyancy forces can lead to energy savings and achieve thermal comfort and high air change rates through secure openings. These are advantageous for controlling indoor airborne pathogens and external air and noise pollution. However, there is lack of detailed evidence and guidance is needed to gain optimum performance from available natural ventilation systems. This research is a proof of concept investigation into the feasibility and impact of natural ventilation systems targeting airflow rates, thermal comfort, heating energy and control of pathogenic bio-aerosols in hospital wards. In particular, it provides insights into the optimal areas of vent openings which could satisfy the complex three-pronged criteria of contaminant dilution, low heating energy and acceptable thermal comfort for occupants in a naturally ventilated single bed ward. The main aim of this thesis is the structured study of four systems categorised into three groups: Simple Natural Ventilation (SNV) in which single and dual-openings are used on the same external wall; Advanced Natural Ventilation (ANV) which is an emerging concept; and finally Natural Personalised Ventilation (NPV) which is an entirely new concept borne out of the limitations of previous systems and gaps in literature. The focus of this research is in the exploratory study of the weaknesses and potentials of the four systems, based on multi-criteria performances metrics within three architecturally distinct single-bed ward designs. In contributing to the body of existing knowledge, this thesis provides a better understanding of the performances of three existing systems while presenting the new NPV system. The analysis is based on dynamic thermal modelling and computational fluid dynamics and in the case of the NPV system, salt-bath experiments for validation and visualisation of transient flows. In all cases, wards were assumed to be free of mechanical ventilation systems that might influence the natural flow of air. The thesis meets three major objectives which have resulted in the following contributions to current knowledge: An understanding of the limitations and potentials of same-side openings, especially why and how dual-openings can be useful when retrofitted into existing wards. Detailed analysis of bulk airflow, thermal comfort, heating energy and room air distribution achievable from existing SNV and ANV systems, including insights to acceptable trickle ventilation rates, which will be particular useful in meeting minimum dilution and energy requirements in winter. This also includes qualitative predictions of the airflow pattern and direction obtainable from both systems. The innovation and study of a new natural ventilation system called Natural Personalised Ventilation (NPV) which provides fresh air directly over a patient s bed, creating a mixing regime in the space and evaluation of its comfort and energy performances. A low-energy solution for airborne infection control in clinical spaces is demonstrated by achieving buoyancy-driven mixing ventilation via the NPV system, and a derivative called ceiling-based natural ventilation (CBNV) is shown. A comparative analysis of four unique natural ventilation strategies including their performance rankings for airflow rates, thermal comfort, energy consumption and contaminant dilution or removal using an existing single-bed ward design as case study. Development of design and operational recommendations for future guidelines on utilising natural ventilation in single-bed wards either for refurbishment or for proposed designs. These contributions can be extended to other clinical and non-clinical spaces which are suitable to be naturally ventilated including treatment rooms, office spaces and waiting areas. The findings signify that natural ventilation is not only feasible for ward spaces but that there is opportunity for innovation in its application through further research. Future work could focus on related aspects like: impacts of fan-assisted ventilation for a hybrid flow regime; pre-heating of supply air; integration with passive heat recovery systems as well the use of full-scale experiments to fine-tune and validate findings.

La présente thèse porte sur la prédiction numérique de l’impact des transferts thermique et massique sur la qualité de l’air et sur le confort thermique à l’intérieur des cavités ventilées ou non et remplies de polluant. En effet, les cavités ventilées sont généralement considérées comme étant une approximation pour la modélisation des locaux ventilés.Pour mener à bien cette étude, nous avons choisi un modèle numérique basé sur la résolution des équations régissant les transferts de quantité de mouvement, de chaleur et de masse. La première partie du mémoire est consacrée à quelques généralités sur la ventilation, la qualité de l’air et le confort thermique ainsi qu’à la revue bibliographique des travaux réalisés. La démarche suivie est décrite dans le chapitre 2. Celle-ci est basée sur l’approximation de Boussinesq. Le modèle RNG k-ε est utilisé pour traiter la turbulence. La discrétisation des équations est réalisée à l’aide de la méthode des volumes finis associée à l’algorithme SIMPLEC pour traiter le couplage pression-vitesse. Dans la seconde partie, nous considérons d’abord la convection thermique et la convection thermosolutale dans des cavités fermées. Le principal but visé est: a) de valider le modèle considéré en confrontant nos résultats avec ceux de la littérature et b) d’étudier l’influence du nombre de Rayleigh thermique et du rapport de flottabilité. Les résultats obtenus révèlent que le modèle adopté prédit correctement les transferts thermique et massique.Ensuite, nous appliquons cette approche au cas des cavités bidimensionnelles ventilées soumises à des gradients de température et de concentration. Les indices de qualité de l’air et d’efficacité de la ventilation sont calculés et discutés. Nous achevons ce travail en analysant l’influence de la ventilation sur la qualité de l’air intérieur dans une pièce tridimensionnelle en régime transitoire. Cette analyse concerne différents scénarios de ventilation mécanique simple flux en vue de trouver la meilleure configuration en termes d’efficacité et de qualité de l’air intérieur. / This thesis deals with the numerical prediction of heat and mass transfer impact on the air quality and thermal comfort within either ventilated or not cavities filled with pollutants. Indeed, ventilated areas are first modeled to be as ventilated cavities in a first approximation.To carry out this study, we adopt a numerical model based on solving equations governing momentum, heat and mass transfer. The first part of this thesis is dedicated to some generalities on ventilation, air quality and thermal comfort and the bibliographic review of previous works. The adopted approach is described in Chapter 2. It is based on the Boussinesq approximation. The RNG k-ε model is used to handle turbulence. The finite-volume method (FVM) is used to discretize of the set of equations, and the pressure-velocity coupling is achieved via the SIMPLEC algorithm. In the second part, we consider the thermal convection and thermosolutal convection in closed cavities. The main aim is a) to validate the considered model by comparing our results with those of literature, and b) to investigate influence of the thermal Rayleigh number and the buoyancy ratio. Our findings indicate that the model accurately predicts heat and mass transfer.Then, we apply this approach to the case of two-dimensional ventilated cavities subjected to temperature and concentration gradients. The indices of air quality and ventilation efficiency are calculated and discussed. We end this work by analyzing the influence of ventilation on the quality of indoor air in a three-dimensional room in transient regime. This investigation covers different scenarios from the simple flow mechanical ventilation which aims to find the best configuration in terms of efficiency and quality of indoor air.

This thesis presents work on a holistic approach for improving the overall design of solar cooling systems driven by solar thermal collectors. Newly developed methods for thermodynamic optimization of hydraulics and control were used to redesign an existing pilot plant. Measurements taken from the newly developed system show an 81% increase of the Solar Cooling Efficiency (SCEth) factor compared to the original pilot system. In addition to the improvements in system design, new efficiency factors for benchmarking solar cooling systems are presented. The Solar Supply Efficiency (SSEth) factor provides a means of quantifying the quality of solar thermal charging systems relative to the usable heat to drive the sorption process. The product of the SSEth with the already established COPth of the chiller, leads to the SCEth factor which, for the first time, provides a clear and concise benchmarking method for the overall design of solar cooling systems. Furthermore, the definition of a coefficient of performance, including irreversibilities from energy conversion (COPcon), enables a direct comparison of compression and sorption chiller technology. This new performance metric is applicable to all low-temperature heat-supply machines for direct comparison of different types or technologies. The achieved findings of this work led to an optimized generic design for solar cooling systems, which was successfully transferred to the market.