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Most utility's and electricity resellers stimulate changes in their load shape through various demand side management activities. The most common way of altering their load shape is through the implementation of different tariff structures. The thesis investigates the effect of combining hot water load control with heating ventilation and air-conditioning load control to reduce the electricity costs due to a demand tariff that is a direct result of demand side management. The entire study is focused on the demand tariff of the University of Pretoria. Although the study was done on the University of Pretoria the methods developed are universal and can be implemented in any situation where hot water load control and heating ventilation and air-conditioning load control are to be combined. The study presents a detailed literature study on the current developments in the field of hot water and heating ventilation and air-conditioning load control. No current work could be found in which the two control methods are combined. Models were developed for controlling the electricity load and for determining the savings. The heating ventilation and air-conditioning load's and the hot water load's uncontrolled load models respectively had a mean absolute percentage errors of 3.83% and 3.2%. The forecasting method used to determine the available energy for pre-cooling and the start time of shedding had a mean absolute error of 3.2%. A case study of the University of Pretoria was done. The effect of using only hot water load control is presented. The case study was expanded to include structural thermal energy storage and then water thermal energy storage. This expansion was done using the HV AC system in combination with the hot water load control system. With an only 10.3% contribution to the university's maximum demand, the hot water load control reduced the university's electricity account (energy + demand) by 5.44%. The heating ventilation and air conditioning load contribute to 6% of the university's maximum demand. With the structural thermal energy storage using the heating ventilation and air conditioning system, the savings increased to 6.12%. With the addition of a 750m3 water thermal energy storage tank to the heating ventilation and air-conditioning system, the savings increased to 7.14%. / Dissertation (MEng (Electrical Engineering))--University of Pretoria, 2005. / Electrical, Electronic and Computer Engineering / unrestricted

No description available.

Solar chimney is an important passive design strategy to maximize solar gain to enhance buoyancy effect for achieving adequate air flow rate and a desired level of thermal comfort inside a building. Therefore, solar chimney has the potential advantages over mechanical ventilation systems in terms of energy requirement, economic and environmental benefits. The main aim of this project is to study the technical feasibility of a solar chimney incorporating latent heat storage (LHS) system for domestic heating and cooling applications. The research work carried out and reported in this thesis includes: the development of a detailed theoretical model to calculate the phase change material (PCM) mass for solar chimney under specific climatic condition, the development of a CFD model to optimise the channel depth and the inlet and outlet sizes for the solar chimney geometry, experimental and numerical investigations of the thermal performance of the proposed system using a prototype set-up, a parametric study on the proposed system to identify significant parameters that affect the system performance was carried out by using the verified numerical model. The numerical and experimental study showed that the numerical model has the ability to calculate the PCM mass for the proposed system for the given weather conditions. The optimum PCM should be selected on the basis of its melting temperature, rather than its other properties such as latent heat. The experimental work on the thermal performance of the proposed system has been carried out. The results indicated that the LHS based solar chimney is technically viable. The outlet air temperature and the air flow rate varied within a small range during phase change transition period which are important for a solar air heating system. A numerical model was developed to reproduce the experimental conditions in terms of closed mode and open mode. The model results were in a close agreement with the experimental results particularly the simulated results for the discharging process. With the verified model, a comprehensive parametric analysis intended to optimise the thermal performance of proposed the system was performed. The results analysed are quantified in terms of charging/discharging time of the PCM, temperature difference between outlet air and inlet air of the solar chimney, and mass flow rate of the chimney, which are the most important quantities of the proposed system.

Photocopy of typescript. / Digitized by Kansas Correctional Industries

With environmental concern growing in both affluent and developing countries, roof top ventilators, a form of natural ventilation requiring only wind energy to ensure quality air circulation and comfort is becoming a considered choice of many households and industries. Unfortunately, however, many of these ventilators have evolved through trial and error and the flow physics associated with these ventilators is barely understood. The present experimental project was, therefore, undertaken as part of UNSW- Industry collaboration program funded under an Australian Research Council Grant to explore whether the aerodynamics forces acting on these ventilators during their operation could be obtained. A commercial roof top ventilator supplied by industry was, therefore, tested in an open jet wind tunnel of the University of New South Wales and the results are presented in this thesis. A novel feature of this project is the examination of the suitability of ???the three dimensional wake traverse??? technique to the wake of rotating ventilator. This technique has so far been applied with limited success to the wake of lifting bodies of fixed wing configuration only. In the absence of adequate data in the literature on rotating ventilator, the aerodynamics force components obtained by this technique have been compared against force balance measurements. The results show that the wake traverse technique is capable of determining lift and total drag forces associated with the ventilator flow during its operation from the pressure and velocity information gathered downstream of a ventilator in its wake. Generally, from these data, the technique also allows isolation of the profile and induced components of the drag force. However, from the induced drag value, while it is possible to determine the lift force, it is however, found that a more accurate value of lift force can be evaluated using axial vorticity formulation. The availability of the above technique which does not require measurements on the test specimen itself, will aid in providing a cost efficient investigation of the aerodynamic forces and consequently the performance of a roof top ventilator.

With environmental concern growing in both affluent and developing countries, roof top ventilators, a form of natural ventilation requiring only wind energy to ensure quality air circulation and comfort is becoming a considered choice of many households and industries. Unfortunately, however, many of these ventilators have evolved through trial and error and the flow physics associated with these ventilators is barely understood. The present experimental project was, therefore, undertaken as part of UNSW- Industry collaboration program funded under an Australian Research Council Grant to explore whether the aerodynamics forces acting on these ventilators during their operation could be obtained. A commercial roof top ventilator supplied by industry was, therefore, tested in an open jet wind tunnel of the University of New South Wales and the results are presented in this thesis. A novel feature of this project is the examination of the suitability of ???the three dimensional wake traverse??? technique to the wake of rotating ventilator. This technique has so far been applied with limited success to the wake of lifting bodies of fixed wing configuration only. In the absence of adequate data in the literature on rotating ventilator, the aerodynamics force components obtained by this technique have been compared against force balance measurements. The results show that the wake traverse technique is capable of determining lift and total drag forces associated with the ventilator flow during its operation from the pressure and velocity information gathered downstream of a ventilator in its wake. Generally, from these data, the technique also allows isolation of the profile and induced components of the drag force. However, from the induced drag value, while it is possible to determine the lift force, it is however, found that a more accurate value of lift force can be evaluated using axial vorticity formulation. The availability of the above technique which does not require measurements on the test specimen itself, will aid in providing a cost efficient investigation of the aerodynamic forces and consequently the performance of a roof top ventilator.

L’instabilité de la ventilation est un phénomène connu chez l’homme. Elle était jusqu’à présent observée chez l’homme sain en altitude et chez les patients souffrant d’insuffisance cardiaque (IC) et de syndrome d’apnées du sommeil (SAS), d’origine centrale, obstructive ou mixte, le plus souvent pendant le sommeil. Une analyse spectrale rétrospective de tests d’effort en hypoxie a mis à jour une instabilité ventilatoire lorsque le système de contrôle de la ventilation est soumis à une double contrainte, physiologique (exercice modéré) et environnemental (hypoxie simulant une altitude de 2000 à 4800 m d’altitude). Des protocoles prospectifs ont corrélé positivement l’amplitude de ces oscillations de la ventilation au débit cardiaque (Q̇c) et au niveau de ventilation (V̇E), tandis que la période est raccourcie lorsque V̇E et Q̇c augmentent. À l’opposé d’une période des apnées d’environ 1 minute chez les patients IC et SAS, nos observations ont permis de mesurer la période des oscillations ventilatoires à l’exercice et en hypoxie entre 11 et 12 secondes. Les sujets montrant une plus forte réponse ventilatoire à l’hypoxie et une sensibilité plus élevée au CO₂ exhibent une plus grande instabilité ventilatoire. L’hyperoxie et l’hypercapnie ont des effets opposés : alors que l’inhalation d’O₂ ne modifie pas la stabilité du système (vs normoxie), l’hypercapnie hyperoxique exacerbe le phénomène oscillatoire. Un traitement pharmacologique par acétazolamide (ACZ) améliore la stabilité ventilatoire, appuyant ainsi, en regard des données précédentes, le rôle central des chémorécepteurs périphériques dans la survenue des oscillations de la ventilation. Un modèle mathématique du contrôle de la ventilation intégrant, parmi de nombreux paramètres cardiorespiratoires, les sensibilités à l’O₂ et au CO₂, et les interactions périphérique-central, confirme l’implication du niveau d’hypoxie et du délai de convection sanguine entre les poumons et les chémorécepteurs périphériques dans la période des oscillations. Il souligne également le rôle potentiel de l’espace mort dans la survenue de l’instabilité respiratoire. / Breathing instability is a well-known phenomenon in human. Until now, it was observed in healthy subjects at altitude et in patients suffering from chronic heart failure (CHF) or sleep apnea syndrome (SAS), central, obstructive or mixed, mostly during sleep. A retrospective spectral analysis of standard hypoxic exercise test evidenced a ventilatory instability when the control system is submitted to a double stress, physiological (moderate exercise) and environmental (hypoxia, from 2000 to 4800m simulated altitudes). Prospective analyses positively correlated magnitude of the ventilatory oscillations to cardiac output (Q̇c) and ventilation (V̇E), whereas their period is shortened with increasing V̇E and Q̇c. Unlike the one-minute period apneas in CHF and SAS patients, we observed a much shorter period at exercise in hypoxia, between 11 and 12 seconds. Subjects with a higher ventilatory response to hypoxia and a greater sensitivity to CO₂ showed a deeper breathing instability. Hyperoxia and hypercapnia have opposite effects : O₂ inhalation does not alter the system stability, hypercapnia enhances the oscillatory phenomenon. A pharmacological treatment by acetazolamide (ACZ) improves breathing stability, supporting a major role of peripheral chemoreceptors in the genesis of ventilatory oscillations. A mathematical model of ventilation control including, among numerous cardiorespiratory parameters, sensibilities to O₂ and CO₂, peripheral-central interactions, confirms the contribution of hypoxia level and the delay of blood convection between lungs and peripheral chemoreceptors in the oscillations period. It also highlights a potential role of dead space in the onset of breathing instability.