Neste trabalho são apresentados resultados experimentais, de um circuito operando em circulação natural, que permitem analisar o comportamento de um sistema de resfriamento de emergência quando é aberta uma linha de desvio entre a fonte quente e a fonte fria. O trabalho tem ainda a importância de documentar os testes de caracterização hidráulica do circuito experimental, fornecendo inclusive os fatores de perda de pressão específicos para o circuito. Observou-se que, para uma mesma potência, quando é aberta a linha de desvio, a temperatura na saída da fonte quente aumenta substancialmente. Esse aumento ocorre porque a vazão através do aquecedor diminui. A vazão através do trocador de calor (fonte fria) aumenta ligeiramente, sendo sempre a soma das vazões na linha de desvio e no aquecedor. O trabalho mostra ainda que a posição de conexão da linha de desvio com a perna quente determina o sentido de escoamento, podendo ocorrer a inversão a partir de uma determinada cota. Para comprovar a possibilidade de simulação precisa dos experimentos foi ainda desenvolvido um modelo numérico das equações de conservação, utilizando o programa “Engineering Equation Solver” (EES). Esse modelo foi utilizado para reproduzir os experimentos de circulação natural pelo circuito externo. / This work presents experimental results of a circuit when operating in natural circulation. These results allow to analyze the behavior of an emergency core cooling system when a bypass line that connects the hot source with the cold source is opened. This work also reports the hydraulic characterization of the experimental loop, given geometric and hydraulic data including experimental friction factors specific to this circuit. It was observed that, to a fixed thermal power, when the bypass line is opened, the heater outlet temperature increases. This temperature increase is due to the decrease in the flow rate through the heater. The heat exchanger's flow rate is subjected to a small increase. This flow rate is the sum of the bypass line and heater mass flow rates. This work also shows that the vertical position of the connection of the bypass line in the hot-leg determines the flow direction in the bypass line. If the bypass line connection is in the lowest position, the flow is from the cold to the hot-leg. If the bypass connection is in the highest position, the flow is from the hot to the cold-leg. A numerical model used to evaluate friction factors and heat transfer coefficients influence was developed. It was used to confirm the possibility of precise experiments simulation. The conservation equations are solved using “Engineering Equation Solver” (EES), a thermal hydraulics analysis tool. The model was adjusted with natural circulation experimental data and was tested with results of natural circulation without bypass lines.

The thesis presents a comprehensive overview of the context and significance of ventilation cooling techniques and their feasibility in the United States. Passive cooling is one of the more architecturally interesting ways by which architects could make buildings energy efficient. There is great interest in passive systems since they can lead to a huge reduction of energy costs and support more sustainable building solutions. A number of ventilation system options are available to fill the need for a lower cost alternative to active [conventional] systems. It is the non-residential sector where energy consumption is of most concern and integrating passive natural ventilation in new non-residential buildings is receiving a lot of attention internationally and the U.S. building industry. Interest in improving air quality by passive ventilation is also increasing. / Department of Architecture

Passive ventilation and cooling systems can offer energy savings when combined into a mechanical ventilation and cooling strategy for office buildings. At early design stages, it is difficult to predict actual energy savings as current design and calculation tools are limited and do not allow assessment for energy reductions when attempting to use typical passive options such as solar chimneys, rain screen facades, ventilated double facades, passive downdraught evaporative cooling and earth ducts. The only passive systems that are directly incumbent to dynamic thermal modelling software are natural ventilation and external solar shading. Currently, impacts of passive systems on annual building energy performance is unclear and lacks clarity. In hot climates, this is even more problematic as buildings need to endure higher external temperatures and solar irradiation. Understanding minimal energy performance reductions for each passive system can aid with design decisions regarding building ventilation and cooling strategies. The aim of this study is to investigate how existing passive ventilation and cooling system design and operational strategies can be improved to reduce mechanical ventilation and cooling energy consumption for commercial buildings in hot climates. Theoretical commercial building models are created using dynamic thermal simulation software to determine minimum mechanical ventilation and cooling energy values, which are verified against published bench marks, known as base case models. These base case models are simulated using weather data from four different hot climates (Egypt, Portugal, Kenya and Abu Dhabi). Impacts of passive system energy performance are afforded by using either dynamic thermal simulation or fundamental steady state analysis identifying approximate passive ventilation and cooling potentials for reducing mechanical energy. These percentage reductions are created based upon passive system parameters and weather data, using appropriate methodology. From these findings new simplified design guidelines, integration strategies and performance design tools are created including a new passive system energy assessment tool (PSEAT) using Microsoft Excel platform to ensure that a wider audience can be achieved in industry. The design guidance and integration strategies are developed and simplified to enable architects, building services engineers and alike, to apply with speed and accuracy influencing the design process and improve confidence in desired passive solution.

M. Arch.

The transwall system, proposed and developed by Fuchs and McClelland, fulfills the function of a passive solar heating device as well as an architectural element the window. The significance of the transwall system, in the author's opinion, lies in its expression of technologies in an architectural way. Several directions for further development are suggested to modify the transwall system into a multifunction architectural element so as to maximize utility. These architectural uses are: (1) an adjustable thermal mass; (2) a passive cooling device; (3) an interior design element; (4) a component of a convertible greenhouse and living space; and (5) a shading device. / M. Arch.

Mobile homes, like other forms of factory-built housing are ideally adapted to the use of solar energy because of the materials and construction methods used in their manufacturing process. This thesis is written to examine those characteristics of mobile homes which can best be taken into consideration in the attempt to maximize solar efficiency and reduce energy waste. Design factors which effect the adaptation of solar energy to a typical MH unit include: solar access, types of of solar utilization, energy storage, lot orientation, general climatic relationships and MH park design. The paper will conclude with a case study involving the use of these factors in the design process of a MH project in Blacksburg, Virginia. / M.A.

Six houses heated by passive solar energy were monitored during the 1983 - 1984 heating season to determine auxiliary heating fuel used. Predictions were made using the Solar Load Ratio (SLR) method for the expected use of auxiliary heating fuel. Comparisons were then made between actual performance and predicted performance. The SLR method is used for predictions because it is a widely used tool in the design of passive solar houses, and questions have been raised as to its usefulness as a predictor of auxiliary heating fuel consumption. Variables used in the SLR predictions and methodology for monitoring actual energy consumed are examined to explain differences in the predicted and monitored energy used. / Master of Architecture

The nighttime losses from an integral collector storage (ICS) system were investigated. The significance of the sky temperature, wind speed, and ambient temperature on the losses were examined. Outdoor data was taken on several nights to characterize the thermal performance of an ICS system under various environmental conditions. Indoor tests were then performed under an artificial "nighttime sky" environment, with a simulated wind, in an attempt to duplicate the heat losses which occurred outdoors. The standard rating procedure which specifies the conditions for the heat loss tests for ICS systems was analyzed to see how well it characterizes the collector performance at night. Experimental results indicate a synergistic effect between the sky temperature and wind speed. The effects of wind on the losses from the ICS system overshadow the effects of small changes in sky temperature, but larger changes of sky temperature, with a constant wind speed, have a pronounced effect. It is recommended that both of these parameters be taken into account in heat loss tests in standard rating procedures. Indoor tests can duplicate outdoor heat loss results within 8 per cent. The minimum requirement for SRCC rating tests should be to monitor, record, and report the sky temperature. / M.S.

This study presents a comparison of field measurements of energy delivered by five integral collector storage (ICS) passive solar water heater systems installed at various geographic locations in Virginia to predicted values calculated using Annual Performance Methodology (APM). APM is a prediction method developed by Alan Zollner that offers quick and easy comparisons of design option for ICS systems. Several different methods exist today that are meant to predict the performance of this type of system and that might be used as a design tool to help a designer make appropriate design decisions. Some of these methods are quite complicated and do not lend themselves to quick and easy comparisons of various design options. This study measured the amount of energy delivered by five ICS systems over a six month period. The amount of water drawn out of these systems daily was also recorded. This data was compared to predicted values calculated using APM to determine if APM could predict the performance of these systems within plus or minus 15 percent of the measured values. This study demonstrates that APM was able to predict long term performance of ICS systems within plus or minus 15 percent eighty percent of the time. Short term performance however demonstrated variation that in some cases were quite large and could not be considered reliable predictions. / M. Arch.

Passive safety systems are increasingly being utilized in prospective nuclear power plant designs. Indeed, the use of safety systems driven by natural phenomena might be seen as an unmitigated virtue. However, the low magnitude of the forces involved in such systems, combined with the uncertainty inherent in the factors which affect them, pose a problem in the assessment of their reliability when compared to their active counterparts. Hence, the purpose of this thesis is to investigate and apply a state-of-the-art technique in passive reliability assessment, known as the Reliability Methods of Passive Systems (RMPS) methodology, to the isolation condenser system (ICS) of the prospective BWRX-300 small modular reactor (SMR) design. The ICS is a safety system driven by natural circulation which provides emergency core cooling, residual heat removal, and pressure control for the BWRX-300. Using RMPS to analyze the effect that uncertainties in thermal characteristics of the fuel have on ICS operation, the reliability of natural circulation was quantified with a confidence of 99%. This yielded an immeasurably small failure probability. Considering residual uncertainty, an engineering judgment assigned a failure probability of 1.00E-07. This finding was integrated into a Level 1 probabilistic safety assessment, involving analysis of initiating events, event tree analysis, and failure mode and effect analysis (FMEA) of safety systems, including natural circulation. Analysis of sequences leading to core damage resulted in a core damage frequency of 1.23E-07 yr-1. / Passiva säkerhetssystem används i allt större utsträckning i innovativa kärnkraftverkskonstruktioner. Faktum är att användningen av säkerhetssystem som drivs av naturfenomen kan ses som en oförminskad dygd. Den låga storleken på de krafter som är involverade i sådana system, i kombination med den osäkerhet som är inneboende i de faktorer som påverkar dem, utgör ett problem vid bedömningen av deras tillförlitlighet jämfört med deras aktiva motsvarigheter. Därför är syftet med denna avhandling att undersöka och tillämpa en toppmodern teknik inom passiv tillförlitlighetsbedömning, känd som Reliability Methods of Passive Systems (RMPS) metodologi, på isolationskondensorsystemet (ICS) hos den potentiella BWRX-300 liten modulär reaktor (SMR) design. ICS är ett säkerhetssystem som drivs av naturlig cirkulation som ger nödkylning av kärnan, avlägsnande av restvärme och tryckkontroll för BWRX-300. Med hjälp av RMPS kvantifierades den naturliga cirkulationens tillförlitlighet med en konfidens på 99 %, vilket gav en omätligt liten sannolikhet för misslyckande. Med hänsyn till kvarvarande osäkerhet tilldelade en teknisk dom en felsannolikhet på 1.00E-07. Detta fynd integrerades i en nivå 1 probabilistisk säkerhetsbedömning, som involverade analys av initierande händelser, händelseträdsanalys och felläges- och effektanalys (FMEA) av säkerhetssystem, inklusive naturlig cirkulation. Analys av sekvenser som leder till härdskada resulterade i en härdskadafrekvens på 1,23E-07 år-1.