QC 20110616

Since the ancient years, human beings were using holes and caves to protect themselves from weather conditions making it the first known form of exploiting ground’s heat, known as Geothermal Energy. Nowadays, geothermal energy is mainly used for electricity production, space heating and cooling, Ground Coupled Heat Pump (GCHP) applications, and many other purposes depending on the morphology of the ground and its temperature. This study presents results of investigations into the evaluation of the thermal properties of the ground in Cyprus. The main objectives were i) to determine the thermal characteristics of the ground in Cyprus, ii) investigate how they affect the sizing and positioning of Ground Heat Exchangers (GHE) and iii) present the results for various ground depths, including a temperature map of the island, as a guide for engineers and specifiers of GCHPs. It was concluded that there is a potential for the efficient exploitation of the thermal properties of the ground in Cyprus for geothermal applications leading to significant savings in power and money as well. Six new boreholes were drilled and two existing ones were used for the investigation and determination of i) the temperature of the ground at various depths, ii) its thermal conductivity, iii) its specific heat and iv) its density. The thermal conductivity was determined by carrying out experiments using the line source method and was found to vary in the range between 1.35 and 2.1 W/mK. It was also observed that the thermal conductivity is strongly affected by the degree of saturation of the ground. The temperature of the undisturbed ground in the 8 borehole locations was recorded monthly for a period of 1 year. The investigations showed that the surface zone reaches a depth of 0.25 m and the shallow zone 7 to 8 m. The undisturbed ground temperature in the deep zone was measured to be in the range of 18.3 °C to 23.6 °C and is strongly dependent on the soil type. Since the ground temperature is a vital parameter in ground thermal applications, the temperature of the ground in locations that no information is available was predicted using Artificial Neural Networks and the temperature map of the island at depths of 20 m, 50 m and 100 m was generated. Data obtained at the location of each borehole were used for the training of the network. Data for the sizing of GHEs based on the ground properties of Cyprus were presented in an easily accessible form so that they can be used as a guide for preliminary system sizing calculations. With the aid of Computational Fluid Dynamics (CFD) software the capacity of the GHEs in each location and the optimum distance between them was estimated. Additionally, the long term temperature variation of the ground was investigated. For the first time since a limited study in the 1970’s, a research focusing on the determination and presentation of the thermal properties of the ground in Cyprus has been carried out. Additionally, the use of Artificial Neural Networks (ANNs) is an innovative approach for the prediction of data at locations where no information is available. The publication of this information not only contributes to knowledge locally but also internationally as it enables comparison with other countries with similar climatic conditions to be carried out.

This thesis analyzes the implementation of surface bonded piezoelectric actuators to control or minimize the deformation in elastic or viscoelastic cantilever beams due to simultaneous heat and moisture diffusion. The problem is addressed in the context of linearized elasticity and linearized viscoelasticity. The constitutive equations are derived from the balance laws for mass, linear and angular momenta, energy, entropy and the second law of thermodynamics. The constitutive equations for linearized elasticity are then obtained as a consequence of small deformation assumption. The temperature and moisture induced deformation is introduced through the coefficient of thermal expansion CTE and coefficient of moisture expansion CME. The constitutive equations for linearized viscoelasticity are obtained by correspondence principle. The coupled temperature and moisture diffusion equations are obtained as a consequence of Clausius-Duhem inequality. The extent of coupling between heat conduction and moisture diffusion phenomena is studied by varying the ratio of their diffusivities and a non-dimensional coupling parameter. The effect of coupled unsteady heat conduction and moisture diffusion phenomena on the short and long term response characteristics of the beam such as displacement, stress and strain fields is studied. Based on these response characteristics, the magnitude of external actuating voltage required to minimize deformation is predicted. This is followed by a comparative study of the field variables in cases of actuated and unactuated beams. Four materials are chosen for this study; aluminium, epoxy, carbon fiber reinforced polymer with fiber volume fraction of 60 percent, and an epoxy-like viscoelastic material. The viscoelastic material is assumed to be thermorheologically simple. The shift factor is assumed to be a linear function of temperature and moisture fields. To address this problem numerically, a finite difference formulation is presented for the field equations and boundary conditions. This numerical scheme is validated by solving the problem of uniformly loaded cantilever beam and comparing the results with the analytical solution known a priori. The results obtained numerically are validated by comparison with experimental results. It is observed that the under the effect of external actuation, the stress and displacement fields are largely minimized in all four cases chosen for study. The bending in the unactuated viscoelastic beam is more pronounced than bending in the unactuated elastic beam. This is due to the softening of the material with time due to evolving temperature and moisture fields. However, relatively lesser external actuating voltage is necessary to minimize bending in the former case compared to the latter. The magnitude of actuating electric field required in the piezoelectric layer suggests a need to address the problem with in a non-linear framework, no such attempt is made in this study.

Research is performed to assess the potential of surface moisture evaporative cooling from composite plates as a means of reducing the external temperature of military aircraft. To assess the feasibility of evaporative cooling for this application, a simplified theoretical model of the phenomenon is formulated. The model consists of a flat composite plate at an initial uniform temperature, T0. The plate also possesses an initial moisture (molecular water) content, M0. The plate is oriented vertically and at t=0 s, one surface is exposed to a free stream of air at an elevated temperature. The other surface is exposed to stagnant air at the same temperature as the plate’s initial temperature. The equations associated with energy and mass transport for the model are developed from the conservation laws per the continuum mechanics hypothesis. Constitutive equations and assumptions are introduced to express the two nonlinear partial differential equations in terms of the temperature, T, and the partial density of molecular water, ρw. These equations are approximated using a weak form Galerkin finite element formulation and the α–family of time approximation. An algorithm and accompanying computer program written in the Matlab programming language are presented for solving the nonlinear algebraic equations at successive time steps. The Matlab program is used to generate results for plates possessing a variety of initial moisture concentrations, M0, and diffusion coefficients, D. Surface temperature profiles, over time, of moisture bearing specimens are compared with the temperature profiles of dry composite plates. It is evident from the results that M0 and D affect the surface temperature of a moist plate. Surface temperature profiles are shown to decrease with increasing M0 and/or D. In particular, dry and moist specimens are shown to differ in final temperatures by as much as 30°C over a 900 s interval when M0 = 30% and D is on the order of 10–8m2/s (T0 = 25°C, h = 60 W/m2°C, T∞ = 90°C).

abstract: Due to the lack of understanding of soil thermal behavior, rules-of-thumb and generalized procedures are typically used to guide building professionals in the design of ground coupled heat pump systems. This is especially true when sizing the ground heat exchanger (GHE) loop. Unfortunately, these generalized procedures often encourage building engineers to adopt a conservative design approach resulting in the gross over-sizing of the GHE, thus drastically increasing their installation cost. This conservative design approach is particularly prevalent for buildings located in hot and arid climates, where the soils are often granular and where the water table tends to exist deep below the soil surface. These adverse soil conditions reduce the heat dissipation efficiency of the GHE and have hindered the adoption of ground coupled heat pump systems in such climates. During cooling mode operation, heat is extracted from the building and rejected into the ground via the GHE. Prolonged heat dissipation into the ground can result in a coupled flow of both heat and moisture, causing the moisture to migrate away from the GHE piping. This coupled flow phenomenon causes the soil near the GHE to dry out and results in the degradation of the GHE heat dissipation capacity. Although relatively simple techniques of backfilling the GHE have been used in practice to mitigate such coupled effects, methods of improving the thermal behavior of the backfill region around the GHE, especially in horizontal systems, have not been extensively studied. This thesis presents an experimental study of heat dissipation from a horizontal GHE, buried in two backfill materials: (1) dry sand, and (2) wax-sand composite mixture. The HYDRUS software was then used to numerically model the temperature profiles associated with the aforementioned backfill conditions, and the influence of the contact resistance at the GHE-backfill interface was studied. The modeling strategy developed in HYDRUS was proven to be adequate in predicting the thermal performance of GHE buried in dry sand. However, when predicting the GHE heat dissipation in the wax-sand backfill, significant discrepancies between model prediction and experimental results still exist even after calibrating the model by including a term for the contact resistance. Overall, the thermal properties of the backfill were determined to be a key determinant of the GHE heat dissipation capacity. In particular, the wax-sand backfill was estimated to dissipate 50-60% more heat than dry sand backfill. / Dissertation/Thesis / M.S. Design 2012

Cette thèse aborde la question de la modélisation des transferts thermiques dans les milieux poreux soumis à de hautes températures. Un modèle macroscopique hors équilibre thermique local entre phases est obtenu par changement d’échelle. Cette procédure tient compte à l’échelle locale du couplage entre rayonnement et autres modes de transfert. Le modèle de rayonnement repose sur l’équation de transfert radiatif généralisée (GRTE) et, à la limite courante d’un milieu macroscopiquement optiquement épais, sur la loi de Fourier radiative. L’originalité de cette procédure réside dans l’application de la méthode de prise de moyenne volumique (VAM) aux équations de bilan local, dans lesquelles les transferts radiatifs sont inclus. Cette homogénéisation couplée soulève trois difficultés : - les différents transferts sont de natures différentes. Le système matériel (site de transferts conductifs et convectifs) coexiste avec le champ des photons qui est homogénéisé par une méthode statistique reposant sur la caractérisation des propriétés radiatives au moyen de fonctions de distribution continûment définies sur le volume du milieu poreux. - les échelles de longueur mises en jeu dans la procédure de changement d’échelle doivent être compatibles entre elles. On établit que la séparation des échelles, requise par la prise de moyenne volumique, est compatible avec l’échelle de longueur caractéristique de l’homogénéisation statistique radiative, seulement limitée par la résolution d’une tomographie du milieu. - le phénomène d’émission dépend de la température de la matière. Cette température spécifique au calcul radiatif est obtenue en appliquant un opérateur de prise de moyenne à la température de la matière sur une échelle locale représentative. En pratique, c’est la résolution de cette prise de moyenne qui définit l’échelle des couplages locaux avec la méthode VAM. Le modèle macroscopique résultant est appliqué à la résolution d’un problème unidimensionnel et stationnaire. Dans ce cas simple, le rôle du couplage avec le rayonnement à l’échelle locale est mis en évidence. / This thesis deals with the modeling of heat transfer in porous media subjected to high temperature. An upscaling procedure yields a macroscopic model based on local thermal non-equilibrium. This procedure accounts for local scale coupling effects between radiation and other transfer modes. Radiation modeling uses the generalized radiation transfer equation (GRTE) and, at the commonly encountered limit of a macroscopically optically thick medium, the radiative Fourier law. An original feature of this procedure is the application of the volume averaging method (VAM) to local conservation equations in which radiation transfer is included. This raises three major challenges: - the physical natures of the various transfer modes involved are different. The material system (in which conduction and convection occur) coexists alongside with the photon field, which is homogenized using a statistical method based on the characterization of the radiative properties through statistical distribution functions, continuously defined over the whole volume of the porous medium. - the length scales involved in the upscaling procedure must be compatible with each other. The compatibility of the scale separation constraint (required by the VAM) with the length scale of the radiative homogenization technique (which is limited by the resolution of a tomography of the medium) is established. - the emission phenomenon depends on the temperature of matter. This temperature, specific to the radiation calculation, is obtained by applying a dedicated averaging operator. This operator is associated with an averaging volume whose length scale has to be representative at the local scale. In practice, the resolution of this averaging procedure defines the scale of the coupling between the VAM and the radiation model. The resulting macroscopic model is applied to a one-dimensional, steady case. The solving of this simple case shows the influence of local coupling effects.

The aim of this work was to investigate the effect on horizontal ground heat exchanger performance of changing soil and load parameters, and pipe horizontal separation distance for ground-coupled heat pumps under Egyptian conditions.Egypt possesses a variety of energy resources; namely fossil and renewable. The amount of renewable energy available is significant and must be utilized perfectly for the sake of achieving sustainable use of energy resources. Soils in Egypt vary widely from being clay with its thermal conductivity of 1.11 (for clay particles) to sand with its thermal conductivity of 5.77 (for sand particles). Two soil samples were chosen from the literature to be used in the investigation held in this work with boundary conditions that match the weather and ground temperature distribution conditions in Egypt.Conduction heat transfer in soils is a very complicated process especially when it is combined with time dependant boundary conditions and temperature dependent thermophysical properties of the medium. A MATLAB code was used to estimate thermophysical properties of the soil samples with three different moisture contents (0, 0.2, and saturation %) and the upper boundary condition bases on two surface dryness conditions (dry and wet). The results of the code were fed to Abqaus/CAE to analysis and predict the temperature distribution in these soils with implementing the time dependant boundary conditions to investigate the ground thermal behaviour of these soils. Also the temperature distribution around two pipes per trench of horizontal ground heat exchanger with applying synthetic load based on estimated cooling and heating degree days for one set of weather conditions. The horizontal separation distance between pipes was investigated by changing it to be 0.2, 0.3, 0.4, and 0.5 metres.Both the MATLAB code and Abaqus environment were validated against measured data published in the literature and their results agreed well with this data.The results of the simulation showed that the ground thermal behaviour depends mainly on the boundary conditions applied on the model. Dry soils are the worst being affected by the variation of the boundaries, because of its low volumetric heat capacities. The moisture content in the soil should be kept around 0.2 or above to get the most benefits from the presence of moisture in the vicinity of ground heat exchangers. The effect of the soil surface dryness is less significant than that of the moisture content of the entire system but it is more controllable than the moisture content. Also it was found that the horizontal separation distance (HSD) between pipes must be selected on the bases of prior knowledge of the site parameters soil type and moisture level. The results showed that the 0.4m HSD is the optimum HSD for the conditions and load profile included in this study.

Les matériaux hygroscopiques, et tout particulièrement le bois et ses dérivés possèdent des propriétés complexes rendant difficile la modélisation des transferts couplés de chaleur et de masse dans les parois incluant ces matériaux. De ce fait, très peu d'outils numériques sont aujourd'hui capables de prédire correctement la performance hygrothermique de l'habitat bois. L'objectif de ce travail est de caractériser expérimentalement les transferts chaleur-masse dans les parois des constructions bois afin de valider un outil numérique destiné à simuler le comportement hygrothermique des parois comportant des matériaux hygroscopiques. Dans un premier temps, les notions théoriques et les études antérieures sur les transferts couplés chaleur - masse sont présentés. Ensuite, nous donnons un descriptif détaillé du dispositif expérimental conçu pour caractériser les transferts couplés chaleur-masse dans les parois. Les expériences de caractérisation des performances hygrothermiques des parois fournies par les industriels partenaires du projet TRANSBATIBOIS dans lequel s'inscrit cette thèse sont également abordées. Nous détaillons par la suite les expériences réalisées ainsi que la phase de confrontation des résultats expérimentaux avec les résultats prédits par le code numérique BuildingPore et l'outil commercial WUFI. La troisième partie de ce travail est consacrée aux expérimentations à l'échelle de l'enveloppe. Nous y présentons une analyse de la performance hygrothermique et des consommations énergétiques des constructions bois à travers le suivi de modules-test exposés au climat extérieur. La dernière partie du travail est consacrée aux dispositifs de suivi de bâtiments. / Coupled heat and moisture transfer through hygroscopic materials, particularly wood and wood-based products are difficult to model. This is partly due to some specific and complex properties of these materials that are often not included in numerical models. Currently, only a few numerical models are able to predict accurately the hygrothermal performance of wooden building envelope. The aim of this work is to assess the heat and moisture transfer in wooden building envelope through experiments and validate the prediction capacity of a numerical model developed to simulate hygrothermal behavior of envelope including wooden materials. After giving a theoretical reminder of the coupled heat and moisture transfer through building envelope and reporting the results of previous studies in this field, we will give details of the experimental investigation on heat and moisture transfer through timber walls. Firstly, the experimental apparatus used for the wall tests is presented. Then, we will analysis the hygrothermal performance of wooden walls provided by the partners of the TRANSBATIBOIS project in which this work was achieved. Experimental works achieved for Buildingpore model validation and results of the comparisons between experimental assessment and numerical predictions with Buildingpore and WUFI are also reported. The third part of this study deals with the experimental assessment of wooden building envelopes exposed to climatic conditions. An analysis of the hygrothermal performance and the energy consumption of wooden test-cells is performed and reported in this part. The latest part concerns experimental works on buildings.

L’objectif général de la thèse est de progresser dans la compréhension du comportement multi-physique des bâtiments en bois et d’améliorer l’évaluation de leur performance énergétique associée au confort hygrothermique. Les professionnels du secteur, ainsi que des études scientifiques, montrent des écarts entre les calculs et les mesures de performance (consommations, confort) de ces bâtiments. Les raisons de ces écarts ne sont pas encore bien élucidées : l’impact de l’humidité et de la chaleur latente dans ces constructions sont souvent mis en avant comme explication probable, bien que cela reste encore du domaine de la recherche. Les travaux les plus récents montrent que les fondements se situent probablement au niveau du comportement hygrothermique des matériaux à la base de bois en régime instationnaire. Ce travail de thèse se focalisera principalement sur deux échelles d’études : échelle matériau et échelle bâtiment. L’un des axes de travail de la thèse portera sur la caractérisation expérimentale des propriétés hygroscopiques de matériaux à base de bois et sur leur modélisation. Le second axe de travail portera sur l’intégration à l’échelle bâtiment de ces matériaux : en modélisation, intégrer l’impact des propriétés spécifiques de ces matériaux dans les assemblages constituants les parois, puis dans les bilans complexes à l’échelle du bâtiment. Une étude expérimentale portera sur une pièce de vie avec une forte présence de bois dans l’enveloppe du bâtiment pour caractériser le confort hygrothermique, et quantifier l’apport de l’inertie hygrique de l’enveloppe sur la performance de l’ambiance en termes de confort. Le cas échéant, des mesures seront également réalisées à l’échelle « paroi » d’une part, sur des constructions réelles d’autre part / The general aim of the thesis is to advance the understanding of multi-physical behavior of wooden buildings and improving the assessment of their energy performance with comfort hygrothermal. Sector professionals and scientific studies show the differences between the calculations and performance measures (consumption, comfort) of these buildings. The reasons for these differences are not yet well understood: the impact of moisture and latent heat in these constructions are often put forward as a likely explanation, although this is still research. The most recent studies show that the foundations are likely to fall at the hygrothermal behavior of materials at the base of wooden unsteady. This work will focus primarily on two studies scales: scale and scale building material. One of the lines of work of the thesis will focus on the experimental characterization of hygroscopic properties of wood-based materials and their modeling. The second strand of work will focus on building wide integration of these materials in modeling, integrating the impact of specific properties of these materials in the walls constituent assemblies and in complex balance sheets at the building scale . An experimental study will focus on a living room with a large presence of wood in the building envelope to characterize the hygrothermal comfort, and quantify the contribution of Hygric inertia of the envelope on performance in terms of the atmosphere comfort. If necessary, measures will also be drawn to scale "wall" on one hand, on real structures on the other

An average heat transfer coefficient, h_bar, is often used to solve heat transfer problems. It should be understood that this is an approximation and may provide inaccurate results, especially when the temperature field is of interest. The proper method to solve heat transfer problems is with a conjugate approach. However, there seems to be a lack of clear explanations of conjugate heat transfer in literature. The objective of this work is to provide a clear explanation of conjugate heat transfer and to determine the discrepancy in the temperature field when the interface boundary condition is approximated using h_bar compared to a local, or variable, heat transfer coefficient, h(x). Simple one-dimensional problems are presented and solved analytically using both h(x) and h_bar. Due to the one-dimensional assumption, h(x) appears in the governing equation for which the common methods to solve the differential equations with an average coefficient are no longer valid. Two methods, the integral equation and generalized Bessel methods are presented to handle the variable coefficient. The generalized Bessel method has previously only been used with homogeneous governing equations. This work extends the use of the generalized Bessel method to non-homogeneous problems by developing a relation for the Wronskian of the general solution to the generalized Bessel equation. The solution methods are applied to three problems: an external flow past a flat plate, a conjugate interface between two solids and a conjugate interface between a fluid and a solid. The main parameter that is varied is a combination of the Biot number and a geometric aspect ratio, A_1^2 = Bi*L^2/d_1^2. The Biot number is assumed small since the problems are one-dimensional and thus variation in A_1^2 is mostly due to a change in the aspect ratio. A large A_1^2 represents a long and thin solid whereas a small A_1^2 represents a short and thick solid. It is found that a larger A_1^2 leads to less problem conjugation. This means that use of h_bar has a lesser effect on the temperature field for a long and thin solid. Also, use of ¯ over h(x) tends to generally under predict the solid temperature. In addition is was found that A_2^2, the A^2 value for the second subdomain, tends to have more effect on the shape of the temperature profile of solid 1 and A_1^2 has a greater effect on the magnitude of the difference in temperature profiles between the use of h(x) and h_bar. In general increasing the A^2 values reduced conjugation.