arXiv subjects

Harry Boyer

Publications and source records attributed to Harry Boyer.

32 records · Page 2Linked to original sources

arXiv2012

A multimodel approach to building thermal simulation for design and research purposes

The designers pre-occupation to reduce energy consumption and to achieve better thermal ambience levels, has favoured the setting up of numerous building thermal dynamic simulation programs. The progress in the modelling of phenomenas and its transfer into the professional field has resulted in various numerical approaches ranging from softwares dedicated to architects for design use to tools for laboratory use by the expert thermal researcher. This analysis shows that each approach tends to fulfil the specific needs of a certain kind of manipulator only, in the building conception process. Our objective is notably different as it is a tool which can be used from the very initial stage of a construction project, to the energy audit for the existing building. In each of these cases, the objective results, the precision advocated and the time delay of the results are different parameters which call for a multiple model approach of the building system

cs.CE↗

arXiv2012

Use of BESTEST procedure to improve a building thermal simulation program

Validation of building energy simulation programs is of major interest to both users and modellers. To achieve such a task, it is essential to apply a methodology based on a priori test and empirical validation. A priori test consists in verifying that models embedded in a program and their implementation are correct. this should be achieved before carrying out experiments. The aim of this report is to present results from the application of the BESTEST procedure to our code. We will emphasise the way it allows to find bugs in our program and also how it permits to qualify models of heat transfer by conduction

cs.CE↗

arXiv2012

A Picard Newton method to solve non linear airflow networks

In detailled buiding simulation models, airflow modelling and solving are still open and crucial problems, specially in the case of open buildings as encountered in tropical climates. As a consequence, wind speed conditioning indoor thermal comfort or energy needs in case of air conditionning are uneasy to predict. A first part of the problem is the lack of reliable and usable large opening elementary modelling and another one concerns the numerical solving of airflow network. This non linear pressure system is solved by numerous methods mainly based on Newton Raphson (NR) method. This paper is adressing this part of the difficulty, in our software CODYRUN. After model checks, we propose to use Picard method (known also as fixed point) to initialise zone pressures. A linear system (extracted from the non linear set of equations) is solved around 10 times at each time step and NR uses this result for initial values. Known to be uniformly but slowly convergent, this method appears to be really powerful for the building pressure system. The comparison of the methods in terms of number of iterations is illustrated using a real test case experiment.

cs.CE↗

arXiv2012

CODYRUN, outil de simulation et d'aide à la conception thermo-aéraulique de bâtiments

This article presents the CODYRUN software developped by University of La Réunion. It is a multizone thermal software, with detailled airflow and humidity transfer calculations. One of its specific aspects is that it constitutes a research tool, a design tool used by the lab and professionnals and also a teaching tool. After a presentation of the multiple model aspect, some details of the tree modules associated to physical phenomenons are given. Elements of validation are exposed in next paraghaph, and then a few details of the front end.

cs.CE↗

arXiv2012

Heat transfer in buildings : application to air solar heating and Trombe wall design

The aim of this paper is to briefly recall heat transfer modes and explain their integration within a software dedicated to building simulation (CODYRUN). Detailed elements of the validation of this software are presented and two applications are finally discussed. One concerns the modeling of a flat plate air collector and the second focuses on the modeling of Trombe solar walls. In each case, detailed modeling of heat transfer allows precise understanding of thermal and energetic behavior of the studied structures. Recent decades have seen a proliferation of tools for building thermal simulation. These applications cover a wide spectrum from very simplified steady state models to dynamic simulation ones, including computational fluid dynamics modules (Clarke, 2001). These tools are widely available in design offices and engineering firms. They are often used for the design of HVAC systems and still subject to detailed research, particularly with respect to the integration of new fields (specific insulation materials, lighting, pollutants transport, etc.). Available from: http://www.intechopen.com/books/evaporation-condensation-and-heat-transfer/heat-transfer-in-buildings-application-to-solar-air-collector-and-trombe-wall-design

cs.CE↗

arXiv2012

Evaluation of the thermal resistance of a roof-mounted multi-reflective radiant barrier for tropical and humid conditions: Experimental study from field measurements

This paper deals with the experimental evaluation of a roof-mounted multi-reflective radiant barrier (MRRB), installed according to the state of the art, on a dedicated test cell. An existing experimental device was completed with a specific system for the regulation of the airflow rate in the upper air layer included in a typical roof from Reunion Island. Several experimental sequences were conducted to determine the thermal resistance of the roof according to several parameters and following a specific method. The mean method, well known in international standards (ISO 9869 - 1994) for the determination of the thermal resistance using dynamic data, was used. The method was implemented in a building simulation code in order to allow the determination of the thermal indicator automatically. Experimental results are proposed according to different seasonal periods and for different values of the airflow rate in the upper air layer.

physics.gen-ph↗

arXiv2012

Parametric sensitivity analysis of a test cell thermal model using spectral analysis

The paper deals with an empirical validation of a building thermal model. We put the emphasis on sensitivity analysis and on research of inputs/residual correlation to improve our model. In this article, we apply a sensitivity analysis technique in the frequency domain to point out the more important parameters of the model. Then, we compare measured and predicted data of indoor dry-air temperature. When the model is not accurate enough, recourse to time-frequency analysis is of great help to identify the inputs responsible for the major part of error. In our approach, two samples of experimental data are required. The first one is used to calibrate our model the second one to really validate the optimized model.

physics.data-an↗

arXiv2012

Energy, cost, and CO 2 emission comparison between radiant wall panel systems and radiator systems

The main goal of this paper is to evaluate the possibility of application or replacement of radiators with low-temperature radiant panels. This paper shows the comparison results of operations of 4 space heating systems: the low-temperature radiant panel system without any additional thermal insulation of external walls (PH-WOI), the low-temperature radiant panel system with additional thermal insulation of external walls (PH-WI), the radiator system without any additional thermal insulation of external walls (the classical heating system) (RH-WOI), and the radiator system with additional thermal insulation of external walls (RH-WI). The operation of each system is simulated by software EnergyPlus. The investigation shows that the PH-WI gives the best results. The RH-WOI has the largest energy consumption, and the largest pollutant emission. However, the PH-WI requires the highest investment.

physics.gen-ph↗

arXiv2012

A genetic algorithm applied to the validation of building thermal models

This paper presents the coupling of a building thermal simulation code with genetic algorithms (GAs). GAs are randomized search algorithms that are based on the mechanisms of natural selection and genetics. We show that this coupling allows the location of defective sub-models of a building thermal model i.e. parts of model that are responsible for the disagreements between measurements and model predictions. The method first of all is checked and validated on the basis of a numerical model of a building taken as reference. It is then applied to a real building case. The results show that the method could constitute an efficient tool when checking the model validity.

cs.NE↗

arXiv2012

Hybrid modelling of a sugar boiling process

The first and maybe the most important step in designing a model-based predictive controller is to develop a model that is as accurate as possible and that is valid under a wide range of operating conditions. The sugar boiling process is a strongly nonlinear and nonstationary process. The main process nonlinearities are represented by the crystal growth rate. This paper addresses the development of the crystal growth rate model according to two approaches. The first approach is classical and consists of determining the parameters of the empirical expressions of the growth rate through the use of a nonlinear programming optimization technique. The second is a novel modeling strategy that combines an artificial neural network (ANN) as an approximator of the growth rate with prior knowledge represented by the mass balance of sucrose crystals. The first results show that the first type of model performs local fitting while the second offers a greater flexibility. The two models were developed with industrial data collected from a 60 m3 batch evaporative crystallizer.

physics.chem-ph↗

arXiv2012

Development of a new model to predict indoor daylighting: Integration in CODYRUN software and validation

Many models exist in the scientific literature for determining indoor daylighting values. They are classified in three categories: numerical, simplified and empirical models. Nevertheless, each of these categories of models are not convenient for every application. Indeed, the numerical model requires high calculation time; conditions of use of the simplified models are limited, and experimental models need not only important financial resources but also a perfect control of experimental devices (e.g. scale model), as well as climatic characteristics of the location (e.g. in situ experiment). In this article, a new model based on a combination of multiple simplified models is established. The objective is to improve this category of model. The originality of our paper relies on the coupling of several simplified models of indoor daylighting calculations. The accuracy of the simulation code, introduced into CODYRUN software to simulate correctly indoor illuminance, is then verified. Besides, the software consists of a numerical building simulation code, developed in the Physics and Mathematical Engineering Laboratory for Energy and Environment (P.I.M.E.N.T) at the University of Reunion. Initially dedicated to the thermal, airflow and hydrous phenomena in the buildings, the software has been completed for the calculation of indoor daylighting. New models and algorithms - which rely on a semi-detailed approach - will be presented in this paper. In order to validate the accuracy of the integrated models, many test cases have been considered as analytical, inter-software comparisons and experimental comparisons. In order to prove the accuracy of the new model - which can properly simulate the illuminance - a confrontation between the results obtained from the software (developed in this research paper) and the major made at a given place is described in details. A new statistical indicator to appreciate the margins of errors - named RSD (Reliability of Software Degrees) - is also be defined.

cs.CE↗

arXiv2012

A numerical approach to evaluating what percentage of a living space is well-ventilated, for the assessment of thermal comfort

A bioclimatic approach to designing comfortable buildings in hot and humid tropical regions requires, firstly, some preliminary, important work on the building envelope to limit the energy contributions, and secondly, an airflow optimization of the building. For the first step, tools such as nodal or zonal models have been largely implemented. For the second step, the assessment of air velocities, in three dimensions and in a large space, can only be performed through the use of detailed models such as with CFD. This paper deals with the improvement of thermal comfort by ventilating around the occupants. For this purpose, the average velocity coefficient definition is modified to be adapted to CFD and the areas involving movement or the living spaces. We propose a new approach based on the derivation of a new quantity: the well-ventilated percentage of a living space. The well-ventilated percentage of a space allows a time analysis of the aeraulic behaviour of the building in its environment. These percentages can be over a period such as one day, a season or a year. These kinds of results are helpful for an architect to configure the rooms of a house according to their uses, the environment, the architectural choices and the constraints related to the design of bioclimatic buildings.

physics.gen-ph↗

arXiv2012

A Comparison between CODYRUN and TRNSYS, simulation models for thermal buildings behaviour

Simulation codes of thermal behaviour could significantly improve housing construction design. Among the existing software, CODYRUN and TRNSYS are calculations codes of different conceptions. CODYRUN is exclusively dedicated to housing thermal behaviour, whereas TRNSYS is more generally used on any thermal system. The purpose of this article is to compare these two instruments in two different conditions . We will first modelize a mono-zone test cell, and analyse the results by means of signal treatment methods. Then, we will modelize a real case of multi-zone housing, representative of housing in wet tropical climates. We could so evaluate influences of meteorological and building description data on model errors.

cs.CE↗

arXiv2012

Natural ventilation - A new method based on the Walton model applied to cross-ventilated buildings having two large external openings

In order to provide comfort in a low energy consumption building, it is preferable to use natural ventilation rather than HVAC systems. To achieve this, engineers need tools that predict the heat and mass transfers between the building's interior and exterior. This article presents a method implemented in some building software, and the results are compared to CFD. The results show that the knowledge model is not sufficiently well-described to identify all the physical phenomena and the relationships between them. A model is developed which introduces a new building-dependent coefficient allowing the use of Walton's model, as extended by Roldan to large external openings, and which better represents the turbulent phenomena near large external openings. The formulation of the mass flow rates is inversed to identify modeling problems. It appears that the discharge coefficient is not the only or best parameter to obtain an indoor static pressure compatible with CFD results, or to calculate more realistic mass flow rates.

physics.flu-dyn↗