Frédéric Miranville

On the thermal behaviour of roof-mounted radiant barriers under tropical and humid climatic conditions: modelling and empirical validation

This paper deals with the empirical validation of a building thermal model, which includes a roof-mounted radiant barrier. We first present the thermal model, developed with a building simulation code prototype, the objective being to increase understanding of the thermal phenomena that govern the behaviour of the whole building. We then describe the experimental test cell, with emphasis on the details of the roof. A sensitivity analysis technique is applied to the model which shows that convective heat transfer is of great importance for the dry-air temperature of the roof air layer. The origin of the disagreement between measurements and model predictions is then identified as being due to one of the convective heat transfer coefficients. Once this is modified the agreement is found to be acceptable.

Identification of Parameters in Building Concentration Dispersion Model

The aim of this work was to simulate the transport of pollutants in buildings. Focusing mainly on the presence of carbon dioxide, we resolved the airflow equations for two typical validation cases. These numerical results were compared to COMIS and CONTAM software, and they were used to evaluate the evolution of carbon dioxide concentration in different rooms. In order to obtain different parameters and filters of the proposed model, we used a statistical method based on Bayesian inference. This statistical adjustment allowed us to obtain a significant variation of contaminants in different cases. This tool seems to be a good candidate for the fitting of models.

Bringing scientific knowledge from research to the professional fields: the case of the thermal and airflow design of buildings in tropical climates

Abstract The need for construction projects to be sustainable is becoming more widely recognised, partly because of diminishing world energy resources, and partly because recent world developments (for example, global warming and increasing oil prices) have made those involved in construction more aware of a new approach to building. We often hear now of buildings with a high environmental rating, of sustainable development, and of improved comfort. The stated objective is to construct comfortable buildings, which use little energy and produce little pollution. This desire on the part of construction project leaders has led to some problems amongst architects, engineers and university researchers who tend to work in isolation from each other. However, the only way to achieve an overall improvement in building design is by close collaboration between the various participants, from when the first sketch of the future building is made. Of course, this task appears difficult because these participants have different approaches, training and ‘tools of the trade’. This article aims to show that efficient cooperation between the professionals involved is possible. We will see that by producing an instructive working document, understandable by all and based on expert rules, it is possible to produce buildings which are adapted to the climate, and to spread the scientific knowledge to the more practical professions. We will illustrate our ideas by describing the methodology we used for a building project in the tropics. Finally, we will present a summary for the period 1997–2001 and will show the impact that such collaborations have had on the design of buildings in tropical climates.

Bayesian Parameter Estimation of Convective Heat Transfer Coefficients of a Roof-Mounted Radiant Barrier System

This paper deals with the application of Bayesian methods to the estimation of two convective heat-transfer coefficients of a roof-mounted radiant barrier system. As part of an empirical validation of the thermal model of the roofing complex, a parametric sensitivity analysis highlighted the importance of convective coefficients in the thermal behavior of a roofing complex. A parameter estimation method is then used in order to find the values of the coefficients that lead to an improvement of the thermal model. However, instead of using a classical parameter estimation method, we used a Bayesian inference approach to parameter estimation. The aim of the paper is to introduce the basic concepts of this powerful method in this simple two-parameter case. We show that Bayesian methods introduce an explicit treatment of uncertainty in modeling and a corresponding measure of reliability for the conclusions reached. DOI: 10.1115/1.2188957

A Simplified Model for Radiative Transfer in Building Enclosures With Low Emissivity Walls: Development and Application to Radiant Barrier Insulation

This paper deals with a simplified model of radiative heat transfer in building enclosures with low emissivity walls. The approach is based on an existing simplified model, well known and used in building multizone simulation codes, for the long wave exchanges in building enclosures. This method is simply extended to the case of a cavity including a very low emissivity wall, and it is shown that the obtained formalism is similar to the one used in the case of the based model, convenient for enclosures with only black walls (blackbody assumption). The proposed model has been integrated into a building simulation code and is based on simple examples; it is shown that intermediate results between the imprecise initial simple model and the more precise detailed model, the net-radiosity method, can be obtained. Finally, an application of the model is made for an existing experimental test cell including a radiant barrier insulation product, well used in Reunion Island for thermal insulation of roofs. With an efficacy based on the very low emissivity of their surfaces and the consequent decrease in radiative heat transfer through the wall in which they are included, the proposed simplified model leads to results very close to those of the reference method, the net-radiosity method.

Experimental Study of the Thermal Performances of a Composite Roof Including a Reflective Insulation Material Under Tropical Humid Climatic Conditions

Publisher Summary This chapter deals with the evaluation of the outdoor performances of a composite roof that is composed of a corrugated iron rooftop, a radiant barrier, and a ceiling made of wood, each component being separated by an air space. This assembly is mounted on a small-scale test cell, named isotest. An isotest is designed for research purposes. It is installed on an experimental platform, dedicated to the complete study of the outdoor performances of radiant barrier systems. The chapter essentially describes the entire experimental disposal in detail. The results are then presented and followed by an analysis. It is noted that the results so obtained tends to confirm the great potential of radiant barrier systems in tropical humid climatic conditions. It also determines that the performances of such an assembly are closely linked to the ventilation conditions in the air space facing the reflective side of the radiant barrier.

Natural Materials for Thermal Insulation: Mulch and Lava-Rock Characterizations

This paper reports on the thermal characterization, via the thermal conductivity, of natural materials, such as mulch and lava rock and their usefulness as building insulation. Experiments were carried out using a scale one monitored wall (i.e. heat flux and temperature sensors) exposed to a heating source on one side and to an air conditioned space on the other. The wall system was composed of an 8.85 cm thick cavity, where the mulch and lava rock were placed. The cavity was enclosed between two layers of pine wood (40 mm thick each). After the experiments and statistical data manipulation, the estimated thermal conductivity of the materials were 0.48 ± 0.001 W.m-1.K-1 and 0.129 ± 0.003 W.m-1.K-1 for mulch and lava-rock, respectively. That is, mulch has a thermal conductivity comparable to that of bulk hemp while lava rock has a thermal conductivity comparable to that of hemp brick. These values indicate the usefulness of mulch, compared to the impracticality of using lava-rocks materials for building insulation.

A Sensitivity Analysis of a Thermal Model of Photovoltaic Panel

This paper deals with a sensitivity analysis of a thermal model. An integrated thermal modelling of photovoltaic panels (PV panels) has been built. In the case studied in this paper, the PV panel is considered like a solar protection of the building. The modelling has been run for Reunion Island climate, which has a strong solar radiation as encountered in tropical and humid conditions. The thermal model studied here has already been presented in a precedent work. In this work, the model has been validated, for comparing the results predicted and that measures showed significant differences. A sensitivity analysis seemed necessary to highlight the parameters that have the most influence on the thermal model. This will see which parameters to focus on during a future optimization of the model.

Heating or Cooling Buildings with PV Walls in Reunion Island

In Reunion Island, many buildings have been equipped with PV panels on their roofs in order to produce electricity. These PV systems were built to increase the penetration of renewable energies in the public electricity grid and so reduce greenhouse effect gases emissions. This type of installation was designed just in order to produce electricity but many works have shown that PV systems integrated to walls can also cool or heat the buildings. This paper presents how PV systems integrated to building can be used to help meeting energy needs in two microclimates of the island by cooling or heating the building where it is installed. To show this, a building simulation code able to model BIPV buildings is used.

Vegetalized Complex Partition (VCP): Impact of a Green Roof under a Humid Tropical Climate, Comparison between Hong Kong and Reunion Island

The aim of this paper is to present the experimental results of a specific vegetated complex partition (VCP) and discuss the conclusions found from an interesting study case in Hong Kong, especially the presence of a strong upward heat flux in winter. The experimented VCP configuration has never been tested in Reunion Island. It is located on a small scale building with a sloped roof covered with steel foil and under a humid tropical climate. From March to August, the extensive VCP reduced the global average heat flow by 91.61% and the ceiling temperature by 9.3°C, with a maximum average reduction of 18.9°C at noon. Compares to the results from Hong Kong, three of the four conclusions have been observed or deduced from the experimented VCPs results. The fourth conclusion (about heat flow loss in winter) has not been observed. But, based on the results, a precision of the explanation of its origin is proposed: the evaporation process act like a heat loss amplifier.