Franck Lucas

Study of moisture in buildings for hot humid climates

Humidity in buildings generates many disorders or disadvantages. A dry-bulb temperature of the air relatively low, strong moisture and wall surface temperatures very low characterize the interior conditions of the highland dwellings in Reunion Island, during the southern winter. This causes many disorders related to phenomena of condensation on walls: deterioration of the envelope, odor of mould. It is thus, significant to precisely know the evolution of the moisture in a building to avoid any disorder on the frame. In this study we will expose a series of experiments carried out on real residences in order to highlight main parameters of the problem. On the basis of these results, numerical simulations were used to extrapolate the behavior of this building on unusual climatic sequences, holding account various improvements of its constitution. A curative study and a preventive study were carried out on two different types of residences. The aim is to propose solutions to prevent deteriorations of the coatings due to the surface condensation.

Steady State Model of a Solar Evacuated Tube Collector Based on Sensitivity Analysis

This work deals with first modelling the dynamical behavior of the solar collector under natural tropical humid conditions. In a second part, this paper proposes a sensitivity analysis which lays on fast method. This analysis is very interesting as it allows pointing out the most influential factors. Finally, it is shown that the output of the model could be approach by polynomial of regression called “metamodele”. This approximation constitutes a local approximation of the output of the solar collector, working under steady state conditions.Copyright

Experimental Ocean Thermal Energy Conversion (OTEC) project on the Reunion Island

Ocean Thermal Energy Conversion (OTEC) is a process able to produce base electricity through the temperature differences existing between warm seawater at the surface and cold depth seawater. Up to now, very few experiments have been conducted and oil prices fluctuations have often prevented results exploitation. Recently, two factors have re-launched researches: a need for the production of a renewable energy ensuring the stability of the electric grid and the increase in oil prices. The purpose of this experiment is to demonstrate the sustainability of an offshore 10 MW power plant. Some issues first need to be examined: heat exchanges, control strategies, cycle risks, working fluids, and thermodynamic cycles. This paper presents an experimental prototype as a first steppingstone of an “Eliminating Risks Program” and as a preliminary installation to the setting up of the first full scale OTEC power plant. The prototype is a reproduction on a reduced scale of a demonstration plant producing an electric power of 10 MW. To reduce costs and hazards of offshore installations (waves, cyclones, maintenance, etc.), decision has been made to build an onshore plant (settled on the Reunion island), creating artificial heat sources with a heat pump. In the first part of the paper, the principle of OTEC will be explained. Then, the prototype detailed: cycle, main components (the electricity production is directly related to the quality of the heat exchanges, so some different heat exchanger technologies are developed), working fluids, heat sources, and control strategies. Finally, results of an experimental parametric analysis will be presented, highlighting the major importance of heat exchanges, within the evaporator. Results show, for instance, that a vertical plate-type evaporator show better capacities than a shell and tube one.

Modeling of Ocean Thermal Energy Conversion (OTEC) Plant in Reunion Island

Renewable Energy has a crucial interest for a remote area like Reunion Island. The supply of electricity based on renewable energy has many advantages but the major drawback is the production of electricity which varies highly according to the availability of the resource (wind, solar, wave, etc...). This causes a real problem for non interconnected electrical grid where intermittent renewable energies should be limited to a maximum of 30%. The ocean Thermal Energy Conversion (OTEC) provides an alternative of electricity production from the available energy of the oceans present all the time. By using surface hot water and deep cold water from the ocean, it is possible to operate a thermodynamics cycle, which will then generate electricity. In this article, in the first part a literary and technological review is carried out in two areas: electricity production and cooling of buildings with deep water. This study establishes a knowledge base on thermodynamic cycles consistent with the OTEC and on dimensional and functional parameters associated with this technology. Steady state simulations are presented to understand the operation of the system. Steady state models will evaluate the potential of the OTEC in distributing base electricity. These simulations will help evaluating the potential for new thermodynamic cycles such as the Kalina cycle. With these tools, a sensitivity study will evaluate the influence of different parameters on the cycle.Copyright

SENSITIVITY ANALYSIS OF A SOLAR COOLING SYSTEM

The aim of this paper is the optimization of Solar Absorption Cooling (SAC) system’s performances. Over the past decade the electricity consumption has significantly increased in Reunion Island during the summer months, which is mainly due to the use of standard air conditioning systems. SAC systems present a good alternative for reducing this consumption. Solar cooling systems are environmentally friendly as they use water and lithium bromide solution as the working fluid.The purpose of this work is to undertake a sensitivity analysis to identify parameters which have a significant influence on the SAC systems performances. The sensitivity analysis has been carried out on numerical models developed at the PIMENT laboratory and validated using RAFSOL experimental data (experimental plant is set up at the IUT in St-Pierre). The results of the sensitivity analysis are used to establish the design and create the control rules to allow for the optimization and ensure the performance of future SAC systems.Firstly, this paper presents the modelization of the SAC system and the sensitivity analysis method used. Secondly, it displays the results from the sensitivity analysis that has been applied to all main components of the plant separately (solar collector field, solar loop and absorption chiller) and to the entire system. Finally, the results are analyzed and discussed.Two types of influential parameters have been distinguished: variables factors and geometrical properties of the plant. This study highlights that the compactness of the installation, the quality of the solar collector, and the control of the temperature at the output of the distribution loop are essential.Copyright

Instrumentation and Simulation of the Hygro-Thermal Conditions of a Green Building: A Study of the Impact of the Post-Occupancy Usages on Thermal Comfort

Post-occupancy evaluations (POEs) are useful for evaluating the success of any building design, but are particularly useful in evaluating green buildings. It is the only opportunity architects and engineers have to learn if their buildings actually work as planned. On the other hand, following the “guidebook” of a green building, i.e. having occupants aware of the particularity of the premise and taught about how it works and what the proper usages are (which are not automatically straightforward), is of prime importance since misuse of a green building can directly lead to discomfort and energy over consumption. In that framework, this paper stresses the link between occupants’ usages and their indoor thermal comfort by attempting a quantification of the impact of each usage on indoor temperature and hygrometry (and thus thermal comfort), showing by the way that, in order a POE to fully give exploitable results, a communication to occupants on proper usages has to be the first step after the delivery of a green building. To study that link, the real case of a green building located in the French tropical island of La Reunion has been used. The overall idea followed in this work lies in two steps: The first one is the creation of a “validated” digital building description obtained thanks to a process of comparison between simulations outputs (DesignBuilder) and field measurements (weather and comfort stations), and to a “block by block” approach that allows independent validations of the description of the fabrics and of the description of the usages. The second step is the utilization of the model obtained in the first step to perform simulations of new usages, as modifications in natural ventilation features (doors, windows open or closed) or in number of occupants, lighting schedule etc. These new simulations lead to the possibilities of comparing situations between each others, and therefore of quantifying the contribution, positive or negative, of each chosen usage to thermal comfort. Eventually, this paper will describe an example of combination of new usages that makes the conditions noticeably more comfortable within the building, stressing that following the good usages in a green building is a first requirement before realizing any POE.