F. Lucas1*, F. Boudehenn2, S. Amblard3, J. Castaing-Lavignotes4, M. Pons5,

N. Le Pierres, D. Stitou7, D. Mugnier8

1 Laboratoire de Physique du Batiment et des Systemes (LPBS) Universite de La Reunion.
2Commissariat a l’Energie Atomique — Institut National de l’Energie Solaire
3Centre Recherche et developpement CIAT
4Laboratoire de Thermique, Energetique et Procedes
5CNRS-LIMSI, BP 133, F-91403 Orsay Cedex, France
6Laboratoire optimisation de la conception et ingenierie de l’environnement — INES
7Laboratoire procedes, materiaux et energie solaire
8TECSOL SA

* Corresponding Author, lucas@univ-reunion. fr
Abstract

In recent years, the world market of air conditioning has been increasing very fast. To meet the occupant comfort demand, solar cooling processes offer an ecological promising alternative to conventional air conditioning process. Indeed, these technologies offer satisfactory comfort in building at a very low energy cost (Electrical consumption can be divided par ten to twenty). To allow a wide diffusion of these technologies it is necessary to reduce the installation cost and to guarantee optimal performances. For instance, the investment costs for solar cooling systems are far higher than classical systems investment. However, the running costs of the solar cooling processes are far lower than the classical ones; the cooling power cost is about ten times higher. By developing tools to help the sizing phase and the optimisation of the solar cooling systems, it will be possible to reduce the installation costs, to improve performance and thus overcome the major drawback for a broader use of this technology.

This paper describes a French research program proposing both an applied and fundamental study of solar cooling processes. Based on the contribution of eight industrial and scientific partners working within four pools, the project investigates the most promising solar cooling technologies as desiccant cooling process (pool 2), absorption cooling process (pool 3) and thermo-chemical cooling process (pool 4). Pool 1 focuses on the comparison and analysis of the three cooling processes covered by the other pools. Using the pool 1 results, pools 2, 3 and 4 propose a theoretical analysis to develop design tools based on modelling of cooling system components, cooling systems, control components and global cooling system coupled with buildings. An experimental survey is also carried out on five experimental facilities in order to perform an exhaustive validation procedure including also a sensitivity analysis and an inter-software comparison. At the end of the project, within 3 years, the partners will provide :

• A thermodynamic analysis of the solar cooling processes,

• Sizing tools suitable for preliminary studies,

• Optimized sizing tools.

Keywords: Solar cooling, energy saving, experimental survey, modeling, design tools, optimization, absorption process, desiccant process, thermo-chemical process.

1. Introduction

Over the past fifteen years, the requirements of the building occupants have changed significantly. There is indeed an increasingly demand for rigorous comfort. The growth prospects of air conditioning markets are important for years to come. Indeed, the world market for air conditioning increased by about 4% per year. In a difficult energy and environmental background, it is urgent to propose bioclimatic passive solutions but also active techniques that can meet the requirements of comfort in buildings without overloading the electricity yield. The solar cooling systems represent this promising alternative to the conventional cooling systems using vapour compression. The state of the art of cooling technology using solar thermal energy to produce cold revealed two large families:

• Closed cycles: these systems produce cooled water by sorption for cooling or dehumidifying. In these systems, mechanical compression is replaced by a thermal compression. The existing systems on the market are absorption (sorption of the refrigerant on a liquid absorbent) or adsorption (sorption of refrigerant on a solid adsorbent) machines. These processes operate through a heat source, which temperature is generally between 60 and 110°C. Their coefficient of performance (COP) is around 0.5 to 0.7 (for single effect systems). These closed cycles represent the majority of existing solar cooling facilities, with a predominant share for absorption technology (60%). The thermochemical processes are also gas sorption systems following a closed cycle. Their principle is based on the use of a reversible chemical reaction between a solid reagent (as BaCl2 for solar applications) and a refrigerant gas (NH3). This process includes two distinct phases (reactive phases) and two intermediate transitional phases (pressurization and depressurization. The COP of the thermo-chemical systems varies from 0.3 to 0.5 in the basic versions.

•The open systems: In these systems, the air is directly treated (cooling, dehumidification) by contact with the refrigerant (water) and the desiccation components. These systems use for the drying either a rotating desiccant wheel (desiccant solid material) or a liquid desiccant bed. The temperature of the hot source necessary for the regeneration of desiccant materials is about 45 to 95°C. The COP of these systems varies between 0.5 and values greater than 1. Open systems are currently a relatively small part of existing facilities (about 10 to 15%), but represent a promising future for solar cooling.

The ORASOL project is intended to study and compare absorption, desiccant and thermochemical solar cooling systems. Six public laboratories and two private companies contribute to this work for a three years period.

This article proposes to define the objectives of the ORASOL project and to give a description of his organization. It will present the experimental facilities used and the expected results.