D. B. Riffel*, F. A. Belo and A. P. F. Leite

Solar Energy Laboratory, Federal University of Paraiba, 58051-970, Joao Pessoa, Brazil
Corresponding Author, dougbr@gmx. net

Abstract

This paper presents the design optimization of an adsorber using a statistical modelling. The energy equations for the adsorber were formulated and its results were introduced in the statistical modelling. Fin-tube heat exchangers were chosen for adsorption beds in order to improve the heat transfer rate. The adsorber here designed is the main component of a 20 kW chiller, which runs mainly on solar energy, with a complementary heat provided by gas. Cold water is produced during night-time in an activated carbon-methanol adsorption chiller and then stored in a tank in order to supply cooled air during day-time. Solar energy is used for regenerating the adsorbent medium by means of highly efficient flat-plate collectors. Thermal energy is stored in a hot-water tank so as to supply the chiller at night. This air conditioning unit is designed to provide thermal comfort to four adjoined laboratory rooms, whose total area is 110m2. The optimized adsorber was obtained for the following values: the hot water temperature of 100 °C with 0.8 kg/s, the cycle period of 40 minutes, 56 tubes and 100 cooper fins of 0.5 mm.

It results in a COP of 0.52 and SCP of 51 W/kg.

Keywords: adsorption, solar cooling, optimization, statistical modelling, simulation

1. Introduction

Solar cooling is an interesting application of solar energy because, the stranger the irradiance, the greater needs for cooling. As a rule, the systems requiring thermal energy as their main power input for generating cooling effect are most dependable on sorption processes. This energy may come from different sources, such as: process heat, residual vapour or solar energy. One of the main advantages of such a system in relation to the conventional vapour compression system lies on its minimum use of electric energy and on its low cost of maintenance.

In the last two decades, absorption chillers, running on natural gas, have been introduced in markets all over the developed world — in the US, Japan, France, Italy, Spain and more recently in Portugal. As to adsorption systems — in spite of several studies that demonstrate their technical feasibilities -, there exist only experimental units, though stand considerable chances of becoming economically viable, especially where thermal comfort applications are concerned.

This paper presents the design optimization of an adsorber, as part of a chiller of a solar/gas air conditioning system, using a statistical modelling. The energy equations for the adsorber were formulated and its results were introduced in the statistical modelling. Plate-fin heat exchangers were chosen for adsorption beds in order to improve the heat transfer rate, increasing the contact area with the adsorbent. Cold water is produced during night-time in an activated carbon-methanol adsorption

chiller and then stored into a tank in order to supply cooling air during day-time. Solar energy is used for regenerating the adsorbent medium by means of highly efficient flat-plate collectors. Thermal energy is stored in a hot-water tank so as to supply the chiller at night. This air conditioning unit is designed to provide thermal comfort to four adjoined laboratory rooms, whose total area is 110m2. Details of this unit can be found in [1].