Investigation of Energy Efficiency in a Zeolite-Water Adsorption Solar Cooling System Utilizing Locally Sourced Materials for the Conservation Chamber

Abstract

Adsorption solar refrigerators are one of the technologies used to produce cold for preserving products. These systems are mainly made up of a collector-reactor, a condenser and an evaporator placed in the enclosure to be cooled. The cold room of an adsorption-based solar cold production unit installed in an open-air area is subject to heat and mass transfer, resulting in fluctuations in temperature and humidity. This paper presents a study of the impact of four different types of composite materials on the regulation of the interior ambience of an agri-food preservation unit by solar cold produced by zeolite/water adsorption. This formulation was proposed on the basis of the materials most commonly used in construction in Burkina Faso. After determining their thermophysical properties, the research was carried out by comparing the materials cut laterite blocks (BLT), compressed earth blocks (BTC), refractory clay and cement breeze block. BLT, then adobe, have a longer heat diffusion time than BTC and hollow breeze-block. They therefore offer better thermal inertia. Thus, the shell of the sideboard is a BTC-insulator-aluminium formulation. The insulation is either imported polystyrene or a locally formulated straw panel. The useful volume of the sideboard is 100 L. The results of the temperature measurements were recorded by the data acquisition system at regular six-minute intervals over a period of eight hours. The results showed that, for a given insulation thickness, heat loss increases with volume. Considering the maximum of the straw panel from 20 mm to 200 mm, the energy saving is 2600 kJ/day. Theoretically, this energy saving would produce 7.5 kg/day of ice. For polystyrene, the gain is 1,200 kJ/day. Furthermore, the overall heat transfer coefficient decreases with increasing thickness. For a thickness of 20 mm, it is 0.25 W/m2K for polystyrene and 0.55 W/m2K for compressed strawboard. When the thickness is increased by 180 mm, for example, these values drop to 0.02 W/m2K and 0.15 W/m2K, respectively. These results for both insulating materials can be explained, in part, by their insulating properties. Polystyrene has a thermal conductivity 4 times lower than that of compressed strawboard. The evaluation of the energy gains of the sideboard shows a considerable advantage in using an envelope composed of earth-polystyrene-aluminium. This was confirmed by the thermal performance coefficients.