Utilization of a Solar Greenhouse as a Solar Dryer for Drying Dates under the Climatic Conditions of the Eastern Province of Saudi Arabia

The goal of this project was to evaluate the feasibility of using a solar greenhouse as a solar dryer for drying dates. We attempted to analyze the thermal performance and thermal balance of the solar greenhouse. An experimental gable-even span greenhouse (solar greenhouse) was installed at the experimental research station at King Faisal University (latitude 25.4ºN, longitude 49.6ºE, and altitude 142 m above sea level) and functioned during October 2010. We evaluated the thermal performance analysis of the solar greenhouse (active or dynamic system) based on the thermal balance equations. The obtained results revealed that the daily average solar energy available outside the solar dryers was 15.921 kWh, and 12.335 kWh was available inside the solar greenhouse for an average effective transmittance of 77.48%. Of the 12.335 kWh available inside the solar greenhouse, 7.414 kWh was converted into useful heat gain that could be used for the drying process, 3.947 kWh was lost by conduction and convection, and 0.686 kWh was lost by thermal radiation. The solar energy available inside the solar greenhouse produced a 14.1°C increase in the inside air temperatures versus the outside temperature (33.6°C) and reduced the relative humidity of the inside air versus the outside air (35.3%) by 9.6%. The daily average overall thermal efficiency of the solar greenhouse during the experimental period was 57.2%. Consequently, 42.8% of the solar energy available inside the solar greenhouse was lost. The predicted thermal balance for the solar greenhouse was well validated with that measured during the experimental period (r= 0.999) indicating an excellent agreement.