Abstract

Large greenhouses are increasingly used for modern farming, occupying vast areas, and consuming considerable amounts of energy to maintain their functionalities. In this study, the performance of an energy-efficient greenhouse comprised of a transparent solar water heater, coupled with a spectrum-shifting material, and a water desalination unit, is investigated. A transparent solar water heater is installed on the greenhouse roof and provides warm water to be used for desalination. The addition of a spectrum-shifting material to the solar water heater can enhance the efficiency of the thermal system by absorbing wavelengths near-infrared waveband (NIR) or shifting the light to a spectrum more favorable to specific crop growth. Moreover, a desalination unit allows the treatment of a wide range of contaminated or saline waters to satisfy the crops’ potable water needs. The investigated desalination system utilizes direct-contact evaporation and condensation through a packed-bed material. Based on the simulation results for Phoenix Arizona, the transparent solar water heater is able to increase the water temperature by up to 25°C, while allowing sufficient light to pass through to maintain plant growth. Moreover, the implementation of a transparent solar water heater decreases the cooling and heating loads. The investigated greenhouse design is able to sustain hydroponic lettuce cultivation, for example, throughout the year, and satisfy the potable water requirements, thus producing up to 400 kg of fresh lettuce per month.

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