The apparatus for atmospheric water harvesting in an arid climate - Prototype design and testing in laboratory conditions

The paper describes the development of a prototype system for water extraction from the air. The aim was to develop a device that allows one to autonomously obtain, without the need for external energy, an annual average of 100 L of water per day during extreme desert conditions. In this paper, a mathematical model simulating the operation of the unit for extracting water from the air in any climatic conditions is presented. Psychrometric calculations for different climatic conditions were carried out for two basic principles: condensation and sorption. The analyses confirmed that devices based on the condensation of water vapour from the air can only be used to a limited extent in extreme desert conditions. The average water production of a condensation-based system is only 20 l/day in Riyadh, with an air flow rate of 2000 m³/h. A unit with a desiccant wheel and an integrated heat pump was designed for water harvesting from the air. The prototype of the unit was tested in a climate chamber with the possibility of adjusting the climatic conditions and the presented mathematical model was experimentally verified. The final prototype designed for a nominal outdoor air flow rate of 2000 m³/h will produce 168 l of water per day under dry desert conditions (Riyadh) with continuous operation. The verification of the computational model allows one to determine the real water production and the required unit performance. An analyses of energy requirements and evaluation of levelized cost of water (LCOW) have been performed. Sorption unit has lower LCOW in target arid desert climate and electricity prices under 0.1 EUR/kWh compared to direct condensation technology.