Water born cooling of closed greenhouses : An enclosed vertical water curtain cooling system

Abstract: The greenhouses play a key role in food sustainable production, the purpose of the greenhouses is to make an artificial suitable environment to grow different kinds of plants. The cost of energy used in the greenhouses to ensure the optimum temperature, humidity, and CO2 concentration, makes up a large part of the final cost of food. Due to global warming, the successive energy crises, and the food crises, the need to make the greenhouses more energy efficient and to utilize renewable energy resources is rapidly increasing. The enclosed water curtain cooling system meets the special requirement of the greenhouse cooling system, and it has potential energy savings when it is integrated with other systems such as heat pumps, underground water sources, and surplus heat energy recovery. This system involves two special nylon foils, and a thin layer of water flows between the two foils, the two foils will be stuck to eachother by the cohesive force of the water-detergent mixture, the detergent was added to decrease the water surface tension and ensure the even distribution of the water-detergent mixture over the nylon foils. In this study, an experimental model of the enclosed water curtain was made and two sets of tests were conducted, the first set was at room temperature around 20°C, and the second test was at room temperature around 25.7 °C with an electrical heater, each set contains three tests to measure the cooling capacity of the curtain, and each test takes 2 minutes, the curtain dimensions were height and width of 1.04 m and 1.20 m respectively. By measuring the difference between the average inlet and outlet temperature of the water-detergent mixture before and after the curtain, and the mixture mass flow rate during the test period, the cooling capacityof the curtain was calculated using the energy balance equation.It was found that the curtain cooling capacity increases with the increase of ambient temperature, The large heat transfer area of the curtain which allows using higher water temperature for cooling, and the useful features of the water membrane like the high absorption of the wavelength of infrared and the high transparency of the wavelength of visible light, make this system meets the special requirements of the greenhouses cooling system. However, to be able to apply this system in real-life, the design of the curtain should be improved, and suitable materials should be chosen to make it more reliable. Also, All tests in this study were conducted in the workshop in the absence of solar radiation, therefore, the actual performance of the curtain needs to be evaluated with the presence of solar radiation, to be able to study the effects of the direct and diffuse solar radiation with various spectrum range.