Water is a vital element of agriculture. Almost 75% of the world's water resources are used for farm irrigation. Using greenhouses in agriculture provides a good environment for plant growth and reduces water consumption. Desalination to obtain freshwater from seawater or brackish water has been used in the arid costal regions and areas that have encountered water shortages. Solar desalination systems integrated into greenhouses have been considered for fresh water production to satisfy their water demand. Two main types of greenhouse integrated desalination systems are used, namely, solar stills and greenhouse-integrated humidification-dehumidification type solar systems. The main objective of this project is to carry out a thermodynamic analysis and a comparison of solar stills and humidification-dehumidification type desalination units. The basic principles, components, types, advantages and disadvantages of solar stills and humidification-dehumidification type greenhouse integrated desalination systems were investigated in detail. A conventional single basin type solar still that includes a basin and a symmetrical tilted condensing cover (greenhouse roof), and a humidification- dehumidification desalination unit that consists of two evaporators and one condenser were selected for detailed analysis. In order to carry out the thermal analysis, some important data such as plant transpiration and evaporation, solar radiation and indoor conditions of the greenhouse were determined. The thermal analysis was based on tomato production. Typical year ambient air temperature, relative humidity, and wind velocity values were taken from TRNSYS 16 for Adelaide conditions. In order to provide a good environment for the tomato crops, the internal conditions of the greenhouse were selected in the range 15-29oC temperature and 60-80% relative humidity. Detailed mathematical thermal models of both conventional solar stills and the new humidification-dehumidification type systems were simulated and the fresh water production of both systems was evaluated by means of MATLAB 7.8. The results were compared with previous experimental results. The results demonstrated that even if the whole roof area is used, the required fresh water supply cannot be produced in the months of May, June and July by the simple solar still system, whereas adequate amounts of fresh water can be produced throughout the year by means of humidification-dehumidification type system. On the other hand, the annual water production of the simple solar still system and humidification-dehumidification type system were determined as 308.5 and 260 m3/year respectively. The thesis also considers the option of water storage for providing water requirement of the greenhouse plants. The parameters that affect the fresh water requirement of the both systems were also considered and their impact evaluated. The effects of the desalination system on the internal environment of the greenhouse were also considered. It was revealed from the results that the use of the solar still system during the period from April to October causes unsuitable greenhouse conditions for the greenhouse crops whilst appropriate conditions for the greenhouse crops were achieved throughout the year in the case of the humidification-dehumidification type system. On these and other grounds, the humidification-dehumidification type system was found more suitable for the given greenhouse and climatic conditions. / Thesis (MEng(MechanicalEngineering)--University of South Australia, 2010

Agricultural greenhouse gas emissions within New Zealand account for 48 percent of all national greenhouse gas emissions. With the introduction of the emissions trading scheme farmers will soon be liable for their emissions, introducing additional physical constraints and financial costs. Farmers that still operate within the sector will have two options to meet emissions targets; to purchase carbon credits from the open market, or mitigate farm level emissions at added costs to the farmer. This study examines the latter case of assessing farm level options for mitigating greenhouse gas emissions, and quantifying the physical and financial costs associated with mitigation strategies. Results show that, based on the assumptions in the study, there are available options for dairy farmers to profitably meet Kyoto protocol emissions targets. Sheep and beef farmers can increase profit, but cannot meet Kyoto protocol emissions targets, through examined scenarios.