Optimisation of a Hybrid Geothermal-Solar-Gas System: A Case Study for a Typical Poultry Shed in New South Wales, Australia Yu Zhou 1 , Guillermo Narsilio 1 , Lu Aye 1 , Olga Mikhaylova 2 , Asal Bidarmaghz 3 , Kenichi Soga 4 1 Department of Infrastructure Engineering, The University of Melbourne, Vic 3010, Australia 2 Golder Associates Pty Ltd, Sydney, Australia 3 Department of Engineering, University of Cambridge, Cambridge, UK 4 University of California-Berkeley, Berkeley, CA, USA Abstract Poultry sheds are used to raise poultries (chickens, turkeys and ducks), and have a unique heating and cooling demand pattern. A significant amount of energy is consumed for the heating and cooling of poultry sheds to maintain an indoor air temperature suitable for the growth and comfort of the poultries according to their age. This energy consumption results in a considerably high greenhouse gas (GHG) emissions and energy expenditure for the poultry shed operation. Previous studies have shown that a large amount of operational and lifecycle cost of heating can be reduced with the adoption of hybrid geothermal-solar-gas systems. In addition to the costs, GHG emissions should also be considered when heating equipment is selected. This paper presents an environmental analysis and optimisation for the sizing of components of a hybrid geothermal-solar-gas system for a typical poultry shed located in Peats Ridge, NSW, Australia. The results reveal that up to 100% of the operational emissions and up to 95% of the lifecycle GHG emissions can be reduced if the current gas heating system is replaced by the hybrid geothermal-solar-gas system. By also considering the lifecycle cost, the Pareto front solutions for this hybrid geothermal-solar-gas heating system has been found. Keywords: Building simulation, poultry sheds, geothermal energy, solar energy. Introduction In Australia, agriculture and the associated processing industry contribute 12% to the national Gross Domestic Product (National Farmer's Federation 2016; NFF 2012). Within the poultry industry, it is estimated that approximately 600 million chickens are raised nationwide (Australian Bureau of Statistics 2016). The scale of this industry results in a significant amount of energy consumption, as well as greenhouse gas (GHG) emissions, primarily for heating and cooling the poultry sheds. An estimation by Zhou et al. (2017) suggested that about A$80 million is spent annually for this purpose and a significant amount of GHG emissions is produced. Since existing cooling systems for chicken sheds can be cost- effective to operate and generate relatively low GHG emissions (for example, if evaporative cooling systems are used), the primary focus of this investigation is on the reduction of costs and GHG emissions for heating poultry sheds. Network piped natural gas and bottled liquefied petroleum gas (LPG) are the primary energy sources for heating in Australia (Allison Ball et al. 2016). The combustion of these fossil fuels results in a significant amount of GHG emissions (0.186 kg CO 2 -e per kWh) (Australian Government. Dept. of the Enviroment 2017). Through refurbishment and partial replacement of current heating systems with high-performance equipment that uses renewable and more sustainable energy sources, lifecycle cost and GHG emission reductions could be potentially achieved. Zhou et al. (2018) has illustrated that both hybrid geothermal-gas heating systems and hybrid geothermal-solar-gas heating systems can reduce the operational and lifecycle heating costs significantly. This paper investigates these systems while further considering the environmental aspect as well. A Ground Coupled Heat Pump (GCHP) system provides low-carbon outcome for space heating and cooling, extracting thermal energy from the ground when operating in heating mode, and rejecting heat into the ground when in cooling mode (Johnston, Narsilio & Colls 2011). If the systems are used for heating, utilising only the ground as the heat source, they are termed Ground Source Heat Pump (GSHP) systems. They comprise a ground heat exchanger (GHE) field (i.e., high density polyethylene (HDPE) pipe embedded into the ground), a heat pump, and a distribution system. GSHP systems have been used for various applications worldwide. They are especially popular in the United States, Canada, Sweden, Austria and China (Lund & Boyd 2016). GSHP systems have also been introduced for the heating of poultry sheds in recent years (Kharseh & Nordell 2011). Some drawbacks of GSHP systems include the high upfront construction costs, typically responsible for the GHEs installation, as well as the embodied energy and associated GHG emissions. However, these can be reduced by coupling GSHPs with other energy sources to form a hybrid system (Eslami-Nejad & Bernier 2011; Kjellsson, Hellström & Perers 2010). For example, gas boilers and gas burners have relatively low installation costs and can be integrated with GSHP systems. To further boost the heating efficiency of GSHP systems, renewable solar thermal systems can also be coupled to form solar-assisted GSHP systems, which will help in the Proceedings of BSO 2018: 4th Building Simulation and Optimization Conference, Cambridge, UK: 11-12 September 2018 358