Energy distribution concepts for Urban Supermarkets including energy hubs
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More and more of the earths population is living in urban areas. This indicates thatusing urban building plots for combined purposes will be important in the future. For thisreason supermarket chains are developing new building concepts that includes supermarketsales area, apartments on the upper floors and parking lots with energy supply hubs forthe new generation of hydrogen/electric vehicles. This master thesis emphasizes this conceptby designing the complete energy system for such a building and taking into accountdemands for heating, cooling and refrigeration. A literature review of subsystems andcomponents relevant for the different parts of the building concept was performed. Thisincludes supermarket refrigeration systems, hydrogen refueling stations, energy systemsfor high performance buildings and thermal storage. Based on the findings from the literaturestudy, a complete design for the building energy system was proposed. The purposeof the energy system is to integrate the different subsystems together to enable heat recovery to use for space heating and domestic hot water, and thereby minimizing the import of primary energy to the building plot. A key feature of the energy system is that it is organized in three circuits with differenttemperature levels. They include a high temperature water circuit for domestic hot water, amedium temperature water circuit for space heating and low temperature antifreeze circuitconnected to boreholes for heat storage, cooling of ventilation air and as a heat source.Space heating in the building is covered by a low temperature 28/33°C return/supply floorheating system as well as heating of ventilation air. Hour-by-hour energy demand over ayear for space heating and domestic hot water for the building was obtained by developinga model of the building envelope in the software SIMIEN. The data obtained was based onassuming a plausible layout and design for this type of building. The supermarket occupiesthe whole first floor of the building and thirty apartments the three next floors, separatedinto ten apartments on each floor. The building envelope is designed according to the requirements and specifications to the Norwegian passive house standard. Four weeks werepicked from the yearly demand report from SIMIEN to give as input to the simulationof the energy system. The four weeks serves as boundary conditions for a performanceinvestigation of the energy system during spring, summer, fall and winter. To evaluate the chosen design of the energy system three different variants of the system,called case 1, 2 and 3, was developed in the dynamic simulation software Dymola.The three models were simulated for all four weeks and the results compared. Case 1 involvesintegrating the supermarket refrigeration system to the centralized heating systemin the building and delivering waste heat from the gas coolers to space heating and domestichot water. Simulations show that by operating the system in trans-critical mode, heatrecovery could cover the full demand of domestic hot water in the building for all weeks.In addition, the full space heating demand could be covered by heat recovery for the summerand spring week, and reaching a share of 75.4% and 31.4% for the fall and winter week. Remaining heat demand in the building was covered by a R290 ground source heat pump connected to the energy wells on the evaporator side. Case 2 and 3 investigate heat recovery from the hydrogen refueling station in two differentways in addition to heat recovery from the supermarket refrigeration system. Thewaste heat at the hydrogen station is due to the operation of an electrolyser, compressionof hydrogen gas and precooling of hydrogen gas during filling of vehicles. The availablewaste heat/refrigeration load in case 2 and 3 was linked to the daily production level ofhydrogen gas in the electrolyser. The production was assumed constant through the day,and equal for all days of the week, giving a constant waste heat availability. In case 2,an antifreeze cooling circuit from the hydrogen station brings waste heat at 45°C to thecentralized heating system of the building, and the heat is recovered to space heating by aheat exchanger. In case 3, the hydrogen station is integrated entirely with the CO2 boosterrefrigeration system in the supermarket, and the refrigeration demand at the station is covered by it. The first comparison between case 1, 2 and 3 was based on a daily productionof 50 kg of hydrogen fuel, corresponding to 25% of maximum installed capacity. Resultsshowed that case 2 and 3 displayed similar performance for space heating heat recovery,where both could satisfy the space heating demand for summer, spring and fall week, andabout 60% during a winter week. Due to high uncertainty in the demand for hydrogenfuel in the area, a parameter study of the hydrogen production level was carried out. Theproduction level was varied from 10% to 100% and simulated for the winter week. Forboth case 2 and 3, a daily production level of 75% (150 kg) and higher could cover allspace heating demand. In addition, case 3 showed a large potential to supply domestic hotwater, up to 5.5 times the demand of the building at maximum daily production of 200 kghydrogen. Case 1 is considered the minimum integration that should be carried out for thebuilding concept, as large energy savings can be achieved with small modifications to astandard CO2 booster system. If the hydrogen station is to be integrated, the case 3 designis the better option. It can deliver similar performance to space heating as case 2, but canin addition deliver a large supply of domestic hot water. If case 3 design of the system ischosen, delivering domestic hot water to neighbouring buildings should be considered touse the full potential of waste heat that is available.