Design of a solar thermal installation for the production of domestic hot water

Abstract

In this project, the design of a solar thermal installation for the production of domestic hot water (DHW) for a building in Barcelona has been carried out. Firstly, the energy consumption of the building was determined from statistical data provided by the CTE and meteorological data. Subsequently, the collector model has been selected according to its performance characteristics, area and price. The necessary capture area has been calculated to cover the minimum fraction of demand stipulated by the current law by different methods, heuristics and energy balances of the elements of the installation. The energy balances have been made taking into account the heat losses of different elements of the installation determined from the thermal resistances of the selected equipment, as well as convection losses due to the action of the wind. This has meant an iterative calculation, as it was necessary to know beforehand the appropriate dimensioning of the pipes, including insulation, together with the meters of pipe and the layout of the collectors. The collectors have been arranged on the terrace facing south with a 40 degree slope, and properly separated from the surrounding obstacles to minimize losses due to shading. The final result of the collector system has been represented in a plan for easy understanding. Once the catchment area has been determined, the rest of the elements are sized. The support equipment has been sized based on consumption data of the different elements of the houses applying a simultaneity factor, considering a zero solar contribution of the collectors. The design of the heat exchanger was carried out by determining the useful area of exchange and the overall heat transfer coefficient, considering a counter-current exchange. A return network has been designed for the points of consumption furthest away from the DHW storage tank, based on a partial recirculation of the building's consumption. An exhaustive study has been carried out on the load losses of the elements including the necessary accessories (elbows, valves) in order to size the pumping equipment for each circuit. Once the size of all the elements was known, it was possible to determine the amount of fluid that could be found in each circuit, allowing the sizing of the expansion vessels. With all the elements already designed, an environmental study has been carried out to find out the amount of fuel (natural gas) saved and the CO2 emissions avoided. With the data of fuel savings and the costs of the materials of the installation, the economic viability study of the project is carried out for a useful period of 25 years, with the help of a subsidy from the Barcelona City Council.