Investigation on substations in cold district heating grids in the context of a test facility

The building sector is responsible for over one third of the energy demand in Europe and produces the largest amount of greenhouses gas emissions of all sectors. The cold district heating (CDH) systems can contribute to a more efficient use of energy sources so as better integration of waste heat and renewable energy such as geothermal or solar heat. In the context of this transition, the Fraunhofer IEE is planning to set up a district heating test facility called ""District LAB"" for experimental investigation of innovative, grid based supply solutions.The present thesis explores the behaviour between the components in the substations of a DHC system with decentralized heat pumps in a test facility context. This analysis carried out in a simplifying representation through a modelling and simulation thermal investigation network. For this purpose, four scenarios are created at a preliminary phase in a simulation program, starting with a reference scenario based on five substations with decentralised heat pumps and the thermal storage. Besides, the scenarios aim to study different cases, one to cover the heating load only and in a second case the combination with cooling.In a second phase, thermal and efficiency evaluations are carried out on the basis of different investigation parameters. The optimisation of the storage volume and the heat pump size was focused at this stage. In order to achieve the optimal value volume for each substation, the results of heat pump parameters such as switching on/off, coefficient of performance of the heat pumps and overall system efficiency were evaluated as the tank volume varied. In a further phase, the optimisation of the heat pump was carried out in order to design the machine size at a lower power than the calculated winter peak conditions, therefore obtaining a better operation of the. This final phase of analysis led to an improvement of the scenario from the point of view of heat pump operation and the choice of a more suitable storage volume. The reduction in the size of the heat pump has produced positive results in terms of switching on/off of the heat pump control, which means an increase in performance and extension of the lifespan of the heat pump and reduces the heat capacity. the potentials and limitations identified during the analysis of the general behaviour in the substations can be considered useful for the development of the test facility.