Fraunhofer Institute for Solar Energy Systems, Freiburg
Thursday, July 10, 2014, 10:00 - 12:00
Room 02-014, Georges-Koehler-Allee 103, Freiburg 79110, Germany
The work focuses on the optimization of space heating and cooling systems for non-residential buildings like e.g. office buildings. The considered energy supply systems use environmental heat sources and sinks like surface-near geothermal energy, ground water or ambient air. The heat transfer in the rooms is realized by radiant heating and cooling systems with large heat transfer areas that enable a low temperature heating and high temperature cooling. Because the system efficiency strongly depends on the temperature difference between the supply water temperature of the radiant heating and cooling systems and the environmental heat sources/sinks high system efficiencies and low end energy demands are achievable. Unfortunately, long time monitoring campaigns have shown that the system efficiencies are far below the system efficiencies that are possible from the thermodynamic point of view. Firstly, the energy demands for the circulation pumps are very high due to high needed volume flow rates and large hydronic circuits that cause high pressure drops. Secondly, the end energy demands for heat pumps and chillers are high because of unnecessarily high temperature lifts between environmental heat source/sink and radiant heating/cooling system during operation. And thirdly, due to the high thermal mass of the radiant heating and cooling systems the room temperature control is difficult what leads to violations of the thermal comfort requirements and oversupply of the building. The first part of the thesis is the analysis and the optimization of the layout, dimensioning and operation of the hydraulic system. The goal is to identify optimization measures to reduce the end energy demands for the circulation pumps. The analysis is carried out by the evaluation of hydraulic schemes, on-site measurements and measurement data from the operation of monitoring buildings. The second part of the thesis is the development of rule-based control strategies that lead to higher thermal comfort and lower end energy demand. The analysis takes into account the whole system configuration and boundary conditions: (i) hydraulic system layout, (ii) thermal comfort requirements, (iii) efficiency of the heat transformation, (iv) efficiency of the heat distribution and (v) availability of the environmental heat sources/sinks. The identification of optimal control strategies is done by an model-based optimization with a dynamic thermo-hydraulic simulation model of a whole system consisting of heat and cold generation, environmental heat source and sink, heat distribution, heat delivery and building.