Extensive geothermal heat use in cities energetic and economic comparison of options for thermal regeneration of the ground

Geothermal energy as a heat source for heat pumps is increasingly unused in the city of Zürich. However, as indicated by other authors, the renewable potential for shallow geothermal heat use is limited due to the fact that natural regeneration in the absence of ground water flow is slow. Constant heat extractions from dense geothermal heat pump installations continuously cool down the affected ground layer.. In this case boreholes have to be drilled deeper or regenerated in order to avoid freezing around the borehole. The aim of this simulation study is to find the most economic geothermal heat pump concept, which does not lead to borehole freezing after 50 years of operation in areas with dense installations (an exemplary mean geothermal heat extraction of 35kWh/m2/a was supposed for this this study). Therefor a multi-family house with a standard ground source heat pump was simulated for a period of 50 years in Polysun. Various solar concepts, an air heat exchanger concept, a geo cooling concept and also a system without regeneration were added to the system. These concepts were compared under the assumption that all neighboring installations are using an equivalent regeneration strategy as the simulated system For the different system concepts, highly variable total borehole length were needed to avoid freezing, reaching from 1020m for a system with a large glazed collector field to 2160m for the un-regenerated case. The heat cost of the analyzed system concepts was in the range of 21- 27 Rp/kWh. The most cost-effective system concepts according to this analysis are the air heat exchanger or unglazed collectors. Increasing the total borehole meters was not only one of the most expensive options, but also the least sustainable, since the continuation of ground tem-perature decrease after 50 years was more pronounced with this option than for any other option

Competition and Living Lab Platform (Annex 74) Science & Technology (Subtask A) ::topical papers

Within the IEA Technology Collaboration Program (IEA TCP) framework relevant research on building en-ergy performance and renewable energy supply in the built environment was done and published recently. Namely in the Energy in Buildings and Communities TCP, Solar Heating and Cooling TCP and Heat Pump Technology TCP cover technical expertise related to living labs. The purpose of the report is to make this knowledge base available to those who are intending to participate in a living lab competition and those who are on the way to set up their own living lab. With a set of so-called topical papers experts from Annex 74 and other Annexes have summarized the state of the art and research on selected topics to allow a compact overview for future organizers and teams. In the case of modular construction and sustainability in construction the main source was an in-depth technical analysis of former editions of the Solar Decath-lon, mainly the European edition