D2.2 Design principles and test result of deep borehole collector

This report discusses design principles of deep drilling solutions and borehole collector technology. The work explores deep drilling solutions and borehole collector technology aiming at transferring the experiences of experimental deep drilling to business as usual procedure in the built environment. The report also reviews the methods and procedure for improving the economy of drilling, considering air and water-based drilling methods, and combination of these. The report addresses the identification of the most viable, reliable, cost-efficient methods and drilling technologies to drill deeper than current boreholes in densely built urban areas. The risk management procedures for tackling rock quality and installation of the coaxial collector are discussed, based on the large experience gained on the field in the recent years. The suggested collector is a closed loop coaxial collector, and among the advantages of using coaxial heat exchangers, reduced pressure loss compared to U-pipes is one of the most significant. The thermal performance is also improved respect to the U-pipe collectors, having a more balanced heat exchange of the fluid coming downwards and bedrock. The analytical approach was used to evaluate the hourly thermal loads for the Finnish demo site, for the fluid return temperature from the ground for 30 years of operation. The final performance evaluation of the borehole and collector integrated with heat pump, solar PVT panels and building energy systems will be done in the later phase in WP4; PEB implementation and monitoring.

Publication Date: 30 Nov 2020