Research On Innovative Grout For Borehole Heat Exchangers In Multiwell Geothermal Heat Pumps Systems

The district heating industry in the moderate climate countries is turning intensively towards heat pumps. Large systems, especially those with air conditioning, are already mainly built with geothermal heat pumps. These are predominantly based on borehole heat exchangers. They offer the possibility of bidirectional heat energy transfer, which mainly means heating in winter and cooling in summer. The rock mass in such systems acts as a heat and/or cold store. Its role changes seasonally, in winter the rock mass releases thermal energy for heating while storing cold, and in summer it releases cold while storing heat. This mode of operation results in geothermal heat pumps having the highest efficiency ratings, i.e. producing heat/cooling throughout the year. Air source heat pumps, which do not use the storage effect, are a class lower. The presented research results concern the laboratory formulation of a sealing slurry which, through the addition of a new and innovative substance, creates the ability to automatically reduce micro-cracks in the sealing slurry. This contributes to a reduction in permeability. This is a very significant property, especially due to the effective isolation of aquifers. In addition, the tested grout has a higher thermal conductivity coefficient than the base samples, which are made of cement without additives. Obtaining the highest possible thermal conductivity value for the grout has a direct impact on increasing the energy efficiency of the system based on geothermal heat pumps with borehole heat exchangers. Activities in the conducted research were directed towards verification of the possibility of using components that are already used in construction, geoengineering and geotechnics. The experience gained there allowed us to conclude on the significant probability of successful application of analogous grout additives in the sealing/filling technique for borehole heat exchangers and multiwell geothermal heat pump systems. The self-healing method consists of applying a substance to the grout during its preparation, which will then be able to self-repair any damage to the hardened filling grout. The addition of graphite, on the other hand, has a direct effect on increasing heat conduction.