30 May 2005
In Germany approximately half of the heat pumps installed are vertical earth coupled devices. The
contamination of ground water through substances has been legally classified (1999). Water-glycol
mixtures, used in conventional earth coupled heat pumps, are in class 1, which means moderate
contamination. Carbon dioxide has been classified as a substance causing no contamination of ground
Research work at FKW has been done as well theoretically as also experimentally in order to lead the
development of a CO2-earth probe to success regarding the performance and especially the capacity limit
due to critical heat flux as also regarding the optimum charge.
The paper will present the experimental setups, experimental data from the measurements with the
new developed CO2-earth heat probe for heat pumps and the verification of the theoretical investigations.
Using this new development it will be possible to build earth coupled heat pumps with this
industrially manufactured CO2-earth heat tube for effective and environmentally-friendly heat pumps
compared with conventional heat pumps using water-glycol mixtures. Cost considerations show the
applicability of this new pumpless CO2-earth probe instead of the conventional pumping type.