Naturally circulating probes and collectors for ground-coupled heat pumps

Both vertically and horizontally installed heat source systems for ground-coupled heat pumps based on the thermosyphon principle using CO2 as the working fluid have been investigated theoretically as well as experimentally. vestigation of the vertical type (CO2 probe) has started in 1997. During the last years various design and operational parameters have been analyzed in depth, e.g. optimum number of parallel earth probes, probe length, CO2 charge required etc. In Austria up to now more than 100 systems have been installed, and the experience confirms that a heat pump system consisting of heat pump, probe head, and CO2 probe is a reliable, highly efficient as well as environmentally friendly alternative to commonly used ground-coupled systems. eat success with the CO2 probe initiated further research activities on a horizontal type (CO2 collector). The first experimental results carried out with a test rig in the laboratory confirm that CO2 can be used as heat carrier in collectors.