Ground-Source Heat Pump System Research— Past, Present, and Future

systems may be closed-loop (“ground-coupled”) or open-loop. The frequency of use tends to vary regionally, depending to some degree on building load profile, geology, environmental regulations, and human infrastructure. This editorial reviews past research, from the 1940s to present, and looks forward to what advances may be expected in the future. A Swiss patent issued in 1912 to Heinrich Zoelly is the first known reference to ground-source heat pump systems. 2 In the US, some ground-source heat pump systems were installed just prior to World War II 3 and post-war, installations began to take off. At the same time, about a dozen research projects involving laboratory investigations and field monitoring were undertaken by US electric utilities. In addition, analytical investigations by Ingersoll et al. 4 provided some of the theoretical basis for later design programs. After some time, interest in further research waned—apparently, problems with drying around horizontal ground-loop heat exchangers, 5 leakage, 6 and undersizing 7 led to the gradual cessation of new installations. Research began again in the late 1970s after the oil crisis and initially followed much of the same paths as the 1940s research, with an emphasis on experimental testing. This research did lead to solutions for several of the problems associated with the 1940s installations: drying around horizontal ground-loop heat exchangers was resolved with better backfilling techniques, 8 leakage problems were substantially resolved with the use of heat fusion and polybutylene and high-density polyethylene pipe, and undersizing problems were alleviated to some degree with new sizing algorithms 9 and programs 10 implemented on personal computers. 1Lund. J, et al. 2004. Geothermal (Ground-Source) Heat Pumps—A World Overview. Geo-Heat Center Bulletin, September.