This study reports on experiments which were performed on spiral-helical surface water heat exchangers. These heat exchangers, when used as part of a geothermal heat pump system, serve as an alternative means whereby the system can reject heat to or extract heat from the environment. These systems are known as surface water heat pump systems and they serve as a less expensive, yet effective application of geothermal energy. Prior to this work, there was little information available to designers of surface water heat pump system regarding the performance of these heat exchangers. This work serves to bridge some of the remaining gaps by correlating heat exchanger performance in heat rejection and heat extraction modes of operation. From these correlations, design graphs were developed to allow designers of surface water heat pump systems to accurately size the surface water heat exchanger.Mechanical Engineerin