Ground Loop Design (GLD) is a software tool for designing and optimizing ground source heat pump systems. The package enables designers to determine the correct lengths of bore or pipe required for commercial vertical, horizontal and/or pond heat excahngers, optimize the piping configuration for balanced flow and optimal heat transfer, and calculate the annual and lifetime energy/operating/emissions costs associated with each design. The modular program enhances design productivity and permits flexibility in the designing process and customization based on designer preferences. It also has an English/metric conversion engine and is available in many languages, providing applicability to the widest range of equipment and customers.