Cold climate geo-exchange is a requirement for realistic building decarbonization. Heating-dominant geo-exchange systems have decreasing ground heat exchanger (GHX) temperatures from year-to-year. This situation is exacerbated in cold climates where the undisturbed ground temperature is near freezing, even before the GHX is installed. Thermal degradation leads to system failures from the GHX temperatures being driven below the design threshold. Two scenarios are typical for this system type: the system is designed with a massive, expensive GHX that can operate sustainably without continuous temperature degradation, or the system is designed with a smaller, less-expensive GHX that eventually fails due to low temperatures.

GHX solar reheat has been accomplished in systems that were not monitored closely. Little information is available for designers to appropriately incorporate the technology into their designs. For geo-solar systems to be considered, the industry requires the addition of a solar integration module into existing, industry standard GHX sizing software. For software developers to warrant investment in research and development, a proof-of-concept project was required.

This study examines the thermal response of a frozen GHX when a low-cost HDPE solar collector array was used to reheat the ground. The system was installed in 2018 after the minimum heating season temperature of the GHX became too low, which would normally be the point where the system would be abandoned or modified. The control system that was used for the integration of the solar panels and the GHX has remote connectivity and data logging capabilities. The monitoring and data acquisition enabled optimization of the control algorithms to maximize the reheating and ensure that the pump energy use was optimized. The control algorithms and thermal response of the GHX are discussed in this study. The results can be used to formulate modeling tools that can be calibrated against real data.


Believing that renewable energy was key to a sustainable future, Daniel launched Altum Engineering in 2007.
Daniel’s mission is to ensure that renewable energy systems function to their fullest potential. He is a geo-exchange specialist with a focus on optimization of renewable energy systems.
Daniel pairs cutting edge technology with decades of hands-on experience in challenging projects. He uses custom programming and reprogramming of direct digital controls to ensure renewable energy systems are performing at or above their specifications.
Daniel has dedicated his career to reducing greenhouse gas emissions and has been working in the green energy space for 22 years.