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Measuring geothermal energy

Posted by Morgan White on December 7, 2020

         Geothermal heat exchanger systems consist of two main components: (1) heat pumps, and (2) ground loop. The heat pump capacity is associated with the capability of a GHP system to extract heat from the ground. The size of geothermal heat pumps is measured in tons where 1 ton = 12,000 btu/h, and determined according to the profile of the heating and/or cooling demand of the facility. Meanwhile, the loop field and its size in terms of length and depth are based on the size of equipment, soil type, and average temperature, and climate conditions.  

Furthermore, other metrics measure the system performance and its efficiency. Coefficient of Performance (COP) is the ratio of useable thermal energy to the thermal equivalent of the electricity used to operate the system. Energy Efficiency Ratio (EER) represents the ratio between the cooling output (in Btu/h) and the energy (electricity) input (in Watt). Also, The SEER is a measure of central air conditioning efficiency over an entire season. Higher COP, EER, or SEER means higher heat pump efficiency.

         The ground source heat exchanger system can be implemented in conjunction with an existing heating system that depends on another type of energy such as liquid propane. To accurately calculate the reduction in energy usage after the installation of a ground source heat exchanger, the system has to be modeled as a hybrid system. Detailed information (system type, fuel, capacity, power consumption, time of usage) of this hybrid system is needed to assess the adequacy of a GHP system's performance in addressing the building’s heating and cooling needs. Assuming that the ground heat exchanger design data and the existing system are known, then the actual performance metrics of the system may be simulated using commercially available software such as eQuest or GLHEPro.

          Once the system is installed, a data collection system can measure, track, and report the actual performance of the ground heat exchanger system. First, determining the electricity consumption of a GHP system requires sub-metering of the GHP system. Second, is heat exchange performance data. This includes the measured entering/exiting water temperatures and circulation rates for the heat pump over time.  Modern GSHP units already incorporate sensors to monitor energy usage and the entering and exiting fluid temperatures.