Toward a Better Way of Estimating Energy Utilization with Geothermal Heat Pumps: a Collaborative Study Under Annex VIII of IEA Geothermal

Abstract

Ground-source heat pumps or geothermal heat pumps (GHP) have become the main type of geothermal direct use, making up more than 50% on a worldwide basis. We have seen a dramatic increase in GHP installation during the last decade and this high growth rate is expected to continue in the future. The contribution of GHPs to world geothermal statistics is larger, in terms of installed capacity, than in thermal energy produced because of their low capacity factor or equivalent full load hours per year. Different load factors among the various types of utilization, such as heating residential houses, office buildings, and green houses, are often not considered by estimating capacity factors. In contrast to large-scale district heating systems, it is almost impossible to monitor flow rate or thermal load for GHPs, except in applications for large office buildings. Therefore, there is significant uncertainty in the statistics for geothermal energy use with GHPs, both on national and world levels. In order to determine a method for estimating geothermal energy utilization with GHPs as accurately as possible, Annex VIII - Direct Use of Geothermal Energy, a major activity of the International Energy Agency Geothermal Implementing Agreement (IEA Geothermal) initiated a collaborative task (Task D) starting with the comparison of methods used in computing the national statistics of several countries. Each country has its own approach for estimating thermal usage, mostly reflecting major utilization type and climate condition. However, there may be found a recommended method or reference table, if the statistics for each application type and the standard load pattern of each type are made available. Many countries do not separate cooling with GHPs from heating, which causes another uncertainty in the statistics. The main objective of Annex VIII Task D- Guidelines on Statistics for Geothermal Heat Pump Applications, is to develop a suitable form of statistical table to be adopted both for national and for world statistics. The table will include all types of GHP utilization, and consider cooling as well as heating. This will hopefully lead to comparable statistical data, and less confusion. The GHP statistical work is part of the Annex VIII development of guidelines for geothermal direct use statistics.