Use of Underground Air for a Heating and Cooling Energy Source on Jeju Volcanic Island of Korea.

Underground air has been gaining popularity for space heating and cooling on Jeju volcanic island, Korea, because there are many geological and societal limitations in the application of conventional ground source heat pump systems. The underground air temperature on the Jeju Island is very stable, at 15°C–19°C (median 17°C), throughout the year, while the ambient air temperature varies widely. In addition, vesicular basalts widespread in the island facilitate the extraction of underground air. As of 2007, there were 63 underground air facilities used, which were mostly greenhouses for growing fruits, vegetables, flowers, and ornamental shrubs. Practical operations and agricultural studies have revealed that the supply of underground air to greenhouses growing plants saved energy costs and enhanced crop production due to the high CO2 content in the underground air. Despite these advantageous features, there are still some problems that need to be resolved including public grievance relating to potential groundwater contamination due to the drilling of boreholes and lack of technical experiences in optimal system design. Regulations have not been tailored to the use of underground air systems, which is still not officially acknowledged as a renewable energy source and these factors will need to be resolved prior to the sustainable use of underground air. [ABSTRACT FROM AUTHOR]