Subsurface thermal influence of experimental geothermal heat pump system operation for space cooling in Kamphaengphet, Thailand

Abstract

Using natural sources of energy (solar, wind, biomass etc.) may potentially help to mitigate global warming. Low-temperature geothermal resources are among the more abundant natural energy sources. Methods of utilizing low-temperature geothermal resources include both direct use of warm groundwater and geothermal heat pump (GHP) systems. GHP systems may be subdivided into two basic types. One uses water circulated through a subsurface pipe without direct mass exchange between the pipe and the local groundwater aquifer (“closed system”). The other involves direct withdrawal of heated groundwater (“open system”). GHP systems are popularly used worldwide (Rybach et al., 2000; Fridleifson, 2001; Lund,2005). In Sweden, the number of GHP system installation per 100 people in 2005 is about two (Curtis et al., 2005). It is generally considered that GHP systems may be utilized everywhere because of stable temperature of the underground. However, the applicability of the GHP system is not clear for space cooling in tropical region where sufficient temperature difference between underground and atmosphere may not be expected. Aiming at grasping the applicability of GHP systems for space cooling in tropical region, an experimental operation of a GHP system was conducted at Kamphaengphet, Thailand from October, 2006 to March, 2008 (Yasukawa et al., 2009). The depth of the heat exchange borehole, in which U-tube was installed, was 56m. The authors set temperature sensors every ten meters inside the U-tube (at depths of 0, 6, 16, 26, 36, 46 and 56 meters, respectively). As the detail of the GHP system, the results of temperature measurements and calculation of system performances are presented in Yasukawa et al. (2009) in this issue, we attempted to estimate subsurface thermal influence of the GHP system for space cooling by acquiring temperature data of the underground from this test.