The Effect of Pyroclasts in Geothermal Borehole Heat Exchangers Performance on the Volcanic Island of Lanzarote (Canary Islands, Spain)

Abstract

The design of a geothermal heat pump system and geothermal heat exchangers to replace conventional cold and heat production systems in a winery on the island of Lanzarote (Canary Islands, Spain), taking into account its active volcanic geological peculiarities, is presented in this work. Firstly, a study was carried out to estimate the cold and heat needs of the winery during its operation. A calculation program was implemented in Matlab software framework to estimate the influences of the winemaker’s decisions on the cold and heat consumption of the winery. Once the needs were determined, a commercial geothermal heat pump (GHP) was selected, using exhaust heat to produce hot and cold water at the same time. After assessing hot and cold-water consumption along with heat pump requirements, a field of closed-loop borehole heat exchangers (BHE) was designed using a finite element heat transport numerical model. The existing geological profile, characterized by alternating basalt lava flows and pyroclasts, was carefully considered. The high porosity of the pyroclastic layers resulted in a 20.1% reduction in BHE performance compared to the initial expectations. Consequently, the depth of the 12 BHE was increased 21.9 additional meters from the original design. Thus, it was concluded that the alternation of basaltic lava flows and pyroclasts is prevalent in volcanic islands, emphasizing the need to attentively account for these pyroclastic layers in such environments.