Seasonal high temperature heat storage with medium deep borehole heat exchangers –a conceptual case study

Abstract

The focus of the presented study is the environment friendly and energy efficient redesigning of a more than 50 years old office and laboratory building. By storing excess heat from solar panels or thermal power stations of up to 110 °C in summer, a medium deep BTES can be operated on temperature levels above 45 °C. Storage depths of 500 m to 1,000 m below surface avoid conflicts with shallow groundwater use and additionally utilizes the geothermal site potential. Groundwater flow is decreasing with depth, making conduction the dominant heat transport process. To reach medium depths the water powered down the hole (DTH) hammer drilling method can be utilized with smaller drill rigs and corresponding small site requirements which results in lower compatible price ranges for medium deep drilling operations compared to conventional rotary mud drilling methods. Feasibility and design criteria of a coupled geothermal-solar thermal case study in crystalline bedrock for the office building are presented and discussed.