Enhanced cold production from geothermal energy using combined absorption and compression cycles.

Cooling with deep geothermal energy is a promising, sustainable alternative to conventional compression cycles and the associated high electrical energy consumption. In this work, combined compression–absorption cooling technologies are compared to the most prominent absorption refrigeration cycles (i.e. single effect, double lift and double effect) for the use with deep geothermal energy. The comparison is conducted on an energetic level, evaluating maximum cold generation and electrical efficiency from both a technological and systemic perspective. The analysis includes geothermal pump power consumption as well as the electrical demand for heat rejection. Detailed numerical models were developed for both the absorption cycles and the compression processes within the combined cycles. The comparison indicates that cascaded configurations do not enhance geothermal cooling and no scenario for their use could be identified. Of the two hybrid cycle options, the lowpressure compressor integration is energetically superior. For fluctuating cooling demand and high ambient temperatures, a demand-driven control strategy for these cycles can enhance geothermal cooling applications. If the cold demand can be covered with conventional absorption chillers and geothermal source temperatures above 70 ◦C are available, they proved to be the best option for the investigated temperature range. The single effect cycle is the most suitable one for the investigated temperature ranges. The combination of a single effect and a double lift cycle leads to approximately 25 % higher cold production. The analysis demonstrates that geothermal cooling is a highly efficient method for providing cold, with even medium- to low-temperature geothermal resources proving to be suitable.