Converting an ice storage facility to a chilled water system for energy efficiency on a deep level gold mine

Abstract

20% of the annual energy usage on a deep-level gold mine is consumed by the refrigeration system. Underground cooling demand also increases significantly with deeper mining activities due to high virgin rock temperatures (VRT). This study therefore focuses on the electricity usage of an ice storage system versus a chilled water system for underground cooling. A savings approach of converting an ice storage system to a chilled water system and varying the water flow through the system was thus implemented. The water flow was controlled by installing variable speed drives (VSDs) on the evaporator and condenser water pumps. The feasibility of the energy-efficiency approach was then simulated with a verified model. Simulation results indicated the feasibility of converting the thermal ice storage to a chilled water system and implementing the energy-efficiency approach on Mine M. An electricity saving of 9% when using a chilled water system was indicated by the simulation. Various problems encountered by the mine with the thermal ice storage system were also a motivation. Further, converting the glycol plant to a chilled water plant gave the mine an additional chiller to sufficiently meet underground demand. An annual summer power saving of 1.5 MW was achieved through the conversion and control strategy.