Continuous Hybrid Cooling; Subsurface Heat Modelling to Establish Feasibility of Absorption Cooling in Oman

Abstract

In a cooperation between The Research Council of Oman, GFZ Potsdam, TU Berlin and the German University of Technology in Oman a pilot project was set up to investigate a Continuous Hybrid Cooling system. This is an alternative air-conditioning system that runs entirely on renewable energy sources. In Oman and other regions with a hot climate air conditioning systems are one of the biggest consumers of electrical power. In Oman 97.5% of electricity is generated by natural gas combustion. In order to reach the goal of low-carbon consumption, a pilot project with absorption cooling that does not rely on fossil energy, could deliver a major contribution. Absorption cooling systems utilize thermal energy to produce chill. Their coefficient of performance depends strongly on the ability to reject heat. The ambient air temperature of Oman is too high to efficiently reject the heat to. The subsurface has a more stable and cooler climate. Subsurface heat rejection is therefore potentially an option. Subsurface heat streams are simulated in different modelling configurations to establish feasibility of absorption cooling in Oman. The simulation is built in COMSOL Multiphysics and expands on previous models. The coupling techniques of 1D, 2D and 3D domains are employed as tools to visualize behavior of subsurface heat streams. The main research questions whether absorption cooling is possible for the climatic conditions of Oman is answered by first establishing the variables. According to the model target heat rejection of 1,500 kW can be achieved, this does remain dependent on the configuration of the system (borehole depth, volume flow through the borehole etc.). The maximum obtainable heat rejection is dependent on the chosen parameters. From the model runs it appears that an increase of depth of the borehole results in a larger heat rejection. A deeper borehole is costlier and has to be evaluated. Due to subsurface heat rejection the temperature increases. This negatively impacts the ability to reject heat to the subsurface and therefore decreases the efficiency of the heat rejection.