Dissipative Losses in Cooling Cycles

To improve the energy efficiencies of cooling cycles, it is important to identify the key sources of internal dissipative losses, thus pinpointing the major inefficient components that require optimization. This chapter conducts a second-law analysis on different cooling systems, including a mechanical vapour compression chiller, an absorption chiller, an adsorption chiller, and an indirect evaporative cooler. Based on thermodynamic states of these systems, the entropy generation rates of each component are calculated which revealed that the compressor, the regenerative heat exchangers and the reactor beds account for the most dissipative losses in mechanical chillers, absorption and adsorption chillers. The exergy efficiency of mechanical chillers can be improved by promoting the heat transfer in the evaporators and the condensers. The system-level entropy generation rates are normalized with respect to the cooling capacities to allow a direct comparison of different systems. The indirect evaporative cooler is found to perform most efficiently among the compared cooling cycles, while the adsorption chiller incurs the most internal dissipations due to poor heat transfer in its porous adsorbents.