CO_2 vapor compression systems

摘要

According to the Regulation implementing the European Directive 2009/125/EC, from the year 2018, chillers with a rated cooling capacity not exceeding 2 MW must fulfil a series of "ecodesign" requirements to be placed on the market and/or put into service. Carbon dioxide (CO_2) as working fluids is, at least initially, not the best solution for air conditioning or chiller units due to its thermophysical properties. However, it is the purpose of this work to demonstrate that CO_2 could be a suitable refrigerant in chillers when certain design changes are implemented to the refrigeration system of the chiller. Simulations have shown that an improvement on the performance of chillers with CO_2 is obtained if ejectors are introduced to unload the compressors of the CO_2 unit. Applying the available expansion work within an ejector lifts the suction pressure of the compressors significantly. Experimental tests have been performed with the Su-perSmart-Rack facility at NTNU/SINTEF. The operation conditions were specified in the aforementioned 'ecodesign' regulation to demonstrate that CO_2 chiller systems can actually fulfil the requirements.