Experimental investigation on integrated two-stage evaporators for CO2 heat-pump chillers

In this experimental study the performance of novel compact evaporator configuration was investigated. What makes this evaporator configuration unique is the integration of a gravity-fed/ self-circulation evaporator loop on one side of a plate heat exchanger (pre-cooling the secondary flow) and an ejector-assisted circulation loop on the other side (after-cooling the secondary flow). The secondary loop is internally connected, which means that larger temperature differences can be obtained with less connection work and space required, compared to previous heat exchanger models. Current CO2 heat-pump chillers available on the market utilize two evaporators to achieve high energy efficiency values. Space saving of the new compact design is a desired solution from vendors. When using this new concept, only one ‘three-circuit’ brazed heat exchanger is needed. The experimental campaign proofed that an ejector integration enables the two-stage evaporation configuration which significantly elevates the compressor suction pressure and improves the overall system performance. These systems can be applied in several market sectors including industrial chillers with high-capacity demands, where the secondary fluid is cooled even below 0°C.