Ammonia Chiller Performance Enhancement by Implementation of Ejector Overfeed Cycle with Brazed Plate Evaporator.

Ammonia has long been considered one the most promising refrigerants for refrigeration applications due to its favorable thermodynamic properties that yield high COP compared to most other common fluids. Evaporator overfeed in ammonia systems is often accomplished by means of a motor-driven pump; however, a simpler and more reliable method for overfeeding would be to use a liquid recirculation ejector. This paper presents the results of a study investigating the improvement that can be achieved in evaporator and cycle performance for a 20 kW nominal capacity ammonia chiller by overfeeding the evaporator. A two-phase ammonia ejector was designed based on previous in-house knowledge and experience with liquid recirculation ejectors; baseline system and ejector overfeed system capacity, COP, and evaporator performance are presented and compared, with simultaneous capacity and COP improvements of 28 and 22 %, respectively, observed with the overfeed system mainly due to the elimination of the superheated portion of the evaporator.