3222 -- Reducing Energy Costs in Vapor-Compression Refrigeration and Air Conditioning Using Liquid Recycle---Part ll: Performance PDF

In Part I, it was shown that ammoniand R-12 are roughly equivalent in performance. Ammonia has the advantage that it requires less high-pressure heat exchange area than R-12. Unfortunately, ammonia has a very high superheat, which may lead to materials or lubrication problems. These problems may be solved by recycling liquid ammonia. Two methods of recycling liquid to a singlestage vapor-compression refrigeration system are explored. The first method recycles condenser liquid to the compressor outlet. This removes superheat by direct liquid evaporation (high heat transfer coefficient) rather than through a desuperheater (low heat transfer coefficient). The size of the high-pressure heat exchanger may be reduced (10% to 20% reduction) or energy efficiency may be improved (1O/o to 5%). The second method recycles condenser liquid directly into the compressor to cool the gases during the compression stroke. This improves the energy efficiency by 10% to 15%.