Reduced condensing pressure operation in industrial ammonia refrigeration systems

Graduation date: 1990A computer model was created using compressor and\ud condenser performance data to simulate vapor-compression\ud ammonia refrigeration system performance under various\ud operating conditions and strategies. The model was used to\ud estimate energy, demand, and cost savings resulting from\ud reduced condensing pressures.\ud Two ammonia refrigeration systems were selected for the\ud investigation into reduced condensing pressure operation.\ud Each refrigeration system was monitored under two modes of\ud operation: high (fixed-head) and reduced (floating-head)\ud condensing pressure. Compressor and condenser fan power,\ud condensing pressure, and ambient dry and wet-bulb\ud temperatures were recorded for a one week period. During\ud the fixed-head period, the condensing pressure was\ud maintained at 145 to 155 psig, which is typical for\ud industry. The condenser fan controls were adjusted for the\ud floating-head period, reducing the average condensing\ud pressures to 117 to 130 psig. Reductions of 9.8% to 11.7%\ud in combined compressor and condenser fan power were observed\ud during the floating-head operation. In addition, none of\ud the potential problems associated with floating-head\ud operation were observed.\ud The model was used to simulate refrigeration system\ud performance during the monitoring periods, using weather\ud data and estimated refrigeration loads as model input.\ud Model predictions were compared with the monitored data to\ud validate the model performance.\ud The model was used to predict monthly and annual\ud energy, peak-demand, and operating costs for a range of\ud condensing pressures. Monthly dry and wet-bulb temperature\ud profiles, and estimates of refrigeration loads were used as\ud input for the model.\ud The model predicted:\ud Annual energy savings of 10.6% to 12.0%,\ud corresponding to 0.63% to 0.83% savings per degree\ud reduction in average condensing temperature.\ud Average monthly peak demand savings of 8.7% to 9.2%,\ud corresponding to 0.53% to 0.64% savings per degree\ud reduction in average condensing temperature.\ud Average annual cost savings of 10.4% to 11.9%,\ud corresponding to 0.62% to 0.82% savings per degree\ud reduction in average condensing temperature.\ud The possibility of minimum condensing pressures,\ud below which the condenser fan operating costs\ud outweigh compressor savings.\ud A significant portion of the possible energy savings\ud (79% to 93%) with no additional equipment or capital\ud cost