Energy Efficient Design, Retrofit and Control of Evaporative Condensers in Ammonia Refrigeration Systems

Ammonia refrigeration systems typically offer many energy efficiency opportunities because of their large power-draw, long runtimes and dynamic operation. Ammonia refrigeration system energy use is highly dependent upon condensing head pressure, which in turn is a function of evaporative condenser capacity and control. This paper investigates the relationship between system energy use, condenser capacity and condenser control. It begins by developing a methodology to determine condenser performance and then to simulate the annual energy use of the compressors and condenser fans. The simulation model, which uses both engineering fundamentals and empirical data, accurately captures synergistic effects between the compressors, the condenser and ambient wet-bulb temperature. Energy savings are then calculated for three cases: installing VFDs on condenser fans, using wet-bulb approach control strategy and increasing condenser performance. To illustrate the effect of climate, these simulations are performed for two different ASHRAE climate zones, Miami, FL and Minneapolis, MN, which are hot and cold climates respectively. The results show that improving the performance of an underperforming condenser is the most cost effective energy conservation measure irrespective of location. However energy savings from installing VFDs on condenser fans and utilizing wet-bulb approach strategy depends on the ambient weather conditions. Next, the internal rate of return is calculated for installing additional condenser capacity beyond standard practices in new construction applications for the same two ASHRAE climate zones. The results indicate that the internal rate of return exceeds 20% for installing twice the baseline condenser capacity. In summary, the paper presents an integrated approach for design, retrofit and control of evaporative condensers in ammonia refrigeration systems. Energy savings derived through the use of this approach can significantly improve energy efficiency of ammonia refrigeration systems.