Comparative analysis of the coefficient of performance of an on-farm direct expansion bulk milk cooler

Abstract

Milk cooling is one of the energy intensive processes in the dairy farm and dairy processing. In a dairy farm, the bulk milk cooler (BMC) should cool milk from a temperature of 35°C to a storage temperature of 4°C. Since the BMC is the major equipment used to extract heat from the milk, it is important to understand the efficiency of the system in a bid to reduce demand in dairy farms. This study presents a comparative analysis on the COP of a direct expansion BMC to establish its performance under the morning (AM) and late afternoon (PM) milking times. A data acquisition system was designed to capture the power consumption of the BMC, refrigerant temperature at the compressor and condenser inlet and outlet points, milk temperature as well as the relative humidity and ambient temperature. Findings from the study showed that on average the COP of the AM milking time was higher (2.20) than that of the PM milking time of the BMC (1.93). It was noted that, increase in milk volume led to increase in the COP such that the peak period with high milk volumes recorded high COP increase by 12.61% and 19.81% for the AM and PM milking times respectively. Notwithstanding, the performance of the BMC was also directly influenced by the change in ambient temperature.