Comparison of electrical energy efficiency for milk cooling in a dairy farm with two milking sessions in Eastern Cape Province of South Africa

Milk cooling is one of the energy intensive operations in a dairy farm, and it accounts for about 20% of the total energy usage. This study focused on determination of electrical energy efficiency for milk cooling in a dairy farm with two milking sessions. After determination of the cooling systems energy utilisation rate and daily average electrical energy utilisation, energy efficiency parameters were calculated for the distinct milking periods on the farm. The energy efficiency parameters considered in this study are; specific electric energy consumption, electric energy productivity and electric energy cost ratio. The experimental work was conducted at an existing dairy farm using a direct expansion bulk milk cooler for raw milk cooling. The farm is located in the Eastern Cape Province of South Africa and has over 800 cows in milking. Since milk cooling is the major energy consumer in dairy farms, data collected from the BMC was used to represent the farm’s cooling energy efficiency under the two milking sessions. A data acquisition system comprising of power and energy meter and temperature sensors was installed at the farm to monitor the energy consumed by the BMC during the milk cooling cycles and the inlet temperature of the milk. On-farm daily records were used to compute the daily milk volume per milking session. According to results; percentage of total daily energy consumed during cooling was found to be 91% and milk storage 9%. The daily average electric energy utilisation value was found to be 131.65 kWh and 97.03 kWh with a specific electric energy consumption of 0.015 kWh/L. The average electric cooling energy productivity was found to be 68.06 L/kWh. The rate of electric energy cost was found to be 0.53%. The results depicted that under two milking sessions the system performance is better in the morning where about 60% of the milk is extracted. However there was no significant difference between the energy efficiency parameters.