Heat recovery for dairies : case studies

Milk production requires purchased energy inputs that are relatively large compared with other farming enterprises. To reduce the purchased energy requirements for heating water on dairies, several dairy equipment manufacturers produce equipment to utilize the waste heat from the milk refrigeration system, for heating water.

Three dairy farms in Tennessee were monitored to determine the quantity of purchased energy that could be saved by heating water using commercial heat recovery equipment. Water heaters and refrigeration equipment were monitored for electrical energy use. Water temperatures were recorded. Hot water use was measured. The energy requirement in each system was compared to a simulated system using only a conventional water heater to meet hot water demand.

Results indicated that heat recovery reduced purchased energy consumption by 40 to 86 percent compared to conventional electric water heaters. Assuming an energy cost of $9.72 per GJ, savings of $423 to $800 per year were realized. Simple payback times for these systems ranged from approximately two to four years.