ENERGY EFFICIENT DAIRY SHED MILK COOLER AND WATER HEATER USING CARBON DIOXIDE AS REFRIGERANT

摘要

The use of CO_2 (R744) as refrigerant continues to spread in various applications. One notable feature of R744-systems is the capability of simultaneously generating hot-water at 85°C efficiently while providing sufficient cooling capacity. In the dairy barn, freshly-extracted raw milk should be cooled immediately, while large quantities of hot-water at 85°C are required to wash and sterilize raw milk pipes and tanks. In this project such heat pumping systems, using R744 as refrigerant, were developed and tested for installation in both old HFC milk coolers using brine in the evaporator, and for new milk coolers using R744 only. A new plate type evaporator withstanding a pressure of 85 bars was developed for the R744 only system. Laboratory and prototype field tests showed that both systems provided cooling capacity within the standard specifications while producing hot water at 85°C. Compared to a baseline R134a system with electric resistance tap water heating, measured energy use for the R744/brine system was approximate 60% lower. Preliminary calculations show that the installation cost of a R744 system would be approximate 20% higher than for a conventional HFC cooling unit without water heating. However, due to reduced tap water heating cost, the payback time based on the current Norwegian electricity prices of 0,8 NOK/kWh could be as low as 1,5 years.