On the hawaiian island of Oahu, two dairies are improving the quality of their milk and saving thousands of dollars per year on power bills with electrically based, high-speed milk-cooling systems. The technologies—designed by the Honolulu-based Hawaiian Electric Co. and two heating/ventilation/air-conditioning manufacturers—were developed as part of a $320,000 effort to improve the quality of Hawaiian dairy products and reduce the energy costs of production.

These twin high-efficiency scroll compressors are part of a commercially available cooling system used to chill the milk drawn from 300 cows twice daily at Evergreen Hillside Dairy Farm on Oahu The system saves approximately $2,400 in annual energy costs.

This public and private effort was needed because of the sharp competition created by lower-priced imports from the mainland. The biggest threat came from California, where much larger dairy farms can take advantage of economies of scale and lower feed, land, and energy costs.

Added to these disadvantages is the challenge of cooling milk in Hawaii. Like mainland dairies, Aloha State milk farmers pump the white liquid directly from the cow's udder to a central storage tank where the milk's temperature is lowered from 98°F to 38°F. This procedure takes just 2 hours in the storage tanks used by 80 percent of California dairies, but is more time-consuming in Hawaii's tropical climate. The longer it takes to chill milk, the more its quality deteriorates, which means a shorter shelf life.

To speed the cooling process at the Mountain View Dairy in Hawaii, engineers from the utility and DLTech in Ithaca, N.Y., designed a glycol-based cooling system using standard air-conditioning equipment. Milk from 950 cows is drawn at Mountain View three times daily, then sent through an 800-gallon glycol storage tank that cools the milk in 30 seconds—the time required for milk to flow through the system.

Glycol is circulated through this storage tank to lower milk temperatures swiftly from 98°F to 38°F

Workers at Evergreen Hillside Dairy Farm on Oahu, meanwhile, milk 300 cows twice a day using a commercially available glycol milk-cooling system made by Dairy Equipment Corp. in Madison, Wis., and purchased by Hawaiian Electric. The system incorporates two high-efficiency scroll compressors with brazed-plate evaporators. The remote mounted condensing units have corrosion-protected fins. Inside the milking room, an adjustable-speed drive controls the existing centrifugal milk pump to meter milk through the plate cooler. Milk is cooled in 3 seconds because the motor moves at 39 hertz per minute. If a large volume of milk is flowing through the system, the motor will increase its speed to 50 hertz.

Brazed-plate evaporators are outfitted with high-efficiency scroll compressors to keep the quality of dairy products from deteriorating in Hawaii's tropical climate

Both dairies are cutting their electrical costs by using energy-efficient vacuum pumps to milk the cows and pipe the milk to the holding tank; they also send water and cleansers through the systems during cleaning. Their previous vacuum pumps ran continually at the maximum anticipated capacity, rather than the actual capacity needed to maintain a constant vacuum. The new cooling systems use adjustable-speed drives with proportional-integral capabilities and a vacuum sensor to regulate the vacuum pump to match the air flow actually needed by the milking system. This translates into annual energy savings of about $6,000 at Mountain View and nearly $2,400 at the Evergreen Hillside.


Return to Index