Utah State University

CALMAC IceBank® Energy Storage Tanks Provides 90 Tons of Cooling Capacity for the Nutritional Food Services Building at Utah State University.

• New High-Efficiency Trane Model RTAC Air-Cooled Series R™ Chiller with CALMAC IceBank® Energy Storage System
• Up to $1300 per Month in Energy Savings

Challenge

The Food Services Building at Utah State University was served by a 30-year-old absorption chiller that needed to be replaced. Full cooling load on the building was estimated at 250-tons. USU considered installing an electric chiller, but the building’s electric service could not handle a 250-ton cooling capacity electric chiller. Upgrading the electrical service would have cost $32,000.

Solution

Trent Hunt, sales engineer at Trane in Salt Lake City, developed a solution akin to eating your cake and having it, too! Hunt proposed taking the money for an electrical upgrade and instead using it to install a new 170-ton capacity air-cooled electric chiller with a 90-ton ice storage system. At full load on a 95-degree day this chiller will draw about 207 kW of electric power. In the ice storage mode with 70-degree nighttime ambient temperatures, the chiller needs to produce only 111 tons and draw only 133 kW, allowing the existing electrical system to suffice. Making ice at night by generating 22 F chilled water/glycol can be 10 percent more efficient than making 44 F chilled water during the day due to lower nighttime ambient temperatures. Shifting chiller load to nighttime has an added benefit in that in most markets, energy is less expensive at night. Further, overall building demand charge is reduced by operating chillers at night since maximum kW used to make ice will not typically exceed daytime electrical use that includes lights, computers, fans, pumps, etc. Compared to a 250-ton chiller without ice storage and drawing 337 kW of power, produces a savings of nearly 130 kW - up to $1300 per month based on a $10 per kW demand charge.

Daytime discharge cooling capacity of the ice storage system is relatively constant. If daytime cooling load is 250 tons, the ice provides 90 tons and the chiller 160 tons. If only 170 tons is required, ice storage supplies 90 tons and the chiller 80 tons. If only 90 tons of cooling capacity is required, the electric chiller can be shut off! In addition to avoiding the cost and work associated with an electrical system upgrade, the ice storage tanks fit in the same location as the old cooling tower that served the absorption chiller. Very little new construction was needed to accommodate the ice tanks and USU can easily add two more ice tanks for 40 more tons of cooling capacity to accommodate increased load or provide cooling for other buildings.

Results

The USU Nutritional Food Services Building now has an efficient, effective and reliable air conditioning system. Reid Olsen, Central Energy Plant Manager at Utah State University, said, "This project has worked out very well for us. The chiller and ice storage system is working very well and we are realizing the projected energy cost savings. This has been a very good solution for Utah State University."

About Utah State University

Since 1888 USU has evolved from a small, agricultural college to an internationally recognized university noted for intellectual and technological leadership in land, water, space and life enhancement. The university has 850 faculty who provide education for more than 23,000 undergraduate and graduate students, including 10,000 in its continuing education sites located throughout Utah. USU occupies 7,000 acres with more than 200 buildings, 63 of which are devoted to academics. USU also has three branch campuses and extension offices in all 29 Utah counties.

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