Alamo Heights School District showcases solar and thermal energy storage

October 2, 2015

Over the past few years, the Alamo Heights Independent School District (AHISD) in Texas has made numerous investments in cost-saving technologies in an effort to improve the performance of facilities on district campuses. One of the most unique and innovative additions to the district's technology profile is CALMAC's IceBank thermal energy storage tanks, which have helped the school to reduce peak energy consumption by over 20 percent. In addition to assisting the district in taking advantage of night-time electricity, the most cost-effective energy pricing on the market, the tanks have also been used to directly supplement the school's solar installations.

Cooling from ice provides alternative to more higher operating costs
CALMAC's IceBank thermal energy storage tanks were installed at the AHISD high school campus in San Antonio in order to help manage the cooling of five buildings spread out over 325,000 square feet, according to Engineered Systems Magazine. Even with the presence of several solar arrays, the school felt it necessary to reduce energy consumption during daytime peak demand hours, when there isn't enough power to meet peak consumption and electricity costs are at their highest.

By utilizing two of the campus' existing three chillers to create ice at night, the school is now able to save money during periods when the campus experiences its afternoon spike in electricity consumption and is simultaneously subjected to high peak demand charges by the local utility. The ice made at night is melted and distributed during the day among the five buildings on campus to keep the students and faculty cool. The ice helps lessen the need to run the facility's chillers during the hottest parts of the school day, reducing costs during those times by a significant margin.

Versatile IceBank energy storage tanks used to supplement solar generation
The flexibility of CALMAC's IceBank energy storage tanks allow the technology to do more than assist campuses in shifting the campus electricity demand schedule and reducing costs. The ability to store electricity in the form of ice is also a boon for the campus in the form of a means of fixing the gaps in the school's solar strategy. Alamo Heights Independent School District currently generates some of its own electricity through solar power - one 500-kW system and an additional five 400 kW of solar arrays make up the campus generation profile, according to the Refrigeration Service Engineers Society. Initially, this solution was engineered to offset peak demand, but the intermittency of solar generation - the possibility of a cloudy or stormy day - made it difficult to rely on solar generation on a daily basis.

The school needed to deploy an energy storage solution that could respond to intermittency in the power grid or peak demand during the day at a moment's notice, regardless of outdoor weather conditions. In addition, the campus planned to expand and needed to address new peak demands. With energy storage, the district was able meet the extra cooling demand of the new structure without adding additional daytime chiller capacity to meet the new load.

More energy storage means facilities can expand without need for additional chillers
Minimizing dependence on large, expensive chillers is another major benefit for school districts that take advantage of thermal energy storage. By introducing the energy storage technology, AHISD sets up its new high school to significantly reduce energy costs by greatly limiting the need to run all of the campus chillers during the most expensive peak periods. Lowell Tacker, principal architect for the firm that designed the school's latest 12,000-square-foot expansion, remarked to Retrofit Magazine on how effectively the energy storage solution limited the need to run the school's chillers despite the fact that the campus footprint was growing.

"The system provides 1,944 ton-hours of cooling capacity. If it's not really hot outside, you don't need the chillers to go on at all, as running the fluid through the stored ice maintains comfortable temperatures," Tacker said.