Thermal Storage Slashes Energy Costs

A Florida school district implemented energy-efficiency measures that saved 30% to 40% on utility costs.

The fi rst St. Lucie County School District building to implement IceBank tanks in the form of a full-storage system was St. Lucie West Centennial High School, Port St. Lucie, FL. S t. Lucie County School District (SLCSD) is a K-12 system in Florida with more than 40,000 students and 5,000 employees. Over the past seven years, the district has made a commitment to creating healthy, energy-effi cient building environments that reduce operating costs. The district has implemented energy-effi ciency upgrades that include an ice-enhanced chiller plant using Calmac Mfg. Corp.’s (Fairlawn, NJ), thermal-energy storage technology, independent metering equipment, and air-cleaning technology. The ice-enhanced chiller plant has allowed SLCSD to save 30% to 40% on utility costs annually—in total, about $5 million in savings to date.

In 2007, SLCSD had one of the highest energy costs/sq. ft. of all the school districts in the state. The facilities within the district were wasting energy, and the schools were faced with a lack of funds. Energy costs within the district were paid from the same pool of finances that covered teacher salaries. This meant energy inefficiencies within the facilities were having a serious financial impact on how much salary revenue was available to educate students.

Acknowledging that the district was in desperate need of energy-efficiency upgrades, SLCSD made a commitment to promote energy-efficiency awareness and improve equipment. St. Lucie assembled an energy-advisory team and partnered with the local utilities that supplied power to the district. Full-time energy manager Sean P. Murray was hired to develop and execute a strategy to reduce utility costs as well as track and monitor results. Murray implemented ice-based thermal energy storage into existing facilities and managed a behavior-modification program. Additional strategies included utility rate-structure modifications, control-system enhancements, and other energy-efficiency upgrades.

Calmac’s IceBank thermal-energy storage was identified as an important solution. Despite drawing power from two utilities that used very different pricing structures, energy storage would allow a facility drawing power from either utility company to shift energy usage away from expensive peak-demand periods.

“We did our homework and looked at a variety of technologies,” said Murray. “After looking at Calmac and looking at some of the other manufacturers, we decided that there was no competition,

that we were going to pick the Calmac tank based on the superior design and operation of those tanks.” CREATING COOLING AT NIGHT The first school to implement IceBank tanks in the form of a full storage system was St. Lucie West Centennial High School, Port St. Lucie, in 2007. In this full-storage system, high-efficiency chillers from Trane, Davidson, NC, create enough cooling at night, when outdoor temperatures are low and energy costs are less that half of what they are during the day, to cool the entire school from noon to 9 p.m. the next day. This cooling load is stored overnight as a block of ice in IceBank tanks. Then, the next day when school opens, the chillers satisfy the cooling-load requirements. At noon, the stored ice is used to cool the school until 9 p.m. without any assistance from the chillers. This system is able to shift roughly 1,200 peak tons of cooling.

Electric-utility cost savings for Centennial High School proved to be about $300,000/yr. By independently metering the chiller plant, Centennial High School was able to identify a 50% reduction in cooling costs due to energy storage. Because of its success, the St. Lucie School District began to install the IceBank energy-storage tanks in their buildings whenever chiller replacement projects became necessary.

Several schools were able to take advantage of Florida Power & Light incentives that cover most of the cost of installation for full-shift storage. However, not every school in the district is powered by Florida Power & Light, Juno Beach, which uses time-of-use pricing (TOU). Many of the educational facilities in St. Lucie are supplied electricity from Fort Pierce Utilities Authority, Fort Pierce, FL, (FPUA). FPUA implements a $10/kW demand charge and does not offer TOU rate incentives to help offset installation cost. It was more effective to use partial-storage systems in those schools.

The facilities using the partial-storage system create and store enough ice to assist but not fully handle peak cooling requirements. Throughout the day, stored energy can be discharged to help the chillers provide cooling. This flexible system operation allows the schools to use smaller, more efficient chiller equipment than was previously required and reduce the peak-demand charge from the utility. One partial-storage system at Lincoln Park Academy, Ft. Pierce, reduced cooling costs by 32%.

With a strong commitment to improving the schools, the St. Lucie district not only installed cost-saving equipment but also promoted energy-efficiency awareness throughout the schools

Displays were installed in multiple sites to showcase that school’s energy performance, which naturally led to friendly competition that was backed by incentives for improvements. These initiatives extended beyond physical upgrades to the facilities and helped change the culture of the school district. For example, due to the increased awareness of energy usage, it became common to group after-school activities into fewer buildings to minimize resource use.

ADDITIONAL UPGRADES

Top. Trane chillers create enough cooling at night, when outdoor temperatures are low and energy costs are less, to cool the entire school from noon to 9 p.m. the next day.

Above. The cooling load is stored overnight as a block of ice in Calmac IceBank tanks. The next day, the chillers satisfy the cooling-load requirements during the morning hours. At noon, the stored ice is used to cool the school until 9 p.m., without any assistance from the chillers.

In addition to the installation of energy storage, other

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upgrades increased heating- and cooling-operation effi - ciency. Independent metering equipment was installed to separately meter various systems. This allowed St. Lucie to gather performance data and ensure optimal results from different upgrades and equipment.

To improve operation of the existing system, control-system enhancements were implemented with minimal costs.

Other strategies were embraced to improve operational efficiency by reducing reheat conditions, including the use of occupancy sensors, which has minimized sub-cooling during unoccupied periods by reducing cooling air flow. Adjustments were also made to the pumping system, which has reduced the amount of chilled-water flow. High-efficiency chiller equipment kept part-load efficiencies below 0.3 kW/ton.

St. Lucie also saw a significant opportunity for savings by reducing outdoor air-intake rates to lower system capacity. The district introduced air-cleaning technologies that leveraged bipolar ionization into some of their facilities to kill mold, bacteria, and viruses, creating a healthier environment for students. In laboratory spaces, green fume-hood filtration systems were used. These systems significantly reduced outside air requirements.

By executing a clearly mapped plan to increase energy efficiency, the St. Lucie School District has been able to garner significant, tangible results. In total, 15 facilities are using Calmac’s IceBank energy-storage tanks. The schools using full-shift strategies for their energy-storage systems have saved more than $615,000 annually in energy costs, a 50% reduction.

Partial-storage strategies are also dramatically reducing operating costs. Lincoln Park Academy is a perfect example. Prior to installation, its 3-yr. average energy costs were $475,000. One year after using partial-energy storage, energy costs were down to $334,000, a 32% annual reduction.

In the 2008-2009 school year, the St Lucie School District was ranked 60th among statewide districts in terms of energy costs/sq. ft. The use of energy storage, in combination with the other energy upgrades, catapulted the district into the top 20.

The district is benefitting from a 30% to 40% reduction in annual energy costs and has saved about $5 million in costs since the initiatives were undertaken. This is the equivalent of salaries for 100 teachers.

“Our board is thrilled with the energy cost savings and we have other school districts, county governments, and colleges wanting to understand what we did here,” said Murray.

“St. Lucie should be commended for the way they completely changed the philosophy throughout the entire school district when it comes to energy efficiency,” said Mark MacCracken, CEO of Calmac. “Everyone has bought into their goals of creating an energy-efficient, healthy learning environment. Their use of energy storage has allowed them to take control of their utility costs and use the savings in important areas, such as teacher salaries.” CBP

DATA CACHE

Want more information? The resources below are linked in our digital magazine at cbpmagazine.com/digital/oct2014.

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Download an ASHRAE Journal article about energy storage: Energy Storage Providing for a Low Carbon Future.

Download the Calmac IceBank Energy Storage Fact Sheet 2014.