In 2013, Bucknell University selected DN Tanks to design and build a 0.9 million gallon Thermal Energy Storage (TES) tank through a competitive bid process. H.F. Lenz provided the specifications and drawings for the TES system. The TES tank is designed for 6,500 ton-hrs of useable thermal storage capacity. This prestressed concrete tank is differentially buried on a sloping hillside next to the central plant and within a few feet of a Structural Engineering lab building. The TES tank provides significant energy cost savings by allowing the University to closely coordinate operation of the chilled water system and the on-site Combined Heat and Power (CHP) plant. The chiller plant generates a significant portion of the campus chilled water requirement by charging the tank over night using low-cost power from the CHP system. The TES system discharges the stored water during peak electric load periods when power would normally be purchased from the local utility. The TES system enables plant operators to reduce output from the electric chillers, thus reducing both peak demand charges and energy purchases from the utility.
In addition, Bucknell uses free-cooling at night in the fall, spring, and winter to charge the TES tank, and then uses that stored chilled water to cool the campus during the peak periods of the day without operating the electric chillers. The TES tank provides the central plant operators with the flexibility to make hourly decisions on how best to operate their chilled water cooling system in conjunction with their existing Cogeneration system. This results in the most economic use of their equipment. According the James Knight, Bucknell University Director of Utilities, the TES tank has the potential to save over $22,000 per year in energy costs.
In 2013 and before the TES system was in operation, the electric load peaked at over 2,000 kW. Then, on a comparable day in 2014 and with the TES in operation, the electric load was just over 1,000 kW. Therefore, the TES system helped reduce the peak electric demand of the University by approximately 1 megawatt. This is an example of how the TES system provides value to Bucknell University on a daily basis.