Cooler heads will prevail—thanks to thermal energy storage

Maintaining a comfortable environment where teaching, learning, and research can thrive is a top priority at UT’s Utilities and Energy Management (UEM). As one might expect, one of our biggest challenges is keeping the 160+ campus buildings cool during those long, hot Texas summers (which tend to begin in spring and last well into fall). Thus, we are constantly exploring new technologies and improvements to our system in pursuit of energy efficiency and optimization. After all, a world-class higher education institution warrants a world-class district energy system to keep it running. Nothing less will do.

Our approach to efficiency

Unlike a city where commercial buildings are independently heated and cooled, UT employs a district energy system, whereby all of our buildings are connected by a giant loop of underground pipes that deliver chilled water from the various chilling stations located around campus. The chilled water flows through fan coils in each building, creating that refreshing blast of cold air we feel when we come inside from the heat. We use a combined heat and power (CHP) system to generate our own electricity and thermal energy, which allows us to capture much of the energy that would otherwise be wasted under a more conventional system. This includes reusing water and steam in a continuous cycle.

The role of TES tanks

A successful district energy system is one that constantly strives for efficiency and optimization. Through the use of thermal energy storage (TES), we have a solution that satisfies both of those needs. As shown in the diagrams below, chilled water is produced at night (charging period) when the temperature outside is lower and chiller operation is more efficient. During the day (discharging period), the chillers can be turned off or run at a minimum because the tanks have been filled overnight with plenty of chilled water to meet the daytime demand, even on those days of record-setting temperatures. This saves a significant amount of energy and expense compared to the cost of operating the chillers during the daylight hours.

Charging Period Disharging Period

On the UT main campus, there are two TES tanks that hold a combined 10 million gallons of water. The first one, completed in 2011, is located behind Creekside Residence Hall; the newer one, constructed in 2016, is located at the corner of Red River and Martin Luther King, Jr. Boulevard. The tanks run simultaneously and are synchronized for optimal operation. The stratified design separates the warm water from the chilled water.

What are the benefits of TES tanks?

Among the many advantages of thermal energy storage technology are the following:

  • Lower installation cost. Installing a water cooling plant is about four times more expensive than installing a TES tank.
  • Extended cooling capacity. The sheer volume of the TES tanks allows us to use our existing water cooling plants to produce more chilled water, which can then be stored for future use.
  • If a chilling station should unexpectedly fail, the water on reserve in the tanks can be used to cool the buildings.
  • A TES tank can also serve as a battery to store energy (chilled water) to support the CHP should a generator trip off line.
  • TES tanks help to optimize our district cooling system, making it 40% more efficient than individually cooled buildings.
  • Cost effectiveness. TES tanks allow us to use far less electricity during peak electrical consumption periods (typically daytime), thereby reducing operational costs.
  • Greater operating efficiency means we use less natural gas to generate electricity for power, which translates to lower carbon dioxide emissions. Going forward, we expect even further reductions in environmental impact.

For more information on our approach to energy optimization, visit: https://utilities.utexas.edu/efficiency/optimization-programs

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