Across from the Henry B. Gonzalez Convention Center, at the corner of Commerce and Bowie streets, sits an unassuming, 1960s-style brown brick building with tall arched windows.
Lettering over the front door reads San Antonio Water System’s Central Cooling Plant.
Passersby might not give it a second thought, but inside that modest building, millions of gallons of water are being quickly chilled and pumped into the AC systems of the largest buildings across the downtown area.
As San Antonio settles into what is promising to be another scorching summer, city and state officials are warning residents and businesses that the state grid could again face emergency conditions, as it did last summer and more notably during 2021’s Winter Storm Uri with fatal results.
Already the state is seeing record-breaking power demands, driven largely by Texas’ booming population growth, the addition of more data centers, and the growth of artificial intelligence and cryptocurrency mining.
As one of CPS Energy’s largest electric customers, SAWS has begun looking at how it can help save energy during times when the state grid is tight.
Earlier this year, SAWS introduced an energy strategy master plan that aims to help take megawatts off the local grid. Playing a key part in that plan is SAWS’ district cooling system, said Chris Wilcut, SAWS’ district cooling and energy strategy director.
“The district cooling system is a win-win for everybody,” Wilcut said, noting it helps instantly reduce the demand for electricity from the local grid. “CPS [Energy] gets the benefits because of the demand reduction when they need it most.”
How the district cooling system helps the grid
District cooling can reduce cooling energy consumption by 50%. These systems also help the customers save money, and reduce the amount of disposable chemicals they utilize, said Elroy Bishop, SAWS Central Cooling Plant operations manager.
SAWS’ downtown district cooling system consists of an underground pipe network filled with recycled water that is chilled at SAWS’ two district cooling plants. Its Central Cooling Plant is responsible for chilling most of the system’s water, and its smaller Cherry Street Cooling Plant which is located over by the Alamodome, explained Bishop.
The chilled water travels from the plants to the 22 buildings within the SAWS downtown cooling system, helping to cool the spaces before returning to the plants to be cooled again. The system is a closed loop, using and reusing the same water for the most part and utilizing SAWS’ recycled water to replace lost water. Buildings within the system include the Alamodome, the convention center, several buildings within Hemisfair Park and many of the area’s hotels.
The chilled water sent to the buildings is typically around 42 degrees Fahrenheit, and can return anywhere from nine to 15 degrees warmer, Bishop noted.
“We try to like to have it between 12 and 15 [degrees],” Bishop said. “That’s the ultimate — what we call Delta T [or change of temperature] — efficiency rating.”
The chilled water runs through the buildings’ HVAC units, helping the buildings save energy because they don’t have to utilize the thicker, harder-to-move alternative of refrigerant.
Water that returns to the plant is “recharged” or chilled by being run through the plant’s industrial chillers. The industrial chillers work much like a regular HVAC system but on a much larger scale, using refrigerant to cool the water. The warmed refrigerant is then cooled using cooling towers that provide water to cool and condense the coolant.
The plant also has a thermal energy storage system that can be utilized, instantly reducing the local grid’s load by 3.5 megawatts as needed — enough energy to power about 875 homes on a summer day, Wilcut said.
“What we do is … run the chillers overnight when energy is cheap, and there’s not a lot of energy demand, and we’re saving the stored energy to create this [ice] slurry,” Wilcut said.
When the state’s grid operator the Electric Reliability Council of Texas (ERCOT) issues statewide conservation calls, SAWS is then able to shut off its industrial chillers and chill the water running through the system utilizing the ice slurry it made the night before instead of using any additional electricity, Wilcut explained.
This is especially beneficial during periods of peak use — such as between the hours of 4 p.m. and 9 p.m. in the summer, Wilcut added.
“It really helps the grid and we’re also [using] energy at night when it’s cheaper, cleaner sources like wind,” he said. These systems are also more energy efficient than all these businesses installing and utilizing their own chilling systems in general, Wilcut added.
Part of a plan
SAWS’ downtown chilled water system is just a piece of the puzzle within the utility’s new energy strategy master plan.
SAWS’ plan aims to reduce SAWS’ “energy intensity” — a measure of energy efficiency calculated by dividing a user’s kilowatt hours per unit — by 10% by 2028.
According to the plan, SAWS currently consumes about 475,000 megawatts of electricity annually — enough electricity to power over 32,000 Texas homes for a year.
While the majority of SAWS’ annual energy use in 2023 came from water production and distribution at about 72%, the district cooling system accounted for about 8% of the utility’s energy use that year, according to SAWS. SAWS’ district cooling system uses roughly 45,000 megawatt hours of electricity annually, according to its energy strategy master plan. A megawatt hour is enough electricity to power the average American home for about a month.
As a part of its larger plan, SAWS aims to implement seven steps to achieve its energy reduction goals, one of which is to pursue low- and no-cost energy conservation measures identified within SAWS’ water, wastewater and district cooling systems, including three potential district cooling projects.
These projects include replacing aged chillers that have reached the end of their useful lifespan, slowing down the system’s pumping speed, and buying and implementing new control software. The combined cost of the three projects is about $1 million and would save the utility an estimated 12,750 megawatt hours per year.
Growth and innovation
SAWS has owned and operated the district cooling infrastructure in downtown San Antonio since 1968. For years, SAWS has noted that its district cooling system is the utility’s only organizational component that is not financially self-sufficient.
In an effort to make its chilled water business turn a profit, and to also grow the system, the SAWS board approved a 12% rate increase for its chilled water commercial customers last year that was expected to raise about $827,000 more in revenue this year.
That is on top of the 10% increase it approved the year before. Prior to that, SAWS had not raised its chilled water rates for downtown customers since 1999, and for Port San Antonio since 2005. SAWS has additional chilled water rate increases planned for 2025, 2026 and 2027.
The utility has considerable space within the existing Central Cooling Plant for expansion and has recently begun construction preparing for this work, Wilcut said. The added space within the plant will be used to install two new additional pumps, as well as sand filters, which will allow SAWS to use fewer chemicals in the water’s filtering system, Bishop added.
“We’re really at a point now where we’re ready to revamp and expand the system and help it be more efficient,” said SAWS senior communications specialist Lillianna Gonzalez. “We’ve got a $50 million rehab plan over the next five years.”
Earlier this month, SAWS announced the addition of the Kimpton Santo hotel to the district cooling system, making it the first new chilled water customer since 2004.
At that time, Mayor Ron Nirenberg called the SAWS district cooling system “an underused asset that is helping reduce energy consumption, cut costs for businesses that take advantage of the service, and protect our environment.”
“I encourage other eligible businesses to take a close look at this opportunity to boost their bottom line and strengthen our sustainability efforts,” he said.
