As part of a recent energy retrofit for the City of Encinitas’ Civic Center, designers and engineers considered several eco-minded options that would reduce the center’s energy consumption while lowering costs — and then employed them all.

Installing photovoltaic panels on the building’s rooftop was considered and incorporated. Ditto, skylights and light tubes.

But perhaps the pièce de résistance is a thermal energy storage solution that keeps the building cool using hardly any electricity during the day. Thermal energy storage works at night by temporarily storing energy — in this case in the form of ice — in large IceBank® storage tanks so the energy can be used during peak energy demand periods.

Already, the system has won local green accolades, earning a San Diego Energy Efficiency award. During the next 25 years, the project will save taxpayers an estimated $4 million in energy costs.

“Every time I look at that rooftop,” said Encinitas Mayor Maggie Houlihan when she learned about the award, “I see a cash register with deposits coming down from the sun.”

Inside the civic center’s three IceBank tanks, a glycol-water mixture circulates through coil tubing at night to freeze water stored inside. During the day, the frozen water melts to cool the water that circulates in the building. Powerful fans blow air past the chilled water in order to cool the building.

Douglas Poffinbarger II, managing principal of Oceanside, Calif.-based PE Consulting Inc., said a thermal energy storage solution made sense for the project. The technology is more popular in parts of the country where electric rates are high — like Southern California.

“Most of the country's utilities have the same problem,” Poffinbarger said. “Everybody is working during the day.” And that’s when the most strain is placed on power grids.

Although renewable energy saving technologies like solar energy and natural lighting are getting more attention now, thermal energy storage is an important part of the green energy equation, Poffinbarger said.

“Solar energy is a ‘plug and play’ technology,” he said. “Thermal storage is more ‘belt and suspenders’ engineering. It’s a little more customized.”

Thermal energy storage is typically used in larger buildings that use chilled water cooler systems, so the system isn’t always a viable option for smaller structures, Poffinbarger said.

“It’s also important to have a client that is interested in taking a holistic approach to saving energy,” he added.

IAMPO Director of Special Services Dave Viola noted that thermal energy storage could be very helpful in attaining the IAPMO board of director’s goal of reducing overall energy and water consumption in buildings by a minimum of 10 percent.

“Thermal storage cooling is an excellent strategy for building owners to consider,” Viola said. “Besides the lower energy costs Associated with shifting the cooling load to a time of day with more economical rates, the technology is green.

“Night time charging for the next day’s cooling load also occurs during the most efficient operating time — at night. The net result,” Viola said, “is a smaller Trane chiller, less energy and refrigerant usage, and lower greenhouse gas emissions.”

Terry Andrews, Western regional sales manager for CALMAC Manufacturing Corp., the firm that manufactured the three IceBank tanks used in the civic center thermal energy storage system, explains how the system works.

At night the chiller charges the IceBank tanks by cooling a heat transfer fluid — a glycol solution that serves as antifreeze — which circulates through coils inside the IceBank tank until the water surrounding the coils in the tank is frozen. “Now, we have low-cost stored energy in the form of ice,” Andrews said.

“The next day, the chiller operates normally by cooling the fluid that is sent to the building’s ‘air handlers.’ The air handlers consist of chilled water coils and a fan that blows air through the coils. “This is the cool air that we feel in the building,” Andrews said.

Conventional cooling continues until the peak electric rate period. For San Diego Gas & Electric, this is from 11 a.m. to 6 p.m. in the summer. Around 11 a.m., conventional cooling with the chiller ends. The warm fluid returning from the building is now sent through the ice tank coils and the fluid comes out cold. From 11 a.m. to 6 p.m., the IceBank tanks cool the building — not the chiller. In the cooler winter months, the IceBank tanks will be able to meet the building’s cooling requirements for longer periods of time.

“Thermal storage requires less energy to produce cool air during the more expensive daytime electric rate periods, since we’re turning off the compressor that is normally used to produce chilled fluid,” Andrews said.

CALMAC got involved with the civic center retrofit when Carlsbadbased Xnergy, an engineering, construction and alternative energy firm, proposed the project to the Encinitas City Council and picked CALMAC to help provide cooling to the civic center.

Due to CALMAC’s three IceBank tanks, the civic center's greatest cost savings were derived from shifting electrical demand to off-peak hours.

Justin Miller, director of business development with Xnergy, said another plus is that the IceBank system doesn’t require much maintenance. “The only real thing is to maintain the glycol solution annually and add water treatment to the IceBank tanks about every other year,” he said.

“The ancillary equipment that works in conjunction with the system — chiller, air handlers, pumps, etc. — have routine preventive maintenance procedures on a quarterly basis,” Miller said.

Andrews said thermal storage systems like the one in Encinitas can also lower maintenance costs. “We’re only freezing and melting tap water,” he said “and routine maintenance on the chiller can be performed during normal working hours when the IceBank tanks are meeting the building loads.” On larger thermal storage installations, other mechanical components (chillers, pumps, ‘cooling towers’) are often downsized, which will help reduce maintenance costs, as well.