Chilled Water Thermal Energy Storage Tanks for Data Centers
In the need to keep data centers online, maintaining optimal temperatures is crucial. One approach is the use of thermal energy storage (TES) tanks. These systems provide an efficient way to balance the cooling load when cooling components of the chilled water system are offline or restarting.
Understanding Chilled Water Thermal Energy Storage
Chilled water is the most common form of thermal energy storage, using concrete or steel tanks to store the water at the typical chilled water supply temperature. Chilled water thermal energy storage involves storing chilled water to be used to cool the equipment in the data center during key times – mostly during power outages that knock the typical cooling equipment off line.
How Chilled Water TES Tanks Work
1. Cooling Production: During typical hours of operation, chillers (water or air cooled) produce cold water that is used to cool the data center. Additional chilled water is produced then stored in large, insulated TES tanks.
2. Energy Storage: The stored chilled water remains at a low temperature in the TES tanks, thanks to the insulation that minimizes thermal loss. The chilled water system will occasionally cycle more chilled water through the TES tanks to maintain a constant lower temperature. These tanks can vary in size, depending on the cooling needs of the data center.
3. Cooling Distribution: During power or chiller outages, the chilled water from the TES tanks is circulated through the data center’s chilled water distribution system via the secondary pumps. When a discharge occurs, chilled water is pumped from the bottom of the tank while an equal amount of warmer water is returned to the top of the tank. This will either allow enough time for the data center cooling plant equipment to restart and be able to cool the data center equipment or allow the data center equipment time to automatically shut down on their own.
Whether in normal standby conditions, discharging, or recharging, a stable stratification of layers of water can be obtained.
Benefits of Chilled Water TES Tanks for Data Centers
1. Increased Reliability and Redundancy: Chilled water TES systems add the layer of reliability and redundancy to data center cooling systems and strategies. In the event of chiller failure or power outages, the stored chilled water will continue to provide cooling, ensuring that critical IT equipment remains within safe operating temperatures.
2. Flexibility: TES systems can allow different schemes for how the data center cooling systems can operate. They typically provide flexibility in updating or replacing cooling equipment or strategies while in operation, allowing data centers to operate continuously while other cooling equipment is brought online.
Implementation Considerations
1. Space Requirements: TES tanks require significant space for installation, which is typically outside to accommodate their size. Data centers need to assess the available space and determine the most efficient placement of these tanks to maximize their effectiveness.
2. Initial Investment: While TES systems offer long-term reliability support, the initial capital investment to increase the size of the tank can be off putting. Data centers must weigh the upfront costs against the projected reliability needs to determine the return on investment.
3. Maintenance: Regular maintenance of TES tanks and associated cooling systems is essential to ensure optimal performance. This includes monitoring water quality, checking insulation integrity, and servicing pumps and controls.
4. Integration with Existing Systems: Data centers need to ensure that TES systems are compatible with their existing cooling infrastructure. Proper integration and controls sequences are crucial for seamless operation and maximum efficiency.
5. There are important hydraulic performance ramifications that should be reviewed when designing and operating a chilled water TES tank. Most tanks are not ASME pressure vessels, meaning that they are vented (open) to atmosphere to mitigate cost and pressure concerns. To prevent air from being entrained in the system, the top of the tank water line will need to be above the highest point in the chilled water system and a positive water pressure should be always maintained.
Case Studies and Real-World Examples
Several data centers have successfully implemented chilled water TES systems, demonstrating their effectiveness and benefits. A quick list of data centers that utilize TES tanks to store chilled water to avoid overall operational downtime to increase reliability (feel free to reach out about the specific names, locations, and other details):
Future Trends and Innovations
As data centers continue to grow and evolve, the role of thermal energy storage is likely to continue as a critical piece of the cooling infrastructure. Even with AI, TES tanks are likely to be crucial to ensure that overheating of the critical equipment does not occur during power outages. Innovations in materials, insulation, and energy management systems will further enhance the applicability of TES tanks.
Chilled water thermal energy storage tanks represent a smart, efficient solution for managing the temporary cooling needs of data centers. As the demand for data processing and storage continues to rise, the incorporation of cooling solutions like TES tanks will be essential in ensuring the reliable operation of data centers worldwide.
