Abstract
Data centers are essential to modern IT infrastructure, supporting critical applications such as cloud services, big data analytics, and digital commerce. Ensuring the reliability and resilience of data centers is paramount, especially with regard to cooling systems, which consume significant energy and are vulnerable to power outages and system failures. Thermal energy storage (TES) tanks offer a promising solution to enhance the emergency backup of data center cooling systems, ensuring business continuity even in the event of power disruptions. This white paper explores the role of TES in emergency backup cooling for data centers, outlining its technical capabilities, operational benefits, and challenges, as well as its impact on cost efficiency and sustainability.
1. Introduction
Data centers require reliable, continuous cooling systems to maintain optimal operating conditions for servers and other electronic equipment. Failures or interruptions to cooling systems can lead to catastrophic consequences, including hardware damage, service downtime, and data loss. As such, providing redundant and resilient cooling capabilities is a critical component of data center disaster recovery and business continuity planning.
Thermal Energy Storage (TES) systems, which store thermal energy in the form of chilled water or phase-change materials, can provide an effective emergency backup solution for data center cooling. By leveraging TES, data centers can ensure that cooling systems remain operational during power failures, prevent overheating, and reduce the risk of service disruption during emergency situations.
This white paper discusses the use of TES tanks for emergency backup cooling in data centers, exploring their operational role, technical implementation, benefits, and potential challenges.
2. The Importance of Emergency Cooling in Data Centers
Cooling systems in data centers are designed to manage the substantial heat generated by servers, storage devices, networking equipment, and other hardware. The risk of failure in cooling systems can stem from a variety of factors:
• Power Outages: Data centers depend on constant electricity supply to power both operational systems and cooling equipment. A loss of power, whether due to grid failure or equipment malfunction, can cause immediate overheating.
• System Failures: Mechanical failures, such as pump malfunctions, compressor breakdowns, or leaks in cooling systems, can also disrupt cooling operations and put critical hardware at risk.
• Natural Disasters: Events like earthquakes, hurricanes, or floods may lead to power supply issues or cause damage to cooling infrastructure, making it impossible to maintain ideal temperatures for IT equipment.
• Operational Errors: Human error, such as incorrect configuration, system mismanagement, or neglect in maintenance, can lead to failures in cooling systems that require quick recovery.
Given these risks, having a reliable backup cooling system is essential to ensure business continuity. Cooling systems must be designed with redundancy, and TES provides an innovative solution for storing cooling capacity in advance for use during emergencies.
3. Thermal Energy Storage (TES) Technology Overview
Thermal Energy Storage systems are designed to store excess cooling capacity during off-peak periods for later use. They can be categorized based on the type of energy they store and the materials used:
• Sensible Heat Storage: This method involves storing heat by changing the temperature of a medium, such as water or air. The medium’s temperature increases or decreases without changing its phase, and the amount of energy stored is proportional to the temperature difference.
• Latent Heat Storage: Latent heat storage uses phase-change materials (PCMs) that absorb or release energy during the phase transition from solid to liquid or liquid to gas. PCMs are highly efficient because they store large amounts of energy without significant temperature fluctuations.
• Thermochemical Storage: This approach stores energy via reversible chemical reactions. However, this method is less common in data centers due to complexity and cost factors.
In the context of emergency backup cooling, sensible heat storage (often through chilled water tanks) and latent heat storage (using PCMs) are the most relevant. These technologies are used to store cooling capacity during periods of low demand, which can then be deployed when there is a failure or disruption in the primary cooling system.
4. Role of TES Tanks in Emergency Backup Cooling
In data center cooling, the integration of TES systems as emergency backups ensures that critical infrastructure remains operational even during cooling system failure. Here’s how TES tanks can function in such a role:
4.1 Backup Cooling During Power Failures
In the event of a power outage or failure of the primary cooling system, TES systems can provide immediate relief. For example, chilled water stored in a large TES tank can be circulated through cooling coils to absorb the heat produced by servers. Depending on the system design, TES can provide cooling for a set duration (from minutes to hours), allowing the data center time to switch to secondary backup power sources, such as diesel generators or uninterruptible power supplies (UPS).
4.2 Reduction of Cooling System Load During Recovery
After a power outage or failure, cooling systems may take time to return to full operation. TES tanks can help by supplying additional cooling capacity until the main system is restored. This reduces the risk of overheating, prevents hardware damage, and minimizes the likelihood of system downtime during recovery.
4.3 Grid Independence and Resilience
TES systems enhance data center resilience by reducing reliance on the electrical grid and preventing peak demand. In case of power grid instability or supply issues, TES provides a reliable backup source of cooling. Moreover, during periods of grid stress, data centers can reduce their cooling load from the grid by relying on stored thermal energy.
4.4 Complementing Existing Redundancy Systems
TES can complement traditional backup cooling methods, such as using backup generators or redundant air conditioning systems. While these systems provide power and airflow redundancy, TES specifically addresses cooling capacity, ensuring that temperature regulation is maintained even in the absence of power.
5. Technical Implementation of TES in Data Center Emergency Cooling
Integrating TES into a data center’s cooling infrastructure requires careful consideration of system design and operational parameters. Below are the key components and steps in implementing TES for emergency backup cooling:
5.1 TES System Components
• Thermal Storage Tanks: These are the core components of the TES system. They are typically insulated tanks filled with chilled water or phase-change material (PCM) that stores thermal energy. There are several types of tanks used for Thermal Energy Storage (TES) in data center emergency cooling. Here are some of the most common ones:
• Chilled Water Tanks
o These are the most common type of TES tanks used in data centers. They store chilled water produced during off-peak hours, which can then be used during peak demand periods or emergencies. Chilled water tanks are typically made of concrete or steel and are insulated to minimize thermal loss.
o Stratified Water Tanks
o Stratified water tanks maintain a temperature gradient, with colder water at the bottom and warmer water at the top. This stratification is maintained by careful design and operation to ensure efficient energy storage and retrieval.
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• Ice Storage Tanks
o Ice storage tanks use the latent heat of fusion to store energy. They freeze water into ice during off-peak hours and then melt the ice to provide cooling during peak hours or emergencies. There are different methods for ice storage, including:
• Ice Harvesting: Ice is formed on the surface of evaporators and then harvested into a storage tank
• External Melt Ice-on-Coil: Ice forms on the exterior surface of coils submerged in the tank
• Internal Melt Ice-on-Coil: Ice forms on submerged tubes or pipes within the tank
• Encapsulated Ice Tanks
o These tanks use small containers or capsules filled with water that freeze and thaw to store and release thermal energy. This method allows for more flexible tank shapes and size.
• Multi-Tank Systems
o Some systems use multiple tanks to store thermal energy. These can include combinations of chilled water and ice storage tanks to provide greater flexibility and redundancy.
Materials and Design Considerations
• Concrete Tanks: Often used for underground storage, concrete tanks can be cast in-situ or precast/pre-stressed, offering flexibility in shape and size.
• Steel Tanks: Commonly used for above-ground installations, steel tanks are durable and can be insulated to improve thermal efficiency.
Each type of TES tank has its own advantages and is chosen based on specific requirements such as space availability, cooling load, and budget.
• Heat Exchange Equipment: Chillers, cooling coils, or heat exchangers transfer thermal energy between the stored medium and the data center’s cooling system. This equipment circulates the stored thermal energy to maintain the desired temperature.
• Control and Monitoring Systems: These systems ensure that the TES operates efficiently, managing when energy is stored and when it is released. Sensors and real-time data analytics can optimize the storage and deployment of thermal energy.
• Integration with Backup Power: TES systems must be integrated with the data center’s emergency power infrastructure, including UPS units and diesel generators, to ensure seamless operation during power outages.
5.2 System Design Considerations
• Capacity Sizing: The TES system should be sized to provide sufficient cooling for the data center during critical failure events, typically for a period of minutes to several hours, depending on the cooling load and the duration of the emergency.
• Redundancy: TES systems should be designed with redundancy to prevent single points of failure. Multiple TES tanks, heat exchangers, and backup power sources can help ensure that cooling is available even if one part of the system fails.
• Performance Monitoring: Continuous monitoring of temperature, pressure, and energy usage ensures that the TES system is operating within optimal parameters and that backup cooling is available when needed.
5.3 Energy Efficiency and Sustainability
TES systems are energy-efficient because they store thermal energy during off-peak hours when electricity costs are low or when renewable energy generation is high. This helps reduce operational costs and minimizes environmental impact. When paired with renewable energy sources, such as solar or wind power, TES can provide a fully sustainable cooling backup solution.
6. Benefits of TES for Emergency Backup Cooling
6.1 Enhanced Reliability and Resilience
The primary benefit of TES in emergency cooling is the enhanced reliability it provides. By storing cooling capacity in advance, data centers can quickly respond to system failures or power outages without risking overheating or downtime.
6.2 Cost Savings
TES systems can help reduce cooling-related operational costs by shifting cooling load to off-peak hours. Furthermore, by providing backup cooling during power disruptions, TES systems reduce the need for costly emergency cooling solutions or external backup resources.
7. Challenges and Considerations
While TES offers numerous benefits, there are also challenges and considerations for its implementation in data center emergency cooling:
• Initial Capital Cost: The upfront investment in TES infrastructure (e.g., storage tanks, heat exchangers, control systems) can be high. However, this cost is often offset by long-term energy savings and reduced operational risks.
• System Complexity: TES systems require careful integration with existing cooling and power systems. They may require new infrastructure and may involve some level of complexity in design, installation, and ongoing maintenance.
• Space Requirements: TES tanks, especially those used for chilled water or PCM, require significant physical space. Data center operators must ensure that sufficient space is available for the installation of backup cooling tanks.
• Maintenance: Regular maintenance is essential to ensure optimal performance. This includes monitoring water quality, checking insulation integrity, and servicing pumps and controls.
• Integration with Existing Systems: Ensuring compatibility with existing cooling infrastructure can be complex. Proper integration and control sequences are crucial for seamless operation
• Thermal Stratification: Maintaining thermal stratification within the TES tank is critical for efficient operation. Preventing de-stratification, which can occur due to water jets entering the tank, is a technical challenge
Considerations
• Reliability and Redundancy: TES tanks provide an additional layer of reliability and redundancy. During power outages or chiller failures, the stored chilled water can continue to cool the data center, ensuring critical IT equipment remains within safe operating temperatures
• Cost Savings: By using stored energy during peak periods, data centers can avoid high electricity costs associated with peak demand
• Environmental Impact: TES systems can reduce the reliance on traditional cooling methods that consume a lot of electricity and often use refrigerants contributing to greenhouse gas emissions
• Scalability: TES tanks can support the scalability of data centers, allowing for future expansion without significant additional cooling infrastructure.
By addressing these challenges and considerations, data centers can effectively implement TES tanks to enhance their cooling strategies, improve energy efficiency, and ensure reliable operation during emergencies.
1. Continuous Cooling During Power Outages: TES tanks store chilled water or ice, which can be used to cool data centers during power outages. This ensures that servers remain operational and do not overheat while backup generators start up, typically taking several minutes.
2. Energy Efficiency: By storing energy during off-peak hours when electricity is cheaper and demand is lower, TES tanks help reduce overall energy consumption and operational costs. This is particularly beneficial during peak demand periods when energy costs are higher.
3. Reliability and Redundancy: TES tanks provide a reliable backup cooling solution, enhancing the resilience of data centers. They can also support scalability, meeting future increases in cooling demand
