Data centers in colder climates can significantly reduce energy consumption by leveraging economizers to take advantage of naturally low ambient temperatures. Water-side economizers, for instance, can use cold outdoor air to lower the temperature of the chilled water loop, reducing or even eliminating the need for mechanical chillers during colder months. This process, known as "free cooling," allows facilities to operate with higher energy efficiency, cutting both power usage and operational costs. Additionally, air-side economizers can introduce cold outside air directly into the data hall when conditions permit, further minimizing reliance on traditional cooling methods. By optimizing economization strategies, data centers in these regions can achieve substantial reductions in Power Usage Effectiveness (PUE) while maintaining thermal reliability for IT equipment.
Data centers in cold climates present a unique opportunity to enhance cooling efficiency through water-side economization (WSE). This method harnesses naturally low ambient temperatures to reduce or eliminate the need for mechanical refrigeration, offering significant energy and cost savings. A well-designed water-side economizer can improve sustainability, extend equipment lifespan, and reduce operational expenses, all while maintaining the reliability essential for mission-critical environments.
Water-side economization functions by using cold ambient air to chill water or another heat transfer fluid, which is then used to reject heat from the data center. By minimizing reliance on chillers, this approach improves energy efficiency and overall system performance.
Water-side economizers provide an energy-efficient cooling solution for data centers by utilizing low ambient temperatures to cool water or a glycol mixture, reducing reliance on mechanical refrigeration. These systems typically operate in three configurations: direct, indirect, and integrated economization. Direct water-side economizers circulate cold water directly through the data hall cooling coils, requiring careful water treatment to prevent contamination. Indirect economizers use a heat exchanger to transfer cooling from an external loop to an internal loop, preventing direct exposure of facility water to outdoor conditions. Integrated economizers combine mechanical cooling with free cooling to optimize energy use, transitioning between economization and chiller-assisted cooling as ambient conditions fluctuate. In colder climates, water-side economizers can operate year-round, achieving significant PUE (Power Usage Effectiveness) reductions and lowering operating costs, especially when coupled with advanced controls that regulate flow rates, bypass valves, and glycol concentration, typically between 20-40% propylene glycol for freeze protection.
Non-integrated water-side economizers operate independently from mechanical chillers, providing full or partial free cooling based solely on ambient conditions. These systems rely on cooling towers, dry coolers, or adiabatic coolers to lower water temperatures, which then circulate through heat exchangers to cool the data center. Unlike integrated systems, non-integrated economizers do not blend free cooling with chiller operation, meaning they are either fully engaged or bypassed depending on external temperatures. This approach can maximize energy savings in cold climates, where prolonged low ambient temperatures allow for extended economization periods. However, they require precise control sequencing to ensure a seamless transition between free cooling and mechanical cooling when temperatures rise, and they may necessitate larger heat exchangers and additional piping infrastructure to handle peak loads without chiller assistance.
Integrated water-side economizers work in conjunction with mechanical chillers, allowing for a seamless transition between free cooling and mechanical cooling. These systems use plate-and-frame heat exchangers to transfer heat from the chilled water loop to the condenser water loop when ambient temperatures are low enough, reducing or even eliminating the need for compressors. Unlike non-integrated economizers, which operate independently, integrated systems modulate cooling sources dynamically, maximizing energy efficiency by partially engaging chillers as needed. This approach is particularly beneficial in cold and temperate climates, where free cooling can be leveraged for a significant portion of the year. Integrated economizers reduce overall chiller runtime, lower power usage effectiveness (PUE), and extend equipment lifespan while maintaining precise temperature and humidity control for data center operations.
Correctly sizing cooling towers for economizer duty in a data center is essential to ensuring efficient and reliable operation while maximizing free cooling potential. The cooling tower capacity must be carefully matched to the heat rejection load of the data hall, considering factors such as water flow rate, approach temperature, wet-bulb temperature, and total system capacity. Typically, cooling towers are sized to provide chilled water at or near the economizer switchover temperature, which varies based on local climate conditions but is often around 10°C (50°F). To optimize efficiency, designers must account for seasonal variations and ensure that the cooling tower can meet peak economizer demand without excessive cycling or water wastage. Oversized cooling towers may lead to inefficient operation and increased maintenance, while undersized units could limit economizer performance and force reliance on mechanical cooling when free cooling should be available.
Additionally, proper fan speed control, heat exchanger selection, and redundancy are key considerations for ensuring smooth economizer operation. Variable frequency drives (VFDs) on tower fans allow for modulation based on real-time conditions, improving energy efficiency and reducing unnecessary water evaporation. The approach temperature—the difference between the tower's cold water temperature and ambient wet-bulb temperature—should be optimized to ensure the tower can consistently provide water at the necessary temperature without excessive energy consumption. Using multiple modular towers rather than a single large unit enhances scalability and redundancy, reducing the risk of downtime. Engineers must also consider glycol concentrations in colder climates to prevent freezing, ensuring that cooling towers remain operational throughout the winter while supporting economizer duty for extended periods.
Seasonal variations significantly impact cooling loads and economization strategies in data centers, with distinct differences between winter and summer operations. During the winter months, the lower ambient temperatures allow for extended use of water-side economization, reducing reliance on mechanical chillers. Cooling towers or dry coolers can provide chilled water at or near the required supply temperature, often below 10°C (50°F), enabling full or partial economization. In some cases, data centers in cold climates can operate in 100% economization mode, where chillers remain off for extended periods, leading to substantial energy savings. However, extreme cold can pose challenges, such as freezing risks in cooling towers, requiring glycol mixtures or the use of dry coolers as a backup.
In contrast, summer conditions present higher cooling loads due to increased outdoor temperatures and humidity, making full economization less viable. The higher wet-bulb temperature limits the cooling tower's ability to produce sufficiently cold water, often requiring mechanical cooling to supplement or entirely replace economizer operation. Hybrid cooling strategies, such as partial economization, can still reduce chiller runtime during mild summer nights or transitional seasons. Additionally, data centers must account for heat rejection efficiency, ensuring that cooling towers, heat exchangers, and chillers are sized appropriately to handle the peak summer demand while maintaining N+1 or higher redundancy for reliability. Proper seasonal tuning of controls, such as adjusting setpoints, fan speeds, and water flow rates, ensures that the economization system operates optimally year-round.
Key Benefits of WSE in Cold Climates
How Water-Side Economization Works
| Component | Function |
| Cooling Towers | Removes heat by evaporative cooling or using dry coolers. |
| Heat Exchangers | Transfers heat between the cooling tower loop and chilled water loop. |
| Pumps | Moves water through the system, ensuring proper flow rates. |
| Control Valves | Regulates water flow between economizer mode and mechanical cooling mode. |
| Sensors & Automation | Monitors temperature, pressure, and flow to optimize operation. |
| Filtration & Water Treatment | Prevents scaling, fouling, and microbial growth in piping and equipment. |
Cooling Tower Selection
Cooling towers in cold climates must be properly winterized to prevent freezing. The three primary cooling tower options include:
For data centers in extreme cold climates, closed-loop glycol cooling is often the best option to mitigate freezing risks.
While glycol prevents freezing, higher concentrations reduce heat transfer efficiency. System designers must balance the percentage used to maintain optimal performance.
Heat Exchanger Selection
Using a loop with headered heat exchangers provides redundancy and ensures operational continuity in fluctuating temperature conditions.
System Redundancy & Control Strategies
Cold climates can be unpredictable, making automatic switchover mechanisms critical for reliability.
N+1 redundancy in critical components is recommended to ensure system resilience.
Free Cooling vs. Partial Mechanical Cooling
Water Quality & Maintenance Considerations
A well-defined water treatment plan is essential to prevent scaling, biofilm buildup, and corrosion.
System Specifications
Performance Under Different Conditions
| Condition | Ambient Temperature (°C / °F) | Cooling Mode |
| Winter | -10°C / 14°F | 100% Free Cooling |
| Fall/Spring | 5°C to 15°C / 41°F to 59°F | Partial Economization |
| Summer | 20°C+ / 68°F+ | Mechanical + Tower Cooling |
| Challenge | Solution |
| Freezing Risks | Use glycol mixtures, heat tracing, and insulated pipes. |
| Reduced Heat Transfer Due to Glycol | Optimize glycol percentage for best efficiency. |
| Ice Formation in Cooling Towers | Use heated basins, low-flow shutdowns, and drain-down systems. Reversing the cooling tower fans can be a temporary option for extreme conditions. |
| Corrosion and Scaling | Implement a water treatment program and use corrosion-resistant materials. |
Designing a water-side economizer for cold climates is a highly effective strategy for improving energy efficiency in data centers. By leveraging ambient cooling, optimizing glycol freeze protection, and integrating smart automation, operators can significantly reduce energy consumption while maintaining high reliability.
The success of these systems depends on proper equipment selection, redundancy planning, and continuous monitoring to ensure performance under extreme conditions. As data centers continue to prioritize sustainability, water-side economization will remain a key design approach for facilities in cold climates.
Cooling Tower Performance Chart for Economization
| Wet-Bulb Temp (°C) | Dry-Bulb Temp (°C) | Chilled Water Supply Temp (°C) | Cooling Tower Efficiency (kW/ton) | Cooling Mode |
| -10 | -15 | 4 | 0.10 | Full Free Cooling |
| -5 | -10 | 5 | 0.12 | Full Free Cooling |
| 0 | -5 | 6 | 0.15 | Full Free Cooling |
| 5 | 0 | 7 | 0.18 | Partial Free Cooling |
| 10 | 5 | 9 | 0.25 | Partial Free Cooling |
| 15 | 10 | 12 | 0.40 | Hybrid Cooling (Economizer + Chiller) |
| 20 | 15 | 14 | 0.55 | Hybrid Cooling (Economizer + Chiller) |
| 25 | 20 | 17 | 0.75 | Chiller-Dominant Mode |
| 30 | 25 | 20 | 0.90 | Chiller-Dominant Mode |
| 35 | 30 | 24 | 1.10 | Chiller-Dominant Mode |
Notes on Cooling Tower Performance
Case Studies and White Papers
Academic & Technical Publications
For specific implementation details or compliance with regional standards, local building codes and energy regulations should also be consulted.
