Ultra-low harmonic drives: the sustainable solution to data center cooling?

By Carl Turbitt, HVAC Drives UK Sales Manager, ABB.

In the face of escalating global energy consumption and the resultant climate crisis, the need to optimize data center efficiency has become a concern. The carbon footprint of data centers has reached unprecedented levels, currently contributing to 3.5 percent of global greenhouse gas emissions, according to the International Energy Agency (IEA). Without decisive action, this figure is only set to rise. 

Addressing data center efficiency, particularly in the context of cooling systems, is paramount. Such cooling systems, essential for managing the heat generated by continuously operational servers and electronic components, can easily account for over 30 percent of a data center's total power usage. The choice between different cooling technologies and components in such systems becomes crucial. 

In this article, we’ll specifically address speed control solutions for cooling – electronically commutated (EC) fans, that integrate a motor, drive and speed controller as a single assembly, versus systems that combine a discrete drive, motor and fan, to show the effect on cooling system performance.

The challenge of sustainable data center cooling

Given the energy demands of densely packed data centers, selecting the right components and configuration for cooling systems is essential for energy savings. When it comes to air movement solutions, the question then arises: which is the greener choice, EC fans, or discrete drive and motor systems? 

While both technologies aim to enhance energy efficiency, they operate differently, with their suitability depending on specific data center needs and operational characteristics. What’s more, a combination of technologies may be necessary for the most efficient and sustainable cooling solution.

The benefits of EC fans

EC fans, known for their energy efficiency through brushless direct current (DC) motor technology and integrated control electronics, offer a considerable reduction in energy consumption. Their integrated design for easier installation, precise speed control and reduced noise levels make them favored in various industries, not least data centers. EC fans contribute to optimized airflow and temperature management, aligning with the need for energy efficiency.

But EC fans have limitations at part loads – the realm in which data center cooling systems tend to operate – where their efficiency drops significantly. Maintenance and replacement also pose challenges, as the entire EC fan unit often needs replacement, impacting cost, operational continuity, and sustainability.

Optimizing systems with drives

Variable speed drives are an alternative, usually standalone speed control solution for fan, pump and compressor motors. These  drives prove a great option for achieving optimal energy efficiency and performance in data center cooling systems, especially when paired with highly efficient fan motors. Ultra-low harmonic (ULH) drives specifically offer advanced design that sets them apart from common nowadays EC fans, offering unique features that make them a sound choice.

1. Partial load efficiency

Data centers operate at partial loads most of the time. This is why it is crucial to select equipment based on its partial load efficiency. 

Fans equipped with highly efficient IE5 SynRM motors and variable speed drives typically achieve greater energy efficiency than EC fans, especially at partial loads—often showing at least a 3% to 5% improvement in efficiency under these conditions.

2. Power quality 

It’s important to know that variable speed solutions, including EC fans and variable speed drives, can generate electromagnetic disturbances in the power network called harmonics which affect the network efficiency and reliability of connected equipment. Furthermore, due to increased current, they impose an extra load on transformers and other power network components, resulting in their overload, unless they are oversized. 

Thanks to their advanced design, ULH drives produce minimal harmonics under various load conditions, keeping the Total Harmonic Distortion of the input current (THDi) below 3%, thereby meeting the strictest power quality standards.

The ULH design not only safeguards data center equipment from the adverse effects of harmonics, but also contributes to a more stable, reliable, and efficient power supply for critical cooling systems. And there is no need to oversize power network equipment to manage harmonic currents, which means direct improvements to the facility’s capital expenditure and carbon footprint.

3. Operational reliability

Reliability is key to successful data center operations. Atlassian reports that the estimated cost of data center downtime ranges from $100,000 per hour to over $540,000 per hour. And the potential reputational damage can have even more severe financial implications. 

Let's evaluate the resilience of the speed control solution to externally-generated power quality issues. It's essential for these systems to be immune to potential power disturbances, which can unexpectedly occur even in mission-critical facilities like data centers. These disturbances can take the form of voltage sags, brownouts, and other forms of undervoltage conditions.

The ability of a speed control solution to maintain operation during power loss (ride-through) and automatically restart is vital for managing cooling systems in data centers. If the supply voltage is off, variable speed drives can continue to operate using the kinetic energy of the rotating motor they control. The drive will stay operational as long as the motor rotates and generates energy that is then fed to the drive. This helps to in avoid the need to restart cooling equipment, which can take several minutes. This feature is particularly crucial in the energy-dense environment of data centers, where the temperature in computer rooms can rise by approximately 2-3 degrees Celsius per minute without active cooling. Such rapid temperature increases can lead to the quick shutdown of IT servers. Therefore, variable speed solutions that are resilient to power quality issues are highly recommended to ensure continuous and reliable cooling.

4. Running multiple fan motors

An important advantage of using standalone drive technology is that a single drive can synchronize the operation of multiple drive motors. 

This configuration reduces the need for individual drives for each motor, as one drive can efficiently control, for example, every three fans. This streamlining lowers system complexity, cost, and power losses. Additionally, synchronizing multiple fans under a single drive ensures even airflow and temperature distribution across the data center, enhancing the cooling efficiency. For redundancy, a standby drive can be on hand to take over immediately should the primary drive fail.

5. System integration and control

HVACR drives commonly include the popular building automation protocol BACnet as a standard feature, streamlining the integration of fan installations into most data center control systems. In contrast, BACnet is only sometimes provided with EC fans, which more frequently rely on Modbus and require an intermediary controller or gateway to enable communication with the data center's BACnet-based system.

Even in cases where EC fans are equipped with BACnet, there is often still a need for an intermediary controller to facilitate general control or to provide manual (hand) control functionality, which is a standard expectation for air handlers and fan walls. However, this additional controller introduces a potential single point of failure risk that could take an entire fan array offline—ironically counteracting the very purpose of having a manual mode. Manual control is designed to be a fallback when the automated controls fail, and it is typically included as a standard feature with most variable speed drives.

6. Ease of maintenance and replacement

When selecting technologies for cooling systems, it’s also important to consider how easy they are to repair or replace. Although packaged EC fan solutions might appear appealing in terms of installation convenience, given that most components come pre-assembled, they have a drawback in the event of a malfunction. Typically, if failure occurs, it's necessary to replace the entire unit, even if only a single component such as a fan bearing or control electronics is defective. From a sustainability standpoint, this approach is not ideal because it results in excessive material use and waste when smaller-scale repairs could be more resource-efficient.

With fans that are operated by standalone drives, maintenance becomes more manageable as you can simply replace a faulty motor or drive, rather than the entire unit. This approach offers a strategic benefit as well, since it prevents data center owners from being tied to a single supplier. Different manufacturers' EC fans lack standardized dimensions, making it challenging to fit a replacement into an array built with fans from another provider.

Adopting a long-term perspective

In the context of the escalating climate crisis and increasing energy consumption by data centers, the choice of cooling technology becomes a strategic decision. Balancing immediate savings with long-term sustainability objectives is paramount. 

While EC fans may seem initially cost-effective, drives, especially ULH ones, present a more economical long-term solution. Besides mitigating harmonic distortion, they enable running multiple fan motors from a single drive, and offer easier system integration, control and maintenance. The comprehensive part load efficiency and minimized failure risk make ULH drives not only a technological leap, but a strategic investment in the sustainable evolution of data center operations, offering unmatched energy savings and reliability in cooling systems.

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