Four questions to ask your cooling solution provider

In 2021 it was estimated the world’s estimated energy consumption was 20,000 TWh. Of this, data centres consu-med just under 200 TWh – one percent of all energy usage. Data centres alone account for 2.7 percent of the EU’s total energy consumption. These figures are set to rise significantly in the coming years as more facilities come on-line. Indeed, it’s reported that energy demand for data centres is predicted to increase by nearly eight times by 2030, feasibly putting it on a similar level to the aviation industry in terms of fuel emissions. This is clearly un-sustainable.

Around 40 percent of energy consumed by a data centre is used for cooling. Fans and chillers are responsible for around a third of this consumption, making them a prime candidate for efficiency improvements. Not only could this significantly lower the carbon footprint of the data centre industry, which has already outgrown that of many countries, but also it could make a substantial difference to operating costs.

For cooling fans in air handling units (AHUs), there are two main competing technologies: electronically commu-tated (EC) fans, and motor + standalone variable speed drive (VSD) arrangements. An EC fan is a self-contained as-sembly comprised of an electric motor, VSD, and fan, all integrated into one package, while a motor and VSD are in-stalled and maintained as two separate devices.The two options are arguably very similar, with the drive providing precise control over the motor’s speed based on actual demand. As such, both technologies can significantly reduce energy usage compared to a fan running without any form of speed control.

Fans, along with pumps, are typically variable torque applications, and take advantage of affinity laws. In practice this means that reducing the speed of a fan by 20 percent, corresponds to a 50 percent reduction in energy con-sumption. Both EC fans and motor-drive packages can both achieve energy savings in this way.

When looking for an effective data centre cooling solution, it can be tempting to go with the cheapest upfront op-tion, which may well be an EC fan. However, to look at price alone is to miss the wider picture. Moreover, what a fan manufacturer tells you about the efficiency of their product may not be the whole story. Here are four questions you should ask your cooling provider before you specify.

What’s the whole life cost?

EC fans are often cheaper based on upfront cost or capital expenditure (CAPEX) alone. However, when we also consider operating expenditure (OPEX), and therefore the Total Cost of Ownership (TCO) over the lifetime of the asset, the proposition changes somewhat. In an EC fan, the motor and drive elements are an integrated solution, which can create problems with heat dissipation. While having one self-contained device may seem convenient on the face of it, this can actually lead to the breakdown of electronic devices within the variable speed drive and the insulation of the motor, which are typically the most common points of failure. With a motor-drive package, both

motor and drive can be situated separately, resulting in less heat accumulation, resulting in a longer lasting sustainable solution, and lower failure rates.

Another aspect to consider is the load profile, or how the fan is actually run on a day-to-day basis. EC fans can deli-ver good efficiency levels at peak loads, but in reality 99% of all fan applications – including data centre cooling sys-tems – rarely run at peak loads, and only then in worst case scenarios. Conversely, a motor-drive arrangement tends to perform better at partial loads, which is typically how it will operate for the vast majority of the time. Ultimately this means you will have to replace your motor and/or drive much less often, creating a more sustainable solution with lower whole life cost.

How easy is it to replace?

We have already established that due to heat dissipation, EC fans can be more susceptible to failures, and therefore require replacement more frequently. However, replacing an EC fan can also create problems. EC fans are typically custom-made to order for a specific application to a particular size, and as such will not always be sized to traditio-nal IEC dimensions. In the event of a failure, this means they must be replaced with a array of the exact same dimen-sions, and with a similar output. Sourcing such a replacement can be a challenge, particularly against the backdrop of long lead times and supply chain delays.

In a motor-drive package, if either the motor or drive fails, it can typically be replaced off the shelf with a similar product from any major manufacturer, as many drives and motors from different vendors can be used interchange-ably. This potentially means less downtime, and greater choice.

How sustainable is it?

The majority of AHUs, particularly in data centres, are large and require multi-fan arrays. EC fans are only available as multi-fan arrays, but this might not be as convenient as it seems. Each fan in the array will have its own drive (or a combination of commutation electronics), irrespective of how many motors or drives are actually required. A se-parate VSD can in fact control multiple fan motors simultaneously, saving large amounts of space. A motor-drive package can also deliver much more power compared to an EC fan. EC fans are only capable of delivering up to 5.5 kW each, and so any cooling system will require lots of them to reach required airflow levels. Because of this, EC fans are often overspecified, and require additional overload protection per unit as well as communications gate-ways in order to be controlled over protocols such as BACnet and modbus adding additional cost and test points.

A motor-drive arrangement on the other hand can go up to 250 kW without breaking a sweat, providing more power with less complexity, and fewer devices to have to maintain and/or replace when the time comes. There are also multiple options available, including single drive and motor, multiple drives and motors, or a combination of both to best suit the application.

What’s the harmonic situation?

Harmonics are not a widely understood concept outside of electrical engineering, yet they can be a big issue for data centres. Harmonics are disruptions to the voltage and current waveforms caused by introducing non-linear loads to the grid. The majority of electronics that have a power supply will generate harmonics to some extent, but often only in very small amounts. However, when you have a building full of these devices, the level of harmonics on the grid can quickly accumulate. Excessive harmonics results in nuisance trips and malfunctioning equipment, as well as reducing system efficiency. It also generates heat, which can lead to premature equipment failure, as well as creating more work for the cooling system itself.

Like many electronic devices, both EC fans and VSDs generate harmonics. However, while modern VSDs have built-in mitigations, EC fans may not dependent on the offering. This is an important question to ask when requesting a solution, as it is not something that you would want to leave to chance. It may also require the use of additional har-monic filters at an additional cost later down the line. ABB’s Ultra-Low Harmonic (ULH) VSDs on the other hand use active front end (AFE) technology to not only ensure optimal performance where harmonics are present on the

grid, but also mitigate them at source, reducing harmonic content by up to 90 percent compared to conventional VSDs.

In summary

EC fans certainly have their place. For small single cell applications operating at peak loads they can provide an effi-cient cooling solution. However, for facilities like data centres, which require vast amounts of cooling, they may not be able to provide everything you need for an effective, reliable and sustainable solution. When you consider what you really need from your cooling system, a separate motor-drive package can often be the more cost-effective and sustainable option, with reduced whole life cycle costs.

To learn more about EC fans, VSDs and other competing cooling technologies, download ABB’s white paper: https://campaign.abb.com/l/501021/2023-02-21/23cd3pk. ABB will also be exhibiting at Data Centre World at ExCeL London on 8-9 March 2023.