Are EC fans the most efficient solution for data centres, or could the addition of ultra-low harmonic (ULH) technology make drives and motors the better option? Carl Turbitt, ABB’s HVAC Drives UK Sales Manager, unpacks the pros and cons.
Data centres are crucial for housing massive amounts of IT equipment, which tend to generate heat. Precise temperature control is essential to keep these facilities operational, and, of course, air conditioning contributes significantly to global carbon emissions.
So, how can data centres stay cool without exacerbating the environmental impact? EC fans or drives and motors?
Right now, two viable options are available: EC fans and separate drives and motors. EC fans are electronically commutated solutions that integrate a fan, motor, and speed control. They’re typically used in large numbers. The alternative is to use drives and motors, where variable-speed drives (VSDs) are added to fixed-speed motors that propel the centrifugal fans traditionally used in precision cooling units. Popular EC fans are often hailed as the cheaper and greener option, but is this really the case? Let’s take a closer look.
Firstly, EC fans can be highly efficient when fully loaded – this is the reason they are often selected for data centre cooling. However, they can exhibit a significant drop in efficiency when only partially loaded, which is where data centres operate most of the time. The result is that the potential efficiency gains are scattered and inconsistent. In contrast, separate drives and motors can be selected and configured for optimum efficiency across a range of load levels. These can then be combined with industry-leading fan designs that outperform the fans connected to the EC motors on the market. The resulting motor-drive package is, therefore, better than EC motors.
When it comes to specifying motors, Synchronous Reluctance Motors (SynRM) are the best choice. They operate quietly, making them ideal for noise-sensitive environments. With the highest IE5 efficiency rating, SynRM motors convert electrical energy into mechanical power with exceptional efficiency, outperforming EC motors at partial loads. Running at cooler temperatures, they have longer operational lifespans, resulting in lower maintenance costs. Another notable feature is their magnet-free design, which eliminates the need for rare earth magnets, making them an eco-friendly choice.
Pairing SynRM motors with a compatible drive, along with industry-leading fan designs, creates the ultimate combination of efficiency and performance. Imagine it like this: EC fans are like sprinters, efficient at full speed, but when they slow down, their performance suffers. Drives and motors, on the other hand, are like long-distance runners, maintaining more consistent efficiency regardless of the pace.
Now, add ultra-low harmonic (ULH) drives, and the gains are even greater. ULH drives bring improvements to the wider electrical network, providing the lowest harmonic disturbance, ensuring that network losses are low, and operational costs are reduced. The latest version of the ecodesign standard recognises the improvements ULH can bring to an electrical network, allowing the drive to offset its component losses by demonstrating greater overall system savings. ULH drives also provide protection against network disturbances, smoothing out ‘brownouts’ in the network and maintaining cooling for critical servers during those disturbances.
Harmonics explained
So, what are harmonics? In an ideal case, the current in an electrical grid is a pure sine wave and does not contain harmonics. In reality, the current deviates from this pure sine wave and contains harmonics, which can cause interruptions, interference, and even downtime for a data centre.
Harmonics exist in any large power supply network and pollute the electricity supply as soon as it is consumed by the facility. They are introduced by the non-linear loads of equipment connected to the network, including everything from photocopiers to electronically commutated motors and variable-speed drives with standard choke designs. Harmonics can disrupt operations immediately if not addressed.
They can cause damage to sensitive electronics, interfere with communication equipment, and provide false readings on measurement devices. They can trip circuit breakers, blow fuses, and cause capacitor failures. The effects also include overheating of transformers, cables, motors, generators, and capacitors.
The problems caused by harmonics result in increased losses because more energy is wasted due to overheating, equipment has a shorter lifespan, and is subject to unreliable operation. In the worst cases, harmonics cause unnecessary and unwanted process interruptions.
One solution is to design equipment to tolerate harmonics in the network, but oversizing leads to higher investment costs, such as increasing the supply transformer or backup generator rating by up to 25%. Instead of attempting to address harmonics with often ineffective actions, such as adding cooling or over-dimensioning equipment, it is better to employ equipment that does not cause harmonics in the first place.
The benefits of using ultra-low harmonic drives include a longer lifespan for your equipment, a smooth network, reduced maintenance, increased uptime, more efficient and reliable operation, prevention of over-dimensioning expensive upstream equipment, and, ultimately, energy savings through distortion reduction.
The cost factor
When comparing the benefits of EC fans versus drives and motors, cost is another critical factor, as facilities worldwide are either fearing or facing the impact of high energy bills on their bottom line. EC fans certainly cost less upfront compared to drives and motors, making them the cheapest solution in the short term.
However, each EC unit has a single integrated speed controller. So, when data centres use multiple EC fans – as they commonly do – this can cause complexity, as there are many potential points of failure. When an EC fan fails, the entire unit needs replacement, often by the same manufacturer. Supply chain issues can lead to delayed deliveries and increased downtime.
Conversely, drives and motors can be cared for as individual parts, making maintenance much easier by comparison. They also have fewer potential points of failure compared to EC fans. Because one ULH drive can run multiple fan motors from a single drive, it’s much easier to pinpoint issues compared to traditional drives and motors.
So, you could think of EC fans as cost-effective smartphones with non-removable batteries. The initial investment can be lower, but when they fail, you’re forced to replace the entire unit. Drives and motors are more like premium smartphones with removable batteries, allowing you to replace individual components as needed.
And the winner Is…
On balance, compared to EC fans, drives and motors appear to be a well-oiled machine. They have fewer points of failure, are easier to maintain, and they perform better at partial loads when SynRM motors are in the picture. ULH drives ensure the network is not wasting energy by keeping the harmonic disturbance to a minimum and riding through mains disturbances. EC fans might not be as green as they seem; they are easier for the air handling unit manufacturer but not as beneficial for the data centre operator, who has to pay the electricity bill and maintain the facility in the future.
ULH drives are the key to sustainable data centres because they minimize harmonics and improve motor control. Furthermore, the cost savings that EC fans bring with favourable upfront price tags are recovered through drives and motors’ lifetime savings.
The takeaway?
Don’t judge a solution by its ‘green’ label. ULH drives are the secret ingredient for truly sustainable data centres, with drives and motors offering long-term savings that make them a worthy contender.
