Data centres benefit from massive energy and CO2 reductions using variable-speed drives

Data centres require massive amounts of power to keep them running smoothly and efficiently. The ever-increasing demand for computing power has a significant impact: with the new technologies, between 20-22 kW of power is required for each single rack, compared to 4-5 kW normally needed in the past. In the future, these environments will become one of the main consumers of power in the world. Carl Turbit of ABB explains

With the continued growth of the internet and electronic banking, the need to deliver data storage solutions that also help improve energy efficiency and the levels of power used within such a centre has never been greater.

All of which affects plant costs: the electrical and mechanical aspects of a new office building are usually equal to 15% of the investment, but with a data centre this value increases to 70%.

Cutting the power overhead

It is estimated that IT applications, including data centres, consume 2% of all electrical energy produced. In the US, this approaches 2.6%, while the EU estimates the power consumption of data centres is set to rise to 93 TWh by 2020.

Most of this power consumption is represented by the IT load, accounting for 40%, while the cooling system runs a close second at 35 percent, with the UPS and lighting accounting for a further 25%.

Power Usage Effectiveness, or PUE, is the most commonly used method of determining the energy efficiency of a data centre. This ratio is the total power entering the data centre divided by the power used by the IT equipment. 

The average data centre in the US has a PUE of 2.0. This means the facility uses one watt of overhead power for every watt delivered to IT equipment. Improving this ratio means reducing overhead power use, mainly by cutting the percentage of power used by the cooling system. 

This can most readily be achieved by using variable-speed control to reduce the speed of motors driving pumps and fans.

Variable-speed drives

Data centre running costs can be significantly reduced by as much as 50% with variable-speed drives (VSDs). These devices control the flow of pumps and air conditioning fans to eliminate the energy waste that is common with conventional pump and fan control methods.

Some 65% of all electrical energy is consumed by motors and yet about 95% of all motors are oversized. A typical data centre may have some 70 fixed speed motor applications with an average power per motor of 7.5 kW. Typical motor power could be in excess of 0.5 MW with running costs in excess of £450,000 per annum. Using VSDs can result in financial savings greater than 20%, resulting in about £90,000 per annum, with a payback in typically one year.

How variable-speed drives work

Many existing pump and fan systems are based on throttling arrangements: the motor is driven at full speed and then the flow of liquid or gas is regulated by valves, vanes, dampers or similar throttling mechanisms. Throttling the output in this way wastes energy. 

A VSD can increase the system’s efficiency by adjusting the motor speed to the correct operation point and eliminating the need for throttling. The reduction in flow causes the absorbed power to drop considerably. Thus a small reduction in speed can make a big difference in energy consumption. A centrifugal pump or fan running at 80% speed consumes only half as much energy as a unit running at full speed. This is because the power required to run a pump or fan changes with the cube of the speed.

Because many pump and fan systems run at less than full capacity for much of the time, VSDs can produce huge savings. If a 100 kW fan is throttled by 20%, for example, the investment in a VSD will have a payback of typically six months based on continuous operation.

In addition to energy savings, VSDS offer other benefits including:

–Lower maintenance costs 

–Starting, stopping and braking can easily be programmed to reduce stress on mechanical equipment 

–Increases equipment life and reduces maintenance requirements for pumps, motors and pipework

–Easily retrofitted into an installation

–Real time clock – Can easily set up programmes with different running speeds at different times or on different days

–Low harmonic solutions available as part of installation design

A free, no obligation energy appraisal is available from ABB providing detailed evidence on how much energy you could save.