Variable speed drives save energy and money

Every manager of a business is looking to find economies within their business energy usage, in an attempt to bring down their energy bills.  One way of doing this, is with variable-speed drives (VSDs).  Already a useful technology in this regard, further advances in recent years, in terms of maintenance and engineering, is yielding yet further benefits in terms of life-cycle costs.

variable speed drive energy savingLet’s look, as an example, at the driving equipment of electric motors.  Motors – within, say, fans or pumps – operate at a constant speed.  Water flow and volume (in the case of a pump) or airflow (in the case of a fan) will be managed by a throttle, such as a valve with the former, or slats with the latter.  However, although the flow is managed, the motor itself continues to chug away at a steady, high, energy-draining rate, even when the machinery is only operating at a reduced pace.

Imagine the heart in your own body.  At times, of course, it needs to pump blood around at a higher rate; perhaps when exercising.  However at other times, for instance when you are sleeping, there is simply no need for it to function at that heightened pace.  That is essentially the role of the variable speed drive… to control these varied loads, and thus operate much more efficiently.

Much of the equipment in a plant will be driven by AC motors and this is where the installation of variable speed drives can really help.  Indeed, using VSDs within pumps, cooling towers and fans could reduce energy usage by around 50% because at lower (variable) speeds, those drives use less power, rather than needing to dissipate it as, for instance, heat.

However, that is not where the story ends.  Operating at a lower power factor (the ratio between active power and total power – the PF), means there is less stress on the moving parts of the machinery at these lower speeds, and therefore fewer vibration problems.  As a consequence, equipment wear will slow down, and the life cycle of that equipment will improve.  With less wear and tear on equipment, a further benefit is therefore that maintenance costs can be reduced.  Think, again, of the health and function of the human heart.

So there’s a double benefit whammy in the use of VSDs: energy savings, plus improved operation and maintenance of the equipment.

How much energy do VSD’s save?

Well there are simple sums that you might be able to calculate.  Some utility companies, for instance, will offer rebates for businesses who have committed to using variable speed drives in their operations – a very simple saving to factor in.  These energy companies understand that the installation of variable speed drives will have a positive benefit on the efficiency of that business, when many are, themselves, committed to maintain their own energy reserves.

Equally, there are other sums that managers might easily be able to calculate, in terms of the savings made versus the initial investment in VSD technology.  Data – including the purchase price  for the VSD conversion, daily / annual flow variability, annual operating days and even operating shifts – can be measured against the initial cost of installing the energy-saving system… the breakeven… and then the ultimate return on that investment.

It is often calculated that the time for that initial investment to pay for itself, and then start returning savings, can be a matter of a few months.  For most businesses, you will find that the ultimate benefits, set against the costs of buying and then setting up the variable speed drive, will always be worth the effort… especially in this current climate of energy efficiency awareness.

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