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ENERGY MANAGEMENT An opportunity too good to miss

It sounds almost too good to be true, but there is a straightforward and cost-effective way for businesses to make big energy savings and reductions in their carbon footprint. The key is the deployment of AC variable speed drives, as Stephen Takhar of Vacon UK explains.

80%, compared with the 1990 baseline, by the year 2050. This commitment has big implications for businesses, because it means that they’re going to be squeezed as never before by legislation designed to force them to reduce energy usage. In fact, the legislative pressures are already starting to be applied. A good example is the CRC Energy Efficiency Scheme, which affects around 20,000 large public and private organisations who will have to monitor their emissions and buy allowances for every tonne of CO2 they produce. In other words, the more energy they use, the more money they’ll have to spend on allowances – and that’s on top of their normal energy bill.


The CRC scheme only applies to large organisations but make no mistake, similar pressures will soon be applied to every business in the land, large or small, if for no better reason than it’s the only hope the government has of meeting its commitment. So what’s to be done and how can organisations drastically reduce their energy usage?

Finding the answer

There are lots of answers such as improved thermal insulation for buildings, intelligent control for heating and lighting, switching to energy efficiency light sources – the list goes on, but there’s one option that really should be considered as too good to miss, and that’s the installation of AC variable speed drives. Yes, this has been said before, but there are still far too many organisations that have yet to go down this road. One of the areas where really big savings can be made is in HVAC plant, which is found in almost every modern building of any size. This plant invariably incorporates motors driving pumps and fans.

In the

old days, when minimising energy consumption wasn’t particularly high on the list of priorities for HVAC plant design, these motors were equipped with simple starters that allowed them to run at full speed or not at all. Any necessary regulation of air or liquid flows was carried out by using diverters or by throttling. In plants of this type, very many of which are still in use, motors have to run at full speed all the time the plant is operating. This is especially bad news, as the plant will have

he UK Government is committed to reducing the country’s greenhouse gas emissions by a staggering

been designed on a worst-case basis. In other words, the motors will have been sized to deal with the coldest and hottest days of the year. At all other times, they’re doing far more work than is necessary. The logical solution is to rip out all the single speed starters along with the throttling and diverter systems and to fit in their place modern AC variable speed drives and a control system that will regulate the speed of the motor so that it matches the actual demand, instead of running flat out ‘just in case’. It’s not hard to see that this will save energy, but just how much energy can be saved might come as something of a surprise.

Saving energy

The energy used by a fan or a centrifugal pump varies as the cube of its speed. This means that when a fan or pump is running at half speed, it uses 0.5 x 0.5 x 0.5 = 0.125 times as much energy as when it is running at full speed. In other words, cutting the speed by 50% reduces the energy usage by 87.5%, which in anyone’s book is a very worthwhile saving. But if AC variable speed drives are

capable of delivering such worthwhile savings, why aren’t they being fitted everywhere? There’s no simple answer. Some organisations may still not be aware of the potential savings that these drives offer, although they’ve hardly been kept secret. Probably the biggest issue, however, is that organisations are concerned about the cost and disruption that’s likely to be involved in installing the new drives.

(ECA) scheme, which means that 100% of their cost can be offset against tax in the year in which they are installed. But the real clincher must surely be the on- going savings on energy expenditure that they provide. In the majority of cases, the cost of fitting AC variable speed drives will be recovered in two years or less, after which the savings go straight to the organisation’s bottom line.

Convincing argument In reality, neither of these concerns is

valid. Variable speed drives are not expensive and, in almost all cases fitting is straightforward and, therefore, inexpensive. The best drives also qualify for the government’s Enhanced Capital Allowances


Now let’s consider the disruption involved in fitting variable speed drives. As has already been noted, this is usually a straightforward task. Modern drives are small and easy to accommodate, and they are available in enclosed versions that can, for example, be mounted directly on a wall without the need for further protection. There may be a need to fit other devices such as flow sensors to provide control signals for the drives, but this should present no problems for an experienced drive installer. The arguments in favour of replacing fixed speed starters with AC variable speed drives are convincing, but it is worth remembering that not all drives are created equal and, while the work is being carried out, it is worthwhile choosing the most appropriate drives for the job. Invariably, these will be types that are specifically designed for HVAC applications. General-purpose industrial types will work, but they tend to offer poor value for money in

HVAC systems as they are likely to need costly add-ons to provide functionality that is already included in HVAC-specific drives. The best HVAC drives, for example, include functions such as real-time clocks that make it easy for the system to be shut down automatically outside normal occupancy hours, PID controllers that allow the motor speed to be controlled directly from flow or pressure sensors, and a sleep option that shuts down the motor completely if the demand falls to zero. Dedicated HVAC drives from leading

manufacturers also have good EMC performance so that even if they are used in large numbers in an installation they do not adversely affect the quality of the electrical supply. Finally, they use components chosen to ensure that the drives provide long reliable working lives. In particular, the latest drives use film capacitors rather than the traditional electrolytic types. Film capacitors not only have longer lives, they are also more environmentally friendly as they have no liquid or semi-liquid electrolyte to create a pollution hazard when they are ultimately discarded.

A real opportunity

When it comes to keeping the government and the accountants happy by reducing carbon footprint and cutting energy costs, fitting AC variable speed drives to HVAC plants really is an opportunity that’s too good to miss. The drives are inexpensive, reliable and easy to install with a minimum of disruption. Always remember, however, that the best results will be obtained by choosing dedicated drives from a supplier with a proven track record in the HVAC sector.


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