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Commercial Angles' Newsletter - September 2001

Energy Audits

The purpose of an energy audit is to reduce operating costs by reducing energy consumption and the government has estimated that most companies can reduce their energy consumption by 10% to 20%. With the Climate Change Levy increasing most companies' energy costs by 10% or more, energy efficiency is even more important now than it was in the past. Experience shows that these savings are usually best achieved by performing an energy audit.

In most industrial sites about two-thirds of the energy is consumed by electric motors. In its lifetime the cost of energy consumed by an electric motor may be 100 times its purchase cost. So the reduction of losses in the motor itself is very important and modern electric motor design can reduce the energy loss in the motor by up to 30%. Many fans and motors are operated at full power constantly, irrespective of process needs, and in some sites this offers the potential of large cost reductions. It is also frequently true that power factor correction equipment does not adequately compensate for inductive loads at all times. In some energy supply agreements surcharges arise from poor power factor correction. An energy audit will identify all these issues and calculate the potential savings to be made.

The first time an energy audit is performed many manhours will be needed to find out where energy is being consumed in an office, warehouse or factory. It is important that a thorough log of consumptions on each spur is made because excessive energy is sometimes used in the most unlikely places. In the case of fluctuating work loads, the monitoring of each energy consuming piece of plant may require several days to complete.

A true story demonstrates the benefits that may arise from such an exercise. In a glass factory all the mains water meters were read at regular intervals and consumptions monitored against factory output. The meters had been read for decades and excessive water consumptions investigated and leaks eliminated. However the expected consumptions had never been calculated. As part of the energy audit extra meters were installed on each water main spur in the plant. Permanent meters were installed in the major consumption areas but the total of the subsidiary meters was always less than the mains consumption. Eventually the reason was tracked down by putting temporary meters on the subsidiary water lines - an eight inch main had been fractured for decades and because the ground was well drained the fracture had never been noticeable. A main road near the factory went through an underpass beneath a railway line and each winter, for as long as anyone could remember, the underpass had flooded, often to such a depth that cars became stuck. After the fracture was mended the underpass never flooded again and the company saved tens of thousands of pounds as a result of the energy audit.

A typical energy audit will not always find such dramatic examples but they are far from unusual. An energy audit should identify the savings to be made by repairing leaks in compressed air systems and steam pipes for example, or the savings to be made by installing variable speed motors in place of motors driven at full power irrespective of need. A good energy audit will calculate from the process requirements what energy consumption should be needed and compare this with actual energy consumption. By ensuring that every fan, motor or compressor is working at the maximum efficiency great savings can be made.

In warehouses and offices significant energy is consumed in lighting and heating. An energy audit will calculate the level of lighting required and show any savings that may be possible using an appropriate distribution of high efficiency lamps. Heating costs can often be significantly reduced by installing insulation and partitions or by using more efficient heating systems, installing air curtains or rapid action doors. Lowering office thermostats by 1 degree can frequently reduce heating costs by 10%.

When deciding whether or not to carry out an energy audit a good starting point is to assume that you will save 10% of your current energy consumption. This gives a guide as to how much to invest in the energy audit. With this information you can then contact a number of local electrical distributors or engineering consultants. When choosing the party to carry out the audit look for these benefits:

clearly identified energy savings.
complete audit results and energy savings calculations.
history of other audits and associated savings.
proposed payback periods.
degree of customer training given as part of the audit process.

Articles from previous newsletters