Energy audits scrutinise your site’s energy use to assist in identifying measures for cost and energy savings. They are an essential part of the effective control of energy costs and consequently form an important part of energy management practice.

Plant and equipment are often the largest consumers of energy within the workplace. Collecting and analysing data of machinery use can highlight areas of significant energy consumption throughout different processes and ascertain potential opportunities for savings. The results from an energy audit should be used to determine the priorities for more detailed investigations; justify investment in energy efficiency measures; identify cases for direct action, e.g., choice of fuel type, change of fuel supply tariff; and help to raise the energy awareness of all staff by providing facts on energy use. 

One of the best methods of conducting an energy audit is to lead an on-site survey. The key factors to consider are the sources of energy use, energy consumption of each item of equipment, past and present energy usage, as well as current performance of facilities, systems and processes.

Data collection

Good data is key to good decisions. This should be at the forefront of the data collection process.  It will also determine how detailed an evaluation can be undertaken.

List your energy requirements from equipment, processes and systems, identify the characteristics of the item(s) and collect historical data of the equipment’s energy use. Invoices are an essential source of information on energy usage, costs and tariffs. It is important to keep and maintain good data records with half-hourly profiles. For invoice data, you should collect copies of all monthly and quarterly energy bills for all fuels. Compare estimated figures with actual figures, and note consumption patterns. Note: delivered energy is not always the same as consumed energy.

There will be other factors to take into consideration, some specific to your own organisation, such as building occupancy, production output, shutdown periods and weather.

In many cases additional information on plant and equipment can be found on or near the plant. Where they are current, these log books can be a useful source of information. These should be checked for accuracy and to ensure that the extracted information relates to the model/item installed. 

In addition to simply writing a record of the survey, it is often useful to capture your walk round by supplementing this with images provided by a digital camera. Not only is this helpful for recording the exact labels on equipment but also to remind the auditor of the route that was taken and strengthen the presentation of findings as the audience can relate to the pictures provided to support your rationale. In circumstances where the audit is over a large complex or covers multiple locations it is valuable to capture images to prevent merging of the observations. They can also help to jog your memory. Often plant and equipment can come in a diverse range. For example the humble light bulb can come in many shapes and sizes, but the type may not always be so apparent. 

Health and safety considerations

An energy audit requires working on-site and, at times, this will involve close proximity to utility and production machinery. Safety considerations are a very important part of any energy audit. The audit team should be thoroughly briefed on safety equipment and procedures and should never be put in a dangerous situation while conducting the audit.

You should be extremely careful making any measurement on electrical systems or high temperature devices such as boilers, heaters, or furnaces. Electrical or asbestos gloves should be worn as appropriate. Auditors should also be very careful when examining any operating piece of equipment, especially those with open drive shafts, belts or gears, or any form of rotating machinery. The equipment operator or supervisor should be notified that the auditor is going to look at the equipment and might need to get information from some parts of the machine.

Final review

On completion of an energy audit, the opportunities for energy savings will generally fall into one of four categories: Management and operations (behaviour change), supply (fuel switching, potential for renewables), plant and equipment (improving efficiency, end of life), and building fabric (air filtration/draughts, insulation)

You also need to determine who the audience will be for the final audit report, and what criteria they may already be using. For example, a simple payback of less than three years is common for low and medium cost items, whereas for large capital items, a net present value or internal rate of return may be required. Often, identifying the criteria on which to base the opportunities will help in their grouping and to decide how you present the findings, as well as managing expectations.

Energy auditing should be a regular occurrence and be incorporated into any formal energy management practices. This process should become cyclical once it reaches the management review stage. 

In a formal energy management process it would be expected that the audit is carried out annually but it may be completed on a shorter time frame depending on the size and impact of energy on the organisation. It may also be prudent to perform an audit before a major redevelopment to provide current information. A full audit would be expected every 2-3 years but should also be dependent on the rate at which a site is changing, or following any major change in circumstances.

Mark Hobbins CEng MEI is a tutor on the Energy Institute (EI)’s energy management training programme. Energy auditing in practice is one of the modules of the EI’s eLearning course on energy management. The first module of this course is free of charge and tackles the role of an energy manager, developing an energy policy and investment in energy efficiency including calculating payback periods.