How to Conduct an Energy Audit

Feb. 26, 2014
Whether your plant is processing food or chemicals, wastewater or steel, the process used to audit your energy usage and find ways to use or waste less of it is much the same.

Whether your plant is processing food or chemicals, wastewater or steel, the process used to audit your energy usage and find ways to use or waste less of it is much the same. Before beginning your energy audit process, it is important to realize that, though there are many energy saving steps that result in short-term payback, the average payback time for investments to increase energy efficiency is five years. The older the facility and its equipment, the greater the probability that the energy savings potential—and your return on investment from corrective actions—will be significant.

Where are you using energy?

There’s no better way to start the audit process than by walking the floor and identifying where and how the facility is using energy. It’s not just about electricity. Any equipment powered by water, air, gas, electricity or steam (a group of power sources often referred to as WAGES), should be the core focus of an energy audit. It often helps to have an outsider’s eyes, such as a system integrator or a vendor, on this walkthrough. They’ve typically been involved in many similar projects and will know what to look for. They also bring a different perspective to the task than a maintenance person, who has different priorities.

Identify the low-hanging fruit

Considering that the average ROI time on energy savings investments is five years, it helps to get some early wins from the audit process that can be achieved with minimal investment.

Look for steam or compressed air leaks. Are there improperly working natural gas regulators? Does the plant have programmable thermostats? How energy-efficient are the lighting fixtures? Do infrared scans detect any hot spots on the electrical equipment?

Also consider the energy-efficiency value to be found in straightforward upgrades of existing equipment. For example, have variable frequency drives been installed on motors serving high-energy-consuming equipment, such as cooling towers? Older cooling towers, for example, tend to have motors that run either slow or fast, with none of the gradients that drives can provide to match energy consumption to different operating conditions.

Go beyond direct asset-related energy use and ask questions like: Is there lighting that’s on when no one is working in a room? Where are the large motor loads, and how and when are they being operated? Are start times being staggered to avoid electrical peak power demand surcharges? Is the plant subjected to extreme seasonal temperature fluctuations between summer and winter?

Understand your electric utility contract

It’s essential to get a working knowledge of the electric utility contract and the billing history for the facility to understand how you’re being billed and what penalties are being charged for over-consumption. Different utilities use different ways to calculate rates and to penalize high consumption.

Determining which of the WAGES energy types are used most in your facility is important for prioritizing corrective actions. Different industries use different types of energy more than others.

Steel plants, for example, are the largest consumers of electrical energy and also incur the most frequent energy spikes because of their use of arc furnaces. The chemical and refining industries, on the other hand, make greater use of compressed air and steam.

Draft a pre-plan

Once you have the initial findings from the walkthrough, draw up a pre-plan to address the obvious areas of waste and identify the processes that consume the most energy. Most older plants are poorly metered. If the only meter in the facility is the one measuring the main utility feed, then it will be impossible to determine which machines or processes are contributing the most to your utility bill.

The pre-plan should identify where meters are to be located to divide and measure energy use among different processes. The information gathered from these sub-meters can then be used to justify capital expenditures and enable you to develop a longer-term plan based on where the best savings are for the least amount of investment.

Most importantly, make sure this plan focuses on the processes used to create the products that contribute the most to the company’s productivity and profitability. It should also define a program of preventive maintenance to maintain energy-efficient production processes and allow you to continue to innovate in the future.

Corrective actions

Companies are taking many corrective steps to increase their energy efficiency. Among the most common:

• Install variable speed drives to match power output with process requirements.

• Take advantage of the software controlling motors to regulate equipment startup times and prevent unscheduled starts.

• Install the most energy-efficient light bulbs and other lighting fixtures.

• Apply automatic lighting controls that turn off lights when rooms are unoccupied.

• Use programmable thermostats to match temperatures within the plant to operating requirements.

• Eliminate leaks in compressed air and steam systems.

• Update capacitor banks to maintain correct power factors when new equipment is installed.

• Install Ethernet-based power management systems. These create an open database of the information collected from your processes that can be used to write custom reports and new applications to address the unique requirements of your facility.

• Make preventive maintenance a priority for maintenance staff by incorporating it into their job descriptions or creating reward programs for meeting PM objectives.

• Changing our attitudes about energy consumption can change our behaviors and lead to energy savings.

There are also more significant capital investments that can be made depending on conditions at your facility.

With electricity rates high and natural gas rates currently low, it may make sense to invest in gas-powered turbines. Justifying that kind of investment, however, requires an analysis of the predictability of rates going forward. Further efficiency can be captured with a co-generation system to produce steam as well as electricity, or even tri-generation if your processes require hot water.

Another possibility is heat recovery. Investment in piping and heat exchange equipment can allow energy to be passed from one process stream to another, reducing the load on utility sources such as steam and cooling water.

How much you can expect to reduce your energy costs will vary from industry to industry and plant to plant. No matter the savings potential at your facility, an energy audit is the first step toward achieving your energy-efficiency goals.

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