Energy Saver: Understand Impact Analysis

April 12, 2016
Focusing on an implementation’s true consequences can lead to more cost-effective results

Undertaking an energy assessment can be a daunting task, but it doesn’t have to be if the energy expert can understand and follow an “impact analysis.” So, this column will cover this methodology and cite a few examples of how to undertake an impact analysis while doing energy assessments.

Published ASME standards for energy assessments provide a good starting point and offer guidelines for conducting these assessments. Nevertheless, our resources — budgets, human resources, and time — are always limited. Hence, there’s a strong need to undertake energy assessments from an impact-level perspective and increase the cost-effectiveness of these efforts. We are still talking about a systems approach; I’m not suggesting cutting any corners while performing energy assessments.


Impact analysis refers to a study that represents the impact (savings or increase) due to changes in operating conditions, best practices, energy efficiency projects, etc. The question you should always ask: “Is this system or component going to see a difference in its operation if we implement a project?” If the answer is “yes,” then it should be included in the impact system. If the answer is “no,” then it doesn’t matter whether you include it or not, and I recommend excluding it. Below are two specific scenarios we come across while undertaking energy assessments that help significantly illustrate the concept.

Impact Energy and Cost

What should be the cost of energy — electricity, natural gas, etc. — used in energy saving calculations? Most often, we use bundled and average costs, but that can result in overstated savings for the projects. If this is a first-level due diligence, then it’s probably okay. However, don’t include fixed costs in energy saving project calculations because they don’t depend on the amount of energy. Classic examples of fixed costs are standby charges, rental and account charges, demand charges (in certain cases), etc. Hence, peel off the fixed charges to drill down to the true impact cost for energy.

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If multiple fuels are used, then focus on the particular fuel that will be reduced when an energy savings project is implemented. Most times, it will be the most expensive fuel, but pay attention to how the control mechanism is set up to ensure that fuel is indeed being reduced. This is the essence of a true systems approach anyway.

Impact Components

Another classic debate revolves around what components to include in the system analysis. It’s clear that our intention in an energy assessment isn’t to recreate the utility bill — every plant already has that information! The focus should be on the impact (change), so, we should be very selective about what components we include or exclude in our system models.

For example, in a pumping system evaluation, two of the three cooling tower pumps are fixed speed, one is variable speed. Most likely, the variable flow pump will be the impact component if the anticipated change doesn’t affect operation of the fixed speed pumps. Therefore, our impact model should ignore the fixed speed pumps and our model results would be identical with or without these pumps.

Certain steam turbine operations provide a more-complex example. Where there are multiple backpressure and condensing steam turbines in a plant, you must systematically understand their operations and be able to eliminate those turbines or operations that the planned change won’t affect. Turbines operating for power generation will depend on the plant load; saving steam really may not impact their operation. Alternatively, a backpressure turbine driving a process compressor isn’t going to see a change if the energy project doesn’t impact the process.

This is a complex topic to discuss and every plant and process is unique. I hope you can use this brief discussion to simplify your analysis without sacrificing the confidence level in your results.

Riyaz Papar, PE, CEM, is director, Global Energy Services, at Hudson Technologies Company, Pearl River, N.Y. He has more than 20 years of experience in industrial energy systems and with best practices. He also is a U.S. Department of Energy (DOE) Steam Best Practices senior instructor and a DOE steam energy expert. He has provided energy consulting services in 100+ industrial plants in the U.S. and internationally. You can email him at [email protected].

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