Guest Column | January 6, 2017

Math Solutions: Energy Dollar Savings Calculations

Wastewater Dan Theobald

By Daniel Theobald, "Wastewater Dan"


Energy efficiency, as defined in wastewater treatment, is using less energy to provide the same service. It can be expressed as energy dollar savings by replacing older, inefficient motors.

Energy is saved when you replace a motor, such as a pump motor, with a newer, more energy-efficient motor. The new motor provides the same service, but uses less energy. This saves energy dollars on your energy bill, and, as an added benefit, reduces the amount of greenhouse gases released into the atmosphere.

This tool for operators, represented through video tutorials, offers mathematical templates to master the energy dollar savings calculation of the number of pump motors requiring change-out to realize a certain annual energy dollar savings.

The tool also provides definitions, explanations, and alternative applications for the calculations beyond the specific examples presented. In addition to operators, it may also serve educators, engineers, regulators, and others.

A representative energy dollar savings math word problem followed by exact step-by-step solutions is presented  below.

In order to realize $10,000 annual energy savings due to pump efficiency, calculate the number out of six (6) older pump motors that require replacement with newer, more efficient pump motors. All motors operate at 50 OUTPUT HP; the old motors’ efficiency is 85 percent and the new motors’ efficiency is guaranteed at 93 percent. The new motors run 74 percent of the time, 365 days per year. With electricity averaging $0.1320 KWH, calculate the number of old pump motors that require replacement with new pump motors in order to realize $10,000 annual energy savings.

Energy Savings Calculation Solutions

Motor Horsepower (HP) Calculation Solutions:

Old motor horsepower (HP):

New motor horsepower (HP):

Horsepower (HP) savings replacing 1 motor:

Energy Savings Calculation Solutions

Annual energy dollars savings by replacing 1 motor:

Number of pump motors requiring replacement to realize $10,000 annual energy dollars savings:

Playlist of 15-plus pump performance efficiency (including Energy Dollar Savings) calculations

Playlist of all 165-plus Math Solutions

This is the Energy Dollar Savings Calculations presentation in my series of “Math Solutions.” If you have specific wastewater math queries, please submit a question

About Dan Theobald:

Known in the industry as “Wastewater Dan,” Daniel L. Theobald, proprietor of Environmental Services (, is a professional wastewater and safety consultant/trainer. He has more than 24 years of hands-on industry experience operating many variants of wastewater treatment processing units and is eager to share with others his knowledge about water conservation.

Theobald serves as an active consultant for industries looking to achieve and maintain improved wastewater treatment at reduced cost. He is a Lifetime Member of the Who’s Who Registry of Professionals and holds numerous certifications from wastewater management regulatory boards and professional organizations. Theobald contributed one chapter to the Water Environment Federation’s ( Manual of Practice # 37 (MOP-37), a technical manual resource guide for biological nutrient removal, published in 2013.

Image credit: "Money," Pictures of Money © 2014, used under an Attribution 2.0 Generic license: