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How to Calculate the Energy Efficiency of a Building

By August 2, 2022August 5th, 2022Energy Efficiency
Low angle photo of energy efficient buildings

Learning how to build an energy-efficient building is becoming more commonplace. Buildings and manufacturing plants account for about two-thirds of carbon dioxide emissions in the United States. As we have new requirements set and soon-to-be taxes implemented on commercial buildings, there is no better time than the present to obtain a better understanding of the process.

Efficiency is the ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing the desired result. Energy efficiency is simply reducing the energy expenditure required for the desired service needed. Energy consumption can be reduced through energy efficiency by using “smart,” innovative products, as well as energy-efficient construction. We are finding our way there in both residential homes, as well as commercial buildings.

Building Energy Efficiency

In the 21st century, devices are designed to waste as little energy as possible. This means that as much of the input energy as possible should be transferred into useful energy, instead of wasted energy. How well a device transfers energy input to useful energy output is referred to as efficiency. Consequently, a very efficient appliance or device will waste very little of its input energy. In contrast, a very inefficient device will waste most of its input energy. It is no different for a building.

When one form of energy is converted into another, some of the energy initially available is lost, often in the form of heat. This can increase the need for HVAC use in a building, thus requiring more energy to be used. Energy efficiency, or the amount of energy produced in proportion to the amount of energy used to produce it, whether evaluating appliances alone or the building on the whole, factors in.

Energy efficiency is calculated by dividing the desired obtained results of lighting or cooling by the initial energy input. For example, an incandescent bulb is approximately 5% energy efficiency (with most of the energy wasted creating heat), a LED lamp over 30%, and a refrigerator has 20 to 50% energy efficiency. On the whole, power generation has an energy efficiency of about 39%. The higher the percentage, the more energy efficient the process is.

Energy Efficiency Formula

In order to calculate anything, you need a formula. The same is true when learning the energy efficiency of a building. The energy efficiency formula is as follows:


The energy efficiency of a building or appliance is denoted by the Greek letter ηη.

For example, if you have a solar module that produces 320 watts of energy from 1500 watts of sunlight, then you would calculate the solar panel’s energy efficiency as:

(320/1500) X 100 = 21.3%

The energy efficiency formula may be used for different forms like electrical energy, heat energy, internal energy, kinetic energy, light energy, etc. According to the law of conservation of energy, energy can neither be created nor destroyed – only converted from one form of energy to another. Therefore, it may be simpler to think ‘desired output’ versus ‘output’. During the energy conversion process, some quantity of energy gets wasted due to irreversibility. The genius of energy efficiency is the intent of streamlining that process in order to reduce waste.

A commercial building owner will need to ensure that their useful energy percentage meets any legislative requirements within that community. Otherwise, that owner may be considered non-compliant and fined accordingly.

Energy Efficient Windows

Inefficient windows, particularly in commercial buildings have a great effect on the overall energy efficiency of your building. As many large buildings are completely encompassed in glass, garnering control in this area can improve the efficiency of your building as a whole as a result of the HVAC running less to achieve the same setpoints.

Growing in popularity are reflective window films that reduce the amount of heat that enters a building. There are also UV blocking window films and solar control window films. All of these options offer intense aid in energy efficiency for any building.

If you would like to learn more about window films for your building, visit our website. We have an educated and diligent staff waiting to answer any questions you may have. Furthermore, we have building modeling and energy engineering services that may help improve your return on investment. There’s no better time than today to become energy efficient.

Improve Energy Efficiency and Security with Sun Control Window Films
Hosted by  James Beale
Learn how sun control window films help improve building energy efficiency, reduce costs, improve occupant comfort, and increase security.


Photo by Matthew Henry

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