Does Energy Efficiency Have A Unit?

Defining Energy Efficiency

Energy efficiency refers to using less energy to perform the same task. According to the World Energy Council, energy efficiency is defined as “using less energy to provide the same service” (Pérez-Lombard et al., 2012). The key concept is providing the same level of service or completing the same amount of work while using less energy input. For example, replacing an older air conditioner with a newer, high-efficiency model can cool a home using significantly less electricity.

Energy efficiency improvements enable us to maintain our quality of life while reducing energy consumption. With efficient technologies, less energy is wasted during every conversion and transmission process as the service is delivered. The International Energy Agency defines energy efficiency as “using technology that requires less energy to perform the same function.” The benefits are many, from saving money to reducing environmental impacts.


Pérez-Lombard, L., Ortiz, J., & Velázquez, D. (2012). Revisiting energy efficiency fundamentals. Energy Efficiency, 6(2), 539-554.

Measuring Energy Efficiency

Energy efficiency can be measured and quantified in several different ways using standard metrics. Some common metrics used to evaluate energy efficiency include:

  • EER (Energy Efficiency Ratio) – Used to rate the efficiency of air conditioners, refrigerators, and heat pumps. Measured in BTUs of cooling per watt of electricity input.
  • SEER (Seasonal Energy Efficiency Ratio) – Similar to EER but accounts for variations in temperature over the year. The higher the SEER rating, the more energy efficient the system.
  • energy efficiency metrics allow fair comparison of systems at different scales

  • MPG (Miles per Gallon) – Measures the fuel efficiency of vehicles. A higher MPG indicates greater efficiency and less fuel required to travel the same distance.
  • Lumens per Watt – Measures light output per unit of electric power for lighting products like LED bulbs. More lumens per watt equates to greater efficiency.

Other metrics like COP (Coefficient of Performance), AFUE (Annual Fuel Utilization Efficiency), and HSPF (Heating Seasonal Performance Factor) are used for specific applications. But in general, higher values for these metrics indicate better energy efficiency and lower energy consumption.


Key Metrics to Evaluate Energy Efficiency in Mobile App Design. (2023). Retrieved from

Integrating Energy Efficiency Metrics into Lab Performance Evaluation. (2023). Retrieved from

Unit of Measurement

The most common unit used to measure energy efficiency is an efficiency ratio, which is simply the useful output divided by the total input. This allows the efficiency of different systems or processes to be compared, even if their absolute energy use differs greatly.

For example, the efficiency of an electric motor can be measured by dividing the useful mechanical work performed by the total electrical energy supplied to the motor. This efficiency ratio would be a unitless number between 0 and 1, or it could be expressed as a percentage. The same approach can be used to measure the efficiency of a power plant, heating system, vehicle drivetrain, or any other energy-converting device.

Ratios are useful for comparing efficiencies because they account for differences in scale. A large power plant and a small electric motor may use vastly different absolute amounts of input energy, but their efficiency ratios can still be directly compared.

Other common units used in energy efficiency include miles per gallon (MPG) for vehicles, lumens per watt for lighting, and Seasonal Energy Efficiency Ratio (SEER) for heating and cooling systems. But in all cases, the basic principle is measuring useful output relative to energy input.

So in summary, energy efficiency fundamentally has no single unit of measurement. Efficiency is a ratio that can be applied across all energy systems and allows fair comparisons between processes at vastly different scales.

Factors Affecting Efficiency

Energy efficiency depends on a variety of factors related to technology, process and system design, and maintenance.

In residential buildings, efficiency can be improved through better insulation, energy-efficient appliances, lighting, heating and cooling systems, and smart energy monitoring systems that adjust usage based on occupancy and other variables (Nair & Gustavsson, 2010). Proper maintenance like sealing air leaks and ductwork also minimizes energy waste.

Industrial facilities can improve efficiency by upgrading to more efficient motors, pumps, boilers, and manufacturing processes. Optimizing process design to reuse waste heat and utilize cogeneration helps maximize energy utilization (Zhang et al., 2021). Implementing preventative maintenance procedures and equipment monitoring can minimize losses as well.

In transportation, more fuel efficient vehicle designs, proper tire inflation, removing extra weight, and regular maintenance help maximize mileage. Systems like public transit, carpooling, walking, and biking infrastructure also improve overall transportation energy efficiency.

Improving Efficiency

Energy efficiency can continually improve through ongoing innovation and optimization efforts. There are many examples of technologies that have dramatically increased efficiency over older versions.

One area that has seen major efficiency gains is lighting. The widespread adoption of LED lighting has reduced the amount of electricity required for lighting by up to 80-90% compared to traditional incandescent bulbs. LEDs last years longer and contain no toxic chemicals like mercury.

Insulated windows have also led to significant efficiency improvements in buildings. Multiple panes separated by gas or vacuum insulation drastically reduce heat transfer compared to single pane windows. High efficiency windows can reduce energy lost through windows by up to 50%.

In the transportation sector, hybrid vehicles have increased efficiency by capturing energy normally lost during braking and reusing it to assist the engine. Hybrid drivetrains allow the engine to turn off when stopped and reduce engine load in low power conditions. Fuel efficiency in hybrid vehicles can be 50% better than conventional gasoline engines.

Technology innovations like these demonstrate the vast potential for improving energy efficiency across all sectors of the economy. Continued research, development, and adoption of cutting edge efficiency solutions will be key for meeting energy and climate goals going forward.

Energy Efficiency Trends

Historical data shows that energy efficiency has improved significantly across sectors in recent decades. According to a report from the UN Economic Commission for Latin America and the Caribbean, between 1990 and 2008, global energy intensity (a measure of energy efficiency) improved by 1.3% per year ( The industrial sector saw energy intensity improvements of 1.5% per year, while the residential sector improved by 1% per year over that period.

Projections indicate continued improvements in efficiency going forward, largely driven by technological advances. The International Energy Agency’s Energy Technology Perspectives 2017 report projects that global energy intensity could decrease by an average of 2.7% per year from 2015 to 2060 in their ‘best case’ scenario. This is attributed to factors like improved insulation, lighting, appliances, heating/cooling systems, and industrial processes. Emerging technologies like smart grids, sensors, and advanced materials are also expected to enable greater efficiency.

Efficiency Policies

Governments around the world implement policies aimed at increasing energy efficiency in a variety of sectors. Some common policy approaches include building codes, appliance standards, vehicle fuel economy standards, and industrial regulations. Building codes require new buildings to meet certain energy efficiency criteria and are implemented at the local, state, or national level. For example, building codes may require high-efficiency heating, ventilation and air conditioning (HVAC) systems, increased insulation, energy efficient windows, and LED lighting.[1]

Appliance and equipment standards set minimum energy performance requirements for various products like refrigerators, washing machines, and industrial motors. The standards help remove the least efficient products from the market. Vehicle fuel economy standards require automakers to meet fleetwide average fuel economy targets. These regulations have significantly improved the on-road fuel economy of passenger vehicles over the past decades.[2]

While regulations can effectively increase efficiency, critics argue they can also increase upfront costs for consumers and businesses. There is debate around finding the right balance between costs and long-term energy savings from efficiency. Some believe incentives and information programs are preferable to mandatory standards. Overall, research shows an “energy efficiency gap” exists where cost-effective efficiency opportunities are not always implemented due to various market barriers. Well-designed policies can help overcome these barriers and achieve greater energy savings.[1]

Regardless of the exact policy approach, governments play an important role in harnessing energy efficiency’s benefits like lower energy bills, increased competitiveness, energy security, and reduced emissions.


Economic Impacts

Energy efficiency improvements can have significant positive economic impacts. By reducing energy use, energy efficiency lowers utility bills for households and businesses. This puts more money in consumers’ pockets to spend elsewhere in the local economy. For example, a 2021 study by researchers at the University of Chicago found that residential demand-side energy efficiency projects in India reduced household electricity expenditures by 6-10% (

Energy efficiency also stimulates job creation and economic growth. There is growing demand for energy auditors, technicians, engineers and other skilled workers needed to implement efficiency projects. According to one analysis, investments in energy efficiency create twice as many jobs as comparable spending on fossil fuel sources ( Energy cost savings from efficiency improvements further spur economic activity as households and businesses redirect expenditures toward other goods and services.

Environmental Benefits

Improving energy efficiency provides significant environmental benefits by reducing energy waste, pollution emissions, and mitigating climate change. According to the EPA, the energy we waste in the US alone accounts for over 800 million metric tons of CO2 emissions annually ( The International Energy Agency estimates that energy efficiency improvements could reduce global CO2 emissions by 12 billion metric tons by 2050, representing 40% of the abatement required to limit global warming to 2°C (

When less energy is wasted, fewer fossil fuels need to be extracted and burned to power buildings, appliances, and manufacturing processes. This directly lowers emissions of greenhouse gases like carbon dioxide that drive climate change. It also reduces air pollutants like sulfur dioxide, nitrogen oxides, particulate matter, and mercury that harm human health. For example, an energy efficiency program targeting refrigerators in the US is estimated to have cumulatively avoided over 4 million tons of CO2 emissions by 2016 (

Furthermore, energy efficiency protects ecosystems by reducing extraction, mining, drilling, and land disruption for fossil fuel production. The World Resources Institute calculates that doubling global energy productivity could avoid the conversion of an area larger than India for energy production by 2030 ( The environmental benefits of using less energy clearly make efficiency an essential climate change solution.


Energy efficiency is quantified by comparing the useful output of an energy conversion process to the energy input required to drive that process. The standard unit of measurement for energy efficiency is the ratio of useful energy output to energy input. Key points on how efficiency is measured and improved include:

  • Energy efficiency is calculated by dividing the useful output of a system by the energy input into the system.
  • Higher efficiency ratings indicate more useful energy output per unit of input.
  • Factors like technology, operations, and maintenance affect energy efficiency.
  • Policies, investments, and optimization strategies can improve efficiency over time.
  • Increasing efficiency provides economic benefits through cost savings and environmental benefits by reducing pollution and resource use.

In summary, energy efficiency is a quantifiable metric with many potential benefits. Continued efforts to measure and improve efficiency will be important for providing affordable, clean energy services.

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