What Is The Source Energy Factor?

Table of Contents

What is Source Energy?

Source energy refers to the total amount of raw energy required to operate a building. Unlike site energy, which only accounts for energy consumed on-site, source energy considers the energy used to extract, process, generate, and deliver energy to a site.

For example, while site energy only captures the electricity used in your building, source energy accounts for all the raw fuels required to create that electricity at the power plant. This includes the energy lost during generation, transmission, and distribution of electricity.

Source energy provides a more complete assessment of a building’s energy use because it considers upstream inefficiencies. While site energy focuses on consumption, source energy reveals the demand a building places on the energy infrastructure. For this reason, source energy is often used as a metric for building energy performance and greenhouse gas emissions.

Why Source Energy Matters

Source energy is an important concept in analyzing the total energy impact of buildings and systems. While site energy only accounts for the energy directly consumed onsite, source energy considers the raw fuel required to generate and deliver that energy. This provides a more complete picture of energy efficiency.

For example, only looking at site electricity usage overlooks generation and transmission losses at power plants. 1 kWh of electricity consumed onsite actually requires around 3 kWh of source energy from raw fuels like coal, natural gas, or uranium. Source energy factors account for these upstream impacts.

Similarly, source energy considers the extraction, processing and transportation of fossil fuels for heating. Using source energy highlights the substantial embedded energy costs in delivered fuels like natural gas.

By evaluating source energy, buildings can optimize their efficiency across the full energy supply chain. Reductions in source energy lead to real reductions in the raw fuels required to operate buildings. Focusing on source energy also encourages the use of renewable energy generated onsite, since it has much lower upstream impacts. Overall, source energy provides a more holistic and impactful approach to energy performance.

How Source Energy is Calculated

Source energy is calculated by taking the amount of energy directly used onsite at a building (known as site energy) and multiplying it by a source energy conversion factor. This conversion accounts for the losses in generation, transmission, and delivery of the energy source.

For electricity, the conversion factor accounts for generation inefficiencies at the power plant as well as transmission and distribution losses along the grid. For natural gas, the conversion factor accounts for losses in extraction and pipeline transport. The conversion factors differ based on the region and primary energy sources used for electricity generation.

So for an example, if a building used 100 kWh of electricity onsite, and the source energy conversion factor for electricity was 3.0, then the source energy usage would be calculated as:

Source Energy = Site Energy x Conversion Factor

Source Energy = 100 kWh x 3.0 = 300 kWh

This means it took 300 kWh of raw primary energy to deliver 100 kWh of site electricity to the building after all the losses along the way. Source energy provides a more holistic view of the true energy footprint of a building.

Source Energy Conversion Factors

Source energy conversion factors are used to calculate the source energy consumption of buildings. These conversion factors account for the losses that occur in generating and transmitting energy to the building site. The factors vary for different energy types and depend on the generation mix and transmission infrastructure in a given region.

Some standard reference source energy conversion factors have been defined. For U.S. electricity, a factor of 3.14 is commonly used, reflecting an average of 32% grid efficiency across generation, transmission and distribution losses. For natural gas, a factor of 1.05 accounts for delivery and leakage losses. Other factors have been specified for oil, propane, steam and chilled water.

These reference factors provide standard multipliers to convert site energy use to source energy use. They enable reasonable comparisons of energy performance across different regions and building types. However, the conversion factors also have limitations, as the true upstream losses can vary significantly based on the local energy infrastructure.

Source Energy in Building Standards

Source energy is an important metric that is incorporated into many building energy codes and standards around the world. Building codes specify the minimum energy efficiency requirements for new and renovated buildings. By accounting for source energy, building standards incentivize efficiency improvements that reduce energy losses during generation and transmission.

For example, ASHRAE Standard 90.1, which provides the baseline for building energy codes in the United States, includes requirements for maximum allowable source energy use per square foot for different building types. This encourages building designers to reduce waste and consider site-to-source energy conversion factors in their efficiency strategies. The International Green Construction Code (IgCC) also references source energy as part of its performance-based compliance path.

Additionally, green building standards like LEED reference source energy metrics. LEED points are earned by minimizing source energy use intensity. By evaluating whole building energy performance on a source energy basis, LEED provides a more complete picture of energy efficiency which captures upstream losses.

Overall, source energy factors help provide a common metric for energy efficiency in building standards and codes. Focusing on source energy reduction incentivizes holistic energy design approaches and conservation strategies.

Source Energy in LEED

Source energy plays an important role in LEED building certification. LEED, which stands for Leadership in Energy and Environmental Design, is a green building rating system developed by the non-profit U.S. Green Building Council (USGBC).

One key area that LEED certification evaluates is a building’s energy performance. To assess this, LEED uses source energy as the metric. Source energy accounts for all the raw fuel required to operate a building, including power generation and transmission losses. By using source energy, LEED provides a more holistic view of a building’s energy use.

In LEED v4, the latest version of the rating system, buildings must meet minimum source energy use intensity (EUI) requirements to earn points under the Optimized Energy Performance credit. The lower the source EUI, the more points are earned. Buildings must undergo whole building energy modeling using source energy to determine their EUI.

Tracking and reducing source energy usage is an important part of designing and operating energy efficient, sustainable buildings. LEED’s use of source energy factors helps motivate the design and construction of greener buildings that minimize raw fuel usage.

Criticisms and Limitations

While source energy is an important metric in building energy analysis, it has some key limitations and criticisms:

One major issue is that source energy factors can vary significantly by region based on the local energy mix. A building in a region powered mostly by renewable energy will have a much lower source energy use than an identical building in a region powered by coal or other fossil fuels. This makes source energy comparisons across different geographies challenging.

Relatedly, critics argue that source energy unfairly penalizes buildings in regions with higher fossil fuel use for their electricity. A building owner has little control over the upstream energy sources powering their local grid, so some view judging them based on source energy as problematic.

There are also debates around whether the “full fuel cycle” approach accurately captures all impacts from energy production and distribution losses. The way source energy factors attempt to account for these losses is viewed by some as arbitrary and lacking in transparency.

Additionally, source energy does not capture other environmental externalities from energy use like water consumption and emissions. While source energy provides a simple singular metric, it does not tell the full story of a building’s energy impact.

Overall, source energy gives an incomplete picture of sustainability that oversimplifies the complex interactions between buildings, energy grids, and the environment. It remains a useful benchmark, but must be applied carefully with an understanding of its limitations.

Improving Source Energy Factors

There are several ways that source energy factors can be improved to better reflect efficiency:

Regularly update the source energy conversion factors to account for changes in the energy grid like increasing renewable energy.
Develop more granular, regional or local source energy factors that reflect geographic differences in energy sources.

Create separate source energy factors for marginal energy sources versus average energy sources.
Adjust the calculations to better account for transmission and distribution losses.
Develop industry-specific source energy factors that reflect different energy uses.

Allow the use of custom source energy factors based on specific energy sources used.
Provide guidance on calculating source energy factors for onsite renewable energy.

By improving the accuracy and specificity of source energy factors, buildings can get credit for using efficient and clean energy sources.

Source Energy Trends

Over the past few decades, there have been some notable trends in source energy use globally. As countries continue to develop and populations grow, total energy consumption has steadily increased. However, the composition of energy sources has shifted. Use of renewable energy sources like solar and wind has expanded rapidly in many parts of the world. Energy efficiency has also improved in many sectors, thanks to better technology, design, and construction practices.

Fossil fuels like oil, coal, and natural gas still comprise the majority of global energy use. But their share is declining as alternatives become more cost-competitive. The transition away from fossil fuels is expected to accelerate in the coming years to combat climate change. This will likely involve further growth in renewables and nuclear power. Energy storage solutions will also help enable the transition.

More focus is being placed on calculating and reducing source energy use in buildings and infrastructure. Building energy codes are being updated to account for source energy use reduction targets. This encourages holistic energy efficiency and renewable energy use in new construction and major renovations. Tracking source energy savings over time can help identify priorities and opportunities to further improve efficiency across communities and cities.

The Future of Source Energy

The future looks promising for advancements in how source energy is calculated and utilized. As technology improves, source energy factors may become more accurate and reflective of actual energy use. There is interest in developing more granular, hourly source energy factors that account for variable renewable energy and emerging technologies like energy storage. Dynamic source energy factors could help better optimize building energy efficiency.

Source energy may also expand beyond the building use phase to include embodied carbon from construction and materials. This would provide a more comprehensive view of a building’s lifetime energy use. New software tools and improved data collection will likely assist in estimating source energy earlier in the design process. This will allow teams to run source energy simulations to optimize decisions and reduce waste.

Source energy could be integrated into outcome-based building codes, setting source energy budgets rather than prescriptive requirements. There is also discussion around source energy disclosure requirements for real estate transactions. This would help better inform home and building buyers. Overall, an increased focus on reducing source energy demand will continue driving efficiency gains and carbon reductions in the built environment.