A building's energy use refers to the energy required to operate and sustain the project once it's occupied. By calculating the energy a building consumes annually, architects can better predict the projects' cost as it is directly linked to a building's energy consumption. cove.tool reports a projects site energy which is the energy used within the bounds of the project. Another way of considering energy is called source, for more information on both check out this article from Energy Star.

One useful way of looking at energy is to normalize over the area of a building. This allows for comparison (benchmarking) between buildings of different sizes. The per area usage or energy per square foot per year (kBtu/ft2/yr), more commonly known as the EUI or energy use intensity is energy metric reported by cove.tool

When running energy simulation one must understand the toll each design decision will take on altering the EUI. Depending on the building assembly, glazing percentages, active and passive strategies implemented, loads, and costs can drastically spike and leave building owners and tenants paying millions more annually. Knowing the EUI values of design decisions and other iterations, one can get the best value for performance. To learn more about the breakdown of EUI, check out this article.

FAQ. Is the EUI in cove.tool site or source energy? Does it include Primary or Secondary energy?

A. The EUI represented in the tool & reports is Site energy consumption. This is the total energy used within the bounds of the site and doesn't include transmission losses, fuel factors etc. The energy may represent both primary (fossil fuel) and secondary (electricity, steam) energy, but that depends on your selected energy type on the baseline energy page (show below).

Key Energy terminologies

  • Energy Use Intensity (EUI) - refers to the energy required to operate and sustain the project once it's occupied. The metric is expressed as the energy per square area per year (kBtu/ft2/yr for IP, kWh/m²/yr for Metric).

  • Source Energy - represents the total amount of raw fuel that is required to operate the building. It incorporates all transmission, delivery, and production losses. By taking all energy use into account, this assessment of energy provides a complete overview of the energy efficiency in a building.

  • Site Energy - is the amount of heat and electricity consumed by a building as reflected in your utility bills. Looking at site energy can help you understand how the energy use for an individual building has changed over time. Site energy may be delivered to a building in one of two forms: primary or secondary energy.

  • Primary Energy - is the raw fuel that is burned to create heat and electricity, such as natural gas or fuel oil used in onsite generation. A full list of fuel types can be seen here.

  • Secondary Energy - is the energy product (heat or electricity) created from a raw fuel, such as electricity purchased offsite from the grid or heat received from a district steam system.

The Difference between Source and Site Energy

The EPA has determined that source energy is the most equitable unit of evaluation. Commercial buildings use all types of energy, from electricity to natural gas to steam. A unit of primary and a unit of secondary energy consumed at the site are not directly comparable because one represents a raw fuel while the other represents a converted fuel. Therefore, to assess the relative efficiencies of buildings with varying proportions of primary and secondary energy consumption, it is necessary to convert these two types of energy into equivalent units of raw fuel consumed to generate that one unit of energy consumed on-site. To achieve this equivalency, EPA uses source energy. For more detailed information on source energy, read Portfolio Manager Technical Reference: Source Energy.

When primary energy is consumed on-site, the conversion to source energy must account for losses that are incurred in the storage, transport, and delivery of fuel to the building. When secondary energy is consumed on-site, the conversion must account for losses incurred in the production, transmission, and delivery to the site.

However, the conversion from site to source energy is fairly independent of building design choices (except in the case of fuel switching). Because of this and the more common usage of site energy use in the industry, cove.tool reports site energy for projects.

Site vs. Source Energy - archtoolbox.com

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