Energy footprints map the flow of energy supply, demand, and losses in U.S. manufacturing industries. Each footprint illustrates:
- What energy is purchased from utilities (electricity, fossil fuels), generated onsite, and transported to the local electric utility grid.
- Where and how energy is used within a typical plant, from central boilers to electric motors.
- Where energy is lost due to inefficiencies, both inside and outside the plant boundary.
Energy losses represent immediate opportunities to improve efficiency and lower energy consumption through the implementation of best energy management practices, improved energy systems, and new technology. The footprints try to represent an average picture of energy use for each industry. Actual energy use in a plant will vary from the industry average.
The concept and method of energy footprint calculations presented here is different than that of ecological footprint, which is the biologically productive land and water area that a population requires to produce the resources it consumes and absorb the waste it generates, using prevailing technology.
Understanding Energy Footprints
To assist in targeting energy-savings opportunities for energy systems, energy footprints were developed to map the flow of energy supply and demand in U.S. manufacturing industries. Identifying the sources and end-uses of energy helps to pinpoint areas of energy-intensity and characterize the unique energy needs of individual industries. A generic energy footprint is shown in Figure 1.
On the supply side, an energy footprint provides details on the energy purchased from electric utilities, the energy that is generated onsite (both electricity and byproduct fuels), and excess electricity that is transported to the local grid (energy export). On the demand side, a footprint illustrates where and how energy is used within a typical plant, for example in a central boiler, process heaters and motors. Most importantly, an energy footprint identifies where energy is lost due to inefficiencies in equipment and distribution systems, both inside and outside the plant boundary. Losses are critical, as they represent immediate opportunities to improve energy efficiency and lower energy consumption through best energy management practices and improved energy systems.
As Figure 1 shows, the energy supply chain begins with the electricity, steam, natural gas, coal, and other fuels supplied to a plant from off-site power plants, gas companies, and fuel distributors. Many industries generate byproducts and fuels onsite, and these are also part of the energy supply. Notable examples are the use of black liquor and wood byproducts in pulp and paper mills, still gas from petroleum refining processes, and light gas mixes produced during chemicals manufacture. Byproduct energy is included in fossil energy supply totals. Renewable energy sources such as solar energy, geothermal energy, and wind power are shown separately.
Once energy reaches the plant (indicated by green area), it flows either to a central energy generation utility system (e.g., steam plant, power generation, cogeneration) or is distributed immediately for direct use. Central energy systems generate electricity and steam for process use, and sometimes create more energy than is needed at the plant site. When this occurs, the excess energy is exported off-site to the local grid or another plant within close proximity.
Fuels and power (see blue area) are often routed to energy conversion equipment that is generally integrated with specific processes. The converted energy goes to processes and unit operations, where it drives the conversion of raw materials or intermediates into final products. Energy losses occur all along the energy supply and distribution system (red arrows in Figure 1). A simplified flow of losses from energy supply through industrial processing is shown in Figure 2. Energy is lost in power generation and steam or compressed air systems, both off-site at the utility and on-site within the plant boundaries, due to equipment inefficiency and mechanical and thermal limitations. Energy is lost in distribution and transmission systems carrying energy to the plant and within the plant boundaries.
Losses also occur in energy conversion systems (e.g., heat exchangers, process heaters, pumps, motors) where efficiencies are thermally or mechanically limited by materials of construction and equipment design. In some cases, heat-generating processes are not optimally located near heat sinks, and it may be economically impractical to recover the excess energy. With some batch processes, energy is lost during off-peak times simply because it cannot be stored. Energy is lost from processes whenever waste heat is not recovered and when waste by-products with fuel value are not utilized.
The energy footprints represent an average picture of energy use and losses across an industry. Through them we can begin to assess the relative losses due to inefficiencies as well as sources of energy-intensity. They also provide a baseline from which to calculate the benefits of improving energy efficiency.
Energy footprints from various sectors
Industries were selected based on their relative energy-intensities, contribution to the economy, and relative importance to energy efficiency programs. Industries not selected for individual energy footprint analysis include oil and gas extraction, coal products, printing facilities, furniture, and miscellaneous unclassified manufacturing. However, with the exception of oil and gas extraction, energy consumption for these industries is included in the overall manufacturing energy footprint.
- U.S. Manufacturing Sector Total Energy Input for Heat and Power
- U.S. Manufacturing Energy Footprint
- U.S. Manufacturing Sector Total Energy Input
Food, Beverages, and Tobacco
Establishments in the Food Manufacturing subsector transform livestock and agricultural products into products for intermediate or final consumption by humans or animals. The food products manufactured in these establishments are typically sold to wholesalers or retailers for distribution to consumers, but establishments primarily engaged in retailing bakery and candy products made on the premises not for immediate consumption are included.
Industries in the Beverage and Tobacco Product Manufacturing subsector manufacture beverages (alcoholic and nonalcoholic) and tobacco products. Redrying and stemming tobacco is included in the tobacco products sector while ice manufacturing is included with nonalcoholic beverage manufacturing because it uses the same production process as water purification.
- Total Energy Input for Heat and Power
- Supply for Heat and Power
- Food and Beverage Total Energy Input
Industries in the Textile Mills subsector group include establishments that transform a basic fiber (natural or synthetic) into a product, such as yarn or fabric, which is further manufactured into usable items, such as apparel, sheets, towels, and textile bags for individual or industrial consumption. The further manufacturing may be performed in the same establishment and classified in this subsector, or it may be performed at a separate establishment and be classified elsewhere in manufacturing.
Establishments in the Textile Product Mills subsector group manufacture textile products (carpets, rugs, linens, rope, twine, etc.), excluding apparel. With a few exceptions, these industries generally purchase fabric to cut and sew into the final nonapparel textile products.
Industries in the Apparel Manufacturing subsector group are involved in two manufacturing processes: (1) the manufacture of garments using purchased fabric and cutting and sewing, and (2) the manufacture of garments in establishments that first knit fabric and then cut and sew the fabric into a garment. Knitting, when done alone, is classified in the Textile Mills subsector.
Establishments in the Leather and Applied Product Manufacturing subsector transform hides into leather by tanning or curing and fabricating the leather into products for final consumption. It also includes the manufacture of similar products from other materials, including products (except apparel) made from “leather substitutes,” such as rubber, plastics, or textiles. Rubber footwear, textile luggage, and plastic purses or wallets are examples of “leather substitute” products included in this group. The products made from leather substitutes are included in this subsector because they are made in similar ways leather products are made, and they are produced in the same establishments so it is not practical to separate them.
- Textiles Total Energy Input: Footprint 1
- Textiles Total Energy Input: Footprint 2
- Textiles Total Energy Input: Footprint 3
Forest Products Manufacturing
Industries in the Wood Product manufacturing subsector manufacture wood products, such as lumber, plywood, veneers, wood containers, wood flooring, wood trusses, manufactured homes (i.e., mobile homes), and prefabricated wood buildings.
Industries in the Paper Manufacturing subsector make pulp, paper, or converted paper products such as paperboard containers, paper bags, and tissue paper. The manufacturing of these products is grouped together because they constitute a series of vertically connected processes and more than one is often carried out in a single establishment.
- Forest Products Total Energy Input for Heat and Power
- Forest Products Energy Footprint
- Forest Products Total Energy Input
This industry comprises establishments primarily engaged in refining crude petroleum. Petroleum refining involves one or more of the following activities: (1) fractionation; (2) straight distillation of crude oil; and (3) cracking.
- Total Energy Input for Heat and Power
- Petroleum Refining Total Energy Input
- Petroleum Refining Total Energy Input
The Chemical Manufacturing subsector is based on the transformation of organic and inorganic raw materials by a chemical process and the formulation of intermediate or end products. Exceptions include beneficiating operations such as copper concentrating, crude petroleum refining, and aluminum oxide production that are covered in other subsectors.
Plastics and Rubber Products Manufacturing
Industries in the Plastics and Rubber Products Manufacturing subsector make goods by processing plastic materials and raw rubber. Plastics and rubber are combined in the same subsector because plastics are increasingly being used as a substitute for rubber; however, the subsector is generally restricted to the manufacture of products made of just one material, either solely plastics or rubber. Footwear and furniture manufacturing are therefore covered elsewhere.
- Plastics and Rubber Products Total Energy Input for Heat and Power
- Plastics and Rubber Products Total Energy Supply for Heat and Power
- Plastics and Rubber Products Total Energy Input
Glass and Glass Product Manufacturing
This industry comprises establishments primarily engaged in manufacturing glass and/or glass products. They may start with silica sand or cullet, or purchased glass. Glass products that are classified elsewhere include glass wool (fiberglass), optical lenses, ophthalmic lenses, and fiber optic cable.
- Glass & Glass Products, Fiber Glass Total Associated Energy 1
- Glass & Glass Products, Fiber Glass Total Associated Energy 2
- Glass & Glass Products, Fiber Glass Total Associated Energy 3
Establishments classified in this subsector are primarily engaged in manufacturing Portland, natural, masonry, pozzalanic, and other hydraulic cements. Establishments primarily involved in mining, quarrying, or manufacturing lime or manufacturing of ready-mix or dry mix concrete are classified elsewhere.
Iron and Steel Mills
This industry comprises establishments primarily engaged in one or more of the following: (1) direct reduction of iron ore; (2) manufacturing pig iron in molten or solid form; (3) converting pig iron into steel; (4) making steel; (5) making steel and manufacturing shapes (e.g., bar, plate, rode, sheet, strip, wire); and (6) making steel and forming tube and pipe. Establishments primarily engaged in manufacturing ferroalloys or operating coke ovens are classified elsewhere.
- Total Steel Industry Energy Input
- Total Steel Industry Energy Input 2
- Total Steel Industry Energy Input 3
Alumina and Aluminum Production and Processing
This industry is composed of establishments primarily engaged in one or more of the following: (1) refining alumina; (2) making (i.e., the primary production) aluminum from alumina; (3) recovering aluminum from scrap or dross; (4) alloying purchased aluminum; and (5) manufacturing aluminum primary forms (e.g., bar, foil, pipe, plate, rod, sheet, tube, wire).
- Aluminum and Alumina Total Energy Input for Heat and Power
- Aluminum and Alumina Energy Footprint
- Aluminum and Alumina Total Energy Input
This industry group comprises establishments primarily engaged in pouring molten metal into molds or dies to form castings. Establishments making castings and further manufacturing, such as machining or assembling, a specific manufactured product are classified in the industry of the finished product. When the production of the primary metal is combined with the casting, the establishment is classified in sector 331 with the primary metal being made.
Fabricated Metal Product Manufacturing
Industries in the Fabricated Metal Product Manufacturing subsector transform metal into intermediate or end products, other than machinery, computers and electronics, metal furniture, and metal products fabricated elsewhere. Important fabricated metal processes include forging, stamping, bending, forming, machining, welding, and assembling.
Footprint of Fabricated Metals:
Establishments in the Machinery Manufacturing subsector create end products that apply mechanical force, such as the application of gears and levers, to perform work. Although this subsector uses processes similar to those used in Fabricated Metal Product Manufacturing (332), machinery manufacturing is different because it typically employs multiple metal forming processes in manufacturing the various parts of the machine. In addition, complex assembly operations are an inherent part of the production process.
Footprint of Heavy Machinery (farm, mining, industrial equipment):
Computers, Electronics, Appliances, Electrical Equipment Manufacturing
Industry establishments in this subsector manufacture computers, computer peripherals, communications equipment, and similar electronic products, and components for such products.
Industry establishments in this subsector manufacture products that generate, distribute, and use electrical power. Establishments are grouped into Electric Lighting Equipment, Household Appliances, Electrical Equipment (motors, generators, transformers, etc), and Other Electrical Equipment and Component Manufacturing.
Footprints of Computers, Electronics, Appliances, Electrical Equipment:
Transportation Equipment Manufacturing
Industries in the Transportation Equipment Manufacturing subsector produce equipment for transporting people and goods. Although transportation equipment is a type of machinery, an entire subsector is devoted to this activity because of the significance of its economic size in all three North American countries.
- Transportation Equipment Total Energy Input
- Transportation Equipment Total Energy Input 2
- Transportation Equipment Total Energy Input 3
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