When you stumble across an energy efficiency word that you don't know, find a comprehensive definition in our Energy Efficiency Dictionary. Still can't find the definition? Then let us know and we may add the word to the dictionary.
A device which promotes more efficient energy use by matching energy output with demand. Fans and pumps are the most familiar applications associated with this technology. For example, a fan driven by a fixed-speed motor (one which does not take demand into account) will sometimes produce more airflow than is needed, wasting energy. A fan with an adjustable speed drive regulates the speed of the motor to produce only the amount of airflow that is necessary.
The important counterpart to insulation (see “insulation”), air sealing is designed to plug holes or cracks in a home. Even a well-insulated home can suffer air leakage if there are small gaps around doors and windows, holes in the basement, attic or crawlspace, or leaks in the ductwork. Sealing these leaks can make a big difference in a home's comfort and energy bills, though a small degree of ventilation is necessary to ensure proper air quality. More information on sealing. You can also review ENERGY STAR info on air sealing and insulating.
A frequency-based electricity pricing mechanism that provides a system of incentives and disincentives to encourage peak-hour energy production. Improving the stability of power supply in this way avoids sharp fluctuations in frequency, which damage electrical equipment, and prevents power outages and strain on the grid.
An abbreviation for British thermal unit. The term is used to describe the energy content of fuels, and also to describe the power of heating and cooling systems, such as furnaces, stoves, barbecue grills and air conditioners. As a common unit of measurement, it offers a practical means to talk about energy that comes from multiple sources. A Btu can be approximated as the heat produced by burning a single wooden match.
A piece of equipment used to control the starting and operating voltages of electrical gas discharge lights, such as fluorescent and neon lights and high-intensity discharge (HID) lamps. There are three primary types of ballasts: magnetic (the least sophisticated type); electronic and digital (both more efficient options). Electronic ballasts offer many benefits including longer average bulb life, reduced light flicker and reduced ballast hum. Also, since electronic ballasts produce much less heat than magnetic ballasts, they can save energy by reducing the load on the air-conditioning equipment. More information on ballasts from U.S. Department of Energy.
Biogases include the methane and carbon dioxide produced in fermentation and anaerobic digestion of biomass, municipal and biological wastes, as well as the nitrogen, hydrogen, carbon monoxide and methane produced by the gasification of woody biomass. It can be used to produce electricity, such as in sewage works or CHP plants, and can be compressed for more efficient use in vehicles.
Derived from plant materials, waste, landfill gas, and alcohol fuels, biomass is used to produce electricity or thermal energy usually through direct incineration. Biomass also is used to make biofuels, such as biogas or biodiesel, after a biochemical conversion such as composting or transesterification.
A subset of a broader group of construction standards known as building codes. Building energy codes set construction standards for insulation levels (see insulation); window and door specifications (see windows); heating, ventilation, and air-conditioning equipment efficiency (see HVAC); and lighting fixtures and controls (see lighting). By reducing the amount of energy that buildings consume, building energy codes reduce energy use and save consumers money on their energy bills. The Building Codes Assistance Project has more information about building energy codes.
A control system based on a network of electronic devices that monitor and schedule lighting, temperature control, air circulation, water heating and chilling, and security to optimize energy use and maintain a healthy indoor environment.
A term for the outer shell of a structure, the building envelope is what separates the indoor air from the outdoor air. In the winter, a good building envelope will keep warm air in the house and cold air out; in summer, it will do the opposite. An energy audit (see “energy audit”) will likely include a thorough look at the building envelope. Sealing cracks and holes (see “air sealing”) and properly installing insulation (see “insulation”) are ways to keep a building envelop in good condition.
An energy-generating system that provides on-site integrated thermal and electricity production with waste-heat recovery. Steam turbines, gas turbines, or biomass can fuel the system, producing either heat or electricity as the byproduct. CHP systems are more fuel-efficient because of heat-recovery and they avoid distribution losses thanks to on-site generation.
This image from the Environmental Protection Agency shows how conventional generation uses 147 units of fuel to produce 75 units of electricity and heat, whereas CHP uses only 100 units of fuel to produce 75 units of electricity and heat.
Despite higher embodied energy, CFLs use about a quarter of the energy of traditional incandescent bulbs and have a lifespan eight to 15 times longer. Integrated CFLs — with built-in electronic ballasts — can be exchanged directly with incandescent bulbs. Some non-integrated CFLs still have magnetic ballasts, which cause the tubes to flicker when first switched on.
Compact fluorescent light bulb (CFL)
A more efficient version of a traditional light bulb. A CFL can produce the same amount of light as incandescent bulbs, but it uses less energy to do so. A CFL costs about 75 percent less to run, paying for itself in about six months and lasting up to ten years. More information on energy-efficient lighting.
The practice of strategically placing windows, skylights, reflective surfaces or other openings to bring sunlight into a space instead of relying on electric lights. Daylighting aims to create a visually comfortable atmosphere, while saving energy by reducing the need for artificial light. Read more about daylighting from the Efficient Windows Collaborative.
A system of charging consumers for energy use based on their highest rate of consumption during a given period. It is usually applied to industrial and commercial consumers – not residential energy users. Under demand billing, throughout a billing period, a demand meter periodically records the level of power that a customer is using. Customers are charged a certain amount for their total energy consumed, and an additional amount based on their highest level of demand, even though they may operate at this level for only one short period during a month’s billing cycle. For more information, consult factsheet on demand billing (200 kB) from National Grid.
The process of generating energy from small, decentralized sources, such as solar photovoltaic cells and wind turbines. This approach reduces the amount of energy lost in transmitting electricity because the electricity is generated very near where it is used, sometimes even in the same building. In addition, distributed generation minimizes transmission and distribution costs which represent a significant part of electricity’s total cost. More information on distributed generation from the U.S. Department of Energy.
Door sweeps are installed on the insides of exterior doors to guard against cold drafts in the winter and keep out hot air that can seep under doors in the summer. You can purchase vinyl door sweeps, or make your own with a rolled up towel or blanket.
A process that determines a home or building's efficiency, and recommends energy-saving measures that can improve efficiency. An audit can be performed by a home improvement contractor, a utility representative or other professional. More information on energy audits.
Any home improvement project that increases the energy efficiency of a home. Common energy efficiency retrofit projects include adding insulation to the building envelope (see “building envelope“); sealing (see “air sealing”) ducts and leaks; and replacing an HVAC system with high-efficiency equipment. Like other home improvement projects, energy efficiency retrofits increase the value of a home while also making it more comfortable, with the added benefit of reducing the homeowner's energy bills. More information, on energy efficiency retrofits.
The quantity of energy required per unit output or activity; using less energy to produce a product reduces the energy intensity. Similarly, energy efficiency improves when a service is (a) provided with reduced amounts of energy inputs, or (b) enhanced for a given amount of energy input.
A type of software that collects energy-use data, as well as sets energy conservation goals, monitors real-time energy consumption, and provides an interface through which users manage energy use and identify savings opportunities. EMS also incorporates models that detect abnormalities in energy use.
A term for an operation or a process that yields as much energy as it uses for its operation. An example includes wastewater treatment plants using anaerobic digestion that are able to generate electricity from a combined heat and power (CHP) system that uses biogas generated during the anaerobic digestion process.
Energy performance contract
An Energy performance contract is an agreement between a building owner and a private energy services company (ESCO) that uses future energy savings to pay for the cost of a building’s energy efficiency retrofits. A building owner contracts with an ESCO, which then finances, designs, purchases, installs and maintains energy-saving improvements to the building. As the building accrues savings on its utility bills, the ESCO recoups its investment. More information on Energy Performance Contracts (380 kB PDF) from ENERGY STAR.
A government incentive to encourage consumers to make purchases that will improve their energy efficiency. Current federal energy tax incentives cover fuel-efficient hybrid-electric or diesel vehicles and specified energy efficiency upgrades to existing homes. Find more ways to save on your taxes.
Rocket Stoves are characterized by a combined oxygen intake and fuel input opening, as well as a combustion chamber, chimney, and heat exchanger. More complete combustion and directed heat channelization achieve greater combustion efficiency. A Lion Stove feeds air underneath the fuel, from the opposite direction. The fuel blocks the flames from the stove walls, maximizing heat transfer upwards, instead of to the bricks.
A system that utilizes the relatively constant underground temperatures year-round to transfer heat to a building in the winter and vice versa in the summer. This heating and cooling method is clean, requires little energy, and is inexpensive to operate.
Mostly flash steam plants, which take hot water from inside the Earth, use it as steam to power generators, and inject it back into the geothermal reservoir. Dry steam plants use steam directly from the earth to turn the turbines. Binary power plants pump hot water from the geothermal reservoir, transferring the heat to convert another liquid to steam, which powers the generators.
The “traditional” light bulb that has been in use for over a century. In recent years, polices and a general market shift have begun to favor more energy-efficient options such as compact fluorescent lamps (see CFLs), high-intensity discharge lamps, light-emitting diodes (see LEDs). These alternatives produce the same amount of light as incandescent bulbs, but with less energy. The United States has committed to phasing out incandescent bulbs from the marketplace within the next several years. More about energy-efficient lighting.
Any of a variety of materials used to “pad” a home, and keep warm air in and cold air out. The U.S. Environmental Protection Agency (U.S. EPA) ENERGY STAR program estimates that, when used together, insulation and air sealing (see “air sealing”) can reduce heating and cooling bills by up to 20 percent. For more information, consult the DOE's web page on insulating and ENERGY STAR info on insulating and air sealing.
A unit of measurement for temperature. In color temperature, light bulbs with lower K (2000K-4000K) have more orange hues, whereas light bulbs with higher K (7500K-8000K) have more blue hues; therefore, daylight at noon on a clear day is about 6000K, whereas a standard incandescent bulb is about 2500K.
A K uses the same increment as a degree Celsius but starts at absolute zero, with 0K being the complete absence of heat. Temperature and color share the same units because all objects emit light when heated. See color temperature.
The amount of electrical energy consumed when 1,000 watts are used for one hour. A unit of electric power equal to the work done by one kilowatt acting for one hour. See watt.
A more energy-efficient, longer-lasting alternative to traditional lighting options. Unlike incandescent bulbs, LEDs do not have a filament. Instead, an LED’s light is produced by a semiconductor diode. Since approximately 90 percent of an incandescent light’s power use involves heating the filament, this is one principal way in which LEDs are more efficient. learn more about the advantages of LED lights from the U.S. Department of Energy, or consult the Alliance’s factsheet on LED Christmas lights.
A measurement of visible light. The more lumens a light bulb produces, the brighter the light. A traditional, 100-watt incandescent bulb gives off about the same brightness as an energy-efficient, 1600-lm light bulb.
1,000,000 watts or 1,000 kilowatts.
PV modules or “panels” are interconnected PV cells through which electrons excited by the photovoltaic effect produce direct current energy directly from sunlight. PVs are not to be confused with solar thermal, or concentrating solar power (CSP).
The most common method to reduce water system losses and demand in water systems. Generally, reducing water system losses and demand is achieved by decreasing water pressure in supply pipes, anticipating surges, and optimizing altitude changes along delivery lines. Pressure reduction establishes distribution zones; pump control; fixed outlet, time- and flow-modulated control valves; and remote node control.
A way of planning, building and maintaining communities that keeps housing near jobs, shops and schools; offers an array of affordable, convenient transportation options; and protects the environment. Smart growth strategies are used for towns and cities in urban, suburban, and rural areas. To make it easier for residents to get around, smart growth strategies provide several fuel-efficient public transportation options, including subway systems and bus lines.
Reflects the sun’s energy with mirror panels or concave dishes that concentrate heat, as well as power a conventional steam turbine to produce electricity. Not to be confused with photovoltaics.
See “energy tax credit.”
Thermal Storage Tank
Off-Peak Cooling tanks use a chilled eutectic mixture to freeze ice at night during off-peak hours; the thermal storage tank then uses this ice to chill water for air conditioning during the day. Chillers can be 30 to 40 percent smaller due to reduced peak energy use. Heat storage also is an application of thermal storage tanks for use in space and water heating, or electricity generation. Sometimes solar collectors are used to produce the initial heat.
Air handler that uses a VSD to control the speed of a fan blowing air of a constant temperature into a single thermal zone, such as a room or office. VAVs are more efficient than Constant Air Volume (CAV) handlers. CAVs blow a fixed volume of air, varying the temperature with internal heat exchangers, and typically serve thermal zones with a greater area.
A device that varies the electricity input of an electric motor according to the demands of the application. VSDs save electricity and energy costs, and preserve the life of the equipment. VSDs apply to AC motors and also vary the voltage of DC motors.
A unit of power equal to one joule per second. Watts usually measure the amount of electrical energy used by a device at a given moment; in other words, how quickly a devise consumes power. Watts also commonly measure the amount of energy produced by power plants (thermal energy can be measured in watts but is more commonly measured in Btu or joules). In comparison, watt-hours (wh) usually measure the energy consumption of a device or the energy generated by a power plant over a period of time. A device drawing one watt of electricity for one hour would have consumed one watt-hour, and so would a device drawing two watts for half an hour. In this way, watts are like the speed an object is moving, while watt-hours are like the distance that object has traveled. Watt-hours are typically divided by 1,000 to measure in kilowatt-hours, abbreviated kWh. See kilowatt-hour (kwh).
Consists of a rotor, which converts wind energy into low-speed rotational energy; a generator with gears that produce high-rotational speed to generate electric energy; and the support system. Wind energy is the fastest-growing electricity source and has the potential to gain significant market shares in the next decade. Maintenance costs are the greatest hindrance to expansion in the sector.