Energy Glossary

AFUE (annual fuel utilization efficiency): - a measure of heating efficiency on an annual basis. AFUE is defined as the heat transferred to the conditioned space divided by the total fuel supplied (in Btu) for a given heating season. The higher the AFUE rating, the greater the efficiency.
Amp: - the basic unit of electric current, one ampere represents the rate of one coulomb of charge per second. It is defined to be the total net charge flowing across a given cross-sectional area of wire per second.
Ballast: - all fluorescent and most metal halide lamps need ballasts to operate. Because the arc generated in a lamp has almost no electrical resistance, ballasts are provided to regulate the lamp current. Magnetic ballasts consist of a coil in series with the lamp, or may also include a capacitor to improve power factor. Electronic ballasts are more efficient and regulate lamp current by delivering high frequency pulses. Electronic ballasts do not have the large coils and associated heat loss of magnetic ballasts. They not only operate more efficiently themselves, but electronic ballasts can also improve the efficacy of the lamp-ballast system by ten to twenty percent.
Ballast Factor: - the ratio of the light output of a fluorescent lamp to the light output of the same lamp operated on a standard (reference) ballast. The ballast factor is multiplied by the rated lumens to estimate how much light actually comes from the tube. T8 electronic ballasts may have a typical ballast factor of 0.88 to 0.95, but can range from 0.6 to 1.3.
Boiler: - a type of space heating equipment consisting of a vessel or tank where heat produced from the combustion of fuels such as natural gas, fuel oil, or coal is used to generate steam or hot water. Unlike a furnace, air is not forced through the structure; the steam or hot water is circulated through pipes to radiators or baseboards where it warms the surrounding air by convection. The two most common boiler layouts are firetube and watertube.
Btu: - a British Thermal Unit is the amount of heat required to raise one pound of water by one degree Fahrenheit. Approximately equivalent to the thermal energy of a kitchen match.
ccf: - a common billing term that refers to 100 cubic feet of natural gas.
CFC (Chlorofluorocarbon): - a compound consisting of chlorine, fluorine, and carbon. CFCs are very stable in the troposphere. They move to the Stratosphere and are broken down by strong ultraviolet light, where they release chlorine atoms that then deplete the ozone layer. CFCs are commonly used as refrigerants, solvents, and foam blowing agents. The most common CFCs are CFC-11, CFC-12, CFC-113, CFC-114, and CFC-115.
Coefficient of Performance (COP): - a rating more typically found in heat pumps, COP is a measure of how efficiently a heating or cooling system will operate at a single outdoor temperature condition. As an example, the commonly used outdoor temperature condition for a heat pump calculation in the heating mode is 47º F. As is also the case for EER and SEER, a higher COP means higher efficiency.
Coloring Rendering Index (CRI): - a measurement of a light source's ability to render colors the same as sunlight does. Roughly speaking, the CRI indicates the ability of a lamp to allow individual colors to be seen and to distinguish between these colors. On a scale of 1 to 100, light sources should have a minimum color-rendering index (CRI) of 80 for most interior spaces. Ceramic metal halide lamps, the latest "second generation" T8 lamps, T-5 lamps, and most compact fluorescent lamps have a CRI in the range of 82 to 86. Incandescent lamps have a CRI near 100, because they emit all the colors within the visible color spectrum.
Cooling Degree Day (CDD): - the mean daily temperature minus 65° F. If the low temperature is 60° F and the high temperature is 90° F, the mean temperature is 75° F. For this particular day, there are 10 Cooling Degree Days.
Correlated Color Temperature (CCT): - the apparent/perceived color of a light source compared to the color appearance of an ideal incandescent light source at a particular temperature, expressed in degrees Kelvin (K). The CCT rating is an indication of the warmth or coolness of the light, with ratings below 3,200 K referred to as warm, and ratings above 4,000 K considered cool in appearance. As CCT increases, the appearance shifts from reddish white toward bluish white. Cool light is preferred for visual tasks because it produces higher contrast than warm light. The color temperature of a lamp has nothing to do with how hot the lamp will get or how much heat will be given off by the lamp.
Cubic Foot (cf): - one cubic foot of natural gas contains approximately 1,030 Btu at standard temperature and pressure (60°F, 14.7 psi). Other energy billing units include CCF (100 cf, or approximately 103,000 Btu).
Daylighting: - the use of daylight as a primary source of illumination in a space. It has become a more important feature of mainstream construction due to its ability to lower energy costs.
EER (energy efficiency ratio): - a measure of how efficiently a cooling system will operate when the outdoor temperature is at a specific level (usually 95° F). A higher EER means the system is more efficient. EER = Btu of Cooling @ 95° F / Watts used @ 95° F. In the case of a 10 EER, 2 ton air conditioner: 10 EER = 24,000 Btu Out / 2,400 Watts In.
Efficacy: - the ratio of the light output of a lamp (lumens) to its active power (watts), expressed as lumens per watt (LPW). As an example, an incandescent bulb may provide 1700 lumens from a 100 watt light bulb, providing an efficacy of seventeen lumens per watt. Fluorescent lamps have efficacies from thirty to ninety-five lumens per watt, and high intensity discharge lamps (metal halide, high pressure sodium, etc.) can have efficacies exceeding 150 lumens per watt.
Electrical Ground: - an electrical means to intentionally create a low-resistance path that connects to the earth. This enhances safety and equipment protection by preventing the buildup of voltages that could cause an electrical accident or shocking hazard. Proper grounding practices are specified by the National Electric Code, IEEE standards, and building codes to insure uniformity and safety in electrical systems.
Fluorescent: - a glass tube with electrodes at each end and an inside surface coated with one or more types of phosphors. Mercury vapor fills the tube at very low pressure, along with one or more "buffer" gases. Fluorescent lamps from least efficient to most efficient include the T12, T8, and T-5, where the number represents the diameter of the tube in 1/8" increments (e.g., a T12 is twelve eighths, or 1-1/2" diameter). As the diameter gets smaller, glare increases. There are also high output T8 and T5 lamps that produce greater lumen output.
Foot-candle: - the distribution of light on a horizontal surface is called its illumination, which is measured in foot-candles. A foot-candle of illumination is a lumen of light distributed over a one-square-foot (0.09-square-meter) area. Full sunlight produces an illuminance of about 10,000 foot-candles on a horizontal surface. Full moonlight provides an illuminance of about 0.02 foot-candles. Adequate illumination for reading is taken to be about ten foot-candles; machine shop work requires about forty foot-candles. One foot-candle equals 10.76 lux.
Furnace: - a type of space heating equipment with an enclosed chamber where fuel is burned or electrical resistance is used to heat air directly, without using steam or water. The heated air is then blown or forced throughout the building, typically via air ducts, where it enters a room through a register in the floor or the wall to provide heat via convection. Furnaces can be powered by a number of different means such as electric, gas, fuel oil, coal, or wood.
Generator: - supplies backup power to the home in the event of a power outage. Generators should be installed with an automatic transfer switch to enable safe power transfer on and off the electric power grid.
Halogen Incandescent: - also called a tungsten halogen lamp, the filament is surrounded by a hot gas from the halogen family (fluorine, chlorine, bromine, or iodine) to improve efficiency. The halogen gases allow for regeneration of the tungsten filament, thus enabling the filament temperature to be increased for higher efficiency. These lamps are primarily used commercially in theater, store, and outdoor lighting systems.
Harmonics: - non-linear signals inherent in electrical systems that have motors, variable speed drives, capacitors, inductive devices or other electrical circuitry not operating in a purely resistive or linear mode.
HCFC (Hydrochlorofluorocarbon): - a compound consisting of hydrogen, chlorine, fluorine, and carbon. Developed as an interim bridge between CFC and HFC refrigerants, HCFC production and consumption is currently capped in the United States. As of 2020, HCFC-123 can no longer be used in new equipment and production will cease in 2030. HCFC-142b and HCFC-22 will be phased out of new equipment by 2010. According to the EPA, HCFCs contain chlorine and thus deplete stratospheric ozone, but to a much lesser extent than CFCs.
Heating Degree Day (HDD): - 65° F minus the mean daily temperature. If the low temperature is 20° F and the high temperature is 60° F, the mean temperature is 40° F. For this particular day, there are 25 Heating Degree Days.
Heating Seasonal Performance Factor (HSPF): - the ratio of the seasonal heating output in Btu divided by the seasonal power consumption in watts for a heat pump. Like SEER ratings for air conditioners, HSPF is a seasonal measure. HSPF ratings of 7 to 9 are common for air source heat pumps, while geothermal (water source) heat pumps typically have HSPF ratings greater than 10. As an example, an HSPF of 8.5 correlates to 249% efficiency (8.5 / 3.412 x 100).
Heat Pump: - takes advantage of underground thermal energy or outside air to provide space conditioning heating, cooling, and humidity control. Rather than converting chemical energy to heat, as in a furnace, a heat pump works by moving heat. Heat pumps pull heat from the air or earth to provide heat in the winter. In the summer, the heat pump becomes an air conditioner that pulls heat from a building by transferring it to the earth or the air. Heat pumps can be air source (document.cfm?id=354) or water source (geothermal) (document.cfm?id=394), and can also be found in industrial applications. (document.cfm?id=2633, 2758).
Henry Hub: - a popular pricing point for natural gas spot and futures contracts that is traded on the NYMEX and other exchanges, it is physically located in Louisiana at the intersection of nine interstate and four intrastate natural gas pipelines.
HFC (Hydrofluorocarbon): - a compound consisting of hydrogen, fluorine, and carbon developed as a class of replacements for CFCs. Because they do not contain chlorine or bromine, they do not deplete the ozone layer. All HFCs have an ozone depletion potential of zero.
High-Intensity Discharge (HID): - an electric lamp that produces light directly from an arc discharge under high pressure, such as mercury vapor, metal halide, and high and low-pressure sodium. There are large differences in efficiency, color rendering and other characteristics within HID lamps. HID lights require starting times of between two and fifteen minutes before reaching full output.
High-Pressure Sodium (HPS): - these lamps use sodium as the main light-emitting element, though these lamps also contain some mercury. Efficacies can vary from 50 to 150 lumens per watt, and CRIs between twenty and eighty-five. Lighting color is yellowish white, with the disadvantage that the lower CRI yellowish light can make it difficult to distinguish the colors of objects illuminated by it.
Horsepower (hp): - a unit of power, typically ascribed to motors, equivalent to working at the rate of 33,000 ft-lb/minute, or 550 ft-lb/sec. One hp = 746 watts. Can be equated to electrical power in motors, kW = 0.746hp / motor efficiency.
Incandescent: - light is emitted by a hot glowing body, commonly a tungsten filament. Incandescent lighting is characterized by very high CRI, but very low efficiency.
Infrared (IR): - a type of energy that has a wavelength between visible light and microwave energy, the name means "below red" (from the Latin infra, "below"). Energy is transmitted in wavelengths from an infrared emitter directly to the object to be heated. An alternative to convection heating, infrared heating is used in some residential space heaters.
Initial Light Output: - a lamp's output, in lumens, after 100 hours of seasoning.
Instant-start Ballast: - this type of ballast applies a high-voltage across the electrodes up to twice as high as with other starting methods to strike the electric arc. The higher voltage is necessary because the electrodes are not heated prior to starting. It is commonly used in residential fluorescent lighting applications.
Kilovolt-Ampere (KVA): - a unit of electrical power equal to 1,000 volt-amperes.
Kilowatt-Hours (kWh): - the quantity of true power multiplied by time. One thousand watts of power used for one-hour equals one kilowatt-hour. Kilowatt-hours are referred to as true power because they are a measure of that portion of the kilovolt-ampere hours that can be converted from electrical energy into some other form of useful energy, such as heat, light or motion.
Light: - the eye perceives visible light over a range from 380 nanometers (nm) to 780 nm, with a range of 400 to 700 nm quite common. Human eyes typically have a maximum sensitivity of ~555 nm (in the green spectrum). The eye may, however, have some visual response at even wider wavelength ranges.
Low-Pressure Sodium (LPS): - similar to high-pressure sodium lamps, except that the efficacy is higher at the expense of a lower CRI. Some LPS lamps have achieved an efficacy of 180 lumens per watt, but their CRI is very poor, ranging from zero to twenty. Low-pressure sodium bulbs emit a bright yellow light.
Lumen: - the foundation unit for the measurement of visible light.
Lumen Maintenance: - a measure of how well a lamp maintains its light output over time. It is the rated mean light output as a percentage of rated initial light output. Lumen maintenance numbers are usually a percentage of initial light output at 40% of rated life.
Lux: - a measure of illuminance in lumens per square meter. One lux equals 0.093 foot-candles.
Medium Bi-Pin: - a type of connector commonly used on T8 and T12 fluorescent lamps. Two small pins protrude from the lamp ends, which are inserted into a socket in the fixture. T-5 fluorescent lamps use a similar but smaller connector called a miniature Bi-Pin, which is not interchangeable with a medium bi-pin.
Mercury: - this substance has many desirable optical properties, making it the primary light-emitting vapor used in fluorescent lighting. It is also commonly used in high intensity discharge lighting. There are environmental issues associated with the handling of any product that contains mercury.
Mercury Vapor (MV): - the least efficient of the HID lamp types, almost all of their light is emitted by mercury vapors. CRI is on the low end, typically in the range of forty to fifty-five. MV lamps compete with high-pressure sodium and metal halide for outdoor lighting applications where lighting quality is less important. MV lamps have the longest life of HID type lamps, but are not very efficient - with efficacies ranging from 35 to 65 lumens per watt. Lighting color is in the bluish white spectrum.
Metal Halide (MH): - evolved from mercury vapor lamps, MH lamps use a variety of metal vapors, rather than mercury vapor alone to achieve better lighting quality (CRI ratings from sixty to ninety). Metal halide implies that the additional metals include compounds with some of the halogen elements (fluorine, chlorine, bromine, or iodine). MH lamps are not interchangeable with mercury vapor lamps, except in some small sizes. Efficacies range from 75 to 125 lumens per watt.
Microturbine: - a small-scale power generation source typically from 25 to 200 kW that approximately the size of a refrigerator. Advantages include: small number of moving parts, compact size, light-weight, greater efficiency, lower emissions, lower electricity costs, and opportunities to utilize waste fuels. Microturbine systems are comprised of a compressor, combustor, power turbine, generator and often a recuperator.
Phosphors: - crystals that convert the UV light emitted by the mercury vapor into visible light, for use in fluorescent and HID lamps to improve lighting quality. The makeup of the various phosphors determines the color emitted by the fluorescent or HID light.
Radiant Heating: - relies on the concept of radiant heat transfer, in which heat produced by the system radiates to nearby objects and surfaces. Just as the sun heats people and objects it hits even when the air is cold, radiant heating can warm the people and objects in a room without having to warm the air in the room. The most common form of radiant heater is an infrared heater.
Rapid-Start Ballast: - this type of ballast utilizes a method of starting fluorescent lamps in which lamp electrodes are heated prior to starting, using a starter that is an integral part of the ballast. Heating the electrodes before starting the lamps reduces the voltage required to strike the electric arc between the electrodes. A rapid-start system starts smoothly, without flashing.
Refrigerant: - a compound used in a heat cycle that undergoes a phase change from a gas to a liquid and back. The main uses of refrigerants are in chillers, air conditioners, and refrigerators/freezers.
Relative Humidity (RH): - a measure of the amount of water in the air compared with the amount of water the air can hold at a particular temperature. Warmer air has more capacity to "hold" water vapor than colder air. Dew point is a measure of how much water vapor is actually in the air.
SEER (seasonal energy efficiency ratio): - a measure of air conditioner efficiency over an entire cooling season, as opposed to a single outdoor temperature. Residential units are almost always rated in SEER. SEER came into use as a more practical measure, since the temperature outside is not always 95º F. A higher SEER means the system is more efficient. SEER is the total amount of cooling the air conditioner will provide over the entire cooling season divided by the total number of watt-hours it will consume, or SEER = Seasonal Btus of cooling / Seasonal watt-hours used.
Therm: -an energy unit equal to 100,000 Btus. A decatherm is equal to 10 therms.
Thermography: - infrared thermography has been used in predictive maintenance and condition monitoring of electrical hot spots, as well as moisture accumulations in a home. Infrared imagers capture infrared radiation emitted from objects and display these invisible wavelengths as visible light images. They are useful in applications where a variation in temperature, reflection, surface condition, or material may cause a difference in the radiated energy level detected by the equipment.
Ton (refrigerant ton, RT): - defined as the cooling capacity of an air conditioning system. One ton is equal to the Btu thermal content required to melt one ton of ice in a 24-hour period. A 1-ton air conditioner is rated at 12,000 Btu, a 2-ton unit at 24,000 Btu, a 3-ton unit at 36,000 Btu and so forth. It takes 144 Btu of heat to melt 1 pound of ice in 24 hours, or 288,000 Btu to melt a ton (2,000 pounds) in 24 hours. Typical residential central heating systems provide from 1 to 5 tons of cooling. Commercial rooftop units are typically 3 to 20 tons each. Chillers can range from 15 up to 1,500 tons.
Ultraviolet (UV): - electromagnetic radiation of a wavelength shorter than that of visible light, the name means "beyond violet" (from Latin ultra, "beyond"), violet being the color of the shortest wavelength of visible light. UV is also called black light, as it is invisible to the human eye. UV wavelengths are often subdivided into UV-A (380-315 nm), UV-B (315-280 nm), and UV-C (280-10 nm).
UPS (Uninterruptible Power Supply): - provides backup power in the event of a power outage. Home UPS devices in the 300-500VA range are often used to safeguard against data loss in computers. Check the surge protection rating to determine its capability to protect your computer against power surges and transients.
Volt: - the basic unit of voltage, or electric potential difference. It is the difference of electrical potential between two points of an electronic circuit. One helpful description uses a water analogy, equating voltage (volts) to the fluid pressure in a water pipe system, and current (amps) to the actual flow of water.
Watt: - a measure of power that is the product of voltage (volts) and current (amps). It is roughly equivalent to 3.412 Btu/hr. One kilowatt (kW) equals 1,000 watts.