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AFUE (annual fuel utilization efficiency): an efficiency rating that measures the efficiency with which gas and other fossil-fuel-burning furnaces and boilers use their primary fuel source over an entire heating season. It does not take into account the efficiency with which any component of the system, such as a furnace fan motor, uses electricity. AFUE is expressed as a percentage that indicates the average number of Btu worth of heating comfort provided by each Btu worth of gas (or other fossil fuel) consumed by the system. For instance, a gas furnace with an AFUE of 80% would provide 0.8 Btu of heat for every Btu of natural gas it burned.
Air infiltration: the introduction, usually unintentional, of unconditioned outdoor air into a mechanically heated and/or cooled building. Air infiltration can occur through any opening in the home's structure, including seams where walls meet other walls, window or door frames, or chimneys; holes where wires or pipes penetrate walls, floors or ceilings/roofs; and between the loose-fitting meeting rails of double-hung windows or a door door bottom and door threshold. It is one of the major cause of unwanted heat gain and loss and personal discomfort in buildings.
Btu (British thermal unit): a measurement of the energy in heat. It takes one Btu of heat to warm one pound of water by 1° Fahrenheit. Btu can be used either to define an air conditioner's cooling capacity (i.e., the number of Btu of heat that can be removed by the system) or a furnace's heating capacity (i.e., the number of Btu of heat that can be supplied by the system).
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Caulk: a substance used to seal air infiltration points between two immovable objects, such as where exterior or interior wall surfaces meet window or door frames and at corners formed by siding. Most caulks come in tubes and are applied with the use of a special caulk "gun."
Compact fluorescent lamps (CFLs): a light "bulb" using fluorescent technology but designed to be used on many of the same fixtures traditionally used by standard incandescent "A" bulbs. They incorporate a small-diameter looped or swirled tube that is attached to a screw-in base. CFLs provide light levels comparable to 20- to 150-watt incandescent bulbs for 70% to 75% less energy. They also last 10 to 13 times longer than equivalent incandescent bulbs.
Conduction: the transfer of heat through solid objects such as glass, dry wall, brick and other building materials. The greater the difference between the outdoor and indoor temperatures, the faster conduction can occur and the more home a building can gain or lose.
Convection: the transfer of heat to or from a solid surface via a gas or liquid current. Where home heat loss and gain are concerned, heat convection is caused by air (gas) currents that carry heat from your body, furniture, interior walls and other warm objects to windows, floors, ceilings, exterior walls and other cool surfaces.
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COP (coefficient of performance): a measurement of a heat pump's efficiency (in the heating mode) at a specific outdoor temperature - usually 47°F. A COP of 1 indicates that for each unit of energy being used, an equal amount of energy, in the form of heat) is being provided by the system. A heat pump with a COP of 3 would provide three times as much energy in heat as it consumes in electricity at an outdoor temperature of 47°F. COP is also sometimes used to measure the single temperature cooling efficiency of chillers.
Daylighting: the technique of using natural light from windows, skylights and other openings to supplement or replace a building's artificial lighting system. When applied properly, daylighting can reduce a facility's lighting costs. When applied improperly, however, it can not only lead to inappropriate light levels but can also raise the building's cooling costs by introducing high levels of solar heat into the interior of the building.
Dedicated fixture: a lighting apparatus that is designed specifically for use with a particular type of lamp (bulb). For example, the increasing popularity of CFLs has led to the development of a growing number of fixtures - including torchieres, table lamps, ceiling drums, and recessed canisters - dedicated solely for use with compact fluorescents.
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EER (energy efficiency ratio): a measurement of the energy required by a cooling system as it attempts to maintain indoor comfort at a specific outdoor temperature - usually 95°F. The term EER is most commonly used when referring to window air conditioners and geothermal heat pumps. EER equals the number of Btu per hour worth of cooling provided at the specified outdoor temperature divided by the number of watts used to provide that level of cooling.
Efficiency: the degree to which a certain action or level of work can be effectively produced for the least expenditure of effort or fuel. For instance, a light bulb that uses 15 watts of electricity to produce 900 lumens of light would operate with much greater efficiency than one that required 60 watts to produce the same light level.
HSPF (heating seasonal performance factor): a measurement of an all-electric air-to-air heat pump's efficiency (in the heating mode) over an entire season. HSPF is calculated by dividing the total number of Btus of heating provided over the entire season by the total number of watt-hours required to operate the system over the season.
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Insulation: a product that inhibits conductive and convective heat transfer. Some materials are naturally better insulators than others because they contain more "dead air" pockets. These pockets of trapped gas help to slow the movement of heat. However, if processed properly, virtually any product, including glass, cotton, paper, and plastic, can be used to make insulation.
Internal Heat Gain: the accumulation of heat produced by a building's energy systems and appliances and occupants. Depending on the number of occupants and the type and number of energy systems used during the day, it's not unusual for internal heat gain to account for 20% of a home's total summer cooling load.
Kilowatt (kW): 1000 watts.
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Kilowatt-hour (kWh): 1000 watts used for one hour - or any combination of energy multiplied by time that is equivalent to that rate of electrical consumption, such as one watt used for 1000 hours, 10 watts used for 100 hours, or 50 watts used for 20 hours. For example, a 100-watt light bulb left on for five hours each day would consume one kWh every two days. Kilowatt-hour is the primary measure on which U.S. electric companies base most customer billing. The majority of CWLP residential all-electric customers pay an average of 8.9¢ per kWh and non-all-electric customers pay an average of 9.5¢ per kWh, when their rate, State Utility Tax and fuel adjustment charge are all factored. (Cost estimates last updated September 30, 2008)
Low-e: refers to a material designed to reduce the amount of radiant heat that can be transferred through glass or other translucent window coverings. Low-e (which stands for low-emissivity) coatings or films have the ability to re-radiate a high percentage of heat back toward its source. In summer low-e windows can be effective in reducing the amount of solar heat that can enter a house, and in winter they can reduce the amount of furnace-generated heat that can be lost to the outdoors.
Lumen: a unit of light given off by a light source. Lumen is the measurement used to compare the levels of illumination provided by different light sources.
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Payback period: the amount of time it takes to achieve a full return on an investment. For instance, if a high-efficiency air conditioner would cost you $300 more to purchase than a lower-efficiency model but would save you $100 a year in operating costs, your payback period on the extra $300 investment would be three years.
Radiation: a method of heat transfer in which heat is transmitted from surface to surface via infrared waves. Radiant heat warms the surfaces it touches without increasing the temperature of the air through which it travels. All warm bodies radiate infrared energy.
Rate: the amount charged to utility customers per unit of service used. For instance, CWLP electric customers are charged a certain rate for each kilowatt-hour of electricity they consume (see Residential Electric Rates or Business Electric Rates), while water customers are charged per unit of water consumed (see Water Rates). The actual rate charged is based on the type of service provided and, in the case of water customers, whether or not the customer is located inside or outside of the city limits.
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Return on investment (ROI): the annual rate at which an investment earns income. It is calculated by dividing the annual earnings by the investment. For instances, a bank savings account paying $3 per year per $100 investment has an ROI of 3% ($3 / $100). An efficiency investment's ROI comes not from money paid to you, but rather from money saved by you on your energy bills.
R-value: a measurement of a material's ability to resist heat transfer. Insulation products are rated according to the R-value. The higher its R-value, the greater the product's ability to resist heat flow will be.
SEER (seasonal energy efficiency ratio): a measurement of how energy efficient a central cooling system can operate over the course of an entire cooling season. This term is most often applied to central air-to-air heat pumps (in the cooling mode) and air conditioners. SEER is expressed as the dividend of the number of Btu of cooling provided over the season divided by the total number of watt-hours the system consumes. Federal law requires all central split systems now made in the United States to have minimum SEERs of 13.
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Settled density: the amount (depth) of insulation remaining after it has had a chance to settle. This term is most often applied to loose-fill insulations—particularly those made of cellulose. To ensure loose-fill cellulose insulation will maintain its desired insulating value (r-value) once it has settled, you will need to install it to a depth that is 20% to 25% deeper than your settled density r-value actually calls for.
Solar Gain: heat that builds up inside a structure as a result of sunlight that enters through transparent or translucent surfaces, such as windows, and is converted to heat after striking other surfaces inside the building. In summer, solar gain can cause as much as 50% of the interior heat gain in a home.
Thermostat Setback: an intentional effort to control building energy consumption by manually or automatically controlling thermostat settings according to the amount of cooling or heat that is needed at any given time of the day or night.
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U-value: the measurement of how readily heat can flow through glass, brick, drywall and other building materials. U-values, which are expressed in decimals, are the opposite of R-values. The higher the U-value, the less efficient the building material will be.
Vapor barrier: a material designed to resist the migration of moisture through a wall or other building component. As water vapor in the air moves from a warmer to a cooler part of the building it can settle and condense on cooler building components, such as rafters, beams and walls, eventually causing those components to mildew, rust or rot. Vapor barriers, which are impermeable to water vapor migration, help to protect against this possibility. The most common vapor barriers are made of plastic, but other materials, including oil paint, can also serve the purpose.
Watt: a unit of electric power. The amount of power required by electric appliances is expressed in watts.
Watt-hour: a unit of electric energy, equal to one watt used over a period of one hour.
Weatherstripping: a product designed to seal the cracks that exist between two moving parts or one moving and one stationary part of windows, doors and other movable building components. Weatherstripping is used to improve a building's energy efficiency by preventing the unintentional entry of unconditioned outdoor air.
Last updated: 09/30/08
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