One of the more frustrating aspects of energy efficiency is the clutter of technical terms that are attached to products and services that save energy and money. Often, the information that is presented to consumers seems as if it is instead written for scientists.
Therefore we’ll explain a few of these energy efficiency terms, especially those that are becoming more prevalent:
Air Leakage Rating: This measures how much air will leak out of the small gap between the window sash and frame on a window subjected to a 25 m.p.h. wind. The amount of air is measured in cubic feet per minute per linear foot of that gap. This rating is used to determine cold air infiltration rates on homes.
Annual Fuel Utilization Efficiency (AFUE): This measurement tells how efficient a furnace is by calculating how well that furnace converts energy such as natural gas or oil into usable heat.
The rating is a percentage of the annual output of heat coming out of the furnace versus the annual amount of energy going into the furnace.
To receive an Energy Star seal–a federal government rating of approval for energy-efficient devices–a heating system must have an AFUE of 90 or better.
Blower Door: This term describes both a device and a test that allows energy contractors to measure how much heated air leaks through a home’s windows and doors.
A blower door is a large fan that is encased in a sheet of wood and placed in the front door opening of a home. When the fan is started, it exhausts air from the house, thereby emphasizing which cracks and gaps are leaking air into a home.
Conduction: This term describes the passage of cold or warm air through a material such as glass. For example, on a frigid night, the inside of a window pane will feel cold because of this process.
Convection: This term describes how air naturally circulates in a room or home. The convection of air past a cold window on a cold night will transfer some of that cold into the room.
Emissivity: This is a measure of how much heat is emitted from an object via radiation.
Energy Efficiency Ratio (EER): This represents the cooling capacity of a room or window air conditioner. The higher the EER, the more efficient the air conditioner is.
Heat Exchanger: This is a device that is used to exchange heat from one source to another. An example would be the coils on a window air conditioner or refrigerator.
Heat Transfer: This is the movement of heat from one substance to a second. A common example is the movement of heat from the element in your water heater to the water in the tank that surrounds it.
High-Pressure Sodium Lighting: This is a type of high-intensity discharge lamp, in which an electric arc is used to produce powerful, bright light. The lamps are extremely energy efficient and the bulbs in them can last for years.
Kilowatt-Hour (kWh): This is the measurement of electricity that equates to the work done by one kilowatt in one hour.
Utility companies such as ComEd usually measure the electricity used in your home in kilowatt-hours.
One kilowatt-hour equates to 1,000 watts of electricity for one hour; an example of that would be running a 50-watt light bulb for 20 hours.
Low Emissivity (low-e) Coating: This is a nearly invisible coating placed on window glass that retards the amount of heat radiating out through a window as infrared waves.
U-Factor: This is a window energy rating from the National Fenestration Rating Council.
The U-Factor measures the rate of heat loss of a window unit. The lower the U-Factor, the more the window can resist heat loss to the cold outdoors. In the Chicago area, windows should have a U-Factor of 0.40 or less.
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Got a question about home energy or home environmental issues? Write to Energy Q&A, Chicago Tribune, Your Place section, 435 N. Michigan Ave., 4th Floor, Chicago, IL 60611. Or you can e-mail energyqa@aol.com. Questions will be answered only through the column.
