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Glossary of terms

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Please note the glossary represents our understanding of the terms. Please seek professional advice before embarking on a project.





British Thermal Unit: See Btu.


Btu: a unit of energy. One Btu is the energy required to raise one pound of liquid water by 1 degree Fahrenheit from 60 degrees to 61 degrees at a pressure of 1 atmosphere. 3,413 Btus are equivalent to 1 kilowatt hour (kWh).




Carbon Dioxide: See CO2.


CFL or Compact Fluorescent Lamp:  A high-efficiency replacement for a conventional filament lamp.  These work on the same principle as a fluorescent tube, but the tube is miniaturized and coiled to fit in the same space as a standard light bulb.  A CFL works by passing a discharge through a gas, which emits ultra violet light. The light strikes a phosphor coating on the inside of the glass which converts the ultra violet light to visible light.


Climate change:  changes to the earth’s climate over periods of decades, predicted by scientists as a result of increasing levels of carbon dioxide and other greenhouse gases in the earth’s atmosphere. Although the overall temperature of the earth’s atmosphere may increase, climate change may produce cooling in some areas and warming in others, therefore this term is preferred to ‘global warming’.


CO2: Carbon dioxide.  An odorless gas which is naturally present in the atmosphere in small amounts. Carbon dioxide absorbs infra-red radiation, which produces a warming effect in the earth’s atmosphere.  Burning of carbon-based fossil fuels such as coal and oil results in a net release of carbon dioxide into the atmosphere, which causes temperatures to rise, affecting climate.






Energy Star: ENERGY STAR is a joint program of the U.S. Environmental Protection Agency and the U.S. Department of Energy, and seeks to promote the use of energy efficient products and practices. Their website contains a lot of useful information.


Evacuated tube collectors: A form of hot water solar panel, which uses evacuated tubes (a little like thermos flasks) which insulate the hot pipes from the outside world, making them more efficient, particularly in semi-cloudy or cold conditions.



Flat plate collectors: A form of hot water solar panel, arrange as a flat plate. The plate absorbs heat from the sun, heating liquid which circulates through the panel.



Global warming: See climate change.


Green energy: see renewable energy.


Grid-tie system:  A system which generates electricity at the house site (typically using solar, wind, hydro or a fuel-powered generator), with any surplus being exported into the utility grid, earning credits on the electricity bill.  The power grid effectively serves as a giant rechargeable battery.  Grid tie systems do not require local batteries, but do not provide protection from utility power outages.



Horizontal strapping:  Horizontal wood straps on which the drywall is mounted.  Wood is a relatively good conductor of heat. Using strapping minimizes any direct path through wood from inside to outside; there is only a continuous path where the straps cross.  This improves the overall R-rating.


Heat pump:  A system which moves heat from one place to another. This can be used to warm a house in winter by extracting heat from the ground, or a well, and to cool a house in summer, by extracting heat from the house and warming the ground or well.  Air conditioners also work on this principle. Heat pumps can be an efficient way of heating a house, but is usually viable only if the house is well insulated in the first place.


Heating Degree Days:  This is a value which gives an indication of the need to heat (or cool) a building in a given climate. The number of heating degrees in a day is defined as the difference between a reference value of 65°F (18°C) and the average outside temperature for that day. See Wikipedia’s article for more information.


Hydro electric system:  Electricity is generated by using a head of water to drive a turbine, which in turn drives a generator.  ‘Micro hydro’ systems can be used to generate electricity for a single household, if a suitable source of water is available.



Insolation is a measure of solar radiation energy received on a given surface area in a given time.  This varies with location due to various factors such as local weather and latitude. Insolation maps are available on the web and are useful when designing and sizing solar panel systems.  See Wikipedia’s article on insolation for more information.





kWh or  Kilowatt Hour - a unit of energy. 1 kilowatt of power, consumed for an hour, uses one kilowatt-hour of energy.  One kWh equals 3,413 British Thermal Units (Btu).



LED or Light Emitting Diode.  A solid-state light which is very efficient. Electricity is converted directly into light, unlike a filament bulb which uses electricity to heat a wire filament, in which case only a small amount of the energy consumed produces visible light, the rest is given off as heat.


Low emissivity or E2 glass: Low E2 is a special neutral-colored high performance coated glass that helps reduce heat transference.







Off grid:  Electricity is generated at the house site (typically using solar, wind, hydro or a fuel-powered generator) with no connection to a utility electricity supply.  Batteries are normally used to store energy to provide a continuous supply day and night.



Phantom loads: Things which draw electric power even when switched off or in ‘standby’ mode.  Many modern electrical goods consume power when supposedly switched off. Common culprits are things with remote controls and/or a standby mode, such as TVs, DVD players, gaming machines and microwave ovens. Battery chargers and power supplies (the black ‘bricks’ which plug in to a power outlet) also tend to consume phantom power.  Over a 24 hour period, this power adds up. A simple way to reduce phantom loads is to plug them into a single power strip, and turn the whole strip off when not in use. There are also intelligent power strips which switch off automatically - see the Resources section.  When choosing a new appliance, see if you can find out, before buying, how much power it consumes when switched off.


PV Panels or Photovoltaic panels. These are panels which generate electricity directly from sunlight. PV Panels are still quite inefficient, best efficiencies at present are about 15%, (approximately 100-150 W per square meter or yard). Once installed the panels will produce free electricity for many years with minimal maintenance.





R Value  A measurement of insulation.  The higher the value, the more effective the insulation. It is measured in the US as degF.sqFt.hour  per Btu.  Its inverse, U value, is a bit easier to understand - this measures the ability of a surface to conduct heat. The units are Btu/h per degF per square foot.  So if a surface of 1 square foot has a temperature difference of 1 degree Fahrenheit and it conducts 1 btu per hour, it has a U rating of 1.  (and its inverse, R-rating, would also be 1 in this case).  R ratings are useful because if several materials are combined, their R-ratings can be added together to produce an overall R-rating.


Renewable energy:  Energy which is obtained from sources which can be replenished. This includes solar, wind, hydro, and the burning of replaceable fuels such as wood, if harvested sustainably.


Renewable electricity supply:  You can change your electricity provider so that the electricity you consume has been generated using renewable sources such as wind and hydro. This government website provides a useful list of suppliers for each state.  If you are not in the United States, many other countries have similar schemes.



Solar Electric Panels: Also known as PV Panels, these generate electricity from sunlight. See PV Panels for more information.


Solar Space Heating panels:  These panels produce warm air from sunshine.


Solar Water Panels:  Panels which absorb light and heat from the sun to heat water.  These come in two main types, flat panel and evacuated tube. See separate entries in this glossary.









Wind turbine / Wind generator:  A turbine, usually mounted on a tower, is used to capture energy from the wind to produce electricity.








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