Technologies explained

Technologies explained

By Elizabeth Koenig on 03/22/2010

What are carbon offsets?

First calculate your “carbon footprint” by using one of the many online tools (simply perform a search for “carbon offsets” using any search engine). To get an accurate number, you will need to know your utility usage and fuel consumption. Your carbon footprint is the amount of quantifiable carbon dioxide released into the atmosphere based on the amount of energy you consume by your lifestyle. You may realize that there are certain polluting activities that you can’t avoid or reduce any further. You can offset these activities by investing in carbon-reduction projects — called carbon offsets. Through energy efficiency renewable energy, carbon offsets support that may not have happened without your contribution, and they reduce the same amount of carbon elsewhere. For more information on local carbon-reduction initiatives, visit

What is embodied energy?

Embodied energy accounts for all of the energy it takes to produce a product. This includes the energy used in harvesting, processing, manufacturing and transporting all the materials that go into the product. To determine a product’s embodied energy, it is important to also consider how long it will be used, where it will end up when its useful life is over and whether it can be acquired locally. Examples of products with high embodied energy include: raw aluminum, copper, plastics, synthetic carpet and glass. Products with lower embodied energy include: wood, brick and local stone. These products are more natural and require less processing.

Example: To calculate the embodied energy of a piece of lumber, consider the fuel it takes to power the machinery to cut the tree down and take it to a mill, the electricity it takes to run the mill, the energy to heat the kiln to dry the wood and the transportation to take the lumber to the retailer.

What are VOCs?

Volatile Organic Compounds are chemicals that are released into the air as a product dries or cures. They are the smell of paint, adhesives, carpet, bleach and other cleaning products. VOCs are a suspected carcinogen and can cause other health problems, including headaches and nausea. Some products containing VOCs will “offgas” for a certain period of time and then not release any more VOCs into the air, while others take years to completely cure. Look for low- or no-VOC products, and ventilate the home and filter the air properly to minimize the pollutants concentration.

What is passive solar?

Designs that use passive solar take the heat from the sun that enters a house and collect it, store it and distribute it. By building in a way that takes advantage of this free energy source and the local climate, you can conserve energy and save money on heating and cooling bills. Passive solar does not involve any electric components, fans or pumps. A passive-solar building makes use of the solar gain through natural heat movement mechanisms — conduction, convection and radiation — as a way to distribute heat throughout a living space. Typical techniques include window location and glazing type (to let solar gain in and keep it in), thermal mass and proper shading. See the “A primer for passive solar” checklist for more information.

How does a geothermal heat pump work?

A geothermal, or a ground-source, heat pump can serve as a heating and cooling system for buildings. A geothermal system brings heat from the ground into a building in the winter and takes it out of a building and back into the ground in the summer. A few feet below the surface of the ground, the temperature remains relatively constant — even in different parts of the world where there are temperature extremes. A geothermal heat pump system works as a giant heat exchanger between the underground and the building that is to be conditioned. Most geothermal systems circulate liquid through a series of underground pipes (in a loop system) to transfer the heat. An electric compressor heat exchanger takes the heat from the liquid and transfers it to a duct system to use in the building. In the summer, the process is reversed to cool the building.

What is R-value?

The R-value is a unit of thermal resistance used to compare the insulating values of different materials. R-values are most commonly used in rating the effectiveness of insulation. The higher the R-value is, the better the insulation (if installed properly). The R-value needed for a building depends on the climate of that area. The U.S. Department of Energy has separated each county in the nation by climate “zone” that indicates what type of insulation R-value is recommended. Find your county online at See the “Installing installation the right way” checklist for more information.

How do you make windows more efficient?

Anyway you look through it, windows are holes in the thermal envelope of the home and will not be as efficient as insulation. However, window technology has improved in the last few years. Higher thermal resistance is achieved by using a window that has two or more panes of glass filled either with argon or krypton gas in between them. This reduces heat transfer, because of the low thermal conductivity of the gas, which increases its ability to insulate. To further increase efficiency, window manufacturers apply a “low-E” (low emissivity) coating to the glass. The coating is a microscopically thin metal or metallic-oxide layer applied directly on the surface of one or more of the panes of glass. Low-E coated window panes utilize radiation to prevent heat loss or heat gain, depending on which side of the glass is coated. Windows are rated by the National Fenestration Rating Council (NFRC). The U-factor is the first number to look for when assessing a window’s efficiency. It measures the overall heat transfer coefficient of a window unit; it tells you how much heat a window will let through. The U-value is the inverse of the R-value (see R-value). The lower the U-value, the better the product’s resistance to heat flow. Look for a U-value of .35 or less. The other number to look for, the solar heat gain coefficient (SHGC), tells you how much heat comes in through the window.  Look for a SHGC of around .4 to balance enough heat gain in the winter and not too much in the summer.  In passive-solar homes, this value should be higher than in other homes, around a .6.

How does hydropower and microhydro work?

Hydropower is a form of alternative energy derived from flowing water. Small-scale hydropower systems that generate up to 100kW hours of electricity are considered microhydro generators. Microhydro systems usually utilize run-of-the-water systems, instead of large dams or holding tanks, which are commonly associated with larger hydropower projects. Water is diverted into a channel and to a turbine or water wheel. The moving water turns the turbine or water wheel, which turns the shaft that the wheel is attached to. This turning creates energy that can power an alternator or generator to create electricity. Microhydro is a great option if you have enough drop and flow, because the water is constantly moving and not as dependent on weather conditions to provide electricity.