Top 10 Green Heating and Cooling Technologies

Earth is brimming with a limitless source of energy -- geothermal. Deep inside the planet is a lot of hot water and steam. The deeper you go, the hotter it gets. But you don't have to dig too deep to take advantage of this energy. Only a few feet below the surface, the temperature of the water remains constant year round, generally about 42 to 80 degrees Fahrenheit (5.56 to 26.67 Celsius) depending on where you live. A geo-exchange system can use this energy to heat and cool almost any kind of building [source: Minnesota Geothermal Solutions].

Geothermal systems do not directly tap into the heat inside the Earth. Instead, geothermal homes use heat pumps to take advantage of the constant temperature of geothermal wells under the ground. The heat pump can cool a house in the summer and warm it during the winter. Heat pumps have a fluid inside, which could be water or a refrigerant. When it is cold outside, the fluid absorbs Earth's heat and brings it inside to warm the air. In the summertime, the heat exchange works in reverse, cooling the house [source: APH Geothermal].

The sun is the ultimate provider of green energy. Solar power is constant and renewable. It's not going to run out anytime soon. However, you don't need unsightly solar arrays to enjoy the benefits of solar energy. Passive solar energy is simple, has little to no moving parts and requires minimal upkeep. Passive solar-energy systems are designed to use natural principals of heat transfer instead of machines such as furnaces and air conditioners [source: Passive Solar Resources].

Passive solar technology uses the building's walls, windows and floors to collect, store and release the sun's energy. However, passive solar homes still need mechanical equipment, such as a forced-air system or radiant flooring to keep the temperatures cool in the summer and warm in the winter [source: Arizona Solar Center].

The easiest passive solar design systems to install are called "direct gain." In direct gain systems, sunlight passes through windows where the light is converted into thermal energy. The walls and floors directly absorb and store the heat energy. As long as the room temperature is high, the interior of the homes will hold on to the heat. When the temperature drops at night, the stored heat radiates through the living space. Builders can also install plastic or metal water pipes inside a wall. When the sun hits the walls the water in the pipes heats up. That water can be pumped throughout the house as a source of heat [source: Arizona Solar Center].

Some people don't mind outfitting their roofs with solar cells. Solar cells contain photovoltaic materials, which convert sunlight directly into electricity. That electricity can then be used to heat, cool and light a house. Solar cells have been around for decades. They power everything from space ships to calculators. There's one problem, however. Today's cells are not efficient. They covert only about 10 percent of sunlight into energy [source: Herberman].

Moreover, such photovoltaic systems are expensive. Depending on the size, it costs between $27,000 and $36,000 to install a photovoltaic system with solar panels. It would take about 12 to 15 years to recoup all that money on your energy bills. However there are tax rebates and other incentives that can reduce the economic impact of installing an active solar energy system [source: Scherzer].

There are cheaper active solar heating systems on the market, though. Such systems use liquids, including water, or air. In both of these systems, the liquid or air is able to absorb the sun's energy through a collector. Those collectors then transfer the sun's heat directly to the home or into a storage system. From there the heat is dispersed through the house [source: U.S. Department of Energy].

There's nothing like a wood fire on a cold night. Wood is a form of biomass. Biomass is energy that comes from living things, such as trees and plants [source: Biomass.net]. The energy from biomass is natural and renewable. The plants, or other organisms, absorb energy from the sun. Biomass heating systems take that stored energy and convert it into heat energy.

Biomass is sustainable and cheaper than fuel oil, propane and natural gas. Modern large-scale biomass systems burn clean. For example, a woodchip system emits fewer pollutants than a wood stove. Biomass systems do not produce as much carbon dioxide as fossil fuels. When burned, fossil fuels release carbon that was once trapped inside Earth. When biomass is burned, it releases only the carbon the plant would have released upon its death [source: Biomass Center]. Some schools, offices, commercial buildings and homes use modern biomass technology.

How much money can biomass energy save? In 2008, Wisconsin officials announced that the state's schools could save hundreds of thousands of dollars by switching from natural gas to biomass. They said that if schools switched from natural gas to wood biomass, heating bills would be reduced by between 29 and 57 percent. That translates into a savings of anywhere from $53,000 to $75,000 each year [source: Focus on Energy].

Hydronic heating systems have been around for decades. Remember the old radiators in grandma's house? These days, hydronic heating systems are more sophisticated and use hot water piped through tubes that are run under floorboards, through radiators or along base boards [source: HydronicHeating.net]

In hydronic systems, boilers heat liquids using solar energy and geothermal energy. Most of these boilers heat water, but some systems warm other liquids, such as antifreeze. The liquid is pumped through plastic tubing into a heat exchanger, such as a radiator [source: HydronicHeating.net].

In a hydronic system, heat is transferred in three ways: conduction, convection and radiation. During conduction, heat energy moves from object to object, such as a spoon in pot of hot water. When you touch the spoon you can feel it get warm. Radiation is the transfer of energy through electromagnetic waves. You can feel heat radiation from a heat lamp. Boiling water is an example of convection. During convection, warm water rises while the cooler water sinks [source: HydronicHeating.net].

Absorption heating and cooling systems are not driven by electricity, but by solar power, geothermal power or natural gas, with natural gas being the most common fuel. Absorption heat pumps work just like any other heat pump. There are, however, two main differences. First, the absorption heat pump is driven by a natural gas burner instead of electricity. The second difference is that absorption pumps use a water-ammonia solution instead of a refrigerant. During the winter, that solution absorbs Earth's heat and the pump moves the heated liquid into the house to warm the air. In the summertime, the heat exchange works in reverse [source: U.S. Department of Energy].

Biodiesel isn't just for your truck or tractor any longer. Many people are heating their homes with this clean-burning, renewable fuel. For years, homeowners have overlooked biodiesel an alternative for fuel oil. Oil was simply much cheaper. But now, with oil prices on the rise, biodiesel is fast becoming a less expensive alternative. The so-called BioHeat blends contain 5 percent, 10 percent or 20 percent biofuel mixed with heating oil. All these blends can be burned in a conventional oil furnace [source: Cuda].

Biofuels release fewer pollutants, such as carbon dioxide, into the atmosphere, helping decrease heat-trapping gases. Also, biofuels are produced from so-called "energy crops" that include wheat, corn, soybeans and sugarcane, so they are sustainable. There is not enough biofuel to supply everyone who has an oil burner, however. There are only 19 distributors in the United States that supply BioHeat blends to residential customers [source: Cuda].

Ice is wonderful to cool drinks, but can it really cool a modern house or office building? A new company called Ice Energy has developed a system that converts water to ice, which is then used to run an air-conditioning unit.

During hot days, homes and buildings turn up the air conditioning, which uses a tremendous amount of power. Ice-powered air conditioners make ice at night and use it to cool the existing air conditioning units' refrigerant during the day, which decreases the amount of electricity a building uses [source: Ice Energy].

Here's how it works: At night, the unit freezes 450 gallons (1,703.81 liters) of water by circulating refrigerant through a system of copper coils. The water that surrounds the coils turns to ice, which is then stored. As temperatures rise the next day, the existing AC unit stands down, and the ice, rather than the AC unit’s compressor, cools the hot refrigerant, which keeps the building temperature nice and comfortable and cuts overall energy consumption by about 30 percent [source: Ice Energy].

Did you say green coal? For many people, coal might seem like one of the environment's worst enemies. Coal contains 25 to 90 percent carbon, which, when burned, creates noxious greenhouses gases such as carbon dioxide, sulfur and nitrogen oxide. Those gases are responsible for global warming [source: Captain].

Using a process called gasification, scientists have found a way to use the carbon in coal to strip oxygen from water, which produces clean-burning hydrogen gas for fuel. That gas can then be used to run a turbine, which produces electricity. The emissions from the process are then pumped underground, while other pollutants are converted into solids that can be burned [source: Captain].

We all know wind can generate power, but you can also harness the power of wind to generate heat -- and you don't even need a huge windmill in your backyard to pull it off. In 2006, students at Oregon State University proved it could be done when they developed a pint-sized wind turbine-generated water heater. Unlike other water heaters that use electrical heating elements or open flames, the students' wind turbine is completely sustainable and can be bolted to a home's rooftop, or some other location where the wind blows. The key is that there needs to be enough wind to spin the turbine [source: Oregon State University].

When there is sufficient wind, the turbine rotates a number of magnets attached to a metal plate at the opposite end of the shaft. Those magnets spin close to a copper plate, and the magnetic resistance of the spinning magnets warms the plate. As the magnets warm the cooper, water is pumped through a coil of copper tubing mounted on the back of the plate. Not only could their prototype provide a home with hot water, theoretically, that hot water could then be pumped through the house and used as a source of heat [source: Oregon State University].