Top 10 Green Heating and Cooling Technologies Santa Clara University is not only a pantheon of learning in the heart of California's Silicon Valley, but it's also a temple of green technology. In April 2011, the university installed 60 rooftop solar collectors to heat and cool its student center. Engineers designed the large-scale array to run the building's hot water and air conditioning units [source: LaMonica]. The system is very efficient. The solar collectors grab the sun's rays and concentrate their captured energy, heating the building's water to 200 degrees. University officials expect the system to reduce the building's natural gas consumption by 70 percent each year and eliminate 34 tons of carbon dioxide from the atmosphere [source: LaMonica]. The university is leasing the system for 10 years, and during that time, it will pay a fixed price for the energy the solar array produces. The institution also received more than $86,000 in state rebates [source: Santa Clara University].

Santa Clara University is not alone in installing green heating and cooling systems. Other universities, businesses and homeowners are taking advantages of this green technology. Compared to standard heating and cooling systems, going green is better for the environment because it helps eliminate greenhouse gasses. In addition, the efficiency of these green systems allows people to save money on their energy bills, which has the potential to make a huge difference. is my ac unit too smallAccording to the U.S. Department of Energy, heating and cooling account for 56 percent of a home's energy use [source: U.S. Department of Energy].should you cover your air conditioner unit in the winter Green heating and cooling systems fall under two distinct categories: passive and active. in wall ac unit reviews

Passive systems maximize nature's ability to heat and cool without furnaces or air conditioners [source: Green Technology]. Among other things, passive technology includes constructing homes with white or light-colored roofs that reflect the sun's energy instead of absorbing it. As a result, the amount of energy it takes to cool a house is less. Passive designs also use windows that can keep the heat out and cool air in [source: Build it Solar]. Active designs use a variety of mechanical heating and cooling systems. These systems run on solar power, geothermal power or other sources of green energy. The uptick in green-energy use in recent years is slowly having an impact. For one thing, Americans saved more than $19 billion in 2008 by using various green heating and cooling systems [source: U.S. Department of Energy]. But these green systems are not cheap -- some solar collectors cost between $30 and $80 per square foot for installation. The government, however, has incentive programs to help builders and homeowners defray some of the cost [source: U.S. Department of Energy].

Go to the next page to read about the 10 best green heating and cooling options for your home.“AN ABSOLUTE dog's breakfast” is how David Collins describes the standard of fan blades in air-conditioning systems. This might seem to be something that would vex only an engineer like Mr Collins, the boss of Synergetics Environmental Engineering, based in Melbourne, Australia. But it is a big problem. If blades were designed for better aerodynamic efficiency, instead of for being stamped from sheet metal as cheaply as possible, the electricity consumption of many cooling systems could, he says, be cut by a third. Huge effort has gone into warming up buildings as efficiently as possible; less into cooling them down. Most air-conditioning units, like refrigerators, use tubes containing chemical refrigerants which vaporise as they draw heat out of the air passing over them. This chilled air is then circulated with a fan to cool a building, a train or a car. Regulations are outlawing certain refrigerants, such as chlorofluorocarbons, which contain ozone-depleting chemicals.

New developments would make cooling systems greener still because they would use less power. Most air-conditioners using refrigerants consume lots of electricity because they employ mechanical compressors, which are piston-like machinery that squeeze the heated vapours. This turns the refrigerant back into its cooler liquid state to be used again. In countries where electricity is cheaper at night some air-conditioning machines now take a different approach. As the evening beckons, they start making ice. During the day fans blow air over the ice. In southern Europe roughly one in 20 air-conditioned offices is now cooled with ice, cutting electricity bills by about 10%. Even bigger savings could be made with “thermal coolers”. Instead of using a mechanical compressor running on electricity, thermal coolers are powered with hot water. A refrigerant vaporises, absorbing heat from the air to be cooled. Then a salty solution, commonly containing lithium bromide, absorbs the refrigerant vapours.

When the container holding this liquid is bathed in hot water, the refrigerant separates from the salty solution and is recovered to be used again. Thermal coolers are an attractive option in places where hot water is available on the cheap as “waste heat”, for example from coal- or gas-fired power plants. Where winters are short or mild, piping this water for use in district-heating schemes is prohibitively expensive. But if it can be used for air-conditioning as well then the sums change. In Europe, hot water from 50 or so district-heating networks is now also used to power thermal air-conditioning, according to Ursula Eicker, a refrigeration expert at the Stuttgart University of Applied Sciences in Germany. She expects that this number will rise as efficiencies improve. In recent years thermal coolers have worked well with water at about 90°C or hotter. Now some models can be powered by water that is less than 80°C. This is important because in sunny climates rooftop solar panels are capable of heating water to 80°C.

At present solar-cooling equipment is expensive. SolarNext, a German firm, has built a solar system to cool (and heat) a building almost the size of two family homes for about €50,000 ($63,000). Uli Jakob, who led the project, says recouping such an outlay would take a decade or more of energy savings. But he expects costs will fall as production of solar-cooling equipment ramps up. Cars also use water to cool their engines. Once heated, could the water power the air-conditioning too? Sorption Energy, based in Oxford, Britain, is working with Fiat to develop a small thermal cooler that might do the job (and save petrol in the process: by some estimates roughly 5% of all petrol burned in Europe's cars is consumed by air-conditioning units). But drivers may have to wait until their engines warm up before the inside of their vehicles starts to cool down. Evaporative coolers are a cheap alternative to refrigerative air-conditioning. The air near a splashing waterfall or fountain is cooler than the surrounding area because water droplets remove heat as they evaporate.

Spraying water inside a cooling tower while air is blown through will have the same effect. Whereas refrigerative systems reduce the humidity of air (because some water vapour condenses and is drained away), evaporative coolers increase humidity. This means they tend to be more popular in dry climates. However, researchers at the National Renewable Energy Laboratory (NREL) in Colorado have designed an evaporative system that sprays ambient-temperature water into warm air to cool it, but in a way that also lowers the humidity. NREL uses syrupy liquids which contain salty desiccants to soak up the humidity. Hot water is used to heat the syrups and dry them out. NREL's technology, known as “desiccant-evaporative cooling”, is still being developed, but it requires little power, not least because the hot water can be obtained from solar panels. Ron Judkoff of NREL thinks the process will consume only about a fifth of the energy of conventional air-conditioners, depending how dry the climate is to begin with.