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Temperature-resistant stainless steels spur revolutionary home heating units
Nickel magazine, Jun. 02 -- Nickel-bearing stainless steels and other new materials have enabled a
breakthrough in the use of the Stirling engine as an efficient source of residential heat and power. If the
idea catches on with homeowners, the resulting reduction in carbon emissions would be substantial.
Stirling engines are heat engines first patented by Church of Scotland minister Robert Stirling in 1816. They are powered by the expansion and contraction of gas as it is heated and cooled. The piston is driven by pressure fluctuations created by the flow of heat back and forth from the hot end to the cool end of the engine.
The greater the difference in temperature between the hot and cold ends of the engine, the greater the engine efficiency. That's why the new temperature-resistant stainless steels and ceramics are such important ingredients: they allow the engine's temperature to rise to 1,200[degrees symbol]C without corrosion or creep.
Capitalizing on this resistance, Whisper Tech of New Zealand has developed WhisperGen, a combined heat and power (CHP) plant specifically designed for use in the home. "We have spent a huge amount of time experimenting and endurance-testing with various stainless materials [for the heat exchangers and burners]" says David Moriarty, Whisper Tech's managing director, for proprietary reasons, he would not elaborate.
CHP units driven by Stirling engines are currently being tested in a few homes in Britain and the Netherlands. If all the homes in Britain were to convert from boilers to CHP units, the country would reduce emissions enough to meet 61% of its commitment under the Kyoto protocol, according to consultant EA Technology
A larger version of these devices is commonly used as an efficient source of energy in factories and residential highrises. But because the larger units are powered by gas turbines or internal combustion engines, they have been inappropriate for individual homes. Now, thanks to recent advances in Stirling engine technology, home applications are possible.
Home-sized CHP units are smaller, quieter and more energy-efficient than the average domestic furnace. About 70% of the energy value of the natural gas is converted into heat used for space heating and hot water, and 10-25% is converted into electricity. Only 5-15% is lost in the flue gases, compared with about 30% for conventional boilers.
The units have the added advantage of generating electricity that can be used to power the home, reducing dependency on power stations. BG Group of Britain, another supplier, suggests its CHP unit could save the average household [english pounds symbol]200 per year in electricity bills.
Whisper Tech sees a growing market for residential CHPs. Moriarty says the company is in negotiations with manufacturers close to raw materials and potential markets in Europe, where more than six million residential boilers are sold each year. EA Technology expects residential CHP units to capture about 15% of this market within five years.
The WhisperGen unit weighs about 90 kilograms and has dimensions of 450 by 500 by 750 millimetres. It can
run on several different types of fuel, including natural gas, biogas, diesel and kerosene. The unit produces
about 5 kilowatts of heat and about 0.75 kilowatts of electricity and costs slightly more than a
boiler.
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