Stainless Steel World Magazine May 2024 | Page 39

As demographics shift and standards of living rise worldwide , the volume of heated indoor spaces has surged by almost 25 % since 2010 . Minimizing fuel consumption , thereby reducing greenhouse gas emissions , is imperative to reach our climate goals . For these reasons , heating systems must continue to become much more efficient . There are a variety of traditional residential heating systems , depending on the climate , fuel availability , and prevalent technology . However , most systems work by burning some kind of fuel , heating either water in a boiler or air in a furnace . Hot water then circulates throughout the building across a system of tubes , heating the rooms via radiators or radiant floors . Hot air , by contrast , circulates through ducts into the living spaces . Most fuels , whether fossil , such as oil , gas and coal , or renewable such as wood or biogas , create emissions in the form of flue gases . Depending on the fuel , they consist predominantly of nitrogen , CO 2 , and water vapor with small amounts of nitrogen oxides ( NOx ), SO 2 , and particulate matter . These potentially noxious gases are vented to the outside through a flue pipe or chimney . When flue gases cool below their dewpoint at around 56 ° C , the water vapor condenses to form water , which in combination with the other compounds can create aggressive acids . Each heating system has its own particularities and requirements . At less than 60 ° C , the relatively cold flue gases from a gas condensation boiler are very different from those of a wood burning stove that are as high as 600 ° C . The former requires a flue that is resistant to acidic condensates , while the latter needs one that is heat resistant . Surprisingly , both can use the same molybdenumcontaining stainless steels , to last a lifetime . Besides flue gases , circulating and sanitary water can also pose a major corrosion risk in residential heating systems and affect their efficiency . The presence of aggressive substances , especially chlorides and free chlorine , found in treated water , can attack the surfaces of boiler water circuits . With hard water , calcium and magnesium can form insulating scale deposits that reduce thermal efficiency and can cause premature failure of components . Molybdenum-containing stainless steels with their smooth surface and high corrosion resistance provide complete solutions for all things combustive home heating : boilers , stoves and fireplaces , chimney flues and hot water tanks .

Boilers : stainless steel contributes to efficiency The boiler is the heart of a hot water heating system . Depending on the technology , boilers burn gas , oil , wood , or even coal to generate heat . Much of the heat is then transferred through a heat exchanger to a water circuit while unused heat in the flue gases is vented to the outside . To increase efficiency and reduce the environmental impact of a boiler , it is essential to minimize the amount of heat lost this way to the outside and use it to heat the circulating water instead . The cooler the flue gas , the more energy has been used to heat the house and sanitary water for bathrooms and kitchens . Modern condensing boilers , as described in the illustration below , are therefore some of the most highly efficient heating units on the market today . A boiler ’ s durability and performance depend also on the fuel type , how it is operated and maintained , and the material it is made of . The materials used for the combustion chamber and the heat exchanger largely determine the longevity and performance of a boiler . These components , traditionally made from cast aluminum , ceramics , and steel are increasingly produced in Type 316L stainless steel . The 2 % molybdenum in this alloy provides very good resistance to pitting corrosion and good high temperature strength . In the most recent high-efficiency condensing boilers , Type 316 Ti , and in some premium models , even 904L stainless steel are used . With its 4 % molybdenum content , 904L has even better corrosion resistance , practically guaranteeing a long service life .

Stainless steel slips into chimneys The hot gases from boilers , furnaces , and other combustive heating systems must be vented through a chimney . Traditional masonry chimney flues are rarely watertight and aggressive

Schematic functioning of conventional and condensing boilers Conventional boilers have a burner and a heat exchanger in the combustion chamber . The hot gas heats the water in the circuit and then when still hot , it escapes through the flue , losing a lot of the valuable energy to the outside . In contrast , condensing boilers are much more energy efficient , as they use a condenser after the combustion chamber to extract more heat from the flue gas by preheating the incoming water from the heating circuit . Through this , the gas temperature drops below 60 ° C , its “ dew point ”, where it condenses and acids form . The combustion chamber and the condenser are designed to resist corrosive fumes and acidic condensate , respectively . The condenser allows the collection of the condensates , instead of releasing it into the air , reducing air pollution .

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