[ Heat Recovery ]
[ Heat Recovery ]
Indoor heating is extremely energyintensive and a leading source of emissions. Nearly half the energy consumed by buildings is used for space and water heating, according to a 2022 report by the International Energy Agency( IEA). This enormous energy demand is driving a search for untapped sources of warmth in air, water, and waste streams. Thanks to modern heat exchangers and heat pumps, even a small temperature difference can now be turned into useful heat, opening the door to unexpected opportunities.
Transferring the heat A heat exchanger transfers thermal energy between two fluids, i. e. liquids or gases, without mixing them, allowing heat to pass through its thin metal walls while keeping the streams separate. In simple terms, one fluid warms up while the other cools down. A heat pump takes this idea further. It uses a closed refrigerant cycle and two heat exchangers to absorb heat from the environment, for example, from outdoor air, surface water or underground soil, and transfer it to a space where warmth is needed. The refrigerant, a fluid that evaporates at low temperatures, picks up heat in one exchanger and releases it in the other. In essence, a heat pump works like a refrigerator in reverse: instead of removing heat to keep things cold, it captures ambient warmth and concentrates it where needed. Behind this exchange of energy lies a demanding environment; one that calls for materials able to resist heat, moisture, and corrosion day after day. Stainless steel is ideal for this. Depending on the temperature, medium, and location in the system, alloys may range from standard grades to more corrosion-resistant grades like Type 316 with 2 % molybdenum or 6 % molybdenum stainless steels. The molybdenum addition greatly enhances resistance to corrosion, especially in hot, moist, or chemically aggressive conditions. In waste heat recovery systems, corrosion can result from contact with humid exhaust gases, wastewater, or other aggressive media. Exhaust gases can cool below their dew point, forming acidic condensates, while wastewater may contain chlorides, sulfides, or organic compounds that attack metal surfaces over time. Even in closed heat pump circuits, materials must withstand high pressures, temperature fluctuations, and occasional exposure to moisture. Molybdenum-containing stainless steels form a stable, self-healing passive film that protects against these conditions, ensuring long service life even where air, water, and heat constantly interact.
Heat from the Underground London’ s subway, the London Underground, is famously hot. Trains, brakes, and machinery generate warm air that accumulates in the tunnels. Bunhill 2 Energy Centre houses an innovative system that now captures some of this heat. It expands the districtheating network serving a community in Islington borough. A two-meter-wide fan draws warm air from the Underground’ s Northern line through a ventilation shaft. The air passes through a water-filled heat exchanger, which transfers heat from the air to the water. To increase contact between air and metal, the exchanger’ s cooling coil uses stainless steel fins. This maximizes the heat transfer from warm air, a relatively poor conductor, to the circulating water. The air, cooled from about 24 ° C to 14 ° C, is vented outside, while the water is warmed from 8 ° C to 13 ° C before flowing to an ammonia heat pump.
www. stainless-steel-world. net Stainless Steel World May 2026 37