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Engineering heat out of metro tunnels The actual tunnel of the M2 metro line, in Lausanne. © Maurice Schobinger Researchers at EPFL have precisely quantified convection heat transfer in rail tunnels. Using the new model, they estimated how much energy Lausanne could save by fitting the future M3 metro line with a geothermal heat-recovery system, in what would be a world first. Heat transfer happens in various ways in rail tunnels. For instance, when trains brake or accelerate, they produce heat that warms the surrounding air. That hot air mixes with other air in the tunnel and with heat radiating from the ground. Until now, engineers have been unable to accurately calculate the amount of heat that tunnel air contains. Researchers at EPFL’s Soil Mechanics Laboratory (LMS) have overcome that problem by precisely estimating the convection heat transfer coefficient. Their findings have been published in Applied Thermal Engineering. This breakthrough paves the way for innovative applications involving so-called energy tunnels that can supply energy to built environments. The team also tested its model on Lausanne’s future M3 metro line which, once complete, will carry passengers between the city’s train station and the Blécherette district to the north. Enough heat for 1,500 apartments “Our research shows that fitting the heat-recovery system along 50–60% of the planned route – or 60,000 square meters of tunnel surface area – would cover the heating needs of 1,500 standard 80m2 apartments, or as many as 4,000 Minergie-certified energy-efficient units,” explains Margaux Peltier, a scientific assistant at the LMS, whose Master’s research forms the basis of the article. The system also allows heat to be stored so it can be supplied to homes when needed. “Switching from gas-fired heating would cut the city’s CO2 emissions by two million tons per year,” adds Peltier. Her calculation does not include the savings gleaned from metro stations or at the planned rolling-stock depot in the north of the city, which could also benefit from the system. As the temperature naturally stabilizes in underground tunnels, excess heat or cold is evacuated to the surface. The resulting warm airflow can often be felt at metro tunnel entrances. The idea behind the innovation is to harness this surplus warmth in addition to heat naturally present in the ground. The system works in a similar way to a refrigerator, with plastic pipes containing heat-transfer fluid, or simply water, placed at regular intervals inside the concrete tunnel walls and connected to a heat pump. In winter, cold water will be pumped into the pipes, emerging hot at the surface. The opposite will happen in summer. According to the researchers, the system would be cheap and energy-efficient to install and would have a lifespan of between 50 and 100 years, with only the heat pumps having to be replaced every 25 years. Diagram made by the Laboratory of Soil Mechanics. © LMS / EPFL 2019 Heating and air-conditioning Once equipped, heat from the tunnel would cover up to 80% of the heating needs of local apartments throughout winter, with the shortfall preferably coming from other renewable sources. But what makes geothermal systems like these unique is that they work in summer too. “The tunnel would act like a highly reliable, year-round heating and air-conditioning system,” says Peltier, adding that it would make a real difference to keeping Lausanne’s homes cool during hot weather. The system could even chill the ice rink set to be built in the city’s new Métamorphose eco-district. “This article underscores the fact that energy-tunnel technology is mature and could be deployed at district-wide scale,” explains LMS head Lyesse Laloui. “It remains to be seen whether Swiss companies are now prepared to take the lead. Globally, we’ve only seen systems like these used on test sections so far.” The researchers have presented their findings to Lausanne’s utility agency (SIL), local public transport operator (TL), the Canton of Vaud, the prime contractor working on the new metro line, and the City of Lausanne. References Margaux Peltier, Alessandro F. Rotta Loria, Loïc Lepage, Etienne Garin and Lyesse Laloui, “Numerical investigation of the convection heat transfer driven by airflows in underground tunnels”, Applied Thermal Engineering, June 2019. Source: Engineering heat out of metro tunnels (EPFL)
steven36 posted a topic in General NewsHot, dry weather sending reptiles to seek cool and moist places QUEENSLAND • In Australia, snakes sometimes slither into suburban backyards and homes. When the weather gets warm, they lounge in the sun. When it gets hot, they seek cool places: a wall crevice, under a refrigerator, under a barbecue grille, behind an air-conditioning unit. When it gets too hot and dry, they seek places with moisture, as some Australians are quickly learning. Mr Luke Huntley, a snake catcher in Queensland, East Australia, has had to remove snakes from people's bathrooms, as the country experiences a record-setting heatwave. Last week, he removed a 2m-long python that had slithered into an open door and climbed into the shower not only to escape the heat but also to find water. Days earlier, he pulled a small tree snake that had coiled in another homeowner's toilet bowl. "With the hot days and dry weather, these snakes are trying to hydrate and stay cool just like us," Mr Huntley wrote on his Facebook page. Also recently, an unsuspecting woman went into a dimly lit bathroom of a Brisbane home, not bothering to look into the toilet bowl. After she sat down, she felt a "tap" on her skin followed by a sharp pain, Ms Helen Richards told the Australian Broadcasting Corporation. She looked down and saw a python looking up at her. As a polar vortex hits the US Midwest, the extreme opposite is happening in Australia. The heatwave has parched landscapes, triggered damaging wildfires, pushed demand on the power grid to the brink and toppled significant records, Capital Weather Gang's Angela Fritz wrote last week. Temperatures soared to 47.7 deg C last Thursday in Adelaide, South Australia. That is the highest temperature for any capital in Australia, according to Ms Fritz. In the south-eastern corner of the country, overnight temperatures were as high as 36 deg C - the warmest overnight lows for January anywhere in the world. Australia's climate has warmed by just over 1 deg C since 1910, leading to more frequent heatwaves and severe drought conditions, according to the Bureau of Meteorology. Eight of Australia's top-10 warmest years on record have happened in the past 13 years. And with warmer weather come more snake sightings. Snake season starts in September, the beginning of spring in Australia. It goes on throughout the summer, from December to February. Australia has around 140 species of land snakes. As cities and urban development encroach into snake habitats, residents - and their pets - are more likely to encounter snakes, particularly in the spring, University of Melbourne researchers said. "As it warms up and we get a bit more sun, snakes come out to bask," Dr Timothy Jackson, a research fellow at the university's Australian Venom Research Unit, said in September. "When they're warm enough, they get hungry - they may not have eaten for months." Snakes, though, are not to be feared. "This is nothing to be alarmed about, but it does give us an additional reason to pay attention to our surroundings because, as we all know, encounters with snakes don't always end well," Dr Jackson said. "It's important to understand that this isn't because snakes are out to get us. The last thing a snake wants to see when it's out looking for a feed is a giant primate, dog or cat." Unfortunately, that has not always held true. Mr Huntley, the snake catcher, was called a couple of weeks ago to a home where a python ate a house cat. Source