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Light and breezy: A modern airconditioner Series 9 Visit our website at www.news.com.au/dailytelegraph/classmate Contact Classmate at [email protected] or phone 9288 2542 EVERY TUESDAY Cl @ ss mate Editor: Troy Lennon Graphics: Paul Leigh and Will Pearce Series 9 ALTHOUGH heat is necessary for life, the human body can easily become overheated. Many methods have been devised for cooling our food, drink, homes and more directly our bodies. Some of the ways we lower temperatures consume large amounts of energy, while others make use of natural forces and are more environmentally friendly. Find out more Sources and further study: Heating And Cooling by Carol Ballard (Heinemann) Green From The Ground Up by David Johnston & Scott Gibson (Taunton) Cut Your Energy Bills Now by Bruce Harley (Taunton) Marshall Brain’s How Stuff Works (Hungry Minds Inc) When Changing A Lightbulb Just Isn’t Enough by Emily Anderson (Hearst Books) Heating And Cooling by Carol Ballard (Heinemann) Keeping Warm And Cool by Knapp and Woodroffe (Atlantic) Passive Solar House: The Complete Guide To Heating And Cooling Your Home by James Kachadorian (Chelsea Green publishing) Ask the builder — Insulation www.askthebuilder.com/Insulation.shtml Controlling the internal environment www.hi.com.au/qldsciproj/pdf/ eLearning10b.pdf Encyclopaedia Britannica Keeping your cool IF THE human body is subjected to too much heat the cells can overheat and die. The ideal temperature internally for a body is between 36C to 37.5C. People have learned to cope with extremes of heat and cold but prefer the ambient temperature (the temperature of the air around them) to be between about 18C to 30C, depending on personal acclimatisation to cold or heat. Below 24C a body can radiate away excess heat but once the ambient temperature rises above 24C a body needs other ways to cool itself. Part of the brain called the anterior hypothalamus acts as a thermostat for the body detecting when it is too warm and sending out signals for the release of sweat. The sweat evaporates from the skin, dispersing the heat into the air. Excessive sweating can cause dehydration if fluid is not replaced. If the ambient air is too humid the sweat doesn’t evaporate as well and the body can’t cool itself as efficiently. When the body can’t cool itself and loses too much fluid the heart rate increases, breathing speeds up and a person suffers dizziness, headache and nausea. A person may then go into shock as the body tries to conserve fluids, sending them to vital organs such as the heart and lungs away from the limbs and head. This can lead to unconsciousness. If the body is not then cooled down and liquids replaced it can cause serious problems such as brain damage. The blood may also become too thick for the heart to effectively pump it around causing heart failure. Did you know? n In 1988 long-distance runner Mark Dorrity was taking part in a fun run in 42C heat in Wagga. But he did not drink enough fluids and collapsed during the run. His body was unable to cool itself effectively and his temperature shot up to 42.8C, just short of what is considered the fatal limit of 44C. Dorrity experienced a condition known as rhabdomyolysis in which the muscles liquefy and can release toxins into the blood. He fell into a coma and had to have a leg amputated. n The first ancestor of the modern airconditioner was patented by American engineer Willis Carrier who constructed a “Apparatus for Treating Air” for a Brooklyn printing company. n When US president James Garfield was shot in 1881 he developed an infection as a result of doctors probing the bullet. In an attempt to lower his fever, doctors constructed a special room draped with dampened cloth that lowered the air temperature by several degrees. Unfortunately it was not enough to save Garfield’s life. n Most homes use insulation only in the ceiling to keep a home cool, but heat is also transferred through walls and especially through windows. Insulation in the wall cavities and either double-glazed windows (two sheets of glass with an air pocket between), window awnings or shutters help reduce the heat entering the home. n Many times in the past the Earth has cooled down going into what is known as an ice age. Several factors can cause the Earth to cool including a change in the tilt of the planet’s axis, which exposes different parts of the landmass to sun, resulting in less heat being retained by the land. Also large volcanic explosions have caused mini ice ages by blanketing the Earth in cloud, lowering the amount of heat reaching the planet’s surface. n Fans do not actually cool down the air in the room, they circulate air which helps provide energy for sweat to evaporate drawing heat away from the body. Fans use much less energy than airconditioners. The first electric fans were created in the early 19th century to cool factory workers. In the 1880s more compact electric room and ceiling fans were invented. On top of things: A “living roof” at the California Academy of Sciences. The green rooftop keeps the building’s interior cooler than would a standard roof Keeping food cool STORING food at low temperatures slows the growth of bacteria that will break it down. In the past, people used various methods of keeping food cool. People could buy ice imported from frozen lakes and rivers (when it was available) or from mountains. Ice could be stored for months in ice cellars if properly insulated. Some ancient cultures also developed methods of using evaporation to produce ice. But it was not until the 19th century that mechanical refrigeration and ice-making became possible. In the early 20th century before electric refrigerators became more common, people relied on evaporative coolers such as the Coolgardie safe (see below) or what was known as an icebox. This was a small insulated box that had a space for a block of ice to keep the interior of the box cool. People received deliveries of blocks of ice from an iceman who travelled by horse and cart and later truck. Icemen either gathered natural ice (in climates where it was available) or collected ice from ice-making factories. As electric home refrigerators became more affordable in the 1950s and 1960s the icemen stopped operating. Simple solutions TEMPERATURES in outback Australia can sometimes soar to unbearable levels. Without a good supply of water a person can easily dehydrate. But when the water gets warm it can be unpalatable. In Australia the Aborigines had a simple solution, carrying water in slightly porous containers, like animal leather, allowing water to filter through. The evaporation of the water causes heat exchange, meaning heat is drawn from the water to the cooler air blowing across it cooling the water down. Explorer Sir Thomas Mitchell created canvas water bottles using this principle after seeing Aborigines carrying porous kangaroo skin water bottles. The canvas waterbag became standard equipment for bushmen. A gold miner in Coolgardie, Western Australia, named Arthur Patrick McCormick made a box with cloth sides to cool his food and drink, it became known as a Coolgardie safe. Feeling the heat: Sweat is one of the body’s ways to cool itself Thirsty work: A refreshing drink from a waterbag How refrigerators and airconditioners work REFRIGERATORS work by moving heat from inside the fridge to the outside and making sure the inside is insulated from outside heat. In every refrigerator is a tube filled with a gas known as refrigerant. A compressor compresses the refrigerant putting it under high pressure and raising its temperature. It is then pushed through coils known as condensors which dissipate the heat to the surrounding air outside the fridge. The refrigerant condenses into a liquid which is then pushed through coils lining the inside of the fridge. When the refrigerant evaporates in those coils it draws the heat from inside the fridge and the warm refrigerant is then sent back to the compressor. An airconditioner works on a similar principle but fans extract the warm air from a room pushing it across evaporator coils, blowing the cooled air into the room and dissipating the heat outside the house via condensor coils. Insulation ONE of the most environmentally-friendly ways to keep a home cool is to install insulation in the roof and walls. Insulation is made from many substances including wool, fibreglass, polyester, polystyrene and paper fibres. Insulation works by stopping heat being transferred from a warm area to a colder one. Heat is transferred either by radiant waves, by conduction through solid objects, from atom to atom, or by being carried through moving air. Aluminium insulation works by reflecting radiant waves of heat. Some insulation works because it is a poor conductor of heat energy, usually because the molecules are not very densely packed and do not transfer heat easily. Less densely packed material also traps pockets of air, which is a poor conductor of heat when it is not moving. The amount of resistance to heat transfer in insulation is known as its R value, the higher the R value the better it stops heat. Environmentally friendly: Cellulose fibre insulation (above) and batt insulation being installed (below) Live green house FOR its Art & About Festival the City Of Sydney commissioned a display house with many environmentally -friendly features. Architect Martin Urakawa incorporated many different elements to cool the house naturally: Natural ventilation throughout the house facilitates breezes, particularly for the cool noreasterly breezes, such as through timber louvres, timber hatches and opening windows; Low-level and high-level openings to facilitate the removal of hot air near the ceiling and draw in cool air from below; The windows are shaded from direct sunlight in summer to prevent heating up of the interior of house; There is thermal mass in the house due to a water- filled seat. This regulates the internal temperature from temperature fluctuations outside the house; n n n n Ventilation breezes are drawn into the building across vegetation so that the breezes are cooler than if they were drawn across a hot surface. There is a vertical green wall located next to ventilation openings; The ceilings have an example of bulk and reflective insulation. The reflective insulation specifically reflects the radiant heat coming from the roof surface in summer; The house is painted with a Resene Cool Colour technology paints, which prevent dark surfaces from absorbing heat; Energy performance glass and films are installed in the house to illustrate the reduction of solar heat gain through the windows, particularly from western-facing windows. For more information on ways to make a home more sympathetic to the environment see www.cityofsydney.nsw. gov.au/Environment/LiveGreen/Default.asp n n n n Naturally cool: The live green house designed for the Art & About Festival Picture: Courtesy City of Sydney The science of cooling MOST forms of cooling rely on what is known as heat exchange or heat transfer, the movement of heat energy from a warmer object or substance to a cooler one. Cooling is mostly effected through the evaporation of some kind of liquid, evaporation takes a great deal of energy. When the liquid evaporates it draws the heat away from the surrounding air. A B C D E Evaporator coils (cold) Condensor coils (hot) Refrigeration basics A A compressor compresses the refrigerant gas B The compressed gas heats up as it is pressurised C The condensor coils on the back of the refrigerator let the hot gas dissipate its heat D The refrigerant condenses into liquid at high pressure E The high-pressure liquid flows through the expansion valve into the low pressure part of the system F The liquid refrigerant immediately boils and vaporises, its temperature drops to -33C G This travels through the evaporator coils which makes the inside of the refrigerator cold H The cold gas passes back through the compressor and the cycle repeats F Compressor G H Iceman cometh: Horse and cart delivering ice 36
