Environmental Problems, Their Causes, and Sustainability 1

How Can We Cool Houses Naturally? Insulateand Work with NatureWe can cool houses by superinsulating them,taking advantage of breezes, shading them,having light-colored roofs, and using geothermalcooling.Here are some ways to have a cooler house. Use superinsulationand superinsulating windows, openwindows to take advantage of breezes, and use fans tokeep air moving. Block the high summer sun with deciduoustrees and window overhangs, (Figure 18-17,top left), or awnings.Use a light-colored roof to reflect up to 80% of thesun’s heat, compared to only 8% for a roof coloreddark gray. Suspend reflective insulating foil in an atticto block heat from radiating down into the house.Another option is to place plastic earth tubes undergroundwhere the earth is cool year-round. In this geothermalcooling system, a tiny fan can pipe cool and partiallydehumidified air into an energy-efficient house(Figure 18-17, top left).* In warm climates you can alsouse high-efficiency heat pumps for air conditioning.Toronto, Canada’s largest city, cools downtownbuildings by pumping cold water from the depths ofLake Ontario and passing it through building air conditioningsystems. This reduces the use of coal for producingelectricity, cuts greenhouse gas emissions, andslashes summer use of electricity for air conditioningby 90%.How Can We Use Solar Energy to GenerateHigh-Temperature Heat and Electricity?Desert PowerLarge arrays of solar collectors in sunny desertscan produce high-temperature heat to spin turbinesand produce electricity, but costs are high.Several solar thermal systems can collect and transformradiant energy from the sun into high-temperaturethermal energy (heat), which can be used directly orconverted to electricity. These systems are used mostlyin desert areas with ample sunlight.One method uses a central receiver system, called apower tower. Huge arrays of computer-controlled mirrorscalled heliostats track the sun and focus sunlighton a central heat collection tower (top drawing in Figure18-19).Australia is building a different type of powertower in its sunny outback. It will consist of a concretethermal chimney twice the height of the world’s tallestbuilding surrounded by a gigantic sloped solar greenhousewith a diameter of 5 kilometers (3 miles). As the*They work. I used them in a passively heated and cooled officeand home for 15 years. People allergic to pollen and moldsshould add an air purification system, but this is also necessarywith a conventional cooling system.hot air collected by the huge greenhouse flows up intothe tower it will spin 32 giant turbines and produceenough electricity to serve 200,000 homes. Some of theheat collected during the day will be stored in tubesfilled with water. The heat released from this waterafter dark should keep the power plant workingthroughout the night. This project is a miniature versionof how the earth makes wind from solar energy.Another approach is a solar thermal plant in whichsunlight is collected and focused on arrays of oilfilledpipes running through the middle of a largearea of curved solar collectors (bottom drawing inFigure 18-19). This concentrated sunlight can generatetemperatures high enough for producing steam torun turbines and generate electricity. At night or oncloudy days, high-efficiency combined-cycle naturalgas turbines can supply backup electricity as needed.On an individual scale, inexpensive solar cookerscan focus and concentrate sunlight and cook food, especiallyin rural villages in sunny developing countries.They can be made by fitting an insulated box bigenough to hold three or four pots with a transparent,removable top. Solar cookers reduce deforestation forfuelwood and the time and labor needed to collect firewood.They also reduce indoor air pollution fromsmoky fires.Figure 18-19 lists the advantages and disadvantagesof concentrating solar energy to produce hightemperatureheat or electricity. Most analysts do not expectwidespread use of such technologies over the nextfew decades because of high costs, limited suitable sites,T rade-OffsSolar Energy for High-TemperatureHeat and ElectricityAdvantagesModerate netenergyModerateenvironmentalimpactNo CO 2 emissionsFast construction(1–2 years)Costs reducedwith natural gasturbine backupDisadvantagesLow efficiencyHigh costsNeeds backup orstorage systemNeed access tosun most ofthe timeHigh land useMay disturbdesert areasFigure 18-19 Trade-offs: advantages and disadvantages ofusing solar energy to generate high-temperature heat and electricity.Pick the single advantage and the single disadvantagethat you think are the most important.http://biology.brookscole.com/miller14393