Environmental Problems, Their Causes, and Sustainability 1

Direct GainCeiling and north wallheavily insulatedHot airSummersunGreenhouse, Sunspace, orAttached SolariumSummer cooling ventWarmairSuperinsulatedwindowsWintersunWarm airInsulatedwindowsCool airCool airEarth tubesEarth ShelteredEarthReinforced concrete,carefully waterproofedwalls and roofFlagstone floorfor heat storageTriple-paned orsuperwindowsFigure 18-17 Solutions: three examples of passive solardesign for houses.AdvantagesEnergy is freeNet energy ismoderate(active) to high(passive)Quick installationNo CO 2emissionsVery low air andwater pollutionVery low landdisturbance(built into roof orwindow)T rade-OffsPassive or Active Solar HeatingModerate cost (passive)DisadvantagesNeed access to sun60% of timeBlockage of sunaccess by otherstructuresNeed heat storagesystemHigh cost (active)Active system needsmaintenance andrepairActive collectorsunattractiveFigure 18-18 Trade-offs: advantages and disadvantages ofheating a house with passive or active solar energy. Pick thesingle advantage and the single disadvantage that you thinkare the most important.sun to collect solar energy by direct gain. Walls andfloors of concrete, adobe, brick, stone, salt-treated timber,and water in metal or plastic containers storemuch of the collected solar energy as heat and releaseit slowly throughout the day and night. A smallbackup heating system such as a vented natural gas orpropane heater may be used but is not necessary inmany climates.On a life cycle cost basis, good passive solar andsuperinsulated design is the cheapest way to heat ahome or small building in regions with access to amplesunlight. Such a system usually adds 5–10% to theconstruction cost, but the life cycle cost of operatingsuch a house is 30–40% lower. The typical paybacktime for passive solar features is 3–7 years.An active solar heating system absorbs energyfrom the sun by pumping a heat-absorbing fluid (suchas water or antifreeze solution) through special collectorsusually mounted on a roof or on special racks toface the sun (Figure 18-16, right). A typical active collectorhas a flat black surface, a coil through which theheat-absorbing medium such as water is pumped, anda cover consisting of two or three layers of glass.Some of the collected heat can be used directly.The rest can be stored in a large insulated containerfilled with gravel, water, clay, or a heat-absorbingchemical for release as needed. Often these insulatedheat storage containers are located under a house.Active solar collectors can also supply hot waterand are widely used in areas of the world with sunnyclimates. More than 1 million homes in Florida andCalifornia heat all or some of their water with one ormore active solar collectors.Figure 18-18 lists the major advantages and disadvantagesof using passive or active solar energy forheating buildings. Passive solar energy is great for newhomes in sunny areas but cannot be used to heat existinghomes and buildings not oriented to receive sunlightor where trees or other buildings block access tosunlight. Active solar collectors are good for heatingwater in sunny areas. But most analysts do not expectwidespread use of active solar collectors for heatinghouses because of their high costs, maintenance requirements,and unappealing appearance.392 CHAPTER 18 Energy Efficiency and Renewable Energy