100 – (15+15+10+25) = 35%Cavity wall insulation and roofinsulation
Payback time – the time taken to recoup theinitial payment - for these is calculated by:Initial cost ÷ annual savingExampleIt costs £250 to install and fit loft insulation in ahouse. It saves £50 a year.How long is the payback time?SolutionUsing: Payback time = Initial cost ÷ annual savingThen £250 ÷ £50 = 5 years.
U-valuesa) U-values measure how effective a material is as an insulator.The U-value shows how fast heat can transfer through a material.The higher the U-value the faster the heat transfer.b) The lower the U-value, the better the material is as an insulator.Good insulators have a low U-value.
3 and 4 OR 1 and 2U-values for the 20 mm windows are the same orhigher than those for the 16 mm windowstherefore the 20 mm windows are no more energyefficient than 16 mm windows
c) Solar panels may contain water that is heated by radiation fromthe Sun. This water may then be used to heat buildings or providedomestic hot water.
The specific heat capacity of a substance is the amount of energyrequired to change the temperature of one kilogram of the substance byone degree Celsius.E is energy transferred in joules, Jm is mass in kilograms, kgis temperature change in degrees Celsius, °Cc is specific heat capacity in J / kg °CIt indicates how much energy a substance can store.E = m x c x
ExampleHow much energy is required to heat 3 kg of water from20 °C to 100 °C. The specific heat capacityof water is 4200 J/ kg°C.SolutionUsing E = m x c xSubstitutingm = 3 kgc = 4200 J/ kg°CT = 100-20 = 80 °CGives E = 3 x 4200 x 80= 1008000 J
ExampleHow much energy is required to heat 2 kg of water from10 °C to 110 °C. The specific heat capacityof water is 4200 J/ kg°C.SolutionUsing E = m x c xSubstitutingm = 2 kgc = 4200 J/ kg°CT = 110-10 = 100 °CGives E = 2 x 4200 x 100= 840000 J
Other ways of reducing energy loss includereplacing filament bulbs with low energy light bulbsand LED lighting
Replacing old appliances withenergy efficient onesNewer appliances have anenergy label. More efficientappliances are rated A.Other ways of reducing energy loss include
An advertisement in a shop claims that:‘Replacing an old freezer with a new ‘A’ rated freezer will benefit theenvironment.’Do you agree that replacing the freezer will benefit the environment?YESLess electricity used /energy neededLess fossil fuels burnedLess polluting gasesemittedNOOld freezer must bedisposed ofHazardous chemicals insidefreezer eg CFCsLot of Energy used inproducing new freezer