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**Improving our environment**

U-values

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**Heat loss Convection Conduction Radiation**

Heat flows from a hot place to cooler place

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Our homes lose heat

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Thermal image

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**U-values All buildings waste heat**

Different materials lose heat at different rates Homes need to be insulated to reduce heat loss U-values compare rate of heat loss through different materials. They measure how quickly heat travels through a material

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**U-values Measured in W /(m2 oC) W-Watts (heat loss)**

m2-area of material oC-temperature difference

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**Example calculation 25Wats Area of material 2m2**

Temperature difference 20 oC U value = 25 / (2x20) U=0.625 W/(m2 oc) This is a low U value, a good insulator.

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**High and low U-values High value U-values lose heat more quickly**

Low value U-value lose heat more slowly Metals have high U-values (good conductors) Insulators have low U-values, (ie foam)

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Types of materials Low U values

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Types of material High U values

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**Well insulated wall and floor**

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Glass U values

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**Payback time Pay back time = initial cost / annual saving**

Buying insulation costs money But you could save in the long term Over time the money you save on bills equals the money spent, this is payback time.

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**Payback Time and Energy Efficiency**

P1b Keeping Homes Warm 13/04/2017 P Payback Time and Energy Efficiency Copy and complete the table below: Insulation Cost Annual Saving Payback Time (Yrs) Loft Insulation £400 £80 Double Glazing £2,000 £50 Cavity Wall Insulation £600 £60 Draught Excluder £40 £20 5yrs 40yrs 10yrs 2yrs Double Glazing Which type of insulation costs the most? Which type of insulation is the most effective? Which type is the most “cost effective”? Which type pays for itself after 40 years? Loft Insulation Draught Excluder Double Glazing James Ferguson Claydon High School

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**Payback Time and Energy Efficiency**

P1b Keeping Homes Warm 13/04/2017 Payback Time and Energy Efficiency An ordinary light bulb is 8% efficient. If it uses 1,000J of electrical energy how much energy is wasted as heat? useful output energy = efficiency total input X useful output efficiency X total input useful output energy = 0.08 X 1,000 useful output energy = 80J waste energy = 1, waste energy = 920J James Ferguson Claydon High School

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**Payback Time and Energy Efficiency**

P1b Keeping Homes Warm 13/04/2017 Payback Time and Energy Efficiency A gas boiler wastes 260J for every 1,000J of energy it is supplied with. What is the efficiency of this appliance? efficiency = total input energy useful output energy useful output efficiency X total input efficiency = 1,000 740 efficiency = 0.74 efficiency = 0.74 X 100 = 74% How could the waste energy be reduced? Insulate the boiler and hot water tank, lag the pipes and service the boiler James Ferguson Claydon High School

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Copy a complete Heat flows from a hotter place to a _________ place. The heat flow is ________ if the material has a lower U-value. Insulating the wall reduces heat losses because it _______ the walls U value Use these words: cooler, reduces, slower

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