1. Improving our environment
U-values

2. Heat loss Convection Conduction Radiation
Heat flows from a hot place to cooler place

3. Our homes lose heat

4. Thermal image

5. 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

6. U-values Measured in W /(m2 oC) W-Watts (heat loss)
m2-area of material
oC-temperature difference

7. 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.

8. 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)

9. Types of materials
Low U values

10. Types of material
High U values

11. Well insulated wall and floor

12. Glass U values

13. 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.

14. 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

15. 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

16. 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

17. 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