1. Reducing Heat loss

2. Lesson Objectives Students should be able to:
identify the main areas heat energy is lost from houses
identify methods to reduce this loss
calculate payback time
evaluate the cost effectiveness of these materials
use fractions and percentages when calculating heat loss/cost effectiveness

3. 5 main areas heat if lost from a house
In which is the most heat energy lost?
In which area is the least heat energy lost?
Different houses could have different answers – why?
The main area is usually the walls
The lowest area is usually the floor
This can change from house to house – depends on SIZE of house/ number of windows / age (type of walls or windows) / insulation already fitted.

4. Amount of heat lost (J/s)
How much energy is lost
Area
Amount of heat lost (J/s)
% of total heat losses
Insulating materials
Highest
Walls
2nd highest
Roof
Windows
2nd lowest
Draughts/Door
Lowest
Floor
This house loses the most heat energy from the walls and the least from the floor.
Use the numbers below to fill in the table to show the amount of heat lost per second from each area.
180J/s 360J/s 240J/s 120J/s 300J/s
You could use watts instead of J/s

5. Calculating percentages
A percentage is the fraction of the total amount out of 100.
% = number x 100
total
First you need to work out the total energy loss from the house.
Total energy loss =
1200 J

6. The Roof The roof loses 300 J out of 1200 J
Write this as a fraction and calculate the decimal
Fraction = 300 = ______
1200
Write this as a percentage?
(multiply the decimal by 100%)
Roof = 25%

7. Calculate the % heat loss from each area
Percentage = number x 100%
1200
How much energy is lost
Area
Amount of heat lost (J/s)
% of total heat losses
Highest
Walls
360
2nd highest
Roof
300
Windows
240
2nd lowest
Draughts
180
Lowest
Floor
120 30 25 20
You can highlight the biggest % = most heat loss 15 10
REMEMBER – your answers ALWAYS add to 100%

8. Amount of heat lost (J/s)
Reducing heat loss
In pairs, think about different materials people can use reduce heat loss and fill in the final column.
How much energy is
lost
Area
Amount of heat lost (J/s)
% of total heat losses
Insulating materials
Highest
Walls
360 30
2nd highest
Roof
300 25
Windows
240 20
2nd lowest
Draughts/
Door
180 15
Lowest
Floor
120 10
Foam cavity wall insulation
Fibre glass loft insulation
Double glazing
Draught proofing
Carpets with underlay

9. Practice exam question 1
Energy consultants tell their customers how to save money. They explain how people can reduce energy loss from their homes.
This picture shows the percentage energy loss from different parts of a house.
Calculate the percentage energy loss through the walls of the house.
(b) Suggest the two most effective methods of reducing heat loss for this house.
Other areas = = 65%
So Walls = 100 – 65 = 35%
Foam cavity wall insulation ( walls have the biggest % heat loss)
Fibre glass loft insulation (the roof has the next biggest % heat loss)

10. Reducing energy consumption
By reducing heat losses, people can reduce how much energy they use. This means saving money on their energy bills.

11. Savings from energy losses How long will you live in the house.
Some ways of reducing heat loss are very expensive.
People need to think about 3 things before they spend money on insulating these areas.
Installation Cost
Savings from energy losses
How long will you live in the house.

12. Payback time Payback time = Cost of installing savings
This is the time in years to get back the money you have spent on insulation from the savings you have made.
Payback time = Cost of installing
savings

13. Calculate the payback time for each method.
Where is heat lost
Cost of energy losses (£)
Method
Installation cost (£)
Payback time (years)
roof
250
Fibre glass insulation
300
walls
350
Foam filled cavity wall insulation
1050
windows
Double glazing
4500
doors 80
Draught proofing 40
1.2 3 15
0.5
Hint - the savings are made from the energy losses.

14. Which method would you install first?
Draught proofing
Draught proofing is the cheapest and has the shortest payback time.
But other methods have bigger savings from areas with bigger heat losses

15. Cost effectiveness
This compares the TOTAL SAVINGS made over a few years compared to the cost of the insulation.
Using the information in the table, work out the profit made after 5 years for:
Draught proofing
Roof insulation.
Hint – don’t forget to take away the cost of the installation

16. draught proofing Saving = £80 a year = £80 x 5 = £400 Cost = £40
Profit
= £400 - £40
= £360

17. 2. fibre glass in the roof Saving = £250 a year = £250 x 5 = £1250
Cost = £300
Profit
= £ £300
= £950

18. Savings from draught proofing = £360
Savings from Fibre glass insulation = £950
So Fibre glass insulation is the most cost effective over 5 years because it makes the biggest profit.

19. whether or not you will get back your money (payback time) AND
So, when answering questions, you need to look at:
whether or not you will get back your money (payback time) AND
if you do get your money back, how do the total savings over time compare to the cost (profit)
PAYBACK TIME & PROFIT