Reducing Heat loss

Lesson ObjectivesStudents 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

5 main areas heat if lost from a house

1. In which is the most heat energy lost?

2. In which area is the least heat energy lost?

3. Different houses could have different answers – why?

How much energy is

lost Area

Amount of heat lost

(J/s)

% of total heat losses

Insulating materials

Highest Walls2nd highest Roof

Windows2nd 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

Calculating percentages

A percentage is the fraction of the total amount out of 100.

% = number x 100

totalFirst you need to work out the total energy

loss from the house.

Total energy loss = 1200 J

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%

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 3602nd highest Roof 300

Windows 2402nd lowest Draughts 180

Lowest Floor 120

302520

15

10

REMEMBER – your answers ALWAYS add to 100%

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

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.

(a) 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.

1 ...................................................................................................................

2 ...................................................................................................................

Other areas = 25+10+15+15 = 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)

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

Some ways of reducing heat loss are very expensive.

People need to think about 3 things before they spend money on insulating these areas.

1. Installation Cost

2. Savings from energy losses

3. How long will you live in the house.

Payback time

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

Calculate the payback time for each method.Where is heat lost

Cost of energy

losses (£)

Method Installation cost (£)

Payback time

(years)

roof 250Fibre glass insulation 300

walls 350Foam filled cavity wall insulation

1050

windows 300Double glazing 4500

doors 80Draught proofing 40

Hint - the savings are made from the energy losses.

1.2

3

15

0.5

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.........

Cost effectivenessThis 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:

1. Draught proofing

2. Roof insulation.

Hint – don’t forget to take away the cost of the installation

1. draught proofingSaving = £80 a year

= £80 x 5

= £400

Cost = £40

Profit

= £400 - £40

= £360

2. fibre glass in the roof

Saving = £250 a year

= £250 x 5

= £1250

Cost = £300

Profit

= £1250 - £300

= £950

• 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.

So, when answering questions, you need to look at:whether or not you will get back your money

(payback time) ANDif you do get your money back, how do the

total savings over time compare to the cost (profit)

PAYBACK TIME & PROFIT