Efficient Use Of Energy

Question 1

What is payback time?

Answer 1

The amount of time it takes for the savings from buying something to equal the cost

Question 2

How do you work out payback time?

Answer 2

Payback time=initial cost/annual saving

Question 3

What types of heat transfer are involved in cavity wall insulation?

Answer 3

Foam in gal between bricks reduces convection and radiation. Air pockets reduce conduction

Question 4

What types of heat transfer are involved in loft insulation?

Answer 4

Thick layer of fibreglass wool reduces heat loss through conduction and convection

Question 5

What types of heat transfer are involved in hot water tank jacket?

Answer 5

Eg fibre glass wool Reduces heat loss through conduction and radiation

Question 6

What is a U-value?

Answer 6

A measurement of how fast heat transfers through a material

Question 7

Do you want a U-value to be low or high?

Answer 7

The better the insulator the lower the U-value

Question 8

What is specific heat capacity?

Answer 8

The measurement of how much energy a substance can store

The amount of energy needed to raise the temperature of a 1kg substance by 1degree

Question 9

What is the formula for specific heat capacity?

Answer 9

Energy transferred= mass X specific heat capacity X temperature change

Question 10

What are the types of energy?

Answer 10

Light 
Electrical
Heat/ thermal  
Sound 
Elastic 
Gravitational potential 
Chemical 
Kinetic 
Nucleus

Question 11

How do you work out the efficiency of a device?

Answer 11

Useful energy out / total energy in

Useful power out / useful power in

Question 12

What does the thickness of a arrow represent in sankey diagrams?

Answer 12

The thickness of the arrow represents the amount of energy

Question 13

What does the thickness of a arrow represent in sankey diagrams?

Answer 13

The thickness of the arrow represents the amount of energy

Question 14

What is waters specific heat capacity?

Answer 14

4200J/kg degrees Celsius

Question 15

What are the forms of stored energy?

Answer 15

Gravitational potential
Elastic potential
Chemical

Question 16

What is the conservation of energy principle?

Answer 16

Energy can be transferred usefully from one from to another, stored or dissipated but it can never be created or destroyed

Question 17

When is energy useful?

Answer 17

When it can be converted from one form to another

Question 18

Which devices are the most efficient?

Answer 18

Those which have the least ‘wasted’ energy (usually as heat)

Question 19

What is no device?

Answer 19

100% efficient

Question 20

Why is heat energy usually wasted ?

Answer 20

Useful energy is concentrated energy
Wasted heat energy from a device is usually transferred to Cooler surroundings which become warmer so the energy becomes less concentrated (it dissipates)
Total energy is the same but it becomes increasing spread out so can’t easily be used

Question 21

What do heat exchangers do?

Answer 21

Reduce the amount of heat energy that is lost
Pump cool fluid through escaping heat so the temp of the fluid rises
The heat energy in the fluid can be converted into another useful form

Question 22

What types of heat transfer are involved in thick curtains?

Answer 22

Reduces heat loss through conduction and radiation

Question 23

What type of heat transfers are involved in draught proofing?

Answer 23

Strips of foam and plastic around doors and windows reduce heat loss through conduction and convection