Efficient Use Of Energy Flashcards
What is payback time?
The amount of time it takes for the savings from buying something to equal the cost
How do you work out payback time?
Payback time=initial cost/annual saving
What types of heat transfer are involved in cavity wall insulation?
Foam in gal between bricks reduces convection and radiation. Air pockets reduce conduction
What types of heat transfer are involved in loft insulation?
Thick layer of fibreglass wool reduces heat loss through conduction and convection
What types of heat transfer are involved in hot water tank jacket?
Eg fibre glass wool Reduces heat loss through conduction and radiation
What is a U-value?
A measurement of how fast heat transfers through a material
Do you want a U-value to be low or high?
The better the insulator the lower the U-value
What is specific heat capacity?
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
What is the formula for specific heat capacity?
Energy transferred= mass X specific heat capacity X temperature change
What are the types of energy?
Light Electrical Heat/ thermal Sound Elastic Gravitational potential Chemical Kinetic Nucleus
How do you work out the efficiency of a device?
Useful energy out / total energy in
Useful power out / useful power in
What does the thickness of a arrow represent in sankey diagrams?
The thickness of the arrow represents the amount of energy
What does the thickness of a arrow represent in sankey diagrams?
The thickness of the arrow represents the amount of energy
What is waters specific heat capacity?
4200J/kg degrees Celsius
What are the forms of stored energy?
Gravitational potential
Elastic potential
Chemical
What is the conservation of energy principle?
Energy can be transferred usefully from one from to another, stored or dissipated but it can never be created or destroyed
When is energy useful?
When it can be converted from one form to another
Which devices are the most efficient?
Those which have the least ‘wasted’ energy (usually as heat)
What is no device?
100% efficient
Why is heat energy usually wasted ?
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
What do heat exchangers do?
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
What types of heat transfer are involved in thick curtains?
Reduces heat loss through conduction and radiation
What type of heat transfers are involved in draught proofing?
Strips of foam and plastic around doors and windows reduce heat loss through conduction and convection
