Energy and efficiency Flashcards
What is the payback time?
The time it takes to save enough money from heating bills to equal the cost of the initial insulation.
what does a U Value show?
It shows how effective a material is as an insulator.
What is specific heat capacity?
It tells you how much energy something can store.
Whats the formula for specific heat capacity?
E = m × c × θ
The triangle is drawn with the E at the top and the rest under it.
What are the units for each part of the E = m × c × θ formula?
E = energy transferred in Joules - J m = mass in kilograms - kg c = specific heat capacity - J/kg°C θ = temperature change - °C
How much energy is needed to heat 2kg of water from 10 - 100°C?
E = m × c × θ
2×4200×90 = 756,000 J
What does a low U Value show?
The lower the U-value, the better the material is as an insulator.
An empty 200g aluminium kettle cools down from 115 to 10 degrees celsius, losing 19,068 J of heat energy. Whats the specific heat capacity of aluminium?
(Remember the triangle, with E on top)
SHC= 19,068 divided by (105×0.2)
The kettle is 200g so remember to convert into kg!
Name the 9 types of energy?
GLETNECKS!
Gravitational Potential, Light, Elastic Potential, Thermal, Nuclear, Electrical, Chemical, Kinetic, Sound,
GLETNECKS!
What three types of energy are stored energy - Energy not doing anything and waiting to be turned into another form?
The Potentials and Chemical energy:
Gravitational Potential,
Elastic Potential,
Chemical.
What is the conservation of energy principle?
Energy can be transferred stored or dissipated but cannot be created or destroyed.
When is energy ‘wasted’?
When energy is transferred only part of it may be usefully transferred, the rest is ‘wasted’.
What happens to wasted energy?
Why is it less useful?
Wasted energy is eventually transferred to the surroundings, which become warmer.
The wasted energy becomes increasingly spread out and so becomes less useful.
What is the formula to calculate efficiency of a device as a percentage?
useful power out efficiency = total power in × (100%)
What does ALL energy eventually end up as?
Heat
As the heat is transferred to cooler surroundings what happens to the energy?
The energy becomes less concentrated - It dissipates.
what are sankey diagrams?
They show how much energy is being usefully used or wasted.
The thicker the arrow the more energy it represents.
What does the amount of energy transferred by an appliance depend on?
Its power - how fast the appliance can transfer it
The amount of Time its switched on for
What is the formula for the amount of energy transferred?
E = P × T
Energy = Power × Time
What are the standard units for electrical energy?
Kilowatt-hours kWh
Or
Joules J
What are the two different types of units for energy transfer?
E = P × T
Energy = kWh (kilowatt-hours) Power = kW (kilowatts) Time = h (hours)
OR
Energy = J (Joules) Power = W (Watts) Time = s (secounds)
How can you calculate the cost of electricity with two formulas?
E = P × T C = P × PPU
Cost = E × Price per unit
