Heating (302)
Energy: the strength and vitality required for sustained physical or mental activity.
Some rules - It cannot be created or destroyed.
Energy can only be transferred or transformed from one form to another to another
Energy can take many forms (Chemical, Kinetic, Electrical, Thermal, Light, Sound, Potential)
Heating appliences transfer
Electrical heating appliances usually have some sort of element which has a high resistance.
The energy nneded to push the current through the high resistance doesnt dissapear, it turns into heat.
This happens with any resistance, the greater the resistance, the more heat produced.
Units.
Energy is measured in joules (j)
This is the same whatever form the energy takes
However, we are usually less interested in the actual amount of energy as how quickly it is being transferred or transformed.
This is what we call POWER (W) Watts
It is simply the amount of energy transferred or transformed in 1 second
Power = Energy
----------
Time
360 J is transferred in 10 seconds
What is power? 360/10=36
Conduction.
Conduction happens when heat spreads out within an object.
Or transfers from one object to another because they are in contact (touching)
Conduction also works with fluid like air and water.
Convection.
Convection is when the air (or another fluid) around a hot object also becomes hot and rises.
Radiation.
Heat radiation is when heat spreads out in all directions from a hot object. We can see it when things are red or white.
At lower temperatures we need special cameras.
Space heating
Underfloor heating consists of an insulated wire element buried in the floor
It heats up and cools down slowly so is only suitable for background heating.
Avaliable on mesh roll.
Space heating - Storage heating.
Storage heaters make use of cheaper electricity at off peak times (usually at night)
I.e economy 7 (midnight to 7am)
heat is stored in dense thermal blocks and released the following. Usually only used where mains gas is not avaliable.
Heat output is difficult to control and often runs out.
Panel Heaters
Panel contains heating element
works by convection, some radiation.
Radiant heaters
element heated to red-heat
often used in bathrooms.
Heat can be directed by reflectors
Also used in large areas like wharehouses.
Heats objects, not the air.
Water heating
There are two methods of heating water.
Storage heaters:
Water is stored in an insulation tank and slowly heated at a relatively low power over a period of time.
Once hot the tank only needs more heat if hot water is drawn off and replaced by cold water, or if head escapes through the insulation
Instantaneous heaters
No water is stored, cold water is heated quickly at high power just before is comes out of the tap or showerhead
Rate of water flow contols the temperature;.
Immersion tanks.
This is the most econical way to use an immersion heater as they can get very expensive to run on the standard tariff. The element sometimes needs replacing.
Instantaneous water heaters.
A common example is the electric shower
10-12kw typical, sometimes more.
Space-underfloor, night storage, panel, radiant/infared
Water-storage, imersion, instantanous, electrical shower.