Energy Saving Tips
There are two important facts about saving energy in the average home
- A "Set Back" thermostat is the best and easiest way to save on your heating bills. The greater the amount you set back the night time temperature the more money you will save on your energy bill. You may have to start to reheat the house sooner if you set back a large amount, but the only limit to the set back amount is your comfort, like using cold shampoo, tooth paste, walking on cold tile foors, etc.
- Most high heating costs in an older house is the result of cold air infiltration. Infiltration is primarily caused when outside air comes in around windows,doors and from people entering the house. The lesson here is that the best thing you can do to save money on your heating bill is to replace old windows and doors if they are not air tight. There are many other places where outside cold air can enter a house, but they are minor in comparison to old drafty windows and doors.
Below is information on heat transfer and thermodynamics for the really technically minded person. It supports my conclusions above.
First Law of Thermodynamics
Stated simply; The total energy of the universe does not change. This does not mean that the form of the energy cannot change. Indeed, chemical energies of a molecule can be converted to thermal, electrical or mechanical energies.
Heat Transfer is the study of how heat is transmitted from place to place. We are all familiar with the fact heat does move: a metal bar that is heated at one end will become warm at the opposite end as the heat flows from one end to the other. This is an example of conduction heat transfer which is the study of how heat moves through stationary objects. This type of heat transfer is called conduction.
Heat can also be carried along in a fluid. Before air conditioning people used to cool themselves by placing a fan behind an ice cube and blowing cold air on themselves. In this case the air, having been cooled by the ice, carries heat away from our skins as it moves by us. The faster the air moves the more heat will be carried away - this effect is responsible for the "wind chill factor" as well. If the wind is blowing we get colder than if it is not. This type of heat transfer is called convection, and since it relies on fluid flow it is closely related to fluid dynamics.
Finally heat can be radiated by thermal radiation. Standing in sunlight one can feel the sun's warmth even though the sun is millions of miles away and separated from us by avacuum. There is no air or water in space to carry the heat to the earth, but the sun's thermal radiation reaches us nonetheless. This is an example of radiative heat transfer.
Heat conduction is the transmission of heat across matter.
Heat transfer is always directed from a higher to a lower temperature. Denser substances are usually better conductors; metals are excellent conductors.
The law of heat conduction also know as Fourier's law states that the time rate of heat flow Q through a slab is proportional to the gradient of temperature difference:
Q = KA(ΔT/Δx)
A is the transversal surface area, Δ x is the thickness of the body of matter through which the heat is passing, K is a conductivity constant dependent on the nature of the material and its temperature, and ΔT is the temperature difference through which the heat is being transferred. This law forms the basis for the derivation of the heat equation.
In heat transfer, a distinction is made between free and forced convection. Free convection is convection in which motion of the fluid arises solely due to the temperature differences existing within the fluid. Example: hot air rising off the surface of a radiator.
The basic premise behind free convection is that heated matter becomes more buoyant and "rises"; while cooler material "sinks". Free convection occurs in any liquid or gas which expands or contracts in response to changing temperatures when it is exposed to multiple temperatures in an acceleration field such as gravity or a centrifuge. The local changes in density results in buoyancy forces that cause currents in the fluid. In zero gravity, because buoyancy no longer becomes a factor, free convection does not occur.
Forced convection happens when motion of the fluid is imposed externally (such as by a pump or fan). Example: a fan-powered heater, where a fan blows cool air past a heating element, heating the air. When a person blows on their food to cool it, he/she is using forced convection.
Thermal radiation is the energy radiated from hot surfaces as electromagnetic waves. It does not require medium for its propagation. Heat transfer by radiation occur between solid surfaces, although radiation from gases is also possible. Solids radiate over a wide range of wavelengths, while some gases emit and absorb radiation on certain wavelengths only.