Preventing unwanted energy transfers

Devices waste energy for various reasons including friction between their moving parts, electrical resistance, and unwanted sound energy.

In most cases, this waste energy is energy that has been shifted into the environment and raises the temperature of the surroundings. In order to make further use of this energy it has to be retrieved from each individual air particle. Clearly, this is very difficult, if not impossible. It is much better to prevent the energy being shifted, or dissipated, to the surroundings.

It is impossible to completely prevent unwanted energy transfer, the best that can be done is to reduce them. Some of the most common ways to reduce these unwanted energy transfers are:

Lubrication

Frictional forces cause surfaces to heat up resulting in an unwanted energy transfer. Reducing the friction between two surfaces can reduce this unwanted energy transfer.

Friction is sometimes reduced by placing rollers or ball bearings between the surfaces but, most often, oil is used to lubricate the surfaces and allow them to slide smoothly over each other.

Thermal insulation

Heating a house, for example, can be a problem. A great deal of energy is wasted through the windows, doors and roof.

A thermal scanned image of a house losing heat from windows.

There are some simple ways to reduce this loss, including fitting carpets, curtains and draught excluders.

Energy loss through windows can be reduced using double glazing. These kind of windows have air or a vacuum between the two panes of glass. Air is a poor conductor, while a vacuum can only transfer energy by radiation.

Energy loss through walls can be reduced using cavity wall insulation. This involves blowing insulating material into the gap between the brick and the inside wall, which reduces the loss by air circulating inside the cavity, therefore reducing loss by convection through the cavity. Overall the heat loss conducting through the bricks and cavity is reduced; it can be said that the thermal conductivity has been reduced.

Sometimes walls do not have a cavity. Thicker walls transfer heat by conduction more slowly than thinner walls. Adding a material of low thermal conductivity to these solid walls on either the inside or the outside reduces the heat loss because the lower the thermal conductivity of a material, the slower heat passes through the material.

Energy loss through the roof can be reduced by laying loft insulation. This works in a similar way to cavity wall insulation.