Energy - Heating and Insulating

One source of heat loss from buildings is draughts. Cold air coming in from the outside needs to be heated up, otherwise the inside of the house would be at the same temperature as the outside. This uses energy from the heating system and reduces the overall efficiency of the house. As the cold air comes in, it means that warm air is also leaving the building somewhere. Some hi-tech homes are completely sealed to prevent draughts, incoming fresh air from the outside is controlled by using a ventilation system. To prevent the loss of energy to the outside, these usually include an efficient heat exchanger. This transfers the heat from the outgoing air to the air coming in so that the house does not need extra heating.

You will already have studied insulating homes at KS3; there are a lot of similarities with the KS4 work, however, new ideas such as U-values and payback time are introduced as well as revising methods of insulation. U-values are a measure of how well heat can travel through a material so lower U-values are associated with better insulators. The figure is a measure of how many watts of heat energy pass through a metre squared divided by the temperature difference between the opposite sides of the insulating material. In order to be able to compare U-values directly, the materials are measured under standard conditions with carefully controlled air humidity and wind conditions.

You will have met many different types of insulation but the thing that most have in common is that they contain trapped gases, usually air. This is because gases are very poor conductors of heat. When they are trapped, it prevents them from transferring heat by convection. Most heat leaves a building by being conducted through the solids used to construct it. Some heat leaves by convection (draughts) and a small proportion leaves by radiation - all objects above absolute zero emit (give off) infra-red (heat) radiation.

The largest heat loss is through the walls and the roof as these form the largest area of a building. These are the two areas that it pays to concentrate on when planning to insulate a house. Newly built houses have insulation planned as part of the design. Older houses have solid walls and it is most efficient to insulate the outside of these, although most people choose to add insulation to the inside as it is easier and cheaper. Houses built in the second half of the twentieth century and more recently usually have cavity walls. These help to keep houses both warmer and drier with less heating than solid walled houses. Adding insulation into the cavity keeps even more of the heat in, reducing energy consumption for heating even more.