Energy Efficiency by Reducing Heat Transfer  Printable view

Reducing heat transfer is one way of improving energy efficiency. Sometimes we want to keep things cool. In summer we use air conditioners to keep our homes and offices cool and comfortable. Electrical energy is saved if heat entering our rooms is minimized by good insulation. Similarly, energy is also saved when refrigerator walls are well-insulated. In winter, we wear thick clothes to keep ourselves warm. Heat loss from our body to the environment is reduced by our clothing. Vacuum flasks and thermal cookers also reduce heat loss to keep their contents hot.

Fig. 1   We use a thermal cup to keep drinks hot.   Fig. 2   A thermal cooker is effectively a large thermal cup.

In the processes we mentioned above, notice that energy flows from a region of higher temperature to a region of lower temperature. The flow of energy resulting from a difference in temperature between two objects (or two regions) is called heat. There is continuous heat transfer from the hotter object to the colder object (or regions) until the two objects reach the same final temperature.

Fig. 3   (a) Two bodies A and B are of different temperatures, the temperature of A is higher than that of B. (b) When they are in contact, heat is transferred from A to B. (c) Heat transfer will stop when both A and B reach the final temperature.

In order to reduce heat transfer, we must first understand the processes of heat transfer and the factors that affect its rate. There are three main processes of heat transfer, conduction, convection and radiation. We will describe these processes below and see how heat loss can be minimized in daily applications.