# Heat transfers in three ways

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Heat transfers in three ways

# Heat transfers in three ways

30-07-21

The H in HVAC stands for heating, which is a major part of our business. Heat is transferred in three ways, namely conduction, convection and radiation. You experience heat differently with each method: how this works and why it’s important for your HVAC system is the subject of this blog.

We could start with an example of a heat exchanger or an evaporator in a cooling machine but, to keep things simple, let’s use a bonfire to explain the three forms in which heat manifests itself. Gather round, enjoy feeling the heat of the flames on your skin as someone pokes the logs in the fire with a steel rod… We’re all familiar with a bonfire like the one below.

The heat or thermal energy in this fire is transferred in three different ways, namely:

• Thermal conduction
• Thermal convection

Before we go further, set your mind to a molecular level. Everything is made from these minuscule particles. Solid items like the steel rod have their molecules and atoms in a tight grid, while the air between the bonfire and the people sitting around it consists of freely flowing molecules.

Three forms of heat transfer

Conductive heat transfer occurs when a temperature difference exists between two materials in contact with each other. Putting the tip of a steel rod into the fire will cause this kind of heat transfer. The molecules of the rod which are in the fire will heat up and, as they get more excited, bounce against the molecules beside them, transferring the energy from one end of the rod to the other.

## Convection

The air in the direct vicinity of the fire gets heated up through conduction. Heated air rises as cold air takes its place. The atmosphere around us is a mixture of different gases. Hot gas molecules occupy more space than cold air molecules, making them less dense and lighter. As the convection stream rises it heats up the surrounding air. Cold air which drops down will eventually be heated up again and also rise into the sky.