Latent heat

When heat energy is added to a substance, its temperature generally rises, and when heat energy is removed, its temperature generally falls. This is referred to as ‘sensible heat’.

However, when a substance changes state, such as from a solid to a liquid, a liquid to a gas or vice versa, this change requires the addition or removal of heat energy, but does not result in a change in the temperature of the substance. This is referred to as latent heat.

There are three categories of latent heat:

• Latent heat of fusion: When a substance changes from solid to liquid (or back).
• Latent heat of vaporisation: When a substance changes from liquid to gas (or back).
• Latent heat of sublimation: When a substance changes solid to gas (or back).

Specific latent heat refers to the heat required to change the state of 1 kg of a substance without a change in temperature, expressed in joules per kilogram.

NB: This should not be confused with the term ‘specific heat’ which refers to the heat energy per unit mass required to raise the temperature of a substance by one degree Celsius.

[edit] Related articles on Designing Buildings

• Advanced phase change materials.
• g-value.
• Heat transfer.
• Law of partial pressures.
• Mass transfer.
• Phase change materials.
• Phase change.
• Refrigeration.
• Sensible heat.
• Specific heat.
• Temperature
• Thermal comfort.
• Thermal indices.
• Thermal mass.
• Thermal optical properties.
• U value.