What is the difference between sensible and latent heat?

Although we more often associate air conditioning with its cooling abilities, we refer to heat when discussing how a particular unit or system performs. In fact, there are two different types of heat we discuss: sensible heat and latent heat.

But what’s the difference between them?

What is sensible heat?

Sensible heat refers to heat you can feel, or sense. This is any heat which can be measured on a thermometer, whether it’s heat from the sun shining on a sunny day, or the flame from a candle. 

When an object is heated, the object’s increase in temperature is sensible heat. Similarly, when heat is removed from an object and its temperature falls, this is also sensible heat – because you can feel the difference. 

What is latent heat?

When we talk about latent heat, we are often referring to the change of state of an element. Many of us were first taught about this in school: solids can become liquids, and liquids can become gases – i.e. ice can become water, and water can evaporate into vapor. All pure substances in nature are able to change their state. And to change state, a substance requires the addition or removal of heat. 
 

The energy that causes these changes is called latent heat.

‘Latent’ means ‘hidden’, and latent heat isn’t something you can feel – it most often refers to the energy involved in a change of state. 

What’s the difference between sensible heat and latent heat?

Here’s an example which clearly demonstrates the difference between latent heat and sensible heat:

You have a pot of water which is currently 20°C, and are going to boil it on a stove. If you had a thermometer in this water, you’d be able to see the temperature – or sensible heat – of the water increase from 20°C to 100°C quite rapidly. (This temperature change is also being caused by the sensible heat from the flame on your stove.)

Once the water reaches 100°C, it begins to boil and turn into steam – the process of water becoming steam is called latent heat. You won’t see an increase in temperature on the thermometer as this happens. That’s because this latent heat is the hidden energy in the molecules of the water. If you had a very powerful microscope, you’d see them vibrate as the water changes state.  

Appreciating the difference between latent heat and sensible heat is fundamental to understanding why and how refrigerant is used in cooling systems. During the cooling cycle in your Daikin system, liquid in the refrigerant absorbs all the heat from its surroundings – latent heat from the air or ground. And, because the refrigerant warms up, it begins to evaporate into a gas. After this, the evaporated refrigerant is compressed, driving the temperature up, and condensed back into a liquid again.

You may also come across the terms ‘total capacity’, ‘sensible capacity’ and ‘latent capacity’ in exploring your Daikin unit, where 'sensible capacity' defines your unit's cooling capacity, and refers to the capacity required to lower temperature, and ‘latent capacity’ is the capacity to remove the moisture from the air. 'Total capacity' refers to the combined sensible and latent heat capacity of the unit.

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