The two forms of heat relevant to air conditioning are:
- Sensible heat
- Latent heat
Understanding these two types of heat is crucial for grasping how air conditioning systems function and how they are rated in terms of their cooling capacity.
What is sensible heat?
Sensible heat is the heat that causes an object's temperature to change. When an object is heated, its temperature rises as heat is added.
This increase in temperature due to the addition of heat is referred to as sensible heat. Conversely, when heat is removed from an object, its temperature falls, and the heat removed is also called sensible heat.
Essentially, sensible heat is the energy exchanged that results in a change in the temperature of a substance without altering its phase.
What is latent heat?
Latent heat, on the other hand, is the heat required to change the state of a substance without changing its temperature. All pure substances in nature can change their state; solids can become liquids (ice to water) and liquids can become gases (water to vapor). These changes of state require the addition or removal of heat, known as latent heat.
A key characteristic of latent heat is that it does not affect the temperature of a substance. For instance, when water boils, it remains at 100°C (212°F) even though heat is continuously added. The added heat is used to change the state of the water from liquid to vapor without raising its temperature. This heat energy absorbed during the phase change is the latent heat of vaporization.
Similarly, when water freezes, it remains at 0°C (32°F) as it transitions from liquid to solid. The heat energy removed during this phase change is the latent heat of fusion. Thus, latent heat is the energy exchanged during a phase change without a temperature change.
Sensible heat vs Latent heat: Explained
Sensible heat causes a change in the temperature of a substance without changing its phase. Heating water from room temperature to boiling involves this type of heat. Latent heat is the energy required to change the state of a substance without altering its temperature. For example, at 100°C, the heat added to turn water into vapor is latent heat.
Air conditioning systems use sensible heat to lower air temperature and latent heat to remove moisture through condensation. Both types are essential for effective cooling and dehumidification.
What is sensible heat in HVAC?
Sensible heat in HVAC refers to the heat energy that changes the air temperature without altering its phase. It directly impacts the indoor climate by raising or lowering temperatures. This type of heat is crucial for maintaining thermal comfort, making it a key component in heating and cooling systems.