In HVAC, what do "latent heats" refer to?

Latent heat refers to the heat that is absorbed or released by a substance when it changes its phase, such as from solid to liquid or liquid to gas, without a change in temperature. This concept is fundamental in HVAC applications, particularly in understanding refrigeration cycles and humidity control.

During phase changes, energy is required to break the bonds between molecules in a solid to form a liquid or to break the intermolecular forces in a liquid to form a gas. This energy is known as latent heat and is crucial for processes like evaporation and condensation. For example, when water evaporates, it absorbs heat from its surroundings, which cools the environment, a principle utilized in air conditioning systems.

In contrast, the other options pertain to different heat transfer concepts. Heat transferred by direct contact refers to conduction, while heat absorbed during temperature changes is related to sensible heat. Heat produced by combustion involves exothermic reactions and does not pertain to the phase changes that latent heat describes. Understanding these distinctions is essential for HVAC professionals when designing system efficiencies and selecting appropriate cooling and heating methods.