Air temperature and moisture content, known as humidity, are the two primary factors that determine how comfortable an environment feels. When the air holds a large amount of water vapor, the atmosphere can feel significantly warmer than the thermometer suggests. This common experience prompts the question of whether removing this moisture load truly results in a physical reduction of air temperature. The relationship between the air’s water content and its temperature involves two distinct forms of heat energy.
Understanding Latent and Sensible Heat
The physical temperature of the air, measured by a thermometer, is defined by sensible heat. Sensible heat is the energy that, when added or removed from a substance, causes a measurable change in its temperature without altering its physical state. Heating a volume of dry air, for example, increases its sensible heat, and the thermometer reading rises.
Humidity, which is water vapor, holds latent heat. Latent heat is the energy absorbed or released when a substance changes state, such as liquid water becoming vapor, without a corresponding change in temperature. When water evaporates, it absorbs latent heat from the surroundings; when it condenses, it releases latent heat.
Removing humidity, or latent heat, does not directly reduce the sensible temperature of the air mass. The removal of water vapor is a change of state, not a reduction of the air’s thermal energy that a thermometer can register. The sensible heat remaining in the air molecules themselves remains unchanged by that process alone.
The Impact of Humidity on Perceived Temperature
While removing humidity does not change the actual temperature reading, it dramatically alters how the human body experiences that temperature. This difference is rooted in the body’s primary method of cooling: thermoregulation. The human body cools itself by producing sweat onto the skin’s surface.
For this natural cooling mechanism to be effective, the liquid sweat must evaporate, changing into water vapor. This phase change requires energy, which the water molecules draw directly from the skin, removing heat from the body. When the surrounding air has low humidity, it readily absorbs this moisture, allowing sweat to evaporate quickly and efficiently, making the environment feel cooler.
High humidity means the air is already saturated with water vapor and has little capacity to absorb additional moisture. When the air is moisture-laden, sweat evaporates very slowly or not at all, leaving it to pool on the skin. The body cannot shed heat effectively, creating the oppressive sensation that makes the heat feel more intense than the sensible temperature suggests. Reducing the humidity restores the air’s capacity for moisture absorption, immediately reactivating the body’s natural cooling system.
Mechanical Removal of Atmospheric Moisture
Technology designed for climate control addresses both sensible and latent heat, but with different primary functions. A typical air conditioning unit is engineered to remove sensible heat, effectively lowering the measurable air temperature. As the warm, humid air passes over the unit’s cold evaporator coil, the air is cooled below its dew point, causing water vapor to condense into liquid droplets.
This condensation is a byproduct of the air conditioner’s cooling cycle and represents the removal of latent heat from the air. The condensed water is collected and drained away, meaning the air conditioner is simultaneously a cooler and a dehumidifier. Air conditioners are highly effective at both lowering the sensible temperature and reducing the humidity, which maximizes comfort.
Dedicated dehumidifiers focus solely on removing latent heat from the air. These devices draw air over a cold coil to condense moisture, then pass the now-dry air over a second, warmer coil before returning it to the room. This re-heating step is necessary because the internal compressor and heat exchanger generate waste heat. Consequently, the air exiting a dehumidifier is often 3 to 8 degrees Celsius warmer than the air that entered, slightly increasing the room’s sensible temperature. Despite this minor rise, the lower humidity level still provides a significant feeling of relief and comfort.