Window air conditioners primarily function to cool the air by removing heat from the room. However, they also have a secondary effect on humidity levels. Let's break down the process to understand why your window air conditioner drops the relative humidity below 40% while the air temperature decreases only slightly.
Cooling Process: Window air conditioners cool the air by passing it over evaporator coils containing a cold refrigerant. As the warm air from the room contacts the coils, heat is absorbed from the air, causing it to cool down.
Condensation: As the air cools down, its ability to hold moisture decreases, leading to condensation. The excess moisture in the air condenses on the evaporator coils, similar to how dew forms on a cold surface. This condensation helps to remove humidity from the air.
Dehumidification: The moisture that condenses on the evaporator coils drips into a collection pan or drains away. This process contributes to reducing the overall humidity in the room.
Now, let's address why the relative humidity drops significantly while the air temperature decreases only slightly:
Cooling Capacity: The primary function of an air conditioner is to cool the air, and it is designed to be efficient in doing so. The cooling capacity is determined by factors such as the size of the air conditioner, the cooling output, and the ambient temperature. In your case, the air conditioner might be designed to provide efficient cooling rather than significant temperature reduction.
Latent Heat Load: In hot and humid areas, a considerable portion of the cooling load is the latent heat load, which is associated with the moisture content in the air. The air conditioner removes both sensible heat (which affects temperature) and latent heat (which affects humidity). Since the air conditioner is primarily designed to handle the sensible heat load, it may not provide a significant decrease in temperature but is more effective in removing humidity.
Insulation and Room Size: The cooling effect of the air conditioner can also be influenced by factors such as the insulation of the room and its size. If the room is poorly insulated or larger in size, the air conditioner may struggle to maintain a significant temperature drop.
In summary, window air conditioners are more effective at removing humidity than drastically reducing the temperature. Their primary purpose is to cool the air, but the condensation and dehumidification processes contribute to lowering the relative humidity in the room.