Grades 6–8 · Machines
How does a dehumidifier collect water from air?
A room can contain water even when no droplets are visible. That water is vapor mixed with the air. A refrigerant dehumidifier uses a fan and two coils to remove some of the vapor and return the air to the same room.
In the diagramA dehumidifier turns some air moisture into liquidRoom air crosses a cold coil and then a warm coilCold coilWarm coilMoist airReturned airWater collectionAir crosses both coils before returning to the room.
Air first passes a refrigerated coil. If the coil cools the nearby air below its dew point, water vapor condenses on the surface. Dew point is the temperature at which that air becomes saturated as it cools. The droplets join and drain into a collection container or drainage route.
The air then crosses a warmer coil. This is the condenser of the refrigerant system, which releases energy absorbed at the cold coil together with energy supplied by the compressor. The returning air has lost some water and is reheated. The appliance can therefore make its surroundings slightly warmer while removing moisture.
Removing vapor reduces the actual amount of water in the air. Warming also changes relative humidity, which compares the existing vapor with saturation at that temperature. These are different effects. Collected liquid has left the room air, while water still present as vapor continues through the machine. The refrigerant stays inside its own pipes and carries thermal energy between the coils; it is separate from the collected water.
About this explanation
Starting knowledge: Know that air contains water vapor and that cooling can cause condensation.
Sources
- US Department of Energy — Consumer Dehumidifiers: Components
- ENERGY STAR · US Environmental Protection Agency — Dehumidifiers: Relative Humidity and Operating Temperature