When dehumidifying (drying) the air, the absolute water content in the air (absolute humidity) decreases. We achieve this in various ways: in this case by mixing drier air.

The situation can be graphically represented in the h-x diagram of wet air. In this case, too wet air P1 (RH1, x1) mixes with (mostly colder) air P2, whose water vapor content is significantly lower than that of air P1. The state of the mixed air M1 is given by the ratio of the amounts P1 and P2.
If the temperature of the air mixture M1 is lower than the air temperature P1, it is necessary to reheat it to the former temperature T_db. After this process, we obtain the resulting state of air M2 with the same temperature as P1, but with a reduced content of water vapour x2 and therefore also with a lower relative humidity RH2 (this procedure is used for example, in swimming pools)