Air heating is the simplest case of a change in the state of the air because it does not increase or decrease the amount of water in the air (x = constant).
Therefore, this process takes place in the h-x diagram on the vertical line, while the relative humidity RH decreases. In order for the air m [kg/s] to reach required temperature it is necessary to supply it with energy Δh [kJ/kg].

   Q =m* Δh   [kW]