Heating and Humidification

During winter it is essential to heat and humidify the room air for comfort. As shown in Figure 8.11, this is normally done by first sensibly heating the air and then adding water vapour to the air stream through steam nozzles as shown in the figure.

Figure 8.11 Heating and Humidification Process

Mass balance of water vapour for the control volume yields the rate at which steam has to be added, i.e., m_w:

 

m_w = m_a (ω₂ − ω₁)

 

where m_a is the mass flow rate of dry air.

From energy balance:

 

Q_h = m_a (h₂ − h₁) − m_wh_w

 

where Q_h is the heat supplied through the heating coil and h_w is the enthalpy of steam. Since this process also involves simultaneous heat and mass transfer, we can define a sensible heat factor for the process in a way similar to that of a cooling and dehumidification process.