Grade-matched air humidification to reduce the required heating-source temperature and capacity

Humidification is vital for human health in residential buildings and critical industrial processes, yet it receives less research attention than cooling and dehumidification. Traditional systems rely on high-grade steam for humidification, consuming substantial thermal energy. While warm water or solution spraying enables enthalpy-increasing humidification with lower-grade heat, grade wastage persists. This study explores optimal heating source temperature grade and capacity for humidification loads, and improves the previously proposed grade-matched method for air treatment process design, then applies the method to design a humidification process for an industrial building case. By integrating low-grade heat recovery and multi-stage heat pumps, the system reduces energy use significantly compared to traditional isothermal and temperature and humidity independent control (THIC) systems. Using water heated to 6.6 °C and 16.0 °C by two heat pumps, fresh air is humidified to 10 g/kg (14.4 °C dew point), lowering heating-source grade requirements. This system reduces the heating-source temperature grade and enables energy recovery between the latent and sensible heat subsystems, thus achieving 28.6 % lower electricity consumption than the THIC system. By eliminating the need for high-grade steam, the system reduces electricity usage by 66.0 % compared to traditional isothermal humidification. This approach supports energy efficiency and global emission-reduction goals.