According to the humidification method, it is broadly divided into steam humidification and mist humidification.

Steam humidification:

Generally speaking, the steam used in steam humidification systems is high-temperature steam, with a latent heat slightly higher than that of water in its gaseous state at normal temperature. Therefore, after air is humidified by steam, its latent heat will increase slightly, causing the dry-bulb temperature of the space to rise by 1 to 2℃. Because the increase in the air's dry-bulb temperature is relatively limited, steam humidification is also referred to as isothermal humidification.

After the liquid water inside the steam generator is heated and vaporized into saturated steam, the steam is directly distributed into the air-conditioning unit or ductwork via a steam distributor. Subsequently, the steam mixes thoroughly and completely with the air, enabling the air to absorb moisture and thereby increasing its humidity level.

1. Generator: Available in various models

① Steam boiler humidification system

Use electric heating, fuel oil, or gas as the heat source. After heating liquid water to saturated steam at a pressure of 1–10 kg/cm²G, the steam is then passed through a pressure-reducing station to lower its pressure to 7–25 PSI. Finally, a distributor evenly disperses the steam into air-conditioning units or ducts for humidifying the air.

② Liquid/Steam Heat Exchange Type Steam Humidification System

Using high-temperature liquids (hot water) or industrial-grade steam, pure water (RO/DI) is heated and evaporated into clean steam via heat exchange. The steam is then evenly distributed throughout the air-conditioning unit or ductwork by a distributor to humidify the air. To prevent impurities generated by the steam boiler from contaminating the steam quality and compromising the cleanliness level of the air-conditioning system, the existing high-temperature steam or hot water can be passed through a tube-in-tube or plate-type heat exchanger to produce low-pressure secondary purified steam for air-conditioning humidification. This system is particularly suitable for applications where high-pressure steam boilers, high-temperature hot-water boilers, or sources of high-temperature waste heat recovery are already in place or need to be implemented; otherwise, it would result in duplicated investment.

③, Electrically Heated Steam Humidification System

The thermal energy generated by passing an electric current through a resistor heats pure water to produce steam, which is then distributed by a diffuser into the air-conditioning unit or ductwork to humidify the air.

④, electrode-type steam humidification system

Electrodes are inserted into water, and after an electric current is applied, the heat generated by the movement of ions in the water heats and evaporates the water into steam. The steam is then distributed by a diffuser into the air-conditioning unit or ductwork to humidify the air.

2. Rapid steam diffusion absorption device:

This involves exploring how to deliver 100% dry saturated steam at low pressure, as well as how to mix it with air in the most efficient and uniform manner, ensuring its rapid absorption over the shortest possible distance and time. When steam encounters cold air, it immediately releases heat and condenses into water droplets. Therefore, steam humidification projects aim to spray saturated dry steam rather than the typical mixture of steam and water. Hence, it is crucial to effectively produce and evenly distribute dry saturated steam. The methods include:

① High-efficiency steam-water separator

②, Long-shaped plastic steel nozzle

③, Jacketed Single-Tube Steam Humidifier Distributor

④, Multi-nozzle design

Mist humidification:

Primarily, tiny water droplets atomized by nozzles or ultrasonic oscillators are distributed throughout the air-conditioning unit or ductwork and mixed with the air. These tiny water droplets absorb sensible heat from the air via heat exchange and convert it into the latent heat of vaporization of water (approximately 584.3 kcal/kg for dry air at 23℃). Eventually, these small water droplets evaporate completely into the gaseous phase, becoming one of the components of the air, while the dry-bulb temperature of the air drops significantly.

During the process of humidification by water mist, the latent heat of vaporization of water is derived from the sensible heat of the air. Moreover, the enthalpy of liquid water at room temperature is significantly lower than that of gaseous water. As a result, after humidification with water mist, the total enthalpy of the air remains nearly unchanged. Therefore, the enthalpy contribution from the vaporization of liquid water to the overall increase in air enthalpy is relatively small. For this reason, humidification by water mist is also referred to as isenthalpic humidification.

When room temperature is high and relative humidity is low—such as in desert regions—using a mist humidification method can effectively increase air humidity and lower air temperature, offering the advantage of energy savings. However, when room temperature is low and relative humidity is also low—for example, during winter—air must first be preheated to significantly raise its dry-bulb temperature, thereby increasing its enthalpy. Only then can mist humidification achieve the desired effect of raising air humidity to an optimal moisture content. Because at low temperatures, air’s heat-transfer efficiency is poor, water droplets take longer to vaporize and require a greater absorption distance. If there isn’t sufficient enthalpy available, the water droplets will keep growing larger and eventually lead to condensation. Therefore, when using mist humidification, it’s crucial to ensure that there’s enough enthalpy provided and that the absorption distance is adequate. In winter, if there’s no suitable source of waste heat and electric heating must be relied upon to raise the temperature (and thus the enthalpy), not only will energy savings fail to materialize, but energy consumption will actually increase even further. Hence, when applying this method, careful consideration must be given to these issues and their associated costs.

①, Is the absorption distance long enough?

②. Are the size of water droplets and the distribution and arrangement of nozzles appropriate?

③, Is it possible to control the humidification amount using a proportional control method?

Proportional output control poses a challenge for mist humidification. Generally, manufacturers claim that their devices can accept proportional control signals ranging from 4 to 20 mA or 2 to 10 V. However, upon closer examination of their structural design, it becomes evident that their humidification output is not actually proportional—it is instead an ON-OFF control system. Since the ON-OFF control method cannot meet the stringent requirements of modern, high-precision air-conditioning systems (a point that is extremely important), if you encounter instruments or equipment that claim to offer proportional output power while accepting proportional signals—whether for steam humidification or mist humidification—you must thoroughly investigate before making any assumptions, lest you be misled.

Note: Absorption distance: For steam humidification, the absorption distance refers to the distance from the nozzle to the first obstacle without condensation occurring. For mist humidification, the absorption distance refers to the distance from the nozzle to the water-drip tray or the first obstacle, within which the designed air humidity level can be maintained.