Physical properties

Whether electrode-type or electric-heating type, both steam humidifiers belong to isothermal humidification, and during humidification, the dry-bulb temperature rises slightly.

When used in conjunction with an air handling system, there is no need to preheat the air to a higher temperature.

Both types of steam humidifiers have very high humidification efficiency, both exceeding 95%.

Power consumption

Both types of steam humidifiers consume 750 W (380 V) of power per 1 kg/h of steam output.

Example: For a humidification capacity of 40 kg/h, whether using an electrode-type or an electric-heating type system, the power requirement is 30 kW. 40 × 0.75 = 30 kW.

Control accuracy

The control accuracy of the electrode-type steam humidifier is ±5%.

The control accuracy of electric steam humidifiers is 2–5% (accuracy depends on the control method and operating conditions).

Working principle

1. Working Principle of Electrode-Type Steam Humidifiers

When water exists in its pure form, it is nonconductive. The reason why tap water—commonly used in daily life—is conductive is that it contains large amounts of mineral salts. The operating principle of electrode-type steam humidifiers relies precisely on water’s conductivity.

When water containing mineral salts enters the humidification tank through the inlet valve, the electrode plates located in the upper part of the tank gradually become submerged as the water level rises. Since water containing mineral salts is a conductor, once the water comes into contact with the electrode plates, an electrical circuit is established. At this point, when we apply a voltage to the electrodes, ions in the water begin to move rapidly, colliding with each other and generating frictional heat. This heat causes the water to warm up and produce clean, saturated steam. The steam is then delivered into the air-conditioning unit or ductwork via a steam diffusion device, thereby achieving the purpose of humidifying the air.

According to the Joule effect, steam production is proportional to the current, and consequently also proportional to the water level. This current is measured using a current transformer. By repeatedly cycling the inlet and outlet valves, the water level, current, and steam production can be precisely adjusted.

As water evaporates, the water level will drop; however, the steam does not carry away the mineral salts dissolved in the water. As a result, the concentration of mineral salts in the water increases, which in turn raises the water’s electrical conductivity. Once the electrical current reaches the upper limit set by the microprocessor control, the drain valve will discharge the highly concentrated water and then replenish it with fresh water via the inlet valve, thereby diluting the solution and protecting the humidification tank. Over time, scale buildup will accumulate on the electrode plates, obstructing the electrodes’ contact with ions in the water and thus affecting the humidification efficiency. Therefore, the humidification tank must be cleaned and replaced regularly.

2. Working Principle of Electric Steam Humidifiers

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

Its primary operating mode involves the control box activating single or multiple sets of electromagnetic relays or SCR silicon-controlled rectifiers according to the humidification demand, thereby controlling the heat output of the electric heating tubes to generate the required amount of humidification.

The electric heating tube is the core component, and its stability, service life, and reliability are extremely important.

The manufacturing method of electric heating tubes involves evenly distributing high-temperature resistance wires in the central position inside a high-temperature-resistant stainless steel tube. The gaps around these wires are densely packed with crystalline magnesium oxide powder, which boasts excellent thermal conductivity and insulation properties. This structural design not only secures the resistance wires in place but also ensures high thermal efficiency and uniform heat distribution. When an electric current passes through the high-temperature resistance wires, the resulting thermal energy is conducted via the crystalline magnesium oxide powder to the surface of the metal tube. From there, the heat is transferred through thermal conduction and convection, raising the temperature of pure water to produce steam, thereby humidifying the air.

Electric heating tube	Evaporation tank

Terms of Use

1. Power Supply:

380V, three-phase five-wire

2. Water supply requirements:

Water pressure: 2–6 bar; water temperature: 4–40℃

Electrode-type steam humidifiers require municipal tap water with a conductivity of 100 to 300 microsiemens, which is optimal.

Electric steam humidifiers require the use of pure water—specifically, deionized water.

Acquisition cost

For the same humidification demand, the cost of an electric-heating humidifier is about 2.5 times that of an electrode-type humidifier.

Humidification Knowledge

1. What are the hazards of scale buildup in electric steam humidifiers?

※ Slow heating

Calcium and magnesium ions present in water undergo chemical reactions at certain temperatures—specifically, when the water temperature exceeds 60°C, the rate of scale formation accelerates. These reactions produce various types of scale, including carbonate scale, sulfate scale, silicate scale, and mixed-scale deposits (which fall into two main categories: salt scales and fouling). These substances have very poor thermal conductivity; when they adhere to the surface of electric heating elements, they reduce the efficiency of energy transfer between the power source and the water. As a result, much of the heat generated is trapped by the scale, leading to a significant slowdown in the heating process and a sharp decrease in the rate of temperature rise.

※ Corrosive electric heating tube

In addition to its strong thermal resistance, scale also exhibits a certain degree of corrosivity. When scale adheres to the surface of an electric heating element, it causes the protective layer of the element to deteriorate, leading to the formation of rust and verdigris. The longer the scale remains adhered, the more severe the corrosion becomes, and once it sticks to the surface of the heating element, it becomes extremely difficult to remove. Moreover, because scale acts as a thermal insulator, the areas of the heating element covered by scale experience progressively higher local temperatures. Eventually, this overheating can cause the wall of the heating element to break down, resulting in a tube rupture.

※ Energy consumption

Scale has poor thermal conductivity, which hinders energy exchange and consequently leads to higher energy consumption.

※ Safety hazard

Scale buildup can cause electric heating tubes to burst, leading to secondary safety hazards.

2. When using an electric steam humidifier, why can only pure water be used, and why can't softened water be used?

Generally, tap water contains high concentrations of calcium and magnesium ions. Water softening and water purification are both water treatment methods. The former primarily uses ion exchange to reduce water hardness; however, besides the issue of exchange efficiency, it also suffers from leakage problems in practical applications, meaning it cannot completely remove calcium and magnesium ions from the water. In contrast, the latter employs RO membranes to directly eliminate calcium and magnesium ions from the water.

The diameter of a calcium ion is 0.0004 micrometers, the diameter of a magnesium ion is 0.0005 micrometers, and the filtration accuracy of an RO membrane is 0.0001 micrometers.

The ultrafiltration membrane has a filtration accuracy of 0.01 microns, whereas commonly available household water filters typically have a filtration accuracy of around 5 to 50 microns.