Air humidification and water treatment explained.

Absolute air humidity

The absolute air humidity is the actual amount of water vapour present in a certain volume of air (usually 1 m3). It is commonly specified as grams per cubic metre of air (g/m3). If you know the temperature, the relative humidity RH can be calculated using these values. The value used to calculate required humidification performance is always absolute air humidity. The difference between the actual and set value plus the change in density must be supplied to the air to achieve the desired air humidity.

Adiabatic cooling

Atomizing water by means of high-pressure nozzles changes it from the liquid to gaseous state. This aggregate transition requires energy that is extracted from the ambient air. Result: the air cools off.


A mixture of finely distributed solid and liquid particles suspended in air. FINESTFOG high-pressure nozzles atomize water to extremely fine droplets that are mixed with air on leaving the nozzle.


CFU stands for colony-forming unit and it is one of the categories used in quantifying microorganisms to assess water quality. Water can be assessed using microbiological methods. Water samples are distributed on suitable culture medium gels. After a certain time, the live cells can be counted in units. In this way the number of microorganisms can be determined. According to the German drinking water ordinance at temperatures of 22 °C and 36 °C, the colony count may not exceed 100/1 ml.

Composite membrane

In FINESTFOG reverse osmosis systems high-quality composite membranes are used. These membranes are made of polymers. The membrane is wound very tightly resulting a very large surface area. The membrane is semipermeable and separates the water molecule from solids (mostly salts and contaminants). Composite membranes can remove 97 to 99% of salts and other contaminants from the water. Particles > 0.0001 µm can be filtered out by a reverse osmosis process. Composite membranes are considered particularly durable.

Dew point

The dew point (or dew point temperature) denotes the temperature at which for a certain water vapour content the air is incapable of absorbing any additional water. If the temperature falls below the dew point condensation occurs in the form of water droplets. Cold surfaces are particulary prone to condensation when the temperature drops below the dew point in rooms with high relative humidity. Condensation can then be observed, for instance, on windows.

Dual-medium nozzle

In air humidification, nozzles that atomize the water by means of pressurized air are called dual-medium nozzles. The performance of the dual-medium nozzle is controlled by adjusting the water pressure and the compressed air supply. Since pressurized air requires comparatively large amounts of energy, significantly more single-medium than dual-medium nozzles are in use today. The operating noise of dual-medium nozzles is also considerably higher. FINESTFOG offers dual-medium nozzles. Documentation and prices are available on request.

Equilibrium moisture content

The equilibrium moisture content is the amount of water in a hygroscopic material (eg, paper, wood, cotton) after extended storage in a room with constant relative humidity and temperature. If the humidity content of the material and air is the same, equilibrium moisture content or moisture balance is reached. Problems occur when the air is consistently too dry. Then humidity is extracted from the material while the air tries to restore the balance. Shrinkage, weight loss or cracking may occur. This is where air humidification steps in. It increases the humidity of the air, which is absorbed by the material until the balance is restored.

Fountain water

Printing presses require »fountain water« for the printing rollers. This water should be of constant quality. One important aspect is the water hardness which should be in the range of 8 to 10 °dH. Reverse osmosis systems initially produce pure water that is still too aggressive for printing rollers. For this reason FINESTFOG adds metered quantity of hardening agent. The result is constant high water quality without fluctuations.

h-x diagram

The Mollier h-x diagram (previously i-x diagram) was named after Richard Mollier in 1923. It serves to determine the state changes of humid air as a consequence of i. a. humidification, dehumidification, warming and cooling. Any creditable calculation of the required humidification performance is always based on the h-x diagram. This means that at least two quantities must be known, eg, the temperature and the desired air humidity.


Unit of electrical conductivity. The quality of pure water is most easily determined by its electrical conductivity: the lower the salt content of water, the lower the conductivity, which is measured in microsiemens (µS). FINESTFOG reverse osmosis systems are equipped with conductivity sensors that trigger a prealarm or alarm when the conductivity of the pure water reaches a limit.


Portion of fluid that passes through (permeates) a filter. Substances trapped by the filtration are referred to as retentate/concentrate. In water treatment equipment, the pure water that passes the membrane is also called permeate. In this context, the terms refers to virtually salt-free, pure water.

Pure water

Water purified by a water treatment system. Water filtered by a FINESTFOG reverse osmosis system is practically free of salt and bacteria (in general approx. 97 to 99% of salt is removed. Purified water is not to be confused with distilled (fully desalinated, demineralized) water.

Relative humidity

Relative humidity is the quantity commonly measured to determine the humidity of air. Usually abbreviated to % RH, it specifies for a certain temperature (eg, 20 °C) the ratio of the current water vapour content to the greatest possible water vapour content. The greatest possible water vapour content always equals 100% relative humidity. This state is also referred to as dew point. At this point the air cannot absorb any more water – any additional water vapour condenses to the liquid state. Air humidification systems regulate the air humidity using humidity sensors.

Reverse osmosis

Osmosis: passage through a semipermeable separating layer for the spontaneous equalization of concentration differentials. Reverse osmosis: a process in which the direction of flow of the natural concentration equalization is reversed by means of pressure.

FINESTFOG reverse osmosis systems produce up to 98% desalinated pure water using semipermeable membranes: the medium (water) in which the concentration of a particular substance (salt) is to be reduced, is separated by a membrane from the medium (water) in which the concentration (salt) is to be increased. A pump subjects this water to a pressure that needs to exceed the osmotic pressure created by concentration equalization (for tap water under 2 bar). This causes pure water molecules to diffuse through the membrane, while contaminants (salts, but also bacteria and the like) are retained. The concentrate containing the contaminants is drained, the pure water is piped to the consumer.

Single-medium nozzle

Type of nozzle through which only one medium (liquid/gas) passes. In the case of FINESTFOG high-pressure humidifiers this medium is water. The atomization is solely the result of the kinetic energy of the water. By contrast, dual-medium nozzles require a second medium (pressurized air) as energy source.

Soft water

Water quality after the extraction of calcium and magnesium ions. FINESTFOG softening units extract the hardeners magnesium and calcium from the water. By way of an ion exchange an equal amount of sodium ions (sodium salt) are added to the water. This »softens« the water. Many people confuse soft water with desalinated water. The softening process exchanges rather than reduces salts. Soft water is therefore only suitable to a certain degree for air humidification.

UV sterilization

Every FINESTFOG air humidification system is equipped with a UV sterilization unit. Ultraviolet radiation is an electromagnetic radiation with a shorter wave length than is visible to the human eye. Ultraviolet radiation is used to treat water, air and surfaces. Because of the speed of the reaction and given a sufficient dose, microbes and bacteria are deactivated (killed off) within a fraction of a second. The UV sterilization is not associated with any resistences due to mutation. Another benefit: in general, no chemicals need to be added.

FIENSTFOG UV sterilization units deploy UV low-pressure lamps. The lamp’s size and rating is determined by the maximum humidification performance expected of the air humidification system. After about a year, the UV lamp performance drops and it should be replaced.

Water softening unit

Water softening systems produce «soft» water from «hard» water. Soft water must not be confused with distilled water or pure water. FINESTFOG water softening systems work with cation exchange resin. The water flows through a column that contains a cation exchange resin. In this column predominantly Ca2+ (calcium) and Mg2+(magnesium) ions are exchanged for an equivalent number of Na+(sodium) ions. The softened water will now contain a proportionately greater amount of sodium ions, but hardly any magnesium and calcium ions. The exhausted ion exchange resin is regenerated by an 8 to 12% sodium chloride solution (cooking salt). Each softening station therefore includes a salt container filled with cooking salt tablets. Water softening units with two resin columns are referred to as pendulum systems. The benefit of these systems as deployed by FINESTFOG is that they provide soft water on a continuous basis.

Water softening systems with just one resin column are not able to produce soft water during regeneration. Therefore they have to regenerate at specific times, which often results in high consumption of salt and water. Softened water is not generally suited for air humidifiers, since the total salt content of the water is not reduced. Water softening systems can be used for pretreating tap water prior to its use in a reverse osmosis system.