Relative humidity decreases: If the temperature in the room rises due to heating whilst the absolute humidity remains constant, the relative humidity decreases because the heated air can hold more water vapour.
Basics and retrofitting
Direkt im Raum Luftbefeuchtung
Contents at a glance
This article explains when and why the air becomes too dry, what simple methods are available for retrofitting a humidifier, and what tips you can follow to maintain optimal humidity levels.
Ideal for retrofitting
Direct room humidification is always the right choice
The basics of air humidification
Relative and absolute humidity explained simply
Practical tips on humidity
Proper ventilation and heating to combat dry air
Ideal for retrofitting
The basics of air humidification
From air humidity to easy retrofitting of a humidification systemDry indoor air occurs mainly during the heating season, when warm air – with consistently low relative humidity – could absorb more water vapour than is actually present. The consequences are noticeable: people suffer from irritated mucous membranes, materials such as wood or paper warp, and sensitive machinery can be damaged by static electricity. With an understanding of how dry air forms and the targeted retrofitting of technical humidification systems, the indoor climate can be optimised in the long term.
One option particularly suitable for retrofitting is the direct room humidification system. Unlike humidification within an air conditioning system, small nozzle humidifiers are installed directly in the room. The units are mounted on the wall or ceiling so as to be barely visible, and spray a micro-fine ‘mist’ of hygienically treated water as required.
With direct room air humidification, it is not necessary to fit out an entire building. Individual floors, departments, open-plan offices, work areas or production halls can also be humidified individually and cost-effectively. Instead of being centrally located in the ventilation and air-conditioning system, the small humidifiers are installed directly in the room. When required, the units spray a micro-fine mist which is immediately absorbed by the room air and distributed evenly. The rapid evaporation also creates a revitalising, refreshing effect and cleans the room air of dust.
By separating the ventilation and air conditioning systems from the water atomisation, the systems can be installed independently of an air conditioning system with minimal structural work. The ultra-fine atomisation is achieved through a water treatment process that removes bacteria and minerals from the water and generates a high pressure of up to 85 bar. The connection between the central water treatment system and the decentralised humidifiers is formed by special high-pressure hoses, no thicker than a finger, as well as power and control cables. The simple and flexible installation makes direct room humidification particularly cost-effective for retrofitting, especially .
Humidity controlled and targeted
Optimal humidity levels are maintained throughout the year by digital control systems that continuously monitor the indoor climate and ensure a constant humidity level. The control system only activates additional humidification when the humidity falls below the desired optimum level. As individually defined humidification zones are established for direct room humidification, different setpoints can also be implemented for rooms with different uses (e.g. offices, laboratories, IT rooms, production halls).
The right water
Water treatment is crucial to the quality and hygiene of air humidification. Untreated water is not suitable for air humidification. The reasons for this lie in the large number of substances present in the water: bacteria, germs, suspended solids, salts and other minerals can pose health risks. A prerequisite is therefore multi-stage water treatment that purifies and disinfects the water and removes all minerals. Integrated water treatment is an integral part of direct room air humidification.
Further information on direct room humidification
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How does dry air form?
How does excessively dry air form, and what factors influence it? Air itself consists of a variety of gases. One of these is water vapour. The amount of water vapour in the air determines the air humidity.
We speak of absolute humidity when describing the total amount of water contained as a gas in one kilogram of air, e.g. 8 g/kg. A key factor in the relationship between air and water is the air’s constant tendency to absorb water vapour until it reaches saturation. For assessing indoor air humidity and defining the optimal humidity level, another value is therefore of crucial importance: relative humidity!
relative humidity describes the amount of water contained in the air in relation to the maximum amount of water it can hold. This ‘percentage saturation’ of the air with water vapour is influenced by the air temperature: warm air can hold a greater amount of water vapour than cold air.
Temperature and relative humidity
The following example illustrates the relationship between temperature and relative humidity. If a room is sealed off from the outside air, it has a constant absolute humidity: water cannot be absorbed from the environment nor released into it. If the indoor temperature rises due to heating whilst the absolute humidity remains constant, the relative humidity falls because the heated air can absorb more water vapour than is available in the sealed room. If windows or doors are opened for ventilation in winter, the indoor air becomes even drier than before. Due to the higher vapour pressure of the warm, dry indoor air, the remaining residual moisture escapes to the outside. The relative humidity drops further. This explains why, particularly in winter, indoor air is often so extremely dry if it is not actively humidified by an additional humidifier.
Constant relative humidity: The temperature and absolute humidity are at the same level. The relative humidity is the same indoors and outdoors.
Relative humidity decreases: If the temperature in the room rises due to heating whilst the absolute humidity remains constant, the relative humidity decreases because the heated air can hold more water vapour.
Constant relative humidity: The temperature and absolute humidity are at the same level. The relative humidity is the same indoors and outdoors.
Practical tips for when the air is too dry
- Proper ventilation: Particularly during the winter months, windows in rooms without central ventilation should be opened wide for a short time (intermittent ventilation).
- Measure humidity regularly: It is advisable to measure relative humidity regularly using a hygrometer. The recommended indoor humidity in living and working spaces is between 40 and 60 per cent (at a room temperature of 20 °C).
- Do not overheat: The optimal room temperature is between 20° and 22 °C.
- Add additional humidity: If the air remains below the desired or required relative humidity for a prolonged period, the installation of humidification systems should be considered. Nozzle systems for direct room humidification can also be easily retrofitted in older buildings.
- Note the certificates: The DGUV’s ‘Optimised Air Humidification’ certificate serves as a decision-making aid for selecting suitable air humidification systems. Furthermore, manufacturers should demonstrate compliance with the current state of the art in accordance with VDI 6022 Part 6 and offer corresponding on-site certification of the installed system.
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Side note: Use of ventilation systems
If a central ventilation system is installed, fresh outside air is continuously drawn in, filtered, temperature-controlled and fed into the relevant room. Exhaust vents remove the stale air from the room. The room is thus constantly flushed with fresh air.
Cold air is heavier than warm air and therefore sinks. This results in unpleasant draughts in the workplace. In addition, the conditioned and humidified fresh air introduced via the ventilation system is pushed outwards by the higher thermal pressure. Some of the introduced humidity therefore escapes continuously before it can be sufficiently distributed throughout the room. The desired optimum humidity levels cannot be achieved. Consequently, the air humidification system is constantly activated to reach the set target values.
If windows or skylights are opened, the entire ventilation system becomes unbalanced. When combined with direct room humidification, the desired humidity levels cannot be achieved.
Direct-air humidification works best when windows and skylights are not left open all the time (intermittent ventilation rather than continuous ventilation). Only then can the system effectively humidify the air.
If windows or skylights are opened, the entire ventilation system becomes unbalanced. When combined with direct room humidification, the desired humidity levels cannot be achieved.
Direct-air humidification works best when windows and skylights are not left open all the time (intermittent ventilation rather than continuous ventilation). Only then can the system effectively humidify the air.
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