Hospital regulations and humidity control

With the growth of healthcare facilities in both number and size in recent years, and the design and building of these facilities becoming increasingly sophisticated and technological, their environmental impact and future maintenance becomes a vital factor to be considered. This is the case with most new buildings, however, humidity control in hospitals has always been of the utmost importance as it needs to be especially efficient and hygienic to meet current regulations and guidelines. Historically, only a small number of non-industrial projects, almost exclusively hospitals, were designed by dedicated engineers who were not usually specialized in humidification and dehumidification. Today we have hospitals of many hundreds of beds in every capital and even in smaller towns and cities, therefore, we think that discussing the application of humidity control equipment directly with the professionals who ensure the quality of these critical facilities is the way forward.

The Importance of humidify control

Most hospital regulations require moisture control within certain limits.

These parameters do not result from an exaggerated or unjustified criterion, these values are based on scientific studies from many universities that find moisture values must be within specific boundaries for the health and safety of both people and buildings.

Humidity: bacteria and viruses

Human resistance to infection is reduced at both the upper and lower extremes of humidity. At low humidity, the usually protective nasal mucous membranes in the nose and upper respiratory tract dry out, exposing the living skin to direct contact with infectious organisms. Conversely, when the humidity is high, mould, mildew and fungus is able grow, which can release volatile, odorous, organic gases and sporesr.

Some of these can reduce our body’s immune response and cause respiratory problems and diseases.

Humidity: mites and insects

Asthma and rhinitis are most often observed in buildings with excess moisture in their structure and with high relative humidity in their environment. With a relative humidity of less than 50%, mites and insects have difficulty retaining enough water to reproduce and with a relative humidity of less than 40%, most insects and mites dry up and die.

Relative humidity and static electricity

When friction occurs between two surfaces, there will be an electrical load from the surface atoms stored on both surfaces, creating a potential difference. Most of the time, when both surfaces are connected to ground, these electrical loads discharge quickly, however, if the electrical resistance of the materials is high, sometimes this load will be released, or discharged, on another surface of lower electrical resistance. This discharge is known as an electrostatic energy discharge.

It is of particular importance to avoid these discharges in environments such as operating theatres, where medical personnel work with metallic, electrical instruments on a patient’s body.


Our bodies cool down by dissipating heat that causes sweat to evaporate. At 21°C in winter we can be cold because we evaporate too much, due to low relative humidity. At 23°C in summer we can be hot even in light clothing because we do not manage to evaporate sweat, due to high relative humidity in the environment.

Factor 1 - Correct system selection

The majority of HVAC engineers associate humidification to one or two types of steam production systems: electric humidifiers and evaporative panel equipment. Although these are widely used, they are not the only option. The industry has developed a multitude of systems to suit each need, incorporating the highest standards of hygiene and the lowest operating costs.

  • Electric steam generators using electrode or resistive heaters
  • Direct steam injection systems manufactured with all components in contact with steam in stainless steel. This uses an existing main clean steam supply.
  • Clean steam generators which utilize existing industrial steam or high temperature hot water. This is the optimal choice in installations where there is an existing steam boiler network.
  • Evaporative panel humidifiers or hygiene-certified water atomizers. The purpose of this equipment is to increase the heat recovery performance of the extraction air in a system
  • Steam distribution systems in duct or air conditioning to avoid condensation. This avoids many of the hygiene and energy efficiency problems.

Selecting the right system for each health facility is the first step towards energy saving. The difference in energy expenditure and carbon footprint generated with the optimum selection are incredibly significant.

Factor 2 - Condensation and absortion distance

A high production of condensation in the ducts leads not only to a high energy consumption, but also hygiene problems that can cause unwanted diseases in critical places such as operating theatres or delivery rooms.

Steam conduction

Project designs must specify the layout required, materials necessary, distances involved and any other relevant information. It should also be clear how to manage steam delivery, condensate, and dispersion systems. All of this is case-specific as there are so many possibilities. Systems can be correctly installed when projects are well defined.

There is rarely discussion on how to correctly deliver steam from where it is produced to, the AHU or duct, nor how to correctly distribute steam within these areas. It is essential that installation is efficient, as condensation causes energy loss in the humidifier and water treatment plant. A hygienic installation is also essential as condensation deposited in areas that are not intended to store water can be a source of bacteria, mould and other unwanted fungi or viruses.

Steam dispersion

Absorption distance is the linear distance between the steam dispersion system and the point where no condensation will occur. Solid objects downstream of this point will not get wet if their temperature remains above that of the air they are in contact with. The absorption distance varies, depending on the thermohygrometric conditions of the air, the geometry of the humidifier section and the load. The system we choose will determine whether condensation occurs.

There is a short payback period for recovering the investment in these systems. This is due to their low cost and the significant ongoing savings that can be achieved.

Factor 3 - Importance of water quality

Each geographical location where a humidifier is to be used has a different water quality, and it is this water quality that is key to determining which type of system is suitable and which other elements would benefit the installation. Humidification is the process of transforming water into steam; therefore, it is especially important that we study the type of feed water to the humidifier. High operating costs or breakdowns can occur if we do not have this knowledge.

Water is known as the universal solvent because virtually everything can be dissolved in water. Therefore, water has a different composition depending on geographical location.

These simple parameters we have to understand:

Drinking or sanitary quality water:

Clean drinking water is a minimum requirement for humidification supply water but this alone is not enough. It can contain many dissolved materials. Clean drinking water ensures good steam quality but does not ensure low maintenance or energy efficiency.

Water hardness:

The harder the water, the greater precipitation of minerals will occur when the water evaporates in humidification. This will lead to greater maintenance requirements and higher energy consumption.

Water descaling:

Above a certain level of hardness, it is recommended to use a softener (and maintain it) for fault-free operation and lower operating costs.

Water conductivity:

The higher the conductivity value (µS) the higher the number of ions. This value is key for electrode humidifiers. Below certain values there is not enough conductivity to perform the process and above certain values energy consumption can be too high. Softened water can affect this.

Demineralized water:

Reverse osmosis reduces mineral content almost completely. It is normally used in facilities where water is needed for hygienic and sterilized processes such as most
modern hospitals.

Factor 4 - Control and maintenance


It is particularly important that the three basic operations in the manual are carried out as often as required. Regulation requirements may vary according to location:

According to Spanish regulations (RITE), if the evaporative humidifier or cooler is less than 70kW, maintenance must be performed at the start of every season (end of summer). If it is larger, it should be done monthly.

Fisair offers an extensive technical assistance network, providing international coverage to solve any type of technical query about our product range. For more information please see:


The monitoring systems and control strategies for air humidity control are especially important. They are not usually very well defined. Focus is on the placement of sensors, protection against condensation, communication with the BMS, which variables are to be controlled and within what range. We recommend that the humidifier controller manages the isothermal humidification and communicates with the BMS for the specifics that are important to you, through digital signals and shared readings.

Control points to monitor:

  • Measurements must be checked in the right place
  • Appropriate choice of the variable to be controlled: %RH or °Cdp (dew point temperature)
  • Use of the appropriate sensors
  • Use of sensors that prevent condensation.

Some application references

Hospital de Son Espases, Mallorca.

More than 120 humidifiers with steam dispersion systems, providing clean steam with minimized absorption distance from a combustion-based, gas-fired heat plant.

Torrejón Hospital, Madrid

Marienhospital, Stuttgart

Hygienic steam direct injection systems with construction of all system components in stainless steel.

Other hospitals where these or other solutions were installed:

  • Hospital Clínico Universitario La Paz (Madrid)
  • Donauisar Klinikum (Bamberg)
  • Klinicki Centar Banja Luka, Hospital (Serbia)
  • Hospital Vall d’Hebrón (Barcelona)
  • Hospital Universitario de León
  • Hospital de Salamanca
  • Hospital Son Dureta
  • Hospital de Toledo 
  • Clínica Universitaria Navarra (CUN)  
  • Hospital de Cruces (Bilbao) 
  • Lahn-Dill-Klinikum, Wetzlar, Alemania  
  • Krankenhaus St. Joseph-Stift, Dresden, Alemania  
  • Klinikum (Oder), Frankfurt, Alemania  
  • UKE Kinderklinik, Hamburgo, Alemania  
  • Klinikum Hardenberg, Georgsmarienhütte, Alemania  
  • CIO (Centrum f. integrierte Onkologie), Köln, Alemania 
  • Uni Klinik Ffm, Frankfurt, Alemania  
  • Kreiskrankenhaus, Aichach, Alemania 
  • KH St. Anna Höchstadt, Höchstadt, Alemania 

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