Dehumidifiers and Humidity Control in Archives and Libraries

Q: What is the best type of humidifier for archive stores?

Typically archives have a very low air change rate so normally systems with a low duty are adequate. For accurate control, a resistive heater steam humidifier rather than an electrode boiler is the preferred solution. This type of humidifier can be fitted with a room distribution fan if there is no central ducted air handling system.

Q: What is the ideal humidity for an archive?

The ideal humidity will be dependent on two aspects, the objects being stored and the temperature stability of the store. For organic items, such as paper, wood and textiles, the ideal will be between 35 and 60%RH within a temperature range of 13 to 20°C. For inorganic items, like metal, the lower range of 11 to 45%RH would typically be ideal.

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Benefits

Proper humidity control in archives, libraries and long-term storage is vital for many reasons.

Preservation of materials

Keeps paper, books, textiles, and artefacts safe from mould, warping and brittleness.

Prevents pests and insects

Deters infestations that could destroy archival materials.

Ensures long-term stability

A consistent environment helps deliver decades and centuries of conservation

Dehumidifiers and humidity control in archives and storage areas

Preventing excessive humidity protects delicate materials such as paper, textiles, wood and leather from damage through moisture absorption, dimensional changes, as well as mould growth. Many pests thrive in humid conditions, such as booklice, silverfish and carpet beetles. This can damage a collection through feeding on archived materials and leaving droppings.

Magnetic and optical media are highly vulnerable to corrosion and data loss in humid conditions. Mould can also pose a health risk to staff and visitors, as well as damage the building fabric through condensation and corrosion.

Condair’s dehumidifiers help leading archives worldwide protect collections by controlling humidity and ensuring long-term preservation.

Humidification and humidifiers for archives

In cold climates, heated indoor air can have very low humidity, which poses a risk to many natural materials. Paper will lose moisture to dry air, shrink and become brittle. Distortions in leather, parchment and textiles can mean book bindings lose their integrity, especially when combined with drying of adhesives.

As static increases in low humidity, electro-sensitive materials like film are put at increased risk in dry conditions.

International standards, such as ISO 11799:2015, reinforce the need to control humidity at levels appropriate for the materials in question and the local climate. It also prioritises minimising fluctuations, as rapid changes in humidity can have the most detrimental impact. Institutions such as the Smithsonian Institution Archives and the National Archives and Records Administration both recommend a minimum humidity of 30%RH, whilst avoiding fluctuations greater than 5%RH in any 24-hour period.

Energy-efficient environmental control

Heating alone is often mistakenly used to reduce relative humidity but does not lower the absolute moisture in the air, leading to high running costs. Dehumidification directly removes water vapour, delivering up to 60% energy savings compared to heating-only strategies. This makes long-term preservation both cost-effective and sustainable.

Use cases for archives

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Projects and references

National Army Museum, UK

The National Army Museum is the leading authority on the British Army and its impact on society past and present. Condair has supplied and installed three Condair RS resistive steam humidifiers to maintain the humidity around the exhibits and archives.

Rijksmuseum, Netherlands

The Rijksmuseum is one of the world's finest art museums with over 1.5km of galleries and artworks by Rembrandt, Vermeer and Van Gogh. The Condair DL hybrid humidifier is maintaining the ideal humidity for the preservation of paintings such as The Night Watch, The Milkmaid and The Merry Drinker.

ARoS Aarhus Art Museum, Aarhus

Condair DL hybrid humidifiers ensure optimal indoor humidity at The ARoS Aarhus Art Museum, protecting over 1,100 paintings and 400 sculptures.

Precise humidity protects millions of books at Bibliothèque Nationale de France

As one of the most recognisable and symbolically powerful architectural landmarks of contemporary Paris, the Bibliothèque nationale de France (Site François-Mitterrand) sets new standards in cultural design, monumental scale and preservation of knowledge. Condair is proud to contribute to this visionary institution with advanced hybrid humidification solutions that protect priceless collections, ensure visitor comfort and guarantee energy-efficient climate control.
Preserving millions of books, manuscripts, maps and artefacts demands rigorously stable climatic conditions. Optimal relative humidity “crucial for preventing damage to paper, bindings and other organic materials“ is reliably maintained by Condair DL hybrid humidifiers.

Quotes from our customers

Ceilite Air ConditioningTim CheshireApplications Engineer Technical Manager

We required an efficient and effective method of humidification that could safely raise relative humidity (RH) in a large archive store for priceless artwork – vital requirements that were successfully met by Condair. There were some challenges posed by the space to work in and the infrastructure of the building, but the excellent installation team overcame the issues without any complaint.

Would I specify Condair’s humidifiers again? Yes, without hesitation.

Olaf Gulbransson Museum, Tegernsee (Germany)Sandra WiedemannResearch Assistant

"We don't have to worry about anything now – that's a great relief compared to before. For us, the DRAABE air humidification system is the optimal solution."

Downloads

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Frequently asked auestions

What is the best type of humidifier for archive stores?

What is the ideal humidity for an archive?

What kind of dehumidifier is best for an archive store?

There are two main types of commercial dehumidifier - condensing and desiccant.

Condensing dehumidifiers operate well provided the store temperature is above 20°C and typically less than 35°C. Humidity levels above 45%RH up to 95%RH are achievable with this technology. Low relative humidity, less than 40% is more difficult to achieve with condensing dehumidifiers, desiccant dehumidifiers are required here .Condensing dehumidifier system have an overall control accuracy of around +/-10%RH. Condensing dehumidifiers either require a drain connection or daily maintenance to empty the condensate tanks. Desiccant dehumidifiers can control to +/-2% , they dont need a drain but do require a exhaust duct to remove the wet air

Desiccant dehumidifiers have a much wider range of operation in terms of temperature, -30°C to +40°C and relative humidity 0-100%. They can achieve much lower relative humidity levels, at less than 10%RH if required, and provide a much more stable overall control, typically +/-2%RH or better. There is no need for a drain connection but a ducted wet air vent is required, to exhaust the moisture externally away from the area being treated.

Why is it so important to control humidity in an archive?

Items made from organic material, such as paper, wood and textiles, will react to changes in humidity and physically change shape. Repeated change as the relative humidity fluctuates will cause structural damage to the item. Additionally, being organic there is a high risk of mould formation at higher humidity levels.

With inorganic items, such as iron or steel, the rate of corrosion (rust formation) is directly proportional to the humidity level. The rate of corrosion can be up to six times greater at 90%RH compared to that at less than 50%RH.

Will heating alone keep an archive dry?

Heating alone will not keep an archive dry. Whilst it will certainly reduce the relative humidity it does not reduce the absolute humidity. Absolute humidity is the mass of water per unit volume of air.Heating will also not change the condensation Dew Point temperature , this is a critical value as its the point where liquid water can form on the object surface.

To “dry” an archive it is necessary to reduce the absolute humidity by physically reducing the quantity of water in the air. This can only be achieved by use of a dehumidifier. Heating alone has a much higher running cost.

Use of a dehumidifier will typically result in a 60% reduction in energy consumption compared to direct space heating."

Get Free Expert Advice

If you want to explore your options for humidity control, Condair's expert sales engineers will visit your site, review your project and talk you through their recommendations.

Alternatively, if you would prefer a call or online meeting, our team are always happy to discuss possible solutions and offer free technical advice.