Temperature and Relative Humidity: How do I put all this into practice?

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Category: Environments
Posted by Conservation Answers(Questions:33:Answers28)
Answered On 25 February, 2014 12:28 am

When it comes to putting all of this information into practice in your own museum, there are a number of practical things you can do. Consider some of the following measures.

  • Assess what your collection needs and determine how vulnerable the contents are to environmental conditions. If, for example, your collection consists entirely of porcelain and glass items in pretty good condition, then controlling temperature and relative humidity will be less of a priority for you than, say, implementing safe handling procedures and reducing vibration in display cases. If your collection is primarily coins, then maintaining conditions of low relative humidity will be important to prevent corrosion.
  • Monitor key areas of the museum, such as the exhibition spaces and storage areas, over a continuous period of time throughout the year, through at least one change of seasons.
  • Identify the areas in your museum that need attention and consider ways in which they can be improved. You may have to prioritise this list as action may be dependent on availability of funds, staff and resources.
  • Assess what maintenance or improvements can be made to your building to buffer the internal environment.
  • Create microclimates for sensitive items by using, for example, display cases and storage boxes.


A frequently suggested method of controlling temperature and relative humidity levels is through the use of air-conditioning. In most of the main texts, this refers to a full system of environmental control in which both the temperature and the relative humidity can be set to prescribed limits. These require a substantial investment in both up-front design and installation costs and ongoing running and maintenance costs.

It is worth remembering that most of the systems commonly in use are designed for human comfort and assumed to be required only during the normal operating hours of the building. Systems designed for the protection of collections will require more detailed specifications in the brief to the architect, engineer and builder, and may be required to operate continuously. The actual times of operation will depend on the design of the building. A carefully designed building may only require the system to operate part of the time, while still ensuring optimum conditions. As mentioned at the start of the temperature and relative humidity section, this is a complex area of museum planning and cannot be covered adequately within the scope of this subject.

There are also 'stand alone' type heating and cooling systems available. The drawback with most of the basic models is that they do not reliably deliver stable conditions of relative humidity. They are designed simply for human comfort and can have an adverse effect on collections by either putting excess moisture into the air, as can occur with evaporative systems, or by over drying the air, as can occur with cooling coil systems.

If you have air-conditioning or you are considering installing air-conditioning, as part of your planning processes we recommend you:

  • understand what conditions you are trying to rectify, (for example, are you trying to reduce the relative humidity or to increase it?) and specify this in the brief to the engineer
  • ask the engineer to outline how the system will operate to deliver the required conditions
  • monitor the performance of the system by continually measuring the temperature and relative humidity using recording instruments such as thermohygrographs or dataloggers

The cost of purchasing, operating and maintaining an air-conditioning system is high. If not adequately maintained and operated, it can cause more severe fluctuations in temperature and relative humidity than having no system at all.


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