| What is Humidity? |
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Water vapour in the air |
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Dew point (in °C or °F) tells us:
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at what temperature condensation will occur, if the air is cooled
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a measure of how much water vapour it holds in absolute terms
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Relative humidity (in %rh) tells us:
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Saturation of the air from 0-100%
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Other units
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Wet Bulb, WB
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Dry-Bulb, DB
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| The need for humidification. |
Water not only covers most of the Earth's surface as oceans, lakes and rivers; it is also a major element in the atmosphere, in its gas form - humidity. Variations in the humidity of ambient air can have undesirable or harmful effects upon surrounding objects. Objects either absorb or give up water content until a point of equilibrium with its environment is reached. Objects such as paper, wool, cotton, tobacco, timber, furniture, plants, animals and even people are affected by relative humidity. Dry atmosphere can cause textiles carpet, wood paper, leather, plastics etc. to shrink, harden, crack, spoil and lose weight. Results can be damaging, expensive and uncomfortable.
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The science of humidification has evolved to compensate for undesirable humidity levels. The benefits of humidification are numerous.
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Increase employee comfort and productivity
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Protect valuable furnishings and art
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Provide the environment for specific processes
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Maintain materials in a required condition
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Reduce incidence of static electricity
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Reduce the likelihood of airborne virus distribution
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| The role of temperature |
Temperature is clearly the most important comfort factor, including radiant temperature (for example influence of the sun). Large differentials in temperature increase comfort ‘complaints’. Draughts increase heat dissipation from the body.
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| The important role of humidity |
Humidity affects the rate at which the body loses heat by evaporation. In hot weather, high ambient humidity reduces comfort levels by limiting the body’s ability to reduce temperature (low differential in body to air water vapour pressure).
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Typical Humidity Requirements. Application % rh
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Museums/Libraries 40-55
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Art Storage 45-50
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Printing 43-50
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Textile 50-60
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Office buildings 20-30
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