Basics

High Pressure
Low Pressure

Adiabatic Cooling
Accessories

Index
Home 

The Physics of Humidification

back to Overview

basic Physics

relative
Humidity

Dew Point

Evaporation Cooling

Air Movement

Watering with Fog

Frost Protection

Relative Humidity

What does "Relative Humidity" really mean ?

One of the major properties of the air around us is the ability to contain water in the form of vapour.
The air surrounding us is never really dry - it contains more or less water vapour. This amount of water, measured usually in grams per cubicmeter or in grams per weight (g/kg) depends strongly on the temperature of the air.
Hot air can take up more water vapour, cold air less.
The maximal amount of water vapour which air of a certain temperature can contain is called the "Saturation Amount". This means that air at a certain temperature carries 100% of the amount of water is can possibly contain - it is "saturated".
The saturation amount depends on the temperature. Values for the saturation amount have been determined experimentally and can be looked up in so-called "Water-Tables".
 

Example 1:
1 m air at a temperature of +30C has a saturation amount of 30,39 g water / m, whereas 1m water at a temperature of +3 can carry only 5,9 g water.
Usually the air around us is not really saturated; sometimes it is crisp and dry, sometimes hot and humid.
The well-being of all organic life - plants, animals and people - depends on the degree of saturation of the surrounding air. In all cases the amount of moisture in the air can be given only as a relative figure - depending on the saturation amount of the current temperature.

Example 2 from real life:
Weather forecast Vienna, Austria, 30. August, 12:00 hrs:
Air temperature +30C, relative moisture 65%

Air at +30C has a saturation amount of 30,39 g/m, 65% of this value are currently there,
which means 30,39 x 0,65 = 19,75 g/m
 

Some recommended values derived from practical experiences: 

    Application

    Relative Humidity

    96% to 60%

    Climatization in conservatories of Botanical Gardens
    (warm- and cold houses)

    85%

    90 - 94%

    75 - 85%

    for people indoors - for instance Hospitals

    52 - 55%

    Print Shops, Paper Storage

    55 - 65%

basic Physics

relative
Humidity

Dew Point

Evaporation Cooling

Air Movement

Watering with Fog

Frost Protection

The Physics of Humidification

back to Overview

home

last modified MAR 2013
Copyright 1990 - 2015 by Plantfog - Ing. Manfred Dolejsi - all rights reserved