CUOGHI SRL

HUMIDIFIERS & DEHUMIDIFIERS

Via Garibaldi, 15 Zona Industriale
35020 Albignasego (PADOVA) ITALY
Tel +39.049.8629099
Fax +39.049.8629135

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Humidity

The air around us is a mixture of gases, composed mainly of nitrogen, oxygen and small percentages of other gases and water vapour. The latter is the principle cause of humidity in the air and is very important for the environment, for our well-being and for the good preservation of all materials.

Water vapour is water that has been transformed into gas and as such is colourless, odourless and tasteless and invisible. Unlike the other gases in the atmosphere, it is present in extremely variable quantities, depending on many factors such as pressure, temperature and the nature of the surrounding environment. Indeed, it may be noted, that during the day the temperature in the desert reaches very high levels (50°C), and the humidity drops to very low levels (15 - 20%).

In a tropical forest, instead, with a very high temperature (40°C) the humidity is also very high (80 - 90%). It may be said that the air is greedy for water vapour, absorbing it from any material available, as well as from people, animals and plants: the more the water the environment has the more humidity there will be. The air, however, cannot absorb water vapour indefinitely. Indeed, if the amount of vapour exceeds a given value, called its saturation point, no more water vapour can be absorbed by the air and it even tries to expel the excess giving rise to the phenomenon known as condensation, i.e. the transformation of vapour into water.

Examples of this phenomenon are the clouds in the sky, the "smoke" coming out of a saucepan, the steaming up of glass, the breath we see coming from one's mouth on cold days etc. All other conditions being equal, the higher its temperature the more vapour the air is capable of retaining. A kg of air at atmospheric pressure and at a temperature of 0°C can only retain 3.8 g of vapour whereas the same quantity of air at 30°C is capable of storing up to 27.4 g of vapour, i.e. 7.2 times more.

Humidity is measured with special instruments called hygrometers or, more technically, psychrometers that give us the percentage in the air. When the instrument reads 100% the air is saturated.
To assess the conditions of the air at various temperatures and the humidity content there is a diagram well-known to all heat technicians called the psychrometric diagram or Mollier's diagram.

Generally, the percentage of humidity present is higher in cooler environments such as cellars or underground or basement rooms. For example, if the outdoor temperature in summer is 28°C and the humidity 70%, a cellar could have a temperature of 22°C. In this case the humidity would be 100% and there would be excessive condensation seeing that the air has reached saturation. The opposite happens in heated rooms. For example on a rainy winter day the outdoor temperature could be 2°C and the humidity 90%. At the same the humidity in a flat heated to 20°C would be about 28%!

There are rooms where, independently of other conditions, the humidity tends to be excessive. This is the case, for example, of those rooms where sports activities are carried on, in locker rooms with showers, in swimming pools, in hairdressing salons, in restaurants, in kitchens, in dance halls, in ironing rooms, laundries, etc.

Having understood what humidity is, let us see why it is so important for our well-being.

Our body is a very delicate machine which, to function properly, must maintain its internal temperature as constant as possible. When the temperature increases, it reacts with various countermeasures which would require a ponderous medical treatise to explain in full.

We will limit ourselves in observing that the main way of expelling excess heat is through the skin.
When a greater quantity of heat is to be expelled perspiration comes into play: the skin is made humid by the perspiration which, when it comes into contact with the air, tends to evaporate.

Evaporation requires a large amount of heat which is taken from the skin and so also from inside the body, which can thus re-establish the correct temperature. All this is very efficacious if the humidity in the air is low enough to guarantee rapid evaporation of the perspiration and therefore efficient cooling. Otherwise the perspiration stays on the skin and the body temperature increases causing a sensation of tiredness typical of stuffy days. Excessive perspiration also causes a loss of mineral salts that further aggravate the situation.

Low humidity also can be harmful since excessive evaporation can irritate the mucous membranes of the nose and bronchi.
Following recent studies, for a person engaged in sedentary activity and wearing light clothes, the ideal conditions of well-being occur when the environmental temperature is between 23...25°C, and the relative humidity is between 40...60%

Most of the materials are also sensitive to humidity. Because of excessive humidity metals tend to oxidise, leather, fur coats, fabric get mouldy, not to mention certain food products, furniture, paintings, frescos which deteriorate faster, and because of the moulds the rooms become unhealthy.

In other cases, instead, it is the lack of humidity that may create problems. This is, for example, the case of textile industries where, if the air is too dry the threads used for weaving become fragile and so the machines cannot operate at the right speed, or again, the large refrigerator warehouses which store vegetables or fruit which, when there is a lack of humidity, lose weight and wither away. A low percentage of humidity favours the formation of electrical charges that, besides causing the well-known "shock" when metal parts are touched, can also cause various other inconveniences in some industrial processes..
Other situations requiring a high percentage of humidity are the hothouses for growing flowers or mushrooms, etc.
At this point it is clear that very often humidity control is necessary not only for the well-being of human beings but also for technological needs.
To control air humidity, studies have been conducted on appliances that can produce humidity (HUMIDIFIERS), as well as appliances for reducing it (DEHUMIDIFIERS) and instruments capable of controlling the humidifiers and dehumidifiers to maintain the desired environmental humidity constant (HUMIDISTATS).
Air humidifiers can be divided into two main categories:

Adiabatic humidifiers
Steam humidifiers

Air dehumidifiers also are divided into two main categories:

Cooling cycle dehumidifiers
Absorption dehumidifiers

The choice of the appliance most suitable for a particular application depends on different factors, both environmental and technological and so it must be chosen with the help of an expert technician skilled in the field.