Moisture content of air on temperature. Relative humidity

Humidity is the amount of water vapor in the atmosphere. This characteristic largely determines the well-being of many living beings, and also affects the weather and climatic conditions on our planet. For normal operation human body it must be within a certain range, regardless of the air temperature. There are two main characteristics of air humidity - absolute and relative:

Periodic winds include monsoons and breezes. If we compare the pressure of the continent and the adjacent ocean, we can see that the pressure on the continent is higher in winter and, conversely, lower during the summer. Therefore, in winter, the wind blows from the mainland to the ocean, and in summer the opposite happens, which leads to a summer mousse that carries moisture and frequent rains. Monsons affect more or less all continental masses except Antarctica; are typical areas of the monsoons of India, the eastern coasts of Asia and others.

A similar phenomenon occurs when dealing with breezes; they may be seas, mountains, valleys, lakes, and subject to mutual pressure differences due to the proximity of day and night. For example, since the land is warmer than the sea during the day and colder at night, coastal regions have a breeze of daytime sea blows blowing from sea to land and another night that blows in the opposite direction.

  • Absolute humidity is the mass of water vapor contained in one cubic meter of air. The absolute humidity unit is g/m3. Relative Humidity is defined as the ratio of the current and maximum values ​​of absolute humidity at a certain air temperature.
  • Relative humidity is usually measured in%. As the temperature increases, the absolute humidity of the air also increases from 0.3 at -30°C to 600 at +100°C. The value of relative humidity depends mainly on the climatic zones of the Earth (middle, equatorial or polar latitudes) and the season of the year (autumn, winter, spring, summer).

There are auxiliary terms for determining humidity. For example, moisture content (g/kg), i.e. weight of water vapor per kilogram of air. Or the temperature of the "dew point", when the air is considered to be completely saturated, i.e. its relative humidity is 100%. In nature and refrigeration technology, this phenomenon can be observed on the surfaces of bodies whose temperature is lower than the dew point temperature in the form of water droplets (condensate), frost or frost.

With a similar mechanism, monsoons and breezes differ only in the length of the cycle; for the monsoons, the cycle is identified with the change of the seasons, for the breezes, with the change of day and night. Finally, local winds are those that blow in special zones of the earth's surface due to equally special reasons, not obeying a certain rhythm.

Such, for example, are the famous northern outskirts, the mistral of the Levant, embarrassment, Tramontana. etc. and many others that do not have much regularity in different areas of the globe. Special winds spin tropical cyclones, famous typhoons Indian Ocean and the seas of China and the hurricanes of the West Indies; other winds are called thunder blasts, those that rise in a whirlwind.

Enthalpy

There is also such a thing as enthalpy. Enthalpy is a property of a body (substance) that determines the amount of energy stored in its molecular structure, which is available for conversion into heat at a certain temperature and pressure. But not all energy can be converted into heat, because. part of the internal energy of the body remains in the substance to maintain its molecular structure.

If air is analyzed vertically to the ground, large differences in temperature, pressure, and moisture content are often found; but if the analysis is carried out horizontally, the characteristics of the air mass are generally the same. At any latitude, air masses are of two main types: those that form on Earth and those that form at sea.

The differences between the two are primarily due to the fact that the land heats up faster than the sea, but also cools faster. In tropical regions in winter, the hot land produces a continental mass of warmer air and drier than the mass of tropical maritime air. At high latitudes, the polar continental air mass has lower temperatures in winter than the polar maritime air mass.

Moisture calculation

Simple formulas are used to calculate humidity values. So, absolute humidity is usually denoted p and defined as


p = m aq. steam / V air

where m water. steam - mass of water vapor (g)
V air - the volume of air (m 3) in which it is contained.

The generally accepted notation for relative humidity is φ. Relative humidity is calculated using the formula:

Continental air masses can move across the sea, and sea air masses can do so on continents. This fact causes changes in the air masses, especially in the fall index. The air at ground level is usually warmer than the air in the upper layers.

In warm regions, the rate of fall is high, and the lower layers containing evaporated moisture increase in convective currents. However, in cold regions, the fall rate is low and there is little vertical air movement. Spain trip - desert cruise. Huge expanses are covered with scrubs and small plants that cover the marble floor. There are trees in the sierras, but no trees when we descend into the plains, which stretch without them to the horizon.


φ \u003d (p / p n) * 100%


where p and p n are the current and maximum values ​​of absolute humidity. The value of relative humidity is most often used, since the state of the human body is largely affected not by the weight of moisture in the volume of air (absolute humidity), but rather by the relative water content.

Humidity is very important for the normal functioning of almost all living beings and, in particular, for humans. Its value (according to experimental data) should be in the range from 30 to 65%, regardless of temperature. For example, low humidity in winter (due to the small amount of water in the air) leads to drying out of all mucous membranes in a person, thereby increasing the risk of colds. High humidity, on the contrary, worsens the processes of thermoregulation and sweating through skin. This creates a feeling of suffocation. In addition, maintaining air humidity is an important factor:

We need trees, in Spain, fifteen billion trees. Trees fulfill many missions that people have, in addition to their own life which we must develop, maintain and care for the very fact of the existence of living beings.

Trees keep the soil in place. On bare slopes, heavy rains that we already have and will continue to have in Spain, drag the soil without significant adhesion to the subsoil. A hill full of trees achieves two effects against the mechanical impact of rain: its leaves slow down the speed of the fall of water, and with it the force of its impact on the ground, and the roots increase the adhesion of the surface layer from the ground to the bowels. The forest creates fertile soil over the years.

  • for carrying out many technological processes in production;
  • operation of mechanisms and devices;
  • safety from destruction of building structures of buildings, interior elements made of wood (furniture, parquet, etc.), archaeological and museum artifacts.

Enthalpy calculation

Enthalpy is the potential energy contained in one kilogram of moist air. Moreover, in the equilibrium state of the gas, it is not absorbed and is not emitted into the external environment. The enthalpy of moist air is equal to the sum of the enthalpies of its constituent parts: absolutely dry air, as well as water vapor. Its value is calculated according to the following formula:

Trees store water in the soil and allow it to seep into underground aquifers. When it rains, the water, instead of running downhill, instead of producing a sudden runoff, is deposited in small depressions between the roots and gradually seeps down to soak the ground and then circulate towards aquifers protected from excessive evaporation.

Trees evaporate a small part of the water collected by their roots. Evapotranspiration, which is called a phenomenon, depends on tree species in its volume per unit of time. But trees evaporate water, and this is extremely important. Well, the real systems of nature are non-linear, like "the rich get richer and the poor get poorer." Rain on the Earth's surface is a critical phenomenon: the atmosphere needs to have more than a certain concentration of water vapor, the amount of water vapor per centimeter or cubic meter, so that the water can condense and precipitate.


I = t + 0.001(2500 +1.93t)d


Where t is the air temperature (°С) and d is its moisture content (g/kg). Enthalpy (kJ/kg) is a specific quantity.

Wet Bulb Temperature

The wet bulb temperature is the value at which the process of adiabatic (constant enthalpy) saturation of air with water vapor takes place. To determine its specific value, an I - d diagram is used. First, a point corresponding to a given state of air is applied to it. Then an adiabatic ray is drawn through this point, crossing it with the saturation line (φ = 100%). And already from the point of their intersection, the projection is lowered in the form of a segment with a constant temperature (isotherm) and the temperature of the wet bulb is obtained.

This concentration is called absolute humidity, and condensation occurs when the absolute humidity exceeds a critical threshold, when the absolute humidity divided by the temperature-dependent threshold humidity exceeds 100%. The threshold humidity is very high when the temperature is high and very low when it is low. The place on Earth with the highest concentration of water vapor in summer is the air above the Sahara desert, but there is no rain because there. relative humidity is very low.

However, say in Asturias, the absolute humidity in summer is low, but it rains because the air temperature is low. Well, it usually requires increasing a few grams of vapor in the air to get saturated so that the relative humidity reaches 100%, corresponding to its temperature. In Spain, it often happens that the air, filled with moisture over the sea or over a swamp, moves on land and begins to rise and cool. But it's not rain because the water vapor was in equilibrium with saturation on the water, but low at 100% when it arrived on land as the hot soil warms the air.

The I-d diagram is the main tool for calculating / plotting various processes associated with a change in the state of air - heating, cooling, dehumidification and humidification. Its appearance greatly facilitated the understanding of the processes occurring in systems and units for air compression, ventilation and air conditioning. This diagram graphically shows the complete interdependence of the main parameters (temperature, relative humidity, moisture content, enthalpy and partial pressure of water vapor) that determine the heat-humidity balance. All values ​​are specified at a specific value atmospheric pressure. Usually it is 98 kPa.

If the slopes are free of trees, the air rises and returns to the sea or swamp without condensation. But if the slopes are full of trees, the small amount of grams that their leaves evaporate is enough to reach a relative humidity of 100% and the formation of condensation and precipitation.

We have a positive case of non-linear feedback: the rich get richer. Forests that need water stimulate precipitation which allows them to grow. The older they are, the more water they evaporate and the more they get from the rain. In Spain, the main mentality comes from the centuries of La Mesta. Part of Spain's economy was sheep's wool, and sheep need grass that doesn't grow well in the forest. Then came mines, Rodalquilar in Almeria, Huelva and Seville, Almaden and many others: They need wood for galleries, to heat ore, for railway sleepers.

The diagram is made in the system of oblique coordinates, i.e. the angle between its axes is 135°. This contributes to an increase in the zone of unsaturated moist air (φ = 5 - 99%) and greatly facilitates the graphic drawing of the processes occurring with the air. The diagram shows the following lines:

  • curvilinear - humidity (from 5 to 100%).
  • straight lines - constant enthalpy, temperature, partial pressure and moisture content.

Below the curve φ \u003d 100%, the air is completely saturated with moisture, which is in it in the form of a liquid (water) or solid (hoarfrost, snow, ice) state. It is possible to determine the state of air at all points of the diagram, knowing any two of its parameters (out of four possible). The graphic construction of the process of changing the state of air is greatly facilitated with the help of an additionally plotted pie chart. It shows the values ​​of the heat-humidity ratio ε at different angles. This value is determined by the slope of the process beam and is calculated as:

The forests were cut down, and each harvest increased the drought: the poor became poorer and poorer. Today we can plant trees again on our lands. The huge Cerro Rico del Potosí mine in Bolivia, the origin of the silver of the Spanish armies and what the government of the Austrian Islands spent before it arrived in Spain lasted 200 years.

Deserts, once created, if not managed, have lasted for thousands of years. We can solve the rain problem in Spain at a very low cost. We can plant, as Joaquín Araujo suggests, billions of trees. Today, planting a tree can cost around 1 euro. 000 million trees a year for 4 years or a billion for 15 years is money that is not visible in a million million annual budget and is wealth for everyone and for hundreds or thousands of years. If you would like to do any scientific research, please submit your question.

where Q is the heat (kJ/kg) and W is the moisture (kg/h) absorbed or released from the air. The value of ε divides the entire diagram into four sectors:

  • ε = +∞ … 0 (heating + humidification).
  • ε = 0 … -∞ (cooling + humidification).
  • ε = -∞ … 0 (cooling + dehumidification).
  • ε = 0 … +∞ (heating + dehumidification).

Humidity measurement

Measuring instruments for determining relative humidity values ​​are called hygrometers. Several methods are used to measure air humidity. Let's consider three of them.

One of the typical characteristics of the Brazilian winter in most of the national territory is the predominance of dry air inland, which makes precipitation difficult. In the south and southeast of the country, as well as in the Center-West part, there are even heavy rains, sometimes intense and temporary, due to the passage of frontal systems. After the passage of a cold front, it is very common for a mass of colder and drier air to last for several days, again making it difficult to rain. So, in general, in most of Brazil, winter is synonymous with dry weather.

  1. For relatively inaccurate measurements in everyday life, hair hygrometers are used. In them, the sensitive element is a horse or human hair, which is installed in a steel frame in a taut state. It turned out that this hair in a fat-free form is able to sensitively respond to the slightest changes in the relative humidity of the air, changing its length. As the humidity increases, the hair lengthens, and as it decreases, on the contrary, it shortens. The steel frame, on which the hair is fixed, is connected to the arrow of the device. The arrow perceives the change in the size of the hair from the frame and rotates around its axis. At the same time, it indicates the relative humidity on a graduated scale (in %).
  2. For more accurate thermotechnical measurements during scientific research, condensation-type hygrometers and psychrometers are used. They measure relative humidity indirectly. The condensation type hygrometer is made in the form of a closed cylindrical container. One of its flat covers is polished to a mirror finish. A thermometer is installed inside the container and some low-boiling liquid, such as ether, is poured. Then, with a manual rubber diaphragm pump, air is pumped into the container, which begins to circulate intensively there. Because of this, the ether boils, lowers the temperature (cools) the surface of the container and its mirror, respectively. Drops of water condensed from the air will appear on the mirror. At this point in time, it is necessary to record the readings of the thermometer, which will show the temperature of the "dew point". Then, using a special table, the corresponding density of saturated steam is determined. And according to them, the value of relative humidity.
  3. A psychrometric hygrometer is a pair of thermometers mounted on a base with a common scale. One of them is called dry, it measures the actual air temperature. The second is called wet. The wet bulb temperature is the temperature that humid air takes when it reaches a saturated state and maintains a constant air enthalpy equal to the initial one, i.e. this is the limiting temperature of adiabatic cooling. At the wet bulb thermometer, the ball is wrapped in a batiste cloth, which is immersed in a container of water. On the fabric, water evaporates, which leads to a decrease in air temperature. This cooling process continues until the air around the balloon is completely saturated (i.e. 100% relative humidity). This thermometer will show the "dew point". On the scale of the device there is also a so-called. psychrometric table. With its help, according to the dry bulb and the temperature difference (dry minus wet), the current value of relative humidity is determined.

Humidity regulation

Humidifiers are used to increase humidity (humidify the air). Humidifiers are very diverse, which is determined by the method of humidification and design. According to the method of humidification, humidifiers are divided into: adiabatic (nozzle) and steam. In steam humidifiers, water vapor is formed when water is heated on the electrodes. As a rule, steam humidifiers are most often used in everyday life. In ventilation and central air conditioning systems, humidifiers of both steam and nozzle types are used. In industrial ventilation systems humidifiers can be placed both directly in the ventilation installations, and as a separate section in the ventilation duct.

The amount of water vapor that air can hold before it condenses depends on the temperature of the air itself: the warmer the amount of water vapor that the air can carry without condensing. When the air condenses and forms a fog or cloud, the relative humidity of the air is 100% since it is already saturated, meaning it already has all the water vapor it can hold at that temperature. adding more water vapor, the amount of vapor that the air carries before condensing also increases, and hence the relative humidity of the air drops.

Most effective method removal of moisture from the air is carried out using compressor-based refrigeration machines. They dehumidify the air by condensing water vapor on the cooled surface of the evaporator heat exchanger. Moreover, its temperature should be below the "dew point". The moisture collected in this way is removed by gravity or with the help of a pump to the outside through the drainage pipe. Exist various types and appointments. By type, dehumidifiers are divided into monoblock and with a remote condenser. According to their purpose, dryers are divided into:

In most cases, this happens in most parts of the country in winter: with sparse precipitation and long periods of drought, there is little water in the atmosphere, with few clouds, the air temperature near the surface rises and holds more and more water vapor, which, however, does not occur anywhere else. Thus, during the hotter periods of those days with little or no cloud cover, the relative humidity of the air "falls".

Dry air causes discomfort in the eyes, nose, lips and airways by drying the mucous membranes. Dry mucous membranes are more sensitive and therefore prone to irritation, especially if they are scratched. Resected mucosae are also more susceptible to microbursts, making them more vulnerable to the entry of viruses and bacteria that can develop infection of varying intensity. In addition, most viruses and bacteria survive longer in a dry environment.

  • household mobile;
  • professional;
  • stationary for swimming pools.

The main task of drainage systems is to ensure the well-being of people inside and the safe operation of structural elements of buildings. It is especially important to maintain the humidity level in rooms with increased moisture release, such as swimming pools, water parks, baths and SPA complexes. The air in the pool has high humidity due to the intensive processes of water evaporation from the surface of the bowl. Therefore, excess moisture is the determining factor for. Excess moisture, as well as the presence of aggressive media in the air, such as chlorine compounds, have a devastating effect on the elements of building structures and interior decoration. Moisture condenses on them, causing mold growth or corrosion damage to metal parts.

Therefore, in winter, the prevalence of colds and flu is more common. Dry air is more likely to cause opportunistic infections such as conjunctivitis. Allergic diseases of the respiratory tract are also relieved, and the more dusty environment greatly disturbs the nose and eyes. With warmer temperatures and rather dry air, as is the case in most winter interiors of the country, perspiration is facilitated and perspiration fluid is easily lost through perspiration. Thus, when implementing exercise in dry conditions the risk of dehydration is high, causing changes in blood pressure, changes in heart rate, possible headaches and, in more severe cases, dysentery, fainting, etc.

For these reasons, the recommended value of relative humidity inside the pool should be maintained in the range of 50 - 60%. Building structures, in particular walls and glazed surfaces of the pool room, should be additionally protected from moisture falling on them. This can be realized by supplying a stream of fresh air to them, and always in the direction from bottom to top. From the outside, the building must have a layer of highly effective thermal insulation. To achieve additional benefits, we strongly recommend the use of a variety of dehumidifiers, but only in combination with optimally calculated and selected


Creation date: 2014/01/08

Temperature

Under the microclimate of the premises is understood the totality of thermal, air and humidity conditions in their relationship. The main requirement for the microclimate is to maintain favorable conditions for people in the room.

As a result of metabolic processes occurring in the body, energy is released in the form of heat. This heat must be transferred to the environment by convection, radiation, thermal conductivity and evaporation, since the human body strives to maintain a constant temperature (36.6ºС). Maintaining a constant body temperature is provided by the physiological system of thermoregulation. For normal life and good health, a person must have a thermal balance between the heat produced by the body and the heat given off to the environment. Under normal conditions, more than 90% of the heat produced is given to the environment (half of the heat is emitted by radiation, a quarter by convection, a quarter by evaporation) and less than 10% of the heat is lost as a result of metabolism.

The intensity of human heat transfer depends on the microclimate of the room, which is characterized by the temperature of the indoor air, the radiation temperature of the room, the speed of movement and the relative humidity of the air. Combinations of these microclimate parameters, in which the thermal balance is maintained in the human body and there is no tension in its thermoregulation system, are called comfortable or optimal. It is most important to maintain, first of all, favorable temperature conditions in the room, since air mobility and relative humidity, as a rule, have insignificant fluctuations. Zones of comfortable combinations tВ and еR for civil buildings in cold and warm periods of the year. In addition to the optimal ones, there are acceptable combinations of microclimate parameters, in which a person feels a little discomfort.

The part of the room in which a person spends most of his working time is called the serviced or working area. Comfort should be provided, first of all, in this area.

The thermal conditions of the room depend mainly on its temperature situation, which is usually characterized by two conditions of comfort. The first condition for the comfort of the temperature environment determines such an area of ​​temperature combinations at which a person, being in the center working area, does not experience overheating, nor hypothermia.

For a calm state of a person, tВ=21…23ºС, for light work - 19…21ºС, for heavy work - 14…16ºС.

The second comfort condition determines the allowable temperatures of heated and cooled surfaces when a person is in close proximity to them. To avoid unacceptable overheating or hypothermia of the human head, the surfaces of the ceiling and walls can be heated up to allowable temperature. The temperature of a cold floor in winter can be only 2-2.5ºС lower than the air temperature of the room due to the high sensitivity of human feet to hypothermia, but not higher than 22-34ºС, depending on the purpose of the premises. The temperature in residential premises should not be lower than 18◦С, and in corner rooms - not lower than 20◦С. Temperature for classrooms should not be lower than 16-18 ◦С for the gym - 16 ◦С; for recreations, corridors, flights of stairs, canteens - 14◦С. The relative humidity of the air in rooms and school premises should be 40-60%, and its mobility should be from 0.1 to 0.15 m/s.

For good health and well-being, it is necessary that the relative humidity is between 40 and 60%. Optimum humidity is 45%. However, in our homes and schools during the winter months, it often does not exceed 10 or 20%. With the start of the heating season, indoor air humidity drops significantly. Such conditions cause rapid evaporation and drying of the mucous membrane of the nose, larynx, lungs, which leads to colds and other diseases. To maintain it at this time, at least 1 liter of water should evaporate per day in a room of 15-18 square meters. High humidity also at any temperature is bad for human health. It may arise due to large indoor plants or irregular ventilation. At higher temperatures, a humidity of about 20% is preferred.

Air humidity

Air is an integral part in the life of every person - it is one of the sources of life. Man cannot live without air. And what is air, what does it consist of and how does it affect a person? atmospheric air is a mixture of various gases and water vapor. Along with the temperature and pressure of the atmosphere, the amount of water vapor in it is important for a person. The influence of air humidity on human life What humidity is better?

Dry air is not good. Dry air acts like a sponge on the skin, pulling moisture out of it, that is, it simply dries the skin, hence wrinkles form faster. Excessively dry air with a relative humidity of less than 40% makes the mucous membranes of the lungs and nasopharynx dry, increasing the risk of infections and bleeding. There are unpleasant sensations of dryness in the mouth and throat, deep cracks in the lips are formed, and the protective functions of the upper respiratory tract are reduced.

High humidity (above 70%) also adversely affects the human body, both at high and low temperatures. At high air temperature and high humidity, a person sweats a lot, but moisture does not evaporate from the surface of the body, which leads to overheating of the body and “heat stroke”. At low temperatures, increased air humidity, on the contrary, leads to a strong cooling of the body, since in humid air, energy losses by convection and heat conduction increase sharply. Wet air indoors creates ideal conditions for the growth of mold and reproduction, the so-called dust mites, which can cause allergies in people prone to these diseases. Humidity of the air, significantly affecting the heat exchange of the body with environment, It has great importance for human life.

Humans are highly susceptible to moisture. It depends on the intensity of evaporation of moisture from the surface of the skin. And the evaporation of moisture is of great importance for maintaining a constant body temperature. At high humidity, especially on a hot day, the evaporation of moisture from the surface of the skin decreases and therefore the thermoregulation of the human body is difficult. In air with high relative humidity, evaporation slows down and cooling is negligible. Heat is more difficult to tolerate with high humidity. Under these conditions, it is difficult to remove heat due to the evaporation of moisture. Therefore, overheating of the body is possible, which disrupts the vital activity of the body. For optimal heat transfer of the human body at a temperature of 20-25 C, the most favorable relative humidity is about 50%.

At low temperatures and high humidity, heat transfer increases and a person is exposed to greater cooling. At high temperatures and high humidity, heat transfer is sharply reduced, which leads to overheating of the body, especially when performing physical work. Heat easier to tolerate when the humidity is lower. So, when working in hot shops, the optimal effect on heat transfer and well-being is exerted by a relative humidity of 20%. The most favorable for a person in average climatic conditions is the relative humidity of 40-60%. Such humidity, for example, is maintained in spacecraft.

To eliminate the adverse effects of indoor air humidity, ventilation, air conditioning, etc. are used. Since students have to spend more time at school during the school year, the state of humidity in classrooms plays an important role. Based on this, we decided to find out whether sanitary standards our office conditions. The measurements were carried out in subject rooms and in a computer class.

Psychrometer

The psychrometer consists of two thermometers. The tank of one of them remains dry, and the thermometer shows the air temperature. The tank of the other is surrounded by a strip of cloth, the end of which is lowered into the water. The water evaporates and this cools the thermometer. The higher the relative humidity, the less intense the evaporation and the smaller the difference in thermometer readings. At a relative humidity of 100%, no water will evaporate at all and the readings of both thermometers will be the same. The relative humidity of the air can be determined from the difference in temperature between thermometers. Psychrometers are usually used in cases where a sufficiently accurate and fast determination of air humidity is required.

Optimal and permissible parameters of temperature and relative humidity in rooms in all educational and preschool institutions

Optimal parameters:

  • temperature 19 C, relative humidity 62%;
  • temperature 20 C - relative humidity 58%;
  • temperature 21 C - relative humidity 55%.

Valid parameters:

  • temperature 18 C - relative humidity 39%;
  • temperature 22 C - relative humidity 31%.
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