At what temperature does dew fall? Dew point in the wall - what is it, how to calculate and find

The dew point is a kind of indicator of the amount of water vapor in the air. As humidity increases, so does the dew point value (at a certain temperature and pressure). The dew point value is expressed in degrees. This is the temperature at which the maximum saturation of the air with water vapor is achieved if they are constantly contained in the air at the same temperature.

The dew point cannot exceed the air temperature. As a result of the contact of a cold surface and warm air, the humidity drops - this phenomenon is called condensation.

Droplets of moisture are obtained, which can transform into fog, frost, cloud or rain. The simplest example is a kettle boiling on the stove, on the hot lid of which you can see droplets of moisture. The temperature of the lid is the dew point in this case.

Knowing the dew point temperature, you can get an idea of the relative humidity of the air. If the dew point temperature is close to the ambient temperature, then the humidity is high ( when matched, fog is obtained!).

Conversely, if the values of the dew point and temperature differ greatly, then we can talk about a low content of water vapor in the atmosphere.

Another simple example can be considered when something is brought into a warm room from a frost. The air above it is cooled, saturated with water vapor and droplets of water condense on things.

In the future, the thing warms up to room temperature and the condensate evaporates. By the way, this phenomenon is due to the recommendation not to immediately turn on household electrical appliances that have been brought in from the cold.

Another, no less well-known example is the misting of windows in the house. Many windows “cry” in winter, condensation falls on them. It must be understood that this phenomenon is largely influenced by two factors - humidity and temperature.

Therefore, if you have a normal double-glazed window and insulation is properly carried out, and there is condensate, it means that not everything is in order with humidity; Possibly poor ventilation.

One of the most interesting physical phenomena is the change in the state of aggregation of water, in particular, the boiling of water. Read more details in the article it is really very interesting. We are sure you will find a lot of new things here.

How to calculate dew point? ^

To find the dew point temperature, cumbersome formulas were previously used. Here is one of them that works fairly at a temperature from 0 to +60С. Tp=b((aT/b+T)+lnRH)/a-((aT/b+T)+lnRH); here a=17.27, b=237.7, RH- relative air humidity, expressed in fractions of a unit, ln is the natural logarithm, Tr- Dew point.

Now you can just go to the Internet and find a calculator on the relevant sites that will show the dew point temperature depending on air temperature and pressure (normal atmospheric pressure is usually taken at 762 mm Hg).

One of the "advanced" ways to calculate the dew point is to use thermal imagers. Some models have this feature. The display shows a thermogram that clearly shows places with temperatures below the dew point.

Table for determining the dew point ^

A more affordable method is to use a household psychrometer. This is a device in which two alcohol thermometers are combined. One of them has special moisturizing, the other is normal, dry.

As moisture evaporates, the humidified thermometer cools. The humidity is lower, the temperature is lower. A humidity value of 100% means that the readings of both thermometers are equal.

Knowing the humidity and temperature displayed on the display, you can calculate the dew point from the table. They are used for quick calculations. The value of the ambient air temperature, humidity and the corresponding dew point value is indicated.

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You can read everything about water aerobics and its benefits for weight loss, the most important, relevant and useful information!

Read all about treatment with living and dead water in the article:
take care of your health!

How to determine the dew point? ^

The correct determination of this parameter is of paramount importance in construction. The possibility of condensation on the walls depends on the correctness of the calculations, which dramatically reduces the durability of structures, and in some cases makes living indoors simply impossible.

Any wall (if it is not made of metal) has this or that moisture. The reason for the formation of condensate lies not only in the material of the walls themselves, but in the thermal insulation, on the correct arrangement of which the place of condensate formation depends. The temperature at which it falls depends on:

air temperature in the room;
humidity in the room.

Using the tables, it can be determined that if the temperature, for example, in a room is + 20 ° C with a humidity of 60%, then moisture will form on any surface with a temperature of 12 ° C and below.

With a decrease in humidity to 40%, condensate will appear on the surface with a temperature below 6C. That is, the lower the humidity, the further the dew point is from the room temperature.

The location of the dew point depends on:

outdoor humidity;
internal humidity;
temperature inside and outside the room;
wall thickness, insulation.

1. How does the dew point behave in a wall without insulation? There are several options for finding it:

between the center of the wall (in thickness) and the outer surface: in this case, the inner wall remains dry;
between the center of the wall and the inner surface: the inner surface can freeze for several days with a sharp decrease in air temperature in the region;
on the surface of the wall indoors: during the winter period, the wall will be wet.

2. When using a heater, the picture will be somewhat different. The place of condensation formation can be located (insulation from the outside):

inside the insulation: this is true with correct thermal calculations - the wall will be dry, the point is calculated correctly;
in any place described above (item 1): this happens if the thickness of the insulation is chosen incorrectly.

3. Internal insulation. In this case, the place of condensate formation moves inside the room; at the same time, the temperature under the heater decreases. The dew point can be:

between the center of the wall and the insulation or at their border in case of a sharp cold snap;
only under insulation: the wall will partially get wet all winter;
inside the insulation: it will get wet during the entire cold period.

How is dew point used? ^

Knowing the location of the dew point, you can correctly calculate the thickness of the insulation, thereby preventing the formation of condensate in an undesirable place.

But there is another question: in what situation should the wall be insulated from the inside, and in which - from the outside? To answer it, it is necessary to take into account all the factors that affect the dew point and its position:

climatic zone;
mode of residence (permanent, temporary) indoors;
what the insulated wall borders on (another room or street);
operation of the ventilation system (including exhaust and correct calculations of the entire system);
the quality of the heating system in the room;
material, wall thickness;
temperature outside and inside the room;
external and internal humidity;
insulation of all elements of the house (floor, walls, ceiling).

Insulation of the room from the inside is possible if the situation is as follows:

permanently reside in the premises;
ventilation functions in accordance with the standards for this room;
the heating works just as well;
all structural elements are insulated in accordance with the requirements for a specific climatic zone;
the wall intended for insulation is sufficiently thick (according to the climatic zone): i.e. insulation thickness in any case must not exceed 50 mm.

Speaking quite simply, then all of the above can be formulated as follows: the warmer the region, the better the heating, ventilation, and the thicker the wall, the greater the likelihood of internal wall insulation.

Practice shows that in the vast majority of cases it is preferable to equip external insulation. In this option, there is much more chance that the dew point will be in the right place.

Why are the windows "crying" ^

There are specific recommendations for the microclimate in a residential area. This is humidity -40-50% and temperature +18-23C. Maintaining these parameters minimizes the possibility of condensation on the glass surface.

Its appearance is also associated with human activity (it also releases moisture!). That is, there should be as many people in the room as sanitary standards allow.

High humidity can also be associated with improper air exchange. Here, too, there are rules: at least 3 "cubes" per "square" area in one hour.

For kitchens, these requirements are even tougher: from 6 to 9 "cubes" per hour, depending on the type of plate ( 9 cu. m/h - for gas). Therefore, it all depends on the quality of ventilation.

There is a contradictory situation; the house was overhauled, the old windows were replaced with double-glazed windows, and mold began to appear in the rooms. What is it connected with?

The fact is that in the course of a complete reconstruction, the heating is changed, modern boilers are installed instead of old gas water heaters, and windows are insulated. By and large, there are fewer opportunities for natural ventilation.

If earlier moisture from the room could escape through leaky window slots, through the exhaust of an old gas column, then now there is no such possibility.

There is only one way out - the development and installation of a new ventilation system. If this is not possible, then just ventilate the rooms and the kitchen more often.

The operational characteristics of a double-glazed window (coefficient "K", in particular) are important, but already secondary.

Possible consequences of choosing the wrong dew point ^

In the cold season, the air coming from a warm room outside is supercooled, manifesting itself in the form of precipitating moisture. The surface is any material that has a temperature below the dew point. As a result, at low outside temperatures, the walls are constantly wet. This leads to the formation of mold, promotes the development of various microorganisms. Subsequently, they can easily end up in the air inhaled by the residents, which leads to diseases of various kinds; for example, asthma.

A building with damp walls will not last long; the process of destruction will inevitably accelerate. Affected by mold, fungus, houses do not “live” for a long time. Therefore, it is important to calculate the correct point at the design stage of the building. Must be correctly selected:

wall material and thickness;
insulation material, its thickness;
method of wall insulation (outside, inside);
a variant of the heating and ventilation system that provides an optimal microclimate (18-23C at 40-50% humidity).

You can calculate the dew point yourself. In this case, it is necessary to take into account the climatic features of the region of residence. If you do not rely on your own strength, then you can contact any serious construction company. Surely there will be a specialist involved in such calculations.

Video of the Usadba TV channel about the importance of determining the dew point before starting construction:

When describing the installation of thermal insulation of structures, unknown phrases are encountered. For example, you should know what "dew point" means. This is easy to explain with an everyday example.

The higher the relative humidity, the higher the dew point and closer to the actual air temperature

Air is a mixture of nitrogen, oxygen, other gases and steam. The temperature at which steam condenses occurs has acquired the concept of dew point. This phenomenon is observed when the kettle boils, and the vapors form water droplets on cold surfaces.

Formula for calculation

This formula can be used to calculate relative humidity from a known dew point

Here, Tp means the point temperature itself, b and a show equal (constant) values, ln is the natural logarithm, T is the indoor temperature, Rh is the relative humidity value.

As can be seen from the formula, the value directly depends on the values of two parameters:

moisture index;
actual temperature readings.

At high relative humidity, the parameter becomes higher and closer to the actual temperature level. To calculate this variable, there is a table with a small parameter step. It can be used to find the required value by measuring the relative humidity and the actual temperature.

Table 1. Determination of the indicator using the ratio of influencing parameters on which the dew point depends

According to the table, we calculate that at a temperature of, for example, 19 degrees and a humidity of 50%, the condensation parameter will be 8.3 degrees.

From this video it becomes clear how thick the insulation should be for the most comfortable conditions:

The term "dew point" in construction

The constantly growing and developing market for building products presents a wide range of materials for thermal insulation. The choice of thermal insulation for industrial and residential premises must be approached properly and during construction, pay attention to the indicator in question.

Incorrect dew point measurement often results in wall fogging, mold, and sometimes structural failure.

The boundary of the transition from low temperatures outside the walls to higher temperatures inside heated structures with the possible formation of condensate is considered by experts to be the dew point. On any surface in the room, the temperature of which is close to the dew point parameter or falls below the value, drops of water will appear. The simplest example: in the middle of some rooms, during cold weather, condensation flows on the window panes.

The main factors influencing the determination of the value are:

climatic factors (temperature value and air humidity outside);
temperature values inside;
humidity indicator inside;
the thickness of the walls;
vapor permeability of thermal insulation used in construction;
availability of heating and ventilation systems;
purpose of buildings.

The correct determination of the dew point is essential in construction

Only if the indicator is measured correctly, in the future it is possible to comfortably operate the building and reduce maintenance costs in the future.

Precise definition

Water vapor most often condenses on the walls themselves or inside their structure if they are not adequately insulated or built. Without insulation, the value will be close to the temperature of the inside of the wall, and in some cases to the wall in the middle of the house. When the temperature inside the enclosing structures is below the indicator, then during a cold snap at a negative temperature outside, condensation will occur.

There are several places where the indicator can be located on non-insulated structures:

inside the structure, close to its outer part, the wall will remain dry;
inside the wall, but close to the inside, the wall becomes wet with temperature changes;
the side of the wall that is in the building will constantly be covered with condensate.

Experts do not recommend insulating rooms from the inside, explaining that when using this method of thermal insulation, the parameter will be under the heat-insulating layer in the middle of the room . As a result, there will be a large accumulation of moisture..

condensate can accumulate in the center of the wall and during cold weather move towards the placement of heat-insulating components;
the place of accumulation of moisture can be the boundary of the building envelope and the insulation layer, which becomes damp and forms mold in the middle of the rooms;
in the middle of the heat-insulating layer itself (it will gradually become saturated with moisture, begin to mold and rot from the inside).

The dew point is formed by three components: atmospheric pressure, air temperature and its humidity.

Styrofoam, mineral wool or other type of insulation must be placed on the outside of the building, which will allow you to place the value in the insulating layer (with this arrangement, the walls inside will remain dry). For a clearer understanding of the parameter, there are graphs of its placement on the walls of houses with insulation, as well as on buildings that do not have an insulation layer. To independently make such a calculation, you can determine the dew point in the wall with a calculator.

Wrong definition of value

The result of errors made during the calculation of parameters will be the constant accumulation of condensate, high humidity, the development of fungal deposits and mold. An industrial, administrative or residential building will not be able to serve for a long time: negative processes will accelerate destruction. Additional costs for ongoing maintenance and overhaul will be required.

Atmospheric air always contains a certain amount of moisture in the form of water vapor, which determines its humidity, and in warm air there is always more than in cold air. At an air temperature of +20 °C and a relative humidity of 60%, the air contains 10.4 g of water vapor per 1 m³ of dry air, which create a partial pressure of 1403 Pa. At a temperature of -10°C and a relative humidity of 60%, the air contains about 1.3 g of steam per 1 m³ of dry air, which creates a partial pressure of 156 Pa. Due to the difference in partial pressures between indoor and outdoor air, a constant diffusion of water vapor from the warm room to the outside occurs through the wall. As a result, under real operating conditions, the material in the structures is in a slightly moistened state.

The amount of moisture in the form of vapor in the air cannot be increased indefinitely - in the end, such saturation with steam occurs that moisture begins to condense in the form of water droplets on any surface, and even on dust particles flying in the air. This is how, for example, raindrops are formed: water vapor in the air collects into droplets if there are particles to which it can “stick”. Over the oceans, water vapor can wet salt particles and form droplets. Or, if the temperature drops to 0°C or even lower, water can freeze on dust particles that are blown into the air by the wind. Ice crystals form from ordinary dust. Other small particles, such as smoke, can also form granules around which water clouds gather. So - back to the topic - this limiting vapor content depends only on temperature and does not depend on air pressure. This steam in its maximum quantity creates, respectively, the maximum pressure and is called the pressure of saturated water vapor or the maximum elasticity of water vapor and is denoted by the letter E, measured in Pascals.

Once again, let's put everything together in one sentence - the maximum elasticity of water vapor E corresponds to the maximum possible saturation of air with water vapor F. The higher the air temperature, the greater the value of E, i.e., the greater the maximum amount of moisture Fmax can be contained in the air.

The relationship between vapor pressure and its quantity is expressed by the formula:

F = 0.00794E / (1 + t/273)

Interestingly, it is impossible to mathematically calculate the value of E or F. In the temperature range from 0°С to +40°С, the vapor pressure E is described by an exponent with an accuracy of ±1%, but as the temperature decreases, the deviation reaches 130% at a temperature of -47°С! The approximate formula looks like this:

The error in the temperature range from 0°С to +40°С is less than 1%, however, in the range from 0°С to -20°С, the error increases to 30%, and by -45°С it exceeds 100%. In the range from +40°C to +50°C, the error is around 3%.

For accurate calculations, tables with experimental data are used, which are given in regulatory documents on heat engineering, for example, in TKP 45-2.04-43-2006:

The elasticity of water vapor in the air, as well as its absolute humidity, does not give an idea of the degree of saturation of the air with moisture, if its temperature is not indicated. For example, if e = 1400 Pa is given, then at an air temperature of +23 ° C this will be only half of its maximum elasticity (E = 2809 Pa). At +12 °C, this corresponds to the complete saturation of the air with moisture, and at +10 °C, water vapor cannot have such elasticity at all. To express the degree of saturation of air with moisture, the concept of its relative humidity was introduced. Relative Humidity air φ is expressed as a percentage as the ratio of the actual elasticity of water vapor in air e to its maximum elasticity Ecorresponding to a given temperature. Therefore, we have:

φ = e / E 100%

From here we can express the partial pressure of water vapor in air, e:

e = E φ / 100.

For example, at 20°C, the maximum partial pressure is E = 2338 Pa. At 40% air humidity, the partial pressure of water vapor e \u003d 2338 40 / 100 \u003d 935 Pa. If the air temperature of a given humidity rises, then its relative humidity φ will decrease, since the value of water vapor elasticity e will remain unchanged, and the value of maximum elasticity E will increase with increasing temperature. On the contrary, when the air is cooled, as its temperature decreases, its relative humidity will increase due to a decrease in the value of E. At a certain temperature, when E becomes equal to e, the relative humidity of the air will be φ \u003d 100%, i.e., the air will reach full saturation with water vapor. This temperature is called the dew point for a given air humidity.

Thus, The dew point is the temperature at which air of a given humidity reaches full saturation with water vapor.

If you continue to cool the air below the dew point, then the elasticity of the water vapor contained in it will decrease according to the values \u200b\u200bof E for a given temperature and an excess amount of moisture will condense, i.e. turn into a liquid state. Such a phenomenon is observed in nature in the form of the formation of fogs near rivers in the summer; when the air cools at sunset, its relative humidity rises and the air temperature falls below the dew point. As the sun rises, as the air warms, its relative humidity decreases: the moisture droplets that form fog gradually evaporate and the fog dissipates. In winter, the formation of fogs is associated either with a decrease in air temperature, or with the influx of masses of warm, moist air, which, cooling when mixed with cold air, condenses moisture, forming fog. The dew point is of great importance for assessing the humidity regime of the fence, and it has to be determined from a given air humidity.

Due to the fact that the very definition of E is experimental, and not calculated mathematically, the dew point is also calculated only approximately and in the range from 0 to + 40 ° C according to the formula:

where a =17.27; b =237.7°C; T = temperature in °C; ln - natural logarithm;

RH = relative humidity in volume fractions (0< RH < 1.0).

But when the result of calculating Tr is less than 0 ° C, the formula begins to differ significantly from reality, therefore, there are again experimentally confirmed tables in the codes of practice. It's better to just use it. For a general idea, I will give a plate with a correctly calculated dew point for different temperatures and humidity from TCP 45-2.04-43-2006 (left).

Or here is my small flash calculator that works correctly in the temperature range -50°С ... +50°С, compiled on the basis of tables from QFT for the range -25 ... +30°С and from the book by Landolt-Bornstein, Physikalich - chemische - Tabellen T II (Berlin, 1923) for the rest of the range. At the same time, the calculator calculates the maximum pressure of water vapor at a given temperature, the pressure of water vapor in the air at a given humidity, calculates the maximum absolute humidity and absolute humidity of the air (the amount of water contained in 1m³). The calculator requires an installed flash player ( https://get.adobe.com/en/flashplayer/)

The dew point is called the cooled air to a certain temperature, in which the vapor begins to condense and turn into dew. In general, this parameter depends on the air pressure in the room and on the street. It is not always easy to determine the value, but it is necessary to do this, since this is one of the most important factors in construction and for a comfortable life and human existence in the room.

With an overestimated dew point, concrete, metal, wood and many other building materials will not give the desired effect when building or repairing a house and will not last long. During the laying of polymer floors, if condensate gets on the surface of the material, in the future, such defects as: swelling of the floor, shagreen, peeling of the coating and much more may occur. It is impossible to visually determine the parameter in the room, for this it is necessary to use a non-contact thermometer and a table.

What factors influence

wall thickness in the room and what materials were used for insulation;
temperature, in different parts of the world it is different and the temperature coefficient of north from south is very different;
humidity, if the airspace contains moisture, the dew point will be larger.

To better understand what it is, and how certain factors can affect the value, consider an illustrative example:

Insulated wall in the room. The dew point will shift depending on the outdoor weather conditions. In the case of stable weather without sharp fluctuations, the dew point will be located closer to the outer wall, towards the street. In this case, there are no harmful indicators for the room itself. If a sharp cold snap occurs, the dew point will slowly move closer to the inside of the wall - this can lead to saturation of the room with condensate and slow wetting of the wall surface.
Externally insulated wall. The dew point has a position inside the walls (insulation). When choosing a material for insulation, you should rely on this factor and correctly calculate the thickness of the selected material.
Insulated wall from the inside. The dew point is between the center of the wall and the insulation. This is not the best option if the weather conditions are too humid, because with a sharp cold snap, in this case, the dew point will sharply shift to the junction between the insulation and the wall, and this, in turn, can lead to disastrous consequences for the wall of the house itself. It is possible to insulate a wall from the inside in a humid climate if the house has a good heating system that is able to maintain a uniform temperature in each room.

If the repair of the house is made without taking into account the weather conditions, it will be almost impossible to eliminate the problems that have arisen, the only way out is to start work again and clean up everything that has been done, which entails a lot of money.

How to correctly identify and calculate (table and formula)

Dew point can be affected by temperature and humidity

It is quite difficult for a person to live in comfort with high humidity. Condensation causes problems both for health (there is a possibility of getting sick with asthma) and for the house itself, especially for its walls. The ceiling and walls from high humidity can become covered with mold that is harmful to humans and difficult to remove, in rare cases it is necessary to completely change the walls and ceiling in order to kill all harmful microorganisms present.

In order to prevent this from happening, you should make a calculation and find out whether it is worth starting repairs in a particular building, insulating walls, or even building housing in this place. It is important to know that for each building the dew point is individual, which means that its calculation will be carried out with slight differences.

Before proceeding with the calculation, one should take into account such factors as: climatic conditions in a particular region, the thickness of the walls and the material from which they are made, and even the presence of strong winds. Absolutely all materials contain low, permissible humidity, a person should make sure that this humidity does not increase and a dew point does not form. When you call a specialist to measure the value in case of high humidity, you will most likely be given an answer that the thermal insulation of the house is not done correctly, the thickness of the material is not suitable, or a mistake was made during installation. To some extent, this person will be right, since it is the correct repair in the house that affects the change in the dew point and the appearance of condensation on the walls to a greater extent.

Table: indicators for determining the dew point

C°	Dew point V S in CO at relative humidity in %
	30%	35%	40%	45%	50%	55%	60%	65%	70%	75%	80%	85%	90%	95%
30	10,5	12,9	14,9	16,8	18,4	20	21,4	22,7	23,9	25,1	26,2	27,2	28,2	29,1
29	9,7	12	14	15,9	17,5	19	20,4	21,7	23	24,1	25,2	26,2	27,2	28,1
28	8,8	11,1	13,1	15	16,6	18,1	19,5	20,8	22	23,2	24,2	25,2	26,2	27,1
27	8	10,2	12,2	14,1	15,7	17,2	18,6	19,9	21,1	22,2	23,3	24,3	25,2	26,1
26	7,1	9,4	11,4	13,2	14,8	16,3	17,6	18,9	20,1	21,2	22,3	23,3	24,2	25,1
25	6,2	8,5	10,5	12,2	13,9	15,3	16,7	18	19,1	20,3	21,3	22,3	23,2	24,1
24	5,4	7,6	9,6	11,3	12,9	14,4	15,8	17	18,2	19,3	20,3	21,3	22,3	23,1
23	4,5	6,7	8,7	10,4	12	13,5	14,8	16,1	17,2	18,3	19,4	20,3	21,3	22,2
22	3,6	5,9	7,8	9,5	11,1	12,5	13,9	15,1	16,3	17,4	18,4	19,4	20,3	21,1
21	2,8	5	6,9	8,6	10,2	11,6	12,9	14,2	15,3	16,4	17,4	18,4	19,3	20,2
20	1,9	4,1	6	7,7	9,3	10,7	12	13,2	14,4	15,4	16,4	17,4	18,3	19,2
19	1	3,2	5,1	6,8	8,3	9,8	11,1	12,3	13,4	14,5	15,3	16,4	17,3	18,2
18	0,2	2,3	4,2	5,9	7,4	8,8	10,1	11,3	12,5	13,5	14,5	15,4	16,3	17,2
17	0,6	1,4	3,3	5	6,5	7,9	9,2	10,4	11,5	12,5	13,5	14,5	15,3	16,2
16	1,4	0,5	2,4	4,1	5,6	7	8,2	9,4	10,5	11,6	12,6	13,5	14,4	15,2
15	2,2	0,3	1,5	3,2	4,7	6,1	7,3	8,5	9,6	10,6	11,6	12,5	13,4	14,2
14	2,9	1	0,6	2,3	3,7	5,1	6,4	7,5	8,6	9,6	10,6	11,5	12,4	13,2
13	3,7	1,9	0,1	1,3	2,8	4,2	5,5	6,6	7,7	8,7	9,6	10,5	11,4	12,2
12	4,5	2,8	1	0,4	1,9	3,2	4,5	5,7	6,7	7,7	8,7	9,6	10,4	11,2
11	5,2	3,4	1,8	0,4	1	2,3	3,5	4,7	5,8	6,7	7,7	8,6	9,4	10,2
10	6	4,2	2,6	1,2	0,1	1,4	2,6	3,7	4,8	5,8	6,7	7,6	8,4	9,2
For intermediate indicators not listed in the table, the average value is determined

Schedule

Thanks to the graph, you can determine the optimal performance

How to calculate: necessary tools and sequence of actions

thermometer;
hygrometer;
non-contact thermometer (can be replaced with a conventional one).

Formula for calculation in frame, brick, multilayer walls with insulation

To calculate the dew point with insulation, the following formulas are used: 10.8 ° C

Using the obtained indicators, draw up a graph with the temperature range T1 placed in the wall and the remaining °C for the insulation. Mark the dew point at the desired location.

What if the value is defined incorrectly?

Consider the places where the dew point can be located in an uninsulated wall:

Closer to the outer surface of the wall. In this case, the appearance of a dew point in the house is minimal, as a rule, the inner wall remains dry.
Closer to the inner surface of the wall. In this case, condensation may occur during a sharp cold snap outside.
In the rarest of cases, the dew point is on the inside wall of a building. In this case, it is almost impossible to get rid of it, and most likely the walls in the house will be a little damp all winter.

In these cases, the problem can be solved by adding vapor barrier layers to the walls. This will help keep water vapor from escaping through the walls into the room, which will prevent dew points from appearing on the walls and ceiling. If the climate is too cold and most of the year the temperature is more than minus 10 degrees, it is worth considering the option of forced entry of heated air into the room. This can be done using a heat exchanger or an air heater.

Video: why condensation and mold appear on the walls

It is important to correctly determine the dew point during the construction phase. This will help to correctly insulate the wall and in the future to avoid the appearance of condensation and mold in the house.

Why do windows, doors, walls sweat? Why do things that are brought from the cold into a warm room become covered with condensate? Why do cold water pipes get wet? - one answer, the surface temperature of the object is lower dew point temperature.

Dew point (Dew point temperature TP) is the temperature at which dew begins to form, i.e. the temperature to which the air must be cooled in order for the relative humidity to reach 100%

From the school physics course, we know that air humidity (water content in the air) is determined by two parameters:

absolute humidity;
relative humidity.

With absolute humidity(f ) everything is clear - this is the amount of water, in grams, contained in one cubic meter of air, the unit of measurement is grams in a cubic meter, g/m3.

f=m/V

V - volume of moist air;

m is the mass of water vapor contained in this volume.

Relative Humidity(RH ) is the amount of water contained in the air relative to the maximum possible amount of water at a given temperature and pressure, the unit of measurement is percent, % .

And with temperature increase, maximum possible amount of water contained in the air increases.

Accordingly, at decrease in temperature – decreases.

With a further decrease in temperature, superfluous» water will start to condense in the form of dew drops- That's what it is Dew point.

A few facts about the dew point.

The dew point temperature cannot be higher than the current temperature.
The higher the dew point temperature, the more moisture is in the air
High dew point temperatures are in the tropics, low in deserts, polar regions.
Relative humidity (RH) around 100% causes dew, frost (frost dew), fog.
Relative humidity (RH) reaches 100% during the rainy season.
High dew points usually occur before cold temperature fronts.

How to determine, calculate the dew point?

The answer is obvious -

1. To determine the dew point, there are special tables,

where the columns indicate the relative humidity in % , in rows – ambient air temperature in °C, in cells at the intersection - the dew point temperature, for the selected humidity and temperature.

For example, relative humidity of 60% is chosen, room temperature is 21 °C at the intersection we see dew point value 12.9 °C.

Accordingly, under these conditions, moisture condensation will occur on cold surfaces (for example, window panes) with surface temperature lower than 12.9 °C.

On specialized sites, there are more detailed tables for determining the dew point, but for "home use" it is quite enough, the table below can be saved, printed and used if necessary.

2. When calculating the dew point temperature, use formulas 1.1 and 1.2.

The formula for an approximate calculation of the dew point in degrees Celsius (only for positive temperatures):

Tp = (b f (T, RH)) / (a - f (T, RH)) , (1.1 )

f (T, RH) = a T / (b + T) + ln (RH / 100) , (1.2 )

Tr – dew point temperature, °С;

a = 17.27;

b = 237,7;

T – room temperature, °С;

RH – relative humidity, %;

ln is the natural logarithm.

Calculate dew point for the same temperatures and humidity.

T= 21 °С;

RH = 60 %.

First we calculate the function f(T,RH)

f (T, RH) = a T / (b + T) + ln (RH / 100),

f(T,RH) = 17.27 * 21 / (237.7 + 21) + ln (60 / 100) =

= 1,401894 + (-0,51083) = 0,891068

Then dew point temperature

Tp = (b f (T, RH)) / (a - f (T, RH)),

Tp = (237,7 * 0,891068) / (17,27 - 0,891068) =

= 211,807 / 16,37893 = 12.93167 °С

So our calculation result Tr = 12.93167 °С .

3. It is much easier to calculate the dew point using " Dew Point Calculator" on our website.

Fill in the values:

Air temperature indoors, ° With . - 21 ;

relative humidity, % . – 60 .

As we see, the dew point value for all three methods is the same:

Tr= 12.9 °С;

Tr\u003d 12.93167 ° С;

Tr\u003d 12.93 ° С.

The difference is only in the number of decimal places.

There are fair questions why do we need this dew point, why do we spend so much time defining or calculating what practical application dew point has?

In places where moisture constantly accumulates, favorable conditions are created for the development of mold, fungal spores, which very negative impact on health nearby of people.