To keep the house dry and warm when performing thermal insulation work, it is important to correctly determine the dew point. If the initial calculation is performed incorrectly, the walls will begin to get wet and traces of condensation will appear. Moreover, the error will become noticeable only after a few years. It will be extremely difficult to fix something, and therefore all the work will have to be done again.
What is dew point?
This is a parameter numerically equal to the temperature at which water vapor begins to condense from cooled air, turning into dew. Its value can vary according to the thickness of the wall with temperature fluctuations inside and outside the building. If the temperature inside is maintained at the same level, and it starts to get colder outside, the dew point will begin to move closer to the inside wall.
The temperature at which steam begins to condense is affected by air temperature and humidity. So, at an air temperature of + 20 °C and a humidity of 50%, dew will fall on a surface cooled to +12.9 °C. To check this, it is enough to bring into the room an object cooled below +12.9C. Condensation will definitely appear on it. If, on the contrary, you open the refrigerator, warm air will begin to flow into it, from which dew will fall. Outwardly, it will look like fog coming out of a refrigerator.
There is also a place in the wall of the house where steam will condense if it is very cold outside. If the wall thickness is insufficient and its surface is cooled to a certain level, dew will begin to appear inside the room. As a result, the wall will constantly get wet and will soon become covered with mold.
That is why, when insulating, it is imperative to calculate the dew point, taking into account the highest and lowest values of humidity and temperature both inside and outside. This will allow you to find out how it will move in space with changes in temperature and humidity. Based on the obtained values, it will be possible to calculate the minimum wall thickness that will provide comfortable conditions inside the house.
How to find the place you are looking for?
Where exactly the steam will condense largely depends on the location of the insulation. This is especially important if the insulation was done from the inside.
The position of the dew point will directly depend on weather conditions. In the absence of significant temperature fluctuations in the outside air, condensation will form closer to outer surface walls. It will be quite comfortable inside the building.
In the event of a sudden cold snap, the desired location will begin to slowly move inward. This can lead to gradual saturation of the interior with condensation and wet walls.
In this case, you should choose wisely thermal insulation material and its thickness to prevent the walls from getting wet. If the thermal insulation of the walls from the outside is done correctly, the dew point will be inside the insulation.
If the installation technology is broken or the thickness of the heat-insulating material is insufficient, then it will be extremely difficult to reduce heat loss.
As the frost intensifies, the humidity inside the building may rise. It is also possible that the walls will get wet.
The desired place when insulating from the inside will be located between the middle of the wall and the insulation. Is not the best option, since when high humidity and a sharp decrease in air temperature, condensation will begin to form at the junction of the insulation and the wall.
As a result, destruction of the insulated surface and heat-insulating material may begin. This option in case of high humidity is only possible if a heating system is installed that can maintain the temperature throughout the house at the same level.
If, when performing thermal insulation work from the inside, the climatic features of a particular region were not taken into account, it will be extremely difficult to eliminate the problems that have arisen. Only possible way out The only solution to this situation is to re-insulate the walls. It is worth noting that internal insulation, according to experts, is significantly inferior to external insulation.
We carry out the calculation
When determining the required value, several factors should be taken into account:
- temperature inside and outside the house;
- air humidity.
Temperature and relative humidity
The value depends on the location of the building. In most cases we will be talking about 20 – 22 °C. For those who live in areas where the five-day period is the coldest, that is -31°C and below, the indicated value will be 21–23°C.
The acceptable value is slightly different. For cold regions it will be 20 – 24 °C. For middle zone the temperature range will expand to 18 – 24 °C. When a calculation is performed, it is usually taken in the first case to be 20 °C, in the second - 22 °C.
Acceptable indicator relative humidity fluctuates between 35–60%. For calculations, you can take 50–55%.
Looking for a table value
To find the desired value, you should use a special table in which the condensation value is presented depending on temperature and humidity. To do this, having decided on temperature and humidity, you can find the desired value at the place where they intersect. So, if the humidity is taken to be 55% and the temperature is 21°C, the dew point is 11.6°C. This means that where the wall cools to 11.6 °C, condensation will form.
To get a more accurate figure, you can determine the condensation value using real data. To do this, you should acquire the following tools:
- an ordinary thermometer;
- hygrometer;
- non-contact thermometer. If you don't have one, you can use the usual one.
You should start searching for the value by measuring the air temperature at a distance of 60 cm from the floor surface. A larger distance from the floor surface will result in incorrect data. In this case, measurements are often carried out by placing the thermometer on the table.
After this, the humidity in the room is measured using a hygrometer. This should be done in the same place where the temperature was measured. The search for the condensation value is carried out in the same sequence as described above.
Is insulation necessary?
Sometimes it can be difficult to decide how much is needed thermal insulation work. Before you start insulating the walls, you should use a special non-contact thermometer to find the surface temperature located at a distance of approximately 60 cm from the floor plane.
If you do not have such a measuring tool, you can use a regular thermometer. To do this, wrap the thermometer in a thin cloth and place it on the surface whose temperature is to be determined. In a quarter of an hour it will be possible to take readings.
Now we need to compare the table value of condensation and the surface temperature. If the difference is more than 4 degrees, we can safely say that there is high humidity in the room, and the dew point is inside.
It will be extremely difficult to cope with the problem on your own. It is advisable to seek help from specialists who can correctly perform the calculation optimal thickness thermal insulation material and its characteristics.
Determining the location of condensation
In order to perform the calculation you need to know:
- thermal resistance coefficients of the wall and insulation, λ1 and λ2, W/(m K);
- wall and insulation thickness, h1 and h2, m;
- air temperature inside the house, t1, °C;
- air humidity, %;
- dew point, °C;
- temperature outside the building, t2, °C.
Before proceeding with the calculation, we assume that the temperature change across the thickness of all layers will be linear. It is necessary to find the temperature at the point of contact between the wall and the insulation. After this, you will need to construct a graph showing the change in temperature along the thickness of the wall. The constructed graph will help you find the desired point.
To do this, you need to find the ratio of the thermal resistance of the wall and the insulation. Using a special formula, it will be possible to find the temperature at the layer boundary. Knowing the temperature on one and the other side of the layer, it will not be difficult to construct a linear graph. It will be possible to track the temperature change throughout the entire thickness of the wall in order to understand exactly where condensation will form.
To perform the calculation, let's assume that we have reinforced concrete wall h1=36 cm, insulated with foam plastic with a thickness of h2=10 cm. For reinforced concrete, the thermal resistance coefficient is λ1=1.7 W/cmK. For foam plastic, this indicator is λ2 = 0.04 W/cmK. Inside the house the temperature is t1= +20 degrees, outside – t2= -10 degrees. Let's take the air humidity inside and outside to be the same - 50%. According to the table, the condensation value will be 9.3 degrees.
To find the thermal resistance of the wall and insulation, it is necessary to find the ratio of their thickness and the thermal resistance coefficient h/ λ. We get h1/λ1=0.36/1.7=0.21 W/m²K for the wall, h2/λ2 0.1/0.04= 2.5 W/m²K for insulation.
Hence, at the layer boundary the temperature will be t1-T=20-2.52=17.48 degrees.
To find where the desired location will be, you should construct an approximate graph characterizing the temperature difference across the thickness of the wall, drawing a straight line through two points. In the place where the temperature is 9.3 degrees, condensation will form.
Analyzing the resulting graph, it is important to understand whether the place of condensation will be in the insulation or not. In this case, even with a significant deterioration in weather conditions, it will be possible to avoid unwanted moisture in the wall. If it ends up outside the layer of thermal insulation material, then it’s time to think about the adequacy of the insulation thickness.
If at the moment it is not possible to improve the thermal insulation of the walls, then heating the room may be the only way out. By heating the air from the inside, it will be possible to shift the condensation point towards the street. As a result, it will be much more comfortable to be inside the building.
Dew point is the temperature at which water vapor from the air begins to condense on surfaces. It happens that in heating season we can observe moisture condensation on windows and sometimes walls. In the latter case, condensation can even lead to the formation of mold.
In this article we will try to understand the concept of “dew point” and learn how to determine the temperature of condensation on surfaces.
What does the dew point depend on?
- Indoor air humidity
- Air temperatures
Let's consider a simple example for understanding: the indoor air has a temperature of +20°C and with an air humidity of 60%, condensation will form on a surface with a temperature below +12°C.
Thanks to the nomogram below, the dew point temperature can be determined more accurately.
Nomogram for determining dew point
- Regular hygrometer— shows relative air humidity as a percentage. It is enough to simply take his testimony.
- Psychometric hygrometer— has two alcohol thermometers with a division value of 0.1-0.5°C. One thermometer is dry, the second has a humidification device. For the convenience of determining the relative humidity in the room, a psychometric table is used.
Having measured these values, then on the nomogram using a ruler we draw a ray from the room temperature scale to the known air humidity, in the place where the ray intersects the “Dew point temperature” scale and will be the desired surface temperature value for your case.
Click on the dew point determination nomogram to enlarge it to full size To determine the level of humidity in a room, it will be useful to buy a hygrometer.
Wall insulation is one of the main issues during construction. At first glance, it may seem that it is very simple to solve it - choose the one that suits the climatic conditions and finances, and insulate it. However, it is not. There are a number technical specifications, which must be completed so that the walls of the house do not become damp inside or freeze outside during the cold season. One of these conditions is to insulate the house so that the dew point is closer to external wall, and in no case - inside the house. To do this, you need to be able to determine where the dew point will be located at different conditions to eliminate the possibility of condensation forming on the walls inside the room.
What is dew point
The dew point is an indicator of the temperature at which maximum saturation of air with steam occurs and it begins to condense. This indicator depends on two main factors: temperature and air humidity.
When at least one of these two quantities changes, the dew point also changes, that is, it constantly moves, just as the temperature and humidity of the air are not constant all the time.
There is a table of dew points at different temperatures and air humidity, developed by specialists. From it you can see under what conditions steam begins to condense. For example, in winter time at standard temperature indoor air +20 0 C and humidity from 50% to 60%, the dew point will range from 9.3 0 C to 12 0 C. That is, condensation should not form inside the room, since under these conditions there are no surfaces with such a temperature .
Let's look further. If the house is +20 0 C, and the temperature outside is -20 0 C, then in the wall there will be a dew point with a temperature of +12 0 C at a relative humidity of 60%. The dew point can move across the thickness of the wall depending on the temperature inside and outside the room, as well as the humidity in the wall itself. The closer the dew point is to inner surface, the more likely it is that the wall will be wet from the inside. And this already creates unfavorable living conditions. By insulating a house, we can shift the dew point, since this changes the temperature of the wall itself.
Where will the dew point be?
There can be three options for wall construction: without insulation, with external and internal cladding. Let's consider where the dew point might be in each of these cases?
- The design is without insulation, then the dew point is located:
- inside the wall closer to the outer surface;
- inside the wall it is shifted to the inner surface;
- on the inner surface - indoors the wall will remain wet throughout the winter period.
2. Available external insulation, then the dew point is:
- inside the insulation - this indicates that the calculation of the dew point and the thickness of the insulation was carried out correctly, and the wall in the room will be dry;
- any of the three cases described in paragraph 1 - the reason is the incorrect choice of insulation and its characteristics.
3. Done interior lining, then the dew point will be:
- inside the wall closer to the insulation;
- on the inner surface of the wall under the cladding;
- in the insulation itself.
From what has been discussed above, it becomes clear that the location of the dew point also depends on such characteristics of the fence as temperature and vapor permeability. Most modern insulation materials practically do not allow steam to pass through, so it is recommended external cladding walls
If you choose internal insulation, then the following conditions must be met in order to:
- the wall was dry and warm;
- the insulation had good vapor permeability and small thickness;
- ventilation and heating functioned in the building.
Knowing possible areas of condensation formation, i.e. location of the dew point, possible for certain climatic zones choose a type and material of insulation that will not create conditions for damp walls inside the house.
There is an opinion that the house should be insulated from the outside, and the insulation in all respects must comply with GOST. Then the dew point will be inside the sheathing, that is, outside the house, and the interior walls will be dry in any season. That is why external insulation is more profitable than internal insulation.
How to remove dew point from a wall (video)
Most of us have probably heard about such a thing as dew point. In this article we will look at what it is and why this physical factor must be taken into account when carrying out work on thermal insulation of a house. The dew point is the distance from the ground where air cooled to a certain temperature forms dew. This indicator depends on several factors. The key is the air pressure inside the building and outside.
It is not always possible to simply determine this indicator. But we note that every owner of a building must determine what the dew point is in the premises of his house, since it affects the comfort of living.
If the dew point in the room is too high, in this case the main Construction Materials – concrete, metal and wood- will not provide desired effect during the construction of a house, and their service life will be short. Here you will need either a high base or additional protection from moisture.
If in interior spaces building, flooring is made of polymer materials, then condensate entering the structure of the material during operation flooring can lead to the following defects:
- bloating;
- detachment;
- shagreen.
Purely visually it is impossible to determine this indicator indoors. To do this you need to use a special device called a non-contact thermometer. In addition to it, you should use a table in which a special chapter describes how to determine this parameter in the walls of a structure and make its correct calculation.
What is dew point in construction?
This term should be understood as an indicator that determines the level of humidity in the air. That is, we can say that the higher the humidity level in the room, the higher the dew point. However, when determining this indicator, two more important criteria must be taken into account:
Not everyone knows that dew point is measured in degrees. As a result, it turns out that dew point - air temperature of a certain value, in which it itself is saturated with moist vapor. However, it is necessary to take into account the fact that the point itself cannot be higher than the air temperature.
It is necessary to remember how condensation occurs: it is formed upon contact warm air with cold surface. To make it clear to everyone how this indicator works in real conditions, it would be correct to consider the occurrence of such a phenomenon as fog. For it to appear, it is necessary that the outside air temperature and the dew point temperature coincide with each other. In other words, taking these indicators into account, you can accurately determine the level of humidity indoors and outdoors.
What factors influence dew point?
Such an indicator as the dew point is influenced by several factors:
- One of the main ones is the thickness of the walls of the room.. Another equally important thing is what materials are used during thermal insulation of the walls of the building. Temperature is also significant. It may vary depending on the area where the building is located. Temperature coefficient at northern territories will differ from regions located in the south.
- Another important factor- this is humidity. If there is moisture in the airspace, the more moisture there is, the higher the dew point will be.
To have an accurate idea of what dew point is and what impact various factors can have on it, let’s look at this factor using examples:
- Uninsulated indoor wall. In this case, the dew point will move. This will happen under the influence of outdoor weather conditions. If the weather outside is stable and there are no sharp temperature fluctuations, then the dew point will be located as close as possible to the outer wall. In this case negative influence the premises itself will not be affected. If a sharp cold snap occurs, the dew point will gradually move to inner part walls. And this can lead to the room being saturated with condensation, resulting in a slow wetting of the wall surfaces.
- Wall with external insulation. The dew point here will be located inside the wall in the thermal insulation layer. When choosing a material for insulating structures, it is necessary to pay attention to this factor and correctly approach the calculation of the thickness of the thermal insulation material.
- Wall insulated from the inside. Here the dew point is located between the insulation and the center of the wall. This option is not the best, because if the outdoor air is dominated by high level humidity, then with a sharp cold snap the dew point will move to the junction between the insulation and the wall. And this can have a very negative impact on the wall. resort to internal insulation the owner can only build if there is an effective heating system inside the house that is able to provide the same temperature regime in each of the rooms of the house.
If weather conditions are not taken into account when carrying out repair work in a house, then it is almost impossible to eliminate the problem. Only correct solution- remove everything that has been done, and then carry out all the work again, but this time correctly, taking into account the dew point. However, this will lead to high costs for building owners.
Determining the dew point and performing the calculation
A person living in a house in which high humidity prevails in the interior is faced with big problems. The presence of condensation leads to health problems. There is a high risk of developing a disease such as asthma. In addition, condensation negatively affects building structures, reducing their service life.
If the humidity level inside the house is high, then Mold forms on the walls and ceiling, which is difficult to get rid of. In such cases, drastic measures have to be taken - replacing the wall and ceiling surface. This is the only way to get rid of harmful microorganisms.
To avoid these unpleasant moments, it is necessary to calculate the dew point in advance. In this way, you can find out whether it makes sense to perform in a separate building renovation work, insulate walls.
It's worth saying that each building has its own individual dew point. This means that the work to calculate it will be carried out with certain differences.
Before proceeding with the calculation of this parameter, the following factors must be taken into account:
During construction, the developer must ensure that the humidity in the materials used during construction does not increase and a dew point does not form. Only a specialist can measure the dew point correctly. If the dew point in the premises of the house is high, the specialist will conclude that the insulation of the building was carried out incorrectly.
This answer can be considered partly correct, since proper insulation the dew point moves, as a result, this indicator changes. In addition, repair work carried out using technology affects the appearance of condensation on the walls.
Instructions for determining the dew point from the table
Tools for determination
To correctly determine the dew point, the following tools will be required during work:
- thermometer;
- hygrometer;
- non-contact thermometer.
Calculation steps
In the room in which the dew point is measured, It is necessary to measure 60 cm from the floor surface and place the thermometer at this height. It can be placed on the table surface. Using a thermometer, you next need to measure the air temperature. Then you should use a hygrometer and measure the humidity in the room. Based on the values in the table, you can determine the dew point.
After this, it remains to find out whether it is possible to carry out work in such a room. For example, the owner plans to insulate the room or install polymer floors in it. To find out whether there is any point in carrying out such work, they resort to using a special non-contact thermometer. To do this, measure a distance of 60 cm from the floor again, after which the surface temperature is measured. If you do not have a non-contact thermometer, then in this case you need to take a regular thermometer and wrap it in a cloth. After 15 minutes, readings must be taken.
At the final stage, it is necessary to compare the two results. If the surface temperature differs by 4 degrees from a certain dew point, this indicates that high humidity prevails in the room and there is a high dew point. In this case, work on insulating structures should be carried out under the supervision of a specialist. Before they begin, calculations must be made of the thickness of the material, which will be optimal for high-quality insulation.
How to solve the problem with the emerging dew point?
There are several possible places on the walls of a building where a dew point may appear:
In such cases, to solve the problem, you can add a vapor barrier to the wall surface. This will ensure that water vapor is retained and will not pass through the walls into the room. And this will eliminate the occurrence of dew point on the surface of the wall and ceiling surface.
Conclusion
Dew point is an important indicator that many developers do not pay attention to during construction. Namely, the service life of building structures depends on it. If this parameter is not taken into account, then the walls will be wet during operation, which can lead to the development of rotting processes in the structure. Mold forms on the walls, and this can negatively affect human health.
When insulating walls, this parameter must be taken into account. Only in this case can high-quality thermal insulation of structures be carried out. To determine this parameter, if the owner of the building does not have experience in this matter, it is better to involve a qualified specialist. He will be able not only to correctly calculate this parameter in the building, but also to give recommendations that will help you carry out repair work efficiently and avoid high humidity in the premises of the house.
The dew point is the temperature to which the air must cool for the water vapor it contains to reach a state of saturation and begin to condense into dew. Simply put, this is the temperature at which condensation occurs.
The dew point temperature is determined by only two parameters: temperature and relative humidity. The higher the relative humidity, the higher the dew point and the closer to the actual air temperature. The lower the relative humidity, the lower the dew point than the actual temperature.
Dew point table
A table with dew point temperature for various temperatures (from -5°C to 35°C) and relative humidity (from 40% to 95%) of indoor air can be found in the reference Appendix R to SP 23-101-2004 “Thermal Thermal Design” protection of buildings." Unfortunately, there are several typos in this table. I have prepared it for you, the typos have been corrected.
Formula for calculating dew point
You can use the formula to approximately calculate the dew point Tp (°C) depending on the air temperature T (°C) and its relative humidity Rh (%):
The formula has an error of ±0.4 °C in the range of air temperature T from 0°C to 60°C, dew point temperature Tp from 0°C to 50°C, relative humidity Rh from 1% to 100%.
Devices with dew point determination
Psychrometer (psychrometric hygrometer) is a device for measuring air humidity and temperature. The psychrometer consists of two alcohol thermometers, one of them is a regular dry thermometer, and the second has a humidification device. Due to the evaporation of moisture, the moistened thermometer cools. The lower the humidity, the lower its temperature. At 100% humidity, the thermometer readings are the same. To determine relative humidity, a psychrometric table is used. Such devices are currently used only in laboratory conditions.
The most convenient in the practice of inspecting buildings are portable electronic thermohygrometers with an indication of temperature and relative air humidity on a digital display. Some models of thermohygrometers also have a dew point indication.
Calculation of dew point in a thermal imager
Some thermal imager models have a built-in function for calculating the dew point in real time and displaying an isotherm on the thermogram, which clearly shows surfaces where the temperature is below the dew point during thermal imaging. This function is available, for example, in the line of thermal imagers for construction purposes (series “B” from “Building”) FLIR Systems.
The dew point isotherm can be added to the thermogram later in a computer processing program. To calculate, you will need to set the air temperature and humidity. The isotherm will shade on the thermogram all surfaces whose temperature is below the dew point. Do not forget that this function shows areas dangerous for condensation only under thermal imaging conditions. If the outside temperature rises and the indoor humidity drops, the dangerous zones will disappear from the thermogram (the structures will be warmer and the dew point will be lower). Below are screenshots of the FLIR and TESTO programs.
Dew point in construction
About the significance of condensation and dew point during operation building structures, the position of the dew point or the plane of possible condensation in the walls, the assessment of structural defects according to the dew point criterion using thermal imaging I will write in one of the following publications.
