Each of us has repeatedly witnessed the formation of water droplets on surrounding objects and structures. This is explained by the fact that the surrounding air is cooled over an object brought from frost. Saturation occurs with water vapor, and dew condenses on the subject.
Misting the windows in the apartment is of the same nature. The reason “windows cry” is because of the condensation processes that are affected by humidity and ambient temperature.
Condensation is closely related to the concept of dew point. For a better understanding of the described phenomena, it is simply necessary to consider this factor in more detail.
Dew point. What is it?
The dew point is the cooling temperature of the surrounding air, at which the water vapor that it contains begins to condense, forming dew, that is, this is the temperature of condensation.
This indicator depends on two factors: air temperature and its relative humidity. The dew point of the gas is higher, the higher its relative humidity, that is, it approaches the actual temperature of the surrounding air. Conversely, the lower the humidity, the lower the dew point.
How to calculate the dew point?
The calculation of the dew point is important in many aspects of life, including in construction. The quality of life in new buildings and premises that have already been commissioned depends on the correct determination of this indicator. So how to determine the dew point?
To determine this indicator, use the formula for the approximate calculation of the dew point temperature Tr (° C), which is determined by the dependence of the relative humidity Rh (%) and air temperature T (° C):
With which instruments is it calculated?
So how is dew point calculated in practice? The definition of this indicator is carried out using a psychrometer - a device consisting of two alcohol thermometers, which measures humidity and air temperature. Nowadays it is used mainly in laboratories.
For the inspection of buildings , portable thermohygrometers are used - electronic devices, on the digital display of which data on relative humidity and air temperature are displayed. On some models, even the dew point is displayed.
Also, the function of calculating the dew point have some thermal imagers. At the same time, a thermogram is displayed on the screen, on which surfaces with a temperature below the dew point are visible in real time.
Dew Point Calculation Table
With the help of household psychrometers, it is easy to measure humidity and ambient temperature. Using the display of this unit, the condensation temperature can be found using the table. According to the calculated indicators of temperature and humidity, the dew point is determined. The table of its calculation has the following form:
How is dew drop temperature determined in construction?
Dew point measurement is a very important stage in the construction of buildings, which must be carried out at the project development stage. The possibility of condensation of indoor air depends on its correctness, and, consequently, the comfort of further living in it, as well as its durability.
Any wall has a certain humidity. That is why, depending on the wall material and the quality of thermal insulation, condensation may form on it. The dew point temperature depends on:
- humidity in the room;
- its temperature.
So, using the table above, you can determine that in a room with a temperature of +25 degrees and a relative humidity of 65%, condensation will form on surfaces with a temperature of 17.5 degrees and below. You should remember the pattern: the lower the humidity in the room, the greater the difference between the dew point and the temperature in the room.
The main factors that affect the location of the dew point include:
- climate;
- temperature inside and outside the room;
- humidity inside and out;
- mode of living in the room;
- quality of functioning of the heating and ventilation systems in the room;
- wall thickness and material;
- insulation of the floor, ceiling, walls, etc.
Features of insulated walls
In many rooms, wall insulation is completely absent. In such conditions, the following dew point behavior is possible depending on its location:
- Between the outer surface and the center of the wall (the inner part of the wall always remains dry).
- Between the inner surface and the center of the wall (condensation may appear on the inner surface under the condition of a sharp cooling of air in the region).
- On the inner surface of the wall (the wall will remain wet throughout the winter period).
How to insulate a wall?
In the insulated wall, the dew point can be located in different places of the insulation, which depends on a number of factors:
- Thermal insulation properties of a heater decrease as its humidity level increases, since water is an excellent heat conductor.
- The presence of insulation defects and gaps between the insulation and the wall surface creates good conditions for the formation of condensate.
- Dew drops significantly reduce the insulating properties of the insulation, and are also helpful for the development of fungal colonies.
Thus, one should understand the risk of using moisture-transmitting materials for wall insulation, since they are susceptible to loss of heat-shielding qualities and gradual destruction.
In addition, be sure to pay attention to the ability of the materials selected for wall insulation to withstand ignition. It is better to opt for materials with an organic content of less than 5%. They are considered non-combustible and are most suitable for warming residential premises.
External wall insulation
An ideal option for protecting the room from damp and cold is external wall insulation (provided that it is made in compliance with technology).
In the event that the insulation thickness is optimally selected, the dew point will be in the insulation itself. The wall will remain completely dry throughout the entire cold period, even with a sharp cooling, the dew point will not reach the inner surface of the wall.
If the thermal insulation thickness was not calculated correctly, some problems may arise. The dew point will move to the interface between the insulating material and the outside of the wall. Condensation may occur in the cavities between the two materials and moisture may accumulate. In winter, when the temperature drops below zero, the moisture will expand and turn into ice, contributing to the destruction of thermal insulation and partly the walls. In addition, constant surface humidity will lead to mold.
With complete non-compliance with the technology and gross errors in the calculations, variants of displacement of the dew point to the inner surface of the wall are possible, which will lead to the formation of condensation on it.
Internal wall insulation
Insulating the wall from the inside is initially not the best option. If the insulation layer is thin, the dew point will be on the border of the insulating material and the inner surface of the wall. Warm air in a room with a thin layer of thermal insulation will practically not reach the inner side of the wall, leading to the following consequences:
- high probability of getting wet and freezing the wall;
- moistening and, as a consequence, the destruction of the insulation itself;
- excellent conditions for the development of mold colonies.
However, such a method of warming the room can be effective. To do this, you must comply with some prerequisites:
- The ventilation system must comply with the regulations and prevent excessive humidification of the surrounding air.
- the thermal resistance of the design of the fence, according to regulatory requirements, should not exceed 30%.
What is the risk of ignoring condensation in construction?
In winter, when the temperature is almost constantly below zero degrees, warm indoor air, in contact with any cold surface, is supercooled and falls on its surface in the form of condensate. This occurs if the temperature of the corresponding surface is below the dew point calculated for the data of temperature and humidity.
If condensation occurs, the wall is in a wet state almost always at low temperatures. The result is the formation of mold and the development of a wide variety of harmful microorganisms in it. Subsequently, they move into the surrounding air, which leads to various diseases of residents, often in the room, including asthmatic disorders.
In addition, houses affected by mold and fungal colonies are extremely short-lived. Destruction of the building is inevitable, and this process will begin with damp walls. That is why it is extremely important to carry out correctly all calculations regarding the dew point at the design and construction stage of the building. This will make the right choice regarding:
- wall thickness and material;
- thickness and material of the insulation;
- a method of wall insulation (internal or external insulation);
- choosing a ventilation and heating system that can provide the optimal microclimate in the room (the best ratio of relative humidity and air temperature).
Calculation of the dew point in the wall can be done independently. In this case, it is necessary to take into account the peculiarities of the climatic region of residence, as well as other previously mentioned nuances. But still, it is better to contact specialized construction organizations that deal with such calculations in practice. And the responsibility for the accuracy of the calculations will lie not with the client, but with the representatives of the organization.