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 cools over the object brought from the frost. Saturation with water vapor occurs and dew condenses on the object.
The fogging of windows in an apartment has the same nature. The reason that “windows are crying” is condensation processes, which are affected by humidity and ambient temperature.
The formation of condensate 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 this?
The dew point is the cooling temperature of the surrounding air, at which the water vapor 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 a gas is higher the higher its relative humidity, i.e. it approaches the actual ambient temperature. Conversely, the lowerhumidity, the lower the dew point.
How to calculate the dew point?
Calculation of the dew point is important in many aspects of life, including construction. The quality of life in new buildings and premises that have long been commissioned depends on the correctness of determining this indicator. So how do you 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 relative humidity Rh (%) and air temperature T (°C):
Using what instruments is it calculated?
So how is the dew point calculated in practice? This indicator is determined using a psychrometer - a device consisting of two alcohol thermometers that measures humidity and air temperature. Mostly used in laboratories these days.
To inspect buildings, portable thermohygrometers are used - electronic devices, on the digital display of which data on relative humidity and air temperature are displayed. Some models even display the dew point.
Also, some thermal imagers have the function of calculating the dew point. At the same time, a thermogram is displayed on the screen, on which surfaces with temperatures below the dew point are visible in real time.
Dew Point Calculation Table
Using household psychrometers, it is easy to measure humidity and temperatureambient air. Using the display of this device, the temperature of condensation can be found using the table. According to the calculated indicators of temperature and humidity, the dew point is determined. Its calculation table looks like this:
How is dew point determined in construction?
Measurement of the dew point is a very important stage in the construction of buildings, which must be carried out even at the stage of project development. The possibility of air condensation inside the room depends on its correctness, and, consequently, the comfort of further living in it, as well as its durability.
Any wall has a certain moisture content. That is why, depending on the material of the wall and the quality of the thermal insulation, condensation may form on it. The dew point temperature depends on:
- indoor humidity;
- its temperature.
Thus, using the table above, it can be determined that in a room with a temperature of +25 degrees and a relative humidity of 65%, condensate will form on surfaces with a temperature of 17.5 degrees and below. The rule to remember is that 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 are:
- climate;
- indoor and outdoor temperature;
- humidity inside and out;
- indoor mode;
- quality of functioning of heating and ventilation systems in the room;
- wall thickness and material;
- insulation of the floor, ceiling, walls, etc.
Features of non-insulated walls
In many rooms, wall insulation is completely absent. Under such conditions, the following dew point behaviors are possible depending on its location:
- Between the outer surface and the center of the wall (the inside of the wall always stays dry).
- Between the inner surface and the center of the wall (condensation may appear on the inner surface if the air becomes colder in the region).
- On the inside of the wall (the wall will remain wet throughout the winter).
How to properly insulate a wall?
In an insulated wall, the dew point can be located in different places of the insulation, which depends on a number of factors:
- The thermal insulation properties of insulation decrease as the level of its humidity increases, since water is an excellent conductor of heat.
- The presence of insulation defects and gaps between the insulation and the wall surface creates good conditions for condensation to form.
- Dew drops significantly reduce the thermal insulation properties of the insulation, and are also a help for the development of fungal colonies.
Thus, one should understand the risk of using moisture-permeable materials for wall insulation, as they are subject to loss of heat-shielding qualities and gradual destruction.
Besides this,be sure to pay attention to the ability of the materials chosen for wall insulation to resist 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
The ideal option to protect the premises from dampness and cold is external wall insulation (provided that it is done in compliance with the technology).
In the event that the thickness of the insulation is chosen optimally, the dew point will be in the insulation itself. The wall will remain absolutely dry throughout the entire cold period, even with a sharp drop in temperature, the dew point will not reach the inner surface of the wall.
If the insulation thickness was calculated incorrectly, some problems may occur. The dew point will move to the border of the junction of the heat-insulating material and the outer side of the wall. Condensation and moisture can accumulate in the cavities between the two materials. In winter, when the temperature drops below zero, the moisture will expand and turn into ice, contributing to the destruction of the thermal insulation and part of the wall. In addition, the constant moisture of the surfaces will lead to the formation of mold.
In case of complete non-compliance with the technology and gross errors in the calculations, it is possible to shift the dew point to the inner surface of the wall, which will lead to the formation of condensate on it.
Internal wall insulation
Insulate the wall from the inside - initially not the bestthe best way. If the thermal insulation layer is thin, the dew point will be at the border of the insulation material and the inner surface of the wall. Warm air in a room with a thin layer of thermal insulation will hardly reach the inside of the wall, leading to the following consequences:
- high probability of getting wet and freezing of the wall;
- moisturizing and, as a result, the destruction of the insulation itself;
- excellent conditions for the development of mold colonies.
However, this method of warming the room can be effective. To do this, you must comply with some prerequisites:
- ventilation system must comply with regulations and prevent excessive humidification of the ambient air.
- thermal resistance of the fence structure, 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, the warm air inside the room, in contact with any cold surface, is supercooled and falls on its surface in the form of condensate. This occurs provided that the temperature of the respective surface is below the dew point calculated for the air temperature and humidity data.
If condensation occurs, the wall is in a wet state almost always at low temperatures. The result of this is the formation of mold and the development in it of a wide variety ofharmful microorganisms. Subsequently, they move into the surrounding air, which leads to various diseases of the residents who are often indoors, including asthmatic disorders.
In addition, houses affected by mold and fungus colonies are extremely short-lived. The destruction of the building is inevitable, and this process will begin precisely with damp walls. That is why it is extremely important to make all the calculations regarding the dew point correctly at the design and construction stage of the building. This will allow you to make the right choice regarding:
- wall thickness and material;
- thickness and material of insulation;
- Wall insulation method (internal or external insulation);
- choosing a ventilation and heating system that can provide an optimal indoor climate (the best ratio of relative humidity and temperature).
You can calculate the dew point in the wall yourself. In this case, one should take into account the peculiarities of the climatic region of residence, as well as other previously given nuances. But still, it is better to contact specialized construction organizations that deal with such calculations in practice. And the responsibility for the correctness of the calculations will lie not with the client, but with the representatives of the organization.
