What is the dew point? How to calculate the dew point?

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. There is a saturation with water vapor, and the object condenses with dew.

The same nature has fogging windows in the apartment. The reason that "windows are crying" are condensation processes, which are affected by the humidity and temperature of the surrounding air.

The formation of condensate is closely related to the concept of the 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 is contained in it starts to condense, forming a dew, that is, the temperature of condensate precipitation.

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?

Calculation of the dew point is important in many aspects of life, including construction. From the correct definition of this indicator depends the quality of life in new buildings and long-abandoned premises. So how to determine the dew point?

To determine this indicator, use the formula for approximate calculation of the dewpoint temperature Tp (° C), which is determined by the dependence of the relative humidity Rh (%) and air temperature T (° C):

By what instruments is it calculated?

So how do you calculate the dew point in practice? The definition of this indicator is made using a psychrometer - a device consisting of two alcohol thermometers, which measures the humidity and air temperature. Nowadays it is used mainly in laboratories.

For the survey of buildings , portable thermo-hygrometers are used - electronic instruments, on the digital display of which data on the relative humidity and air temperature are displayed. On some models, even the dew point is displayed.

Also, some thermal imagers have a dew point calculation function. In this case, a thermogram is shown on the screen, on which real-time surfaces with temperatures below the dew point are visible.

Dew point calculation table

With the help of household psychrometers it is easy to measure the humidity and temperature of the surrounding air. Using the display of this instrument, the temperature of condensation can be found using the table. According to the calculated temperature and humidity, the dew point is determined. The table of its calculation has the following form:

How is the temperature of the dewfall in construction determined?

Measuring the dew point is a very important stage in the construction of buildings, which must be carried out at the stage of project development. From its correctness depends the possibility of condensation of air inside the premises, and consequently, the comfort of further residence in it, as well as its durability.

Any wall has a certain humidity. That is why, depending on the material of the wall and the quality of thermal insulation, it can form condensation. The temperature of the dew point depends on:

• Air 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%, the condensate will form on surfaces with a temperature of 17.5 degrees and below. It should be remembered the regularity: 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 influence the location of the dew point are:

• climate;
• Temperature inside and outside the room;
• Humidity inside and out;
• Mode of living indoors;
• 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, there is no wall insulation . In such conditions, the following dew-point behavior options are possible depending on its location:

1. Between the outer surface and the center of the wall (the inner part of the wall always remains dry).
2. Between the inner surface and the center of the wall (condensation may appear on the inner surface provided there is a sharp cooling of the air in the region).
3. On the inner surface of the wall (the wall will remain wet throughout the winter period).

How to properly insulate the wall?

In the insulated wall, the dew point can be located in different places of the insulation, which depends on a number of factors:

1. Thermal insulation properties of the insulation decrease as the level of its humidity increases, because water is an excellent conductor of heat.
2. The presence of thermal insulation defects and gaps between the heater and the wall surface creates good conditions for the formation of condensate.
3. Dew drops significantly reduce the thermal insulation properties of the insulation, and are also a support for the development of fungal colonies.

Thus, one should understand the risk of using moisture-transmitting materials for insulation of walls, as they are subject to loss of heat-shielding qualities and gradual destruction.

In addition, be sure to pay attention to the ability of the materials chosen for the insulation of walls to withstand the ignition. It is better to choose the materials with the content of organic substances less than 5%. They are considered to be non-combustible and are most suitable for warming living quarters.

External wall insulation

Ideal option for protecting the room from dampness and cold is external insulation of walls (provided that it is performed in compliance with the technology).

In the event that the thickness of insulation is chosen optimally, the dew point will be in the insulation. The wall will remain absolutely dry throughout the cold period, even with a sharp cooling, the dew point will not reach the inner surface of the wall.

If the thickness of the thermal insulation has not been calculated correctly, some problems may arise. The dew point will move to the interface of the thermal insulation material and the outside of the wall. Condensation may form in the cavities between the two materials and moisture may accumulate. In winter, when the temperature falls below zero, the moisture will expand and turn into ice, contributing to the destruction of the thermal insulation and partly the walls. In addition, the constant humidity of the surfaces will lead to the formation of mold.

With complete non-observance of 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 condensation on it.

Internal wall insulation

Warming the wall from the inside - initially not the best option. If the layer of thermal insulation is thin, the dew point will be on the boundary of the insulating material and the inner surface of the wall. Warm air in the room with a thin layer of thermal insulation will practically not reach the inside of the wall, leading to the following consequences:

• High probability of wetting and freezing of the wall;
• Humidification and, as a result, destruction of the insulant itself;
• Excellent conditions for the development of mold colonies.

However, this way of warming the room can be effective. For this, it is necessary to observe certain mandatory conditions:

• The ventilation system must comply with the regulations and do not allow excessive moistening of the ambient air.
• The thermal resistance of the fence construction, according to regulatory requirements, should not exceed 30%.

What is fraught with the neglect of condensate loss in construction?

In winter, when the temperature is almost always below zero degrees, the warm air inside the room, in contact with any cold surface, is supercooled and drops out on its surface in the form of condensate. This occurs provided that the temperature of the corresponding surface is below the dew point calculated for the temperature and humidity data.

If condensation occurs, the wall is wet almost always at a low temperature. The result is the formation of mold and the development in it of a wide variety of harmful microorganisms. 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. The destruction of the building is inevitable, and this process will begin with the 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 make the right choice regarding:

• Thickness and material of walls;
• Thickness and insulation material;
• A method of insulation of walls (internal or external warming);
• Selection of a ventilation and heating system that can provide an optimal microclimate in the room (the best ratio of the relative humidity of air and its temperature).

Calculation of the dew point in the wall can be made independently. In this case, it is necessary to take into account the peculiarities of the climatic region of residence, as well as other nuances given earlier. But still it is better to contact specialized construction organizations that deal with such calculations in practice. Yes, and the responsibility for correctness of calculations will lie not on the client, but on the representatives of the organization.