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De-icing systems for roofs

De-icing systems for roofs The mechanism of formation icings

Precipitation in the form of snow, while on the roof, do not represent any danger. However, if the conditions for snow melting under the influence of a heat source, it turns into water. If the resulting meltwater no way for a quick withdrawal from the roof, upon the occurrence of the corresponding negative temperature it freezes, turning into ice. As conditions for the melting (and the rate of melting) of ice and snow are different, the next short-term effect of the heat source may not be melting, but rather increase ice jams. This mechanism of formation of ice dams can lead to the formation of long icicles in the tens of meters and weighing hundreds of kilograms.

heat source is:
 

  • The atmospheric heat. If the diurnal temperature range with an amplitude reaching 15 0C, then the fluctuations in the range of 3 0: 5 0 C during the day and -6 0 -10 0 C at night are the most favorable conditions for the formation of ice. In the spring, you can add them to the radiation of the sun. Although the surface of ice and snow reflect most of the radiation incident on them, but even a small plaque dirt dramatically increases the absorption coefficient. In addition, fast heat up bare areas roof, and melting is the inside of the layer. Therefore, the formation of frost in the spring is always more intense than in the fall.
  • Proper heat of the roof. Heat occurs on any roof. The minimum extent this occurs on roofs with ventilated attic. However, in recent years has spread the use of attic space to living (the attic), or as a technical floor (where the large number of powerful equipment for heating, ventilation and air conditioning) dramatically changes the requirements for the design of the roof. The lack of effective thermal insulation leads to the fact that beneath the surface of snow lying on the roof (which is a good thermal insulator) is a constant drip melting of snow, and that this process takes place over the entire surface of the roof. Such a roof can be called warm. They are characterized by the formation of ice in a wider range of air temperatures, which in fact can mean danger of icicles for almost the entire cold season.

    Today the most common way to deal with icing - the use of de-icing systems on the basis of the heating cables.
     

de-icing systems on the basis of the heating cables

Application roof de-icing system based on heating cables

The introduction of Frost protection on the basis of the heating cables provided proper design, taking into account the particular design of the roof, allows you to completely eliminate the formation of ice at relatively low prices and low energy consumption, and also to ensure the efficiency of the system organized by the drain in the spring and autumn periods. < br />
Installation of heating cables

De-icing systems work at temperatures below -18 & deg; ...- 20 & deg; C, usually not needed. First, at these temperatures is not icing by the first mechanism and dramatically reduces the amount of moisture in the second. Secondly, under these conditions, the amount of precipitation in the form of snow is also decreasing.

Third, in the melting of snow and water withdrawal for sufficiently long path needs large electric power.

When installing the system it is necessary to bear in mind that the designer must ensure that was the result of 'work' of water free way to complete runoff from the roof.

There are also the boundaries of the capacity of the heating system, established on the basis of practice, failure of which leads to inefficient existing equipment in the specified temperature range, and a significant excess of the latter only leads to a waste of electrical power without any improvement of the system.

These include:

specific power heating cables installed on the horizontal part of the roof. The total power density per unit surface area of ​​the heated part (tray, trough, etc.) must be at least 180-250 W/m2;

  • specific power heating cables in gutters - meet not less than 25-30 W/per meter gutter, and increases as the extension gutter to 60-70 W/m.

    All the above allows to make some general conclusions:


  • Anti-icing system basically 'work' only in spring and autumn periods, as well as during thaws. 'Work' system during the cold period (-15 & deg; ...- 20 & deg; C) not only unnecessary, but can be harmful.
  • The system must be equipped with a temperature sensor and the specialized thermostat, which can be called rather a mini weather station. He has to control the operation of the system and allow for the possibility of adjusting the parameters of temperature taking into account the specific characteristics of the climatic zone, the location and number of storeys of the building.
  • Heating cables should be installed on all the way thawed water, starting from the horizontal gutters and stalls and outlets of ending drain, and in the presence of the entrances to the storm drain - down to the collector below the freezing depth.
  • It is necessary to comply with the standards established by the power heating cables for various parts of the system - horizontal bins and gutters, vertical drains.
     

Standard, designs

The main objectives in the design of roof de-icing systems - make it effective, relatively inexpensive, and apply such methods of attachment, which do not damage would be very critical units of the roof and not to spoil the appearance of the building. This attachment points must be reliable, durable, and do not damage a skin heating cables.

One of the main design principles of attachment is the use of the same materials as for the roof, or are compatible with them.

Safety

Basic requirements are in terms of fire and electrical safety.

To meet them you must fulfill several conditions:
 

  • The system should include only heating cables have the appropriate certificates, including mandatory fire safety certificate. Typically, nonflammable wires or cables that do not support combustion. To use de-icing systems required the manufacturer's recommendations;
  • heating part of the system must be fitted with an RCD or differential automaton with leakage current of less than 30mA (requirements for electrical safety - 10 mA);
  • sophisticated anti-icing system must be split into separate parts with leakage currents in each part does not exceed the above values.

    Heating cables are the main producers have all the necessary certificates and passed approbation as part of anti-icing systems.

    Testing and evaluation

    Tests Frost protection can be divided into two groups: the acceptance and periodicals.

    Routine tests usually begins with tests of insulation resistance heating and distribution cables. Being tested RCD (or Emergency circuit breakers). Are the appropriate protocols, with specific values. The most informative are tested on the operation, during which test the effectiveness of the system.

    It should be noted that the anti-icing system is not instantaneous systems. They are designed to operate in standby mode, and includes just the appearance of precipitation. If the system was not turned on at the beginning of the season, and on the top of a layer of snow has accumulated, it will take time from 6 hours to one day to remove it.

    Difficulties exist at the time of the system in the warm season. It checks the proper functioning of the control apparatus, simulated signals from the sensors, checked the system to enable load mode, turn off the trays, and then drains off.

    Periodic tests are carried out, usually in early autumn to check the technical condition of the system and prepare it for operation. First, the insulation resistance is checked to determine the damaged areas. Then, check the condition of the equipment carried her trial inclusion. After checking the settings made thermostats operating system activation, and it remains a work in standby mode.
     

The hydrophobic composition frost protection

The hydrophobic compositions of anti-icing do not prevent the formation of ice and provide a fast descent newly formed water ice with repeated freeze-thaw cycles, not allowing him to form in large icicles and sinters.

Such hydrophobic composition is applied to metal, concrete and other bases manually by brush, roller or spray onto clean, dry and dusty surface, free from rust, oil, grease, etc. Hardening compositions at temperatures above + 5 0C.

According to the International Academy of Refrigeration (MAX), the adhesive force of water ice to roofing materials of buildings is very high (3 - more than 0.16 MPa, the concrete - 0.22 MPa), and peel tests destroyed the internal structure of the ice, and it rests firmly They remained on the surface of materials. At the same time, the adhesion strength of the ice with anti-icing coating composition and is practically no less than 0.22 MPa.

Coatings that prevent icing are waterproofing, corrosion resistant, environmentally friendly, has high strength and elasticity, maintain high physical and mechanical properties over a wide temperature range, are resistant to UV radiation and precipitation.

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