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Can vapour pass through pir insuoation - Thermal resistance of vapour barrier

Technical information Cold storage Insulation and vapour barriers

Insulation and vapor barrier

The purpose of insulation to reduce heat transfer from warmer ambient interior of the cabin. Many different materials were used for this purpose, but most of the building now with the following:
  1. Mineral fiber of high quality non-flammable bond Rockwool with the vertical structure of the fiber that provides a high level of insulation, high fire resistance and sound characteristics. Rockwool is a water repellent, free (H)CFC and fully recyclable solution to the walls and ceiling of application in hygienic and cold environment, when the internal temperature is above 0C.
  2. Foamed polyurethane. Basic chemicals are mixed in liquid form, foaming agents, and the swell in the low density foam, which sets by polymerization in hard mass. As swelling of the material will be expanded in any form requires, it is ideal for the core sandwich panels, and sheet material, the skins can be flat or profiled. When panels are made mixture is injected between the inner and outer skins and extends to the desired thickness, adjacent to the lining.
  3. Polyisocyanurate (PIR).

    This is one of the most effective heat-insulating materials. Its low density foam shows excellent thermal stability and reduce Flammability, when compared with polyurethane foam. Polyisocyanurate insulation products have excellent thermal conductivity, do not support the growth of fungi, resistant to moisture and (H)CFC - free.
Polystyrene is used until recently, but because of the fire risk, panels made from this material are not acceptable to the insurers for new buildings and many existing. The ability of insulation to reduce heat flux is expressed as resistance or its inverse conductivity. Units last watt per metre Kelvin (W/(m, K)). The values of these materials are used as follows:
  • Mineral fiber 0.030.04 W/(m K)
  • Polystyrene 0.0350.45 W/(m K)
  • Foamed polyurethane 0.0250.03 W(w-K)
  • Polyisocyanurate 0.02 W/(m K)

U-value is used to describe the characteristics of individual panels or building components. It is defined as the speed of the heat flux through a unit area of any building component through the unit of the overall difference in temperature between the two sides of the component. The term 'U' is the total heat conductivity outside and inside, covering all modes of heat transfer. Unit W/m2K.

The insulation material is generally supplied as sandwich panels coated steel outer casing. They must be highly impermeable to water vapor. Humidity in the room will condense on a reel, and if enough cold will freeze. This will decrease the humidity inside the building, and it will, as a rule, the approach saturation pressure on the coil fin temperature. Since this is lower than the vapour pressure of the air, water vapor will attempt to diffuse from the hot side to the cold, through walls (see Fig. 15.4). At the same time, heat passing through the wall, and the temperature at any point within the insulation will be proportional to the distance through it.

At some point through the wall, the temperature will be equal to the saturation temperature of any water vapor, which is allowed to pass through it, and condensation of liquid water will occur in isolation. This process will continue, and the water will travel inside, until it reached that part of the insulation at temperature 0C, where it will freeze. Effect of water to fill the air holes in the story and increase its conductivity. Ice, if formed, will be expanded and split insulation.

This is to prevent the deterioration of insulation, vapor barrier required by warm face. It should be continuous and offer the best possible barrier to the transfer of water, steam. Use impermeable materials on both skins requires a thorough study of sealing the joints. He sometimes thought that plastic insulation materials because they are not easily absorb moisture and vapour barrier. It is not, and no reliance should be placed on a small pair transfer, that they may have.

Great care must be exercised in the wall on the floor junctions, door thresholds and all changes to the direction of the walls and ceilings. In the case of wall-floor-junction, this will often occur in two different types of construction, i.e. : preliminary wall slabs insulation. Satisfactory continuous vapor barrier in need of thorough development.

Any conductive material, such as stone and metal structural elements or refrigerant pipes, which must pass through isolation and conduct heat and the external part can become cold enough to collect condensation and ice. Such a thermal bridges should be separated by some distance, either inside or outside the main skin to avoid this. If outside, vapor barrier, of course, need to be continuous with the basic skin vapor barrier...

 
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