Advantages of polyurethane as thermal insulation (with practical example)
The high insulating capacity of polyurethane is not achieved in the construction with any other commonly used insulating materials. This special feature is due to the structure of small cells that form the foam, and the composition of the insulating gas occluded inside those cells.
Thanks to its low thermal conductivity , polyurethane reaches the thermal insulation values required in the CTE with the minimum thickness, which allows to preserve a larger living area, with the consequent economic benefit.
On the other hand, if polyurethane thicknesses similar to other materials are incorporated, greater thermal resistance and greater energy savings are achieved , which also results in an economic benefit for the user.
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The thermal conductivity of the polyurethane depends on several factors, such as the percentage of closed cell , the size of the cell, the foam gas used, or the insulation thickness installed. In addition, the thermal resistance depends on the conductivity and thickness of the installed insulation. For this reason, the manufacturers of polyurethane systems declare the thermal resistance in the CE Marking and the Declaration of Performance through a performance table.
The thermal conductivity and the thermal resistance of the projected and injected polyurethane are declared by a performance table according to the thickness.
The best value of thermal conductivity, together with the tightness, absence of joints or holes, adaptability to any substrate and adhesion make the polyurethane projected the most effective insulation.
Robust thermal conductivity value
The thermal conductivity value of polyurethane foam is very robust against the effects of aging , such as the presence of moisture, dirt, lack of air tightness, the presence of holes in the insulation, deterioration of the same or the lack of physical integrity.
Humidity
The thermal conductivity of a wet insulating product is greater than that of a dry thermal insulator, in the same way that a wet sweater holds less than a dry sweater. It will be necessary to prevent an insulation from absorbing water, since a thermal insulation with a water content of 1% by volume can increase its thermal conductivity between 75% and 105% (Building Regulations for the Conservation of Fuel and Power. Assessment, BRUFMA). The projected closed-cell polyurethane has water impermeability .
Decrease in insulating capacity due to water.
Dirt
The thermal conductivity will be seriously damaged by the presence of dirt inside the insulation, so it will be preferable that the product used maintain its thermal properties regardless of the dirt present in the environment. The closed cell structure of the projected polyurethane prevents the entry of particles inside it.
- Decreased insulating capacity due to dirt
- Lack of air tightness
If the main sheet is made of a brick factory, or a lightweight block, it is possible that there is air infiltration from the outside to the interior of the chamber. The polyurethane will prevent these infiltrations of cold air . The movements of air through a non-watertight insulation or with joints can reduce the insulation values up to 40% ("Experimental and theoretical investigation of the influence of natural convection in walls with slab type insulation" and "Sensitivity of insulation wall and ceiling cavities to workmanship ").
Decreased insulating capacity due to air infiltration.
Presence of gaps in the insulation
The joints, the upper and lower termination, the blind holes, etc., could produce convection currents that would communicate both sides of the insulation and reduce their effectiveness. It will be necessary to ensure the total absence of gaps in the insulation, since the presence of gaps in 6% of the insulated surface would cause an increase in thermal conductivity of 30% (Retrofitting: Wall insulation and roof spraying, BRUFMA conference 2004). The projected or injected polyurethane, being a product adhered, in continuous and without joints, will not be harmed by this effect.
- Decreased insulating capacity due to joints
Deterioration of the insulation
In all the insulating products, the installation is the most important aspect so that the final product reaches all the declared thermal performances. A bad installation could cause take-offs and removals that will seriously damage the effectiveness of insulation.
- Decrease in insulating capacity due to deterioration.
Physical integrity
The passage of time can lead to settlements and compaction in inconsistent products. The projected or injected polyurethane, being a rigid material , can not suffer these effects.
- Decrease in insulating capacity due to settlement
- All these effects can occur in combination
Great decrease in insulating capacity due to the combination of different effects.
Being the polyurethane projected or injected a continuous product without joints, there is total absence of thermal bridges caused by joints, overlaps, or encounters with the floors, and it is very easy to treat thermal bridges integrated in the facade as pillars, boxes of blind and contour of holes.
Thermal resistance
From the declared conductivity value, and knowing the applied thickness, the thermal resistance can be known by applying the following relationship.
Where:
- R is the thermal resistance, in m² · K / W
- e is the thickness, in m
- ? is the thermal conductivity, in W / m · K
Thermal Resistance value, in m² · K / W, depending on the conductivity and thickness. For intermediate values, it can be interpolated.
- polyurethane values
- Equivalent thickness
The equivalent thickness of an insulating material is that which equals the thermal resistance of another insulating material of known thickness. That is, it is that thickness that makes both materials have the same insulating capacity.
To calculate the equivalent thickness it is necessary to equalize the thermal resistances of both products.
Where:
- R is the thermal resistance, in m² · K / W
- e1 is the thickness of material 1, in mm
- ? 1 is the thermal conductivity of material 1, in W / m · K
- e2 is the thickness of material 2, in mm
- ? 2 is the thermal conductivity of material 2, in W / m · K
Example of thermal behavior of polyurethane as insulating material
We want to establish the equivalence between a given product of thermal conductivity 0.036 W / m · K and thickness 80 mm and the projected polyurethane of conductivity 0.028 W / m · K.
Starting data:
- e1 Thickness of the given product: 80 mm
- ? 1 Thermal conductivity of the given product: 0.036 W / m · K
- ePU Projected polyurethane thickness
- ? PU Thermal conductivity of the projected polyurethane: 0.028 W / m · K
polyurethane example
That is to say: replacing 80 mm of the given product with 60 mm of projected polyurethane, we will be able to equalize the thermal resistance.
Conclusions of the use of polyurethane as thermal insulation material
- Polyurethane is an insulating material with a very low thermal conductivity value.
- The insulation capacity of polyurethane is very robust against the effects of aging to which thermal insulation is usually exposed.
- With the projected polyurethane, the treatment of thermal bridges is very easy.
- The projected polyurethane reaches the maximum level of insulation with the minimum thickness.
