Hoses with sound insulation and the risk of condensation

For reasons of the safety of structures, demand only vapour-proof hoses.


Introduction
Today, elastic hoses with sound and thermal insulation are commonly used for air-conditioning distributions in buildings. Their structure is formed with an inside hose, sound and thermal insulation and the outside insulation. In elastic hoses designed for suppressing noise, the inside hose is perforated. In quality products of renowned producers, the inside perforated hose is completed with a vapour-tight barrier of foil that does not allow permeation of vapour and water.

Significance of the vapour-tight barrier
Thermal and sound insulation maintains its rated values of thermal resistance and sound attenuation only in a dry condition. If the structure of sound insulated hoses does not contain vapour-tight insulation, the carried air and water vapours penetrate through the perforation into the interspace in the hose. Under certain operational conditions, water vapour condenses in the layer of the thermal and acoustic insulation. Its thermal and acoustic properties deteriorate significantly with wetting. Another danger is that condensed water is distributed by the air duct into the building and flows out uncontrollably at the joints and defects of the outer jacket of the hose. It is difficult to find the origin of the incidence of wet places. The tedious procedure of finding out the cause – which is usually assigned to other sources – leads to construction defects and sanctions against the implementing company. The vapour-tight barrier also restricts the outlet of microscopic fibres through the insulation into air ducts.

Risk versus virtual savings
At present, some assembly companies use hoses with sound insulation without vapour-tight barriers in order to decrease costs. However, such companies not only endanger themselves, but also the investor, user and the building. There is a real risk that it will be necessary to replace hoses with the insulation deteriorated with moisture. Such a replacement means in all cases:
- Restriction of the user operation at the site of repairs
- Expensive disassembly and reassembly of plasterboard ceilings
- Repair of the parts of the building damaged by water
- Supply of new hoses and their installation, disposal of destroyed hoses
- Settlement of sanctions for the restriction of the operation to the user of the building

Therefore, if we take into account the amount of expenses for the remediation of the defect condition, the use of cheap hoses without a water-tight barrier is not only irresponsible, but also unjustified from the economic point of view. Depending on the type of the building, operator, size of air ducts, etc., the overall costs may be CZK 5,000 and more for the replacement of 1 meter of a cheap damaged hose


Examples of condensation
For insulated hoses that are not equipped with a water-tight barrier, it is difficult to assess the amount of condensate formed. The overall amount depends on the hose size, relative humidity of air carried away and its temperature, ambient temperature and the volume of air penetrating the interspace in the hose. The last quantity that is difficult to determine is the volume of air that appears in the boundary zone below the dew point temperature. As an example, let us mention the following:

Waste air has ti = +25 °C, a relative humidity of 65%,  the flow rate of air is 5 m/s,  the inside diameter of the hose is 315 mm, air flow V=1,400 m3/hour. With the dehumidification of 1 gram per kg, the amount of condensate is M=1.4 litre/hour. Even a cautious estimation that only 0.001 of the overall air flow enters the insulation means that 0.0014 litres of water per hour stay in the insulation, thus 0.14 litres of water during 100 hours of operation.


Conclusion
Our experience is that from a single 5 m length of replaced hoses in bathrooms or kitchens, frequently more than 10 litres water were poured out. Also, the extent of subsequent construction and operational loss was considerable. An indispensable advantage of hoses provided with a vapour-tight barrier is a zero outlet of the insulation material into air ducts. The microscopic fibres of insulation and damping materials are often considered as responsible for various health problems.