Test Method To Quantify The Wicking Properties Of Porous Insulation Materials Designed To Prevent Interstitial Condensation

Abstract

Applying insulation to the interior side of the wall often is the only option for a thermal retrofit, especially when heritage buildings are concerned. In order to avoid harmful condensation beneath the interior insulation, most systems include a vapor retarding layer which also reduces the drying potential of the wall. Therefore, vapor-permeable insulation materials have been developed that are capable of wicking condensing moisture away from the wall/insulation interface back to the surface in contact with the indoor air. A widely used and extensively studied material with such characteristics is Calcium-silicate. Following an increasing demand, several water-wicking insulation materials have appeared on the market. However, there is no consensus yet on how to quantify their efficiency in preventing critical moisture conditions at the interface.Since the water absorption coefficient of a porous material is dominated by the largest capillaries, this coefficient does not seem appropriate for the characterization of the material's liquid transport properties in the hygroscopic region. Therefore, a new measuring method for wicking insulation materials has been devised. One side of a laterally sealed material sample is controlled at a temperature below the dew-point by a Peltier-unit, while the other side is exposed to the air of a climate chamber. At the dynamic equilibrium of the opposing moisture fluxes (liquid and vapor), moisture distribution recordings are performed using Nuclear magnetic resonance (NMR). This allows the determination of the material's liquid diffusivity function in the hygroscopic region, whose magnitude is a measure for the wicking efficiency of the material.

Hygrothermal performance of a brick wall with interior insulation in cold climate: Vapour open versus vapour tight approach

“…Assessing the share between the flows in these experiments is based on assumptions as both have the same direction and are subjected to rather extreme conditions (water contact and full saturation). To gain more information on this, Binder et al (2010Binder et al ( , 2013Binder et al ( , 2014 proposed a capillary condensation redistribution (CCR) test, where vapour and liquid flows are in opposite directions. In this test, a temperature difference causes a condensation plane inside a material sample while mass change and moisture profile are monitored.…”

Moisture control design has to respond to all relevant hygrothermal loads

“…To be fair, establishing moisture content limits is also a challenge for more sophisticated methods such as hygrothermal simulation models. The main problem with calculating potential amounts of localised condensation is that many modern building materials do not really experience condensation because water vapour is absorbed and redistributed within the pore structure, as, for example, in capillary active insulation materials [24] such as mineralbased insulation panels or masonry blocks and rendering systems with high thermal resistance. Establishing a limit for condensation that happens only on paper respectively in the calculation tool makes little sense.…”

Moisture control design has to respond to all relevant hygrothermal loads

“…To be fair, establishing moisture content limits is also a challenge for more sophisticated methods such as hygrothermal simulation models. The main problem with calculating potential amounts of localized condensation is, that many modern building materials don't really experience condensation because water vapour is absorbed and redistributed within the pore structure, as for example in capillary active insulation materials [24] such as mineral foam insulation or masonry blocks and rendering systems with high thermal resistance. Establishing a limit for condensation that happens only on paper respectively in the calculation tool makes little sense.…”