Heat of Sorption and Moisture Buffering Properties of Building Insulation Materials

Abstract

Latent heat of sorption exchanges in hygroscopic materials can affect thermal comfort, and potentially the heating requirements of buildings, while moisture buffering regulates humidity levels, allowing for a healthy indoor air quality. In this study experiments were conducted to compare the moisture buffering performance of three hygroscopic natural fibre insulation (NFI) materials (hemp-lime, hemp fibre, sheep’s wool) alongside two more conventional materials (glass wool and gypsum plasterboard). Samples with a surface area of 200 × 200 mm were exposed to a cycle of step changes in relative humidity between 53 and 75 %, changing every 12 h in isothermal conditions. Their moisture buffering performance was then determined by their change in mass. Thermocouples were placed on the surface and 15 mm below the surface of each sample to record temperature changes. The hemp-lime sample showed the greatest moisture buffering capacity, around double that of the hemp fibre and sheep’s wool, which had similar performances. In comparison, the mineral wool and gypsum plasterboard samples showed negligible moisture buffering. Temperature changes were greater at 15 mm than at the surface, with the overall balance of heating and cooling approximately equal at dynamic equilibrium. The sheep’s wool saw the largest change in temperature, while the hemp-lime had a higher temperature difference over the whole cycle. These effects will clearly alter internal conditions and should be included in building simulations to determine their impact on energy use.