Numerical analysis of the humidity buffering potential of various hygrothermal coatings under extreme moisture overloading scenarios

Within a closed environment, (e.g. building, car, aircraft) that is hygrically isolated from the exterior climate, one approach that can help reduce the energy required for indoor climate control whilst increasing comfort levels for occupants is to use hygrothermal coatings on top of existing materials. These coatings can re-introduce hygric buffering within the isolated envelope that was lost due to application of retrofitted internal finishes (i.e. – insulation, vapour barriers, paint etc.). The aim of this paper was to perform a parametric analysis using hygrothermal numerical software (WUFI Plus v2.1.1.73) of the humidity buffering potential of various hygrothermal coatings applied to a nominal enclosed indoor environment under extreme moisture loading scenarios and air exchange rates. Three coatings were compared: gypsum plaster, spruce timber and a ‘super absorbent’ desiccant under four building envelope scenarios. The location was chosen as Nottingham, UK and an external climate file was generated to sinusoidally fluctuate exterior relative humidity (RHext) about a median (50%) at constant temperature (T = 23 ºC) for a single peak to peak cycle period of t = 24h. Two sets of increased moisture profiles were applied to the model in order to represent 16 ‘Active Adults’ present in either the morning or evening for a period of t = 4 h. The analysis showed that there was minimal reduction of minimum indoor (RHint) levels when using traditional building materials as interior finishes (i.e. spruce and gypsum), indicating the greater influence of the external environment, RHext on the interior environment as the air exchange rate increased. In contrast, when utilising the super-adsorbent materials, RHint levels remained within the ASHRAE limits (i.e. 40% ≤ RHint ≤ 70% and T = 23 ºC) under both morning and evening overloading schedules and across the full range of air exchange rates.