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Phase change materials (PCMs) could be used in envelopes to moderate indoor temperature while hygroscopic materials could be used in envelopes to moderate indoor humidity. However, it remains unsolved whether these two materials are mixed to generate a better effect than single materials. Therefore, a transient model for coupled heat and moisture transfer through hygroscopic PCMs (HPCMs) was presented. The numerical cases of periodic boundary conditions and realistic weather conditions were conducted to investigate the heat and moisture transfer characteristics of three gypsum-based HPCMs containing different mass ratios of microencapsulated PCMs. Quantitative analyses were conducted to capture the effects of hygrothermal properties on heat and moisture transfer characteristics of HPCMs. The numerical results show that the mixing of PCMs and hygroscopic materials could generate a better temperature-humidity controlling effect than pure hygroscopic material, and the condensation risks inside the envelopes could also be reduced. Both the studied cases indicate that the HPCMs could be applied in building envelopes to passively moderate the indoor temperature and humidity simultaneously, reducing the building energy consumption and condensation risks inside the envelopes. The effects of hygroscopic and moisture transfer properties on temperature-control performance of HPCMs are relatively small, while the thermal properties play an important role in the improvement of temperature-humidity controlling performance of HPCMs with the increase of PCM concentration. [ABSTRACT FROM AUTHOR]

This paper aligns with the rising interest in improving indoor comfort and health of occupants by moisture buffering with hygroscopic materials and the use of bio-based materials with low embodied emissions. The study focuses on literature on light timber frame walls (LTFW) with bio-based insulation and hempcrete walls, both without a vapor barrier. The aim is to highlight the consequences of omitting the vapor barriers in such wall assemblies and to ensure their durability. This review examines two main questions. Firstly, is there a risk of mold growth in LTFW with bio-based insulation and no vapor barrier? Secondly, are there possible links between these building envelopes and the indoor climate and its potential effects on occupants? The findings show that the risk of mold growth in vapor-open walls depends on the external climate, user behavior and applied materials. It is influenced by several factors such as vapor pressure difference, water vapor resistance ratio, exterior finishing, presence of a ventilated cavity, and the hygroscopic properties of insulation materials. Vapor-open walls exhibit a higher risk of mold growth between insulation and exterior lining compared to walls with vapor barriers. Additionally, there is a lack of field studies that visually examine mold growth in vapor-open buildings. While simulations suggest that vapor-open buildings with hygroscopic insulation can buffer interior relative humidity fluctuations, supporting field studies are limited. Further research and field studies are needed to improve the understanding of vapor-open or permeable building and its implications on mold growth as well as on the indoor climate and effects on occupants. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of a series of novel wood fibre, sepiolite and expanded perlite (WSE)-based mortars that have been developed by Hunan University. The evaluation investigated the influence of morphology structure and the effect of different hot-humid environments on hygroscopic properties of WSE-based mortar to form breathable wall which can provide a moderation of moisture, indoor air quality and thermal insulation of building. The microstructure, thermal conductivity, mechanical properties and hygroscopic properties of WSE-based mortar specimens were assessed to characterize the relationship between performances of the material. WSE is an inorganic porous fibre-aggregate mixture. The hygroscopic properties of the mortars can be greatly improved by adding the WSE fibres-aggregates, especially under high temperature (40℃) and high relative humidity (98%) during summer. The addition of admixture can improve the properties of WSE-based mortar to meet requirements of special performances (such as compressive strength) without affecting the hygroscopic properties. The WSE-based breathable wall is a good moisture buffering controller that could improve indoor air quality. The evaluation presented in this paper should provide the design fundamental for development of breathable wall for future built environment, to allow optimizing the boundary conditions for energy saving and control of indoor humidity environment by incorporating the mortars as finishing materials. [ABSTRACT FROM AUTHOR]

As simultaneous heat and mass transfer between building envelopes and indoor air is complicated and expensive to measure in laboratory and field experiments, a numerical model is important in understanding and extrapolating experimental results. In this paper a numerical model that solves simultaneous heat and mass transfer between building envelopes and indoor air is verified using the field measurements presented in Part I of this paper. The verification results show that the model is able to predict the transfer of water vapor, CO2, and SF6 between the building envelope and air. The model is then applied to investigate the humidity, comfort, and air quality in a bedroom of a wooden building located in four European countries (Finland, Belgium, Germany, and Italy). The numerical results show that moisture transfer between indoor air and the hygroscopic structure significantly reduces the peak indoor humidity (up to 35% RH), percent dissatisfied with warm respiratory comfort (up to 10%) and the percent dissatisfied with indoor air quality (up to 25%). [ABSTRACT FROM PUBLISHER]

In this paper, measurements are presented which quantify the mass transfer of tracer gases and water vapor between indoor air and a permeable and hygroscopic building envelope. The transfer of tracer gases through the envelope requires the entire envelope to be permeable, while the transfer of moisture requires sufficient hygroscopic mass to be in contact with the indoor air. The results show that mass transfer can improve the indoor air quality and climate. The diffusion of gases through the building envelope significantly increases the effective ventilation rate for poorly ventilated rooms, but only moderately increases the effective ventilation for well-ventilated rooms. Moisture transfer, on the other hand, has a significant influence on the indoor humidity for both poorly and well-ventilated rooms. [ABSTRACT FROM PUBLISHER]