Background
Moisture buffering has become an important topic especially when talking about ventilation. Some buildings are usually built without any additional attention given to material choice. This is usually seen in residential areas and office parks. Typically the material that is stated to be the best moisture buffer performance is cellular concrete due to its porous nature. Almost all other building materials are usually expected to buffer at a moderate rate. Regardless, some attention to material choice should be given to address the variations of atmospheric humidity. This is especially true in programs where people are required to be indoors for the majority of the day. Elevated humidity levels can damage the building as well as have a number of adverse effects on the human body. According to ASHRAE, interior humidity should not surpass a 65% dew point if the space is to be considered comfortable. Bacteria and viruses which would cause an occupant to fall ill typically thrive in air that maintains a relative humidity above 60%.
In light of the headed trajectory of the current climate, active sustainable building technologies are often selected to reduce the implications of the changing climate and/or enhance the qualities of interior spaces. However, many of these active technologies can consume more energy and water than they are conserving. In colder climates technologies such as solar power, cool roofs, and green walls tend to be either less effective or require frequent maintenance. Green walls have become a prevailing technology in light of the current headed trajectory of the climate. The dominant uses of green walls include but are not limited to regulating both air quality and humidity. However, green walls demand maintenance obligations which if ignored could create moisture-related issues as well as weaken building both structurally and aesthetically over time. The added moisture and added weight can eventually compromise a building’s waterproofing layer. While green walls have many benefits to their respective environments, they may also cause financially detrimental complications. A prime example of this is the construction of the UK's first living wall in Islington, North London. The wall remained lush for 3 years until eventually all the plants died due to poor maintenance and lack of design sensibility. A London council was then accused of wasting £100,000 when the original intent was to provide a vertical Greenland which would regulate humidity whilst simultaneously providing the aesthetics of view. Whilst this was an exterior green wall, it raises the question of could this have been avoided by providing instead a façade with moisture buffering properties and a green roof for the aesthetics?
Literature Review
Zhang, Mingjie, Menghao Qin, Carsten Rode, and Zhi Chen. “Moisture Buffering Phenomenon and Its Impact on Building Energy Consumption.” Applied Thermal Engineering 124 (September 2017): 337–45. https://doi.org/10.1016/j.applthermaleng.2017.05.173.
This study utilizes the moisture buffer value to calculate the moisture uptake/release by hygroscopic materials exposed to different types of humidity variations. A high moisture buffering capacity of materials could significantly improve the indoor environmental quality of buildings and reduce their latent heat load by passively controlling the indoor moisture condition. According to the results, energy savings could amount to 25%-30% for climates in temperate and semi-arid regions when using hygroscopic materials. The hygroscopic materials that were tested are gypsum board, Aerated Concrete, Concrete and Wood-fiber board. The two highest energy saving hygroscopic materials that were tested were the wood-fiber boards and the aerated concrete.
This study utilizes the moisture buffer value to calculate the moisture uptake/release by hygroscopic materials exposed to different types of humidity variations. A high moisture buffering capacity of materials could significantly improve the indoor environmental quality of buildings and reduce their latent heat load by passively controlling the indoor moisture condition. According to the results, energy savings could amount to 25%-30% for climates in temperate and semi-arid regions when using hygroscopic materials. The hygroscopic materials that were tested are gypsum board, Aerated Concrete, Concrete and Wood-fiber board. The two highest energy saving hygroscopic materials that were tested were the wood-fiber boards and the aerated concrete.
Cascione, Valeria, Carl-Eric Hagentoft, Daniel Maskell, Andy Shea, and Pete Walker. 2020. "Moisture Buffering in Surface Materials Due to Simultaneous Varying Relative Humidity and Temperatures: Experimental Validation of New Analytical Formulas" Applied Sciences 10, no. 21: 7665. https://doi.org/10.3390/app10217665
Research was conducted to understand material reactions to different environments and to improve the simplified model. According to the study, the development of the experiment is a simplified model, which makes it feasible to predict the potential future impact of climate changes on buildings without the need for complex and memory consuming computational methods. For this experiment , a climate chamber was constructed. Using the climate chamber, two hygroscopic materials (clay and gypsum) were tested. Based on the results, gypsum has a higher moisture capacity than clay due to its porosity and pore structure.
Research was conducted to understand material reactions to different environments and to improve the simplified model. According to the study, the development of the experiment is a simplified model, which makes it feasible to predict the potential future impact of climate changes on buildings without the need for complex and memory consuming computational methods. For this experiment , a climate chamber was constructed. Using the climate chamber, two hygroscopic materials (clay and gypsum) were tested. Based on the results, gypsum has a higher moisture capacity than clay due to its porosity and pore structure.
Initial Potential Experiment Trajectory
Plant measurements during day and night (picotech.com)
*Approach was disregarded as the experiment no longer requires the presence of a plant
*Approach was disregarded as the experiment no longer requires the presence of a plant
Gong, Xue-Wei, Guang-Hui Lü, Xue-Min He, Binoy Sarkar, and Xiao-Dong Yang. “High Air Humidity Causes Atmospheric Water Absorption via Assimilating Branches in the Deep-Rooted Tree Haloxylon Ammodendron in an Arid Desert Region of Northwest China.” Frontiers in Plant Science 10 (May 8, 2019). https://doi.org/10.3389/fpls.2019.00573.
This study investigates the reaction of terrestrial plants when exposed to levels of high humidity vs moderate humidity conditions. After moisture was absorbed with the plant's branches, the plants leaves began to degenerate. The reaction of a plant to humidity depends highly on the species of plant. Aquatic plants for instance do not experience a similar reactions since they are used to being in conditions with levels of high humidity.
This study investigates the reaction of terrestrial plants when exposed to levels of high humidity vs moderate humidity conditions. After moisture was absorbed with the plant's branches, the plants leaves began to degenerate. The reaction of a plant to humidity depends highly on the species of plant. Aquatic plants for instance do not experience a similar reactions since they are used to being in conditions with levels of high humidity.
Design of high humidity experiment.
Vox, Giuliano, et al. “Green Façades to Control Wall Surface Temperature in Buildings.” Building and Environment, vol. 129, 2018, pp. 154–166., https://doi.org/10.1016/j.buildenv.2017.12.002.
The use of green façades can increase evapotranspiration in the summer and thermal insulation in the winter, while also shading the building physically. A two-year experiment was conducted to investigate these benefits. In this study, perforated bricks were used to construct three vertical walls: two walls were covered with evergreen plants and the third wall was left uncovered. This research fills the gap in literature concerning the lack of data on building thermal performance in the Mediterranean climate area for all seasons in the year.
The use of green façades can increase evapotranspiration in the summer and thermal insulation in the winter, while also shading the building physically. A two-year experiment was conducted to investigate these benefits. In this study, perforated bricks were used to construct three vertical walls: two walls were covered with evergreen plants and the third wall was left uncovered. This research fills the gap in literature concerning the lack of data on building thermal performance in the Mediterranean climate area for all seasons in the year.
Widiastuti, Ratih, et al. “Data on Records of Temperature and Relative Humidity in a Building Model with Green Facade Systems.” Data in Brief, vol. 28, 2020, p. 104896., https://doi.org/10.1016/j.dib.2019.104896.
A realistic study of the impact of vertical greening on an indoor thermal environment was presented in this paper. In this study, actual wall to wall ratio models were built rather than a fictional model without windows. This model was examined in an annual cycle elevation which entertained both hot seasons and cold seasons. According to the findings, existing research overstated the positive effects of vertical greening on the indoor thermal environment in hot seasons, while ignoring its possible negative effects in cold seasons.
A realistic study of the impact of vertical greening on an indoor thermal environment was presented in this paper. In this study, actual wall to wall ratio models were built rather than a fictional model without windows. This model was examined in an annual cycle elevation which entertained both hot seasons and cold seasons. According to the findings, existing research overstated the positive effects of vertical greening on the indoor thermal environment in hot seasons, while ignoring its possible negative effects in cold seasons.