The Synergy of Living and Water Wall in Indoor Environment-Case Study in City of Brno, Czech Republic

sustainability Article The Synergy of Living and Water Wall in Indoor Environment—Case Study in City of Brno, Czech Republic Katarina Cakyova 1,2,* , Marian Vertal 3, Jan Vystrcil 2, Ondrej Nespesny 2, David Beckovsky 2, Ales Rubina 4, Jan Pencik 2and Zuzana Vranayova 3   Citation: Cakyova, K.; Vertal, M.; Vystrcil, J.; Nespesny, O.; Beckovsky, D.; Rubina, A.; Pencik, J.; Vranayova, Z. The Synergy of Living and Water Wall in Indoor Environment—Case Study in City of Brno, Czech Republic. Sustainability 2021,13, 11649. https://doi.org/10.3390/su132111649 Academic Editors: Luis PérezUrrestarazu, Panayiotis A. Nektarios and Katia Perini Received: 10 September 2021 Accepted: 17 October 2021 Published: 21 October 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1Center for Research and Innovation in Construction, Faculty of Civil Engineering, Technical University of Košice, Vysokoškolská4, 042 00 Košice, Slovakia 2Institute of Building Structures, Faculty of Civil Engineering, Brno University of Technology, Veveˇrí331/95, 602 00 Brno, Czech Republic; [email protected].cz (J.V.); nespesny[email protected].cz (O.N.); beckovsky[email protected].cz (D.B.); [email protected] (J.P.) 3Institute of Architectural Engineering, Faculty of Civil Engineering, Technical University of Košice, 042 00 Košice, Slovakia; [email protected] (M.V.); [email protected] (Z.V.) 4Institute of Building Services, Faculty of Civil Engineering, Brno University of Technology, Veveˇrí331/95, 602 00 Brno, Czech Republic; [email protected].cz *Correspondence: [email protected]; Tel.: +421-944-731-360 Abstract: The indoor environment that surrounds us and the elements in it affect not only our mood but also the air quality. Vegetation elements are currently more popular, especially for their aesthetic value but also because of the fact that they affect the physical parameters of the indoor environment such as temperature and humidity. Water elements are a similar example. The presented paper combines these two elements to achieve the best possible level of thermal comfort. Experimental verification of the influence of the living wall on air temperature and humidity took place during the heating season in the city of Brno in the space of the university, while three scenarios were created: the effect of the living wall in a semi-open space, an enclosed space, and a space with a water wall with regulated water temperature. The potential of the water wall is determined based on experimental verification in laboratory conditions. The results show that the synergy of the living and water wall in the indoor space may eliminate the risk of too-low humidity during the heating season. Keywords: living wall; water wall; thermal comfort; water consumption; experimental measurement; heating season 1. Introduction In the world of rapid urbanization and pressure on space, as a consequence, urban areas must provide adequate space for people to live in. Studies have shown a beneficial relationship between the natural environment, such as green spaces, and health [ 1 , 2 ]. Exposure to the natural environment has been associated with better mental health [ 3 ] and lower risk of morbidity and mortality [ 4 , 5 ]. Various studies deal with the relationship between the natural environment and improvement of social interaction [ 6 ], decreasing stress levels [ 7 ], and lower exposure to air pollution [ 8 ] or noise [ 9 ]. Similarly to green bodies, blue bodies that are represented by rivers, lakes, and fountains, or other artificial water elements may also have a positive impact on human wellbeing [ 10 ]. In particular, studies have found relationships between blue spaces and increased physical activity [ 11 ], improved mental health [ 3 ], and well-being [ 12 , 13 ] but also social interaction [ 14 ]. The synergy of green and blue spaces in the urban environment also proves to be beneficial in the fight against the so-called urban heat islands (UHI), which the urban areas face more often due to climate change and human activities [ 15 – 18 ]. Most of the studies deal with a cooling effect in combination with green and blue spaces by evapotranspiration, which is the sum of evaporation and plant transpiration from Earth 0 s land and water surface to the atmosphere. The cooling effect of blue–green space has been recognized as a promising Sustainability 2021,13, 11649. https://doi.org/10.3390/su132111649 https://www.mdpi.com/journal/sustainability Sustainability 2021,13, 11649 2 of 23 approach to mitigating urban heat islands (UHI) [ 19 ]. Evaporative cooling might be one of the highly efficient methods of passive cooling for urban spaces and buildings [20]. In the context of high urbanization [ 21 ] and spatial requirements of the population, based on the fact that people spend about 80–95% of their time inside buildings [ 22 ], the inclusion of green construction solutions, such as green roofs and facades [ 23 ], as well as indoor green and blue elements, is currently a trend in building design. The use of previous findings regarding urban green and blue bodies may also lead to the development of the use of natural elements in indoor environments. The living and water walls represent the most commonly used natural elements in building interiors [ 24 ]. As in the case of exterior elements, in the interior, these elements have the potential to improve the physiological and psychological health of people [ 25 , 26 ], especially in school and work environments [ 27 ]. Students who are exposed to the natural environment report low levels of stress, fatigue, health complaints, and better attention [ 28 , 29 ]. Studies [ 30 , 31 ] have also shown that patients exposed to the natural environment recover faster and spend less time in hospitals. These psychological benefits might be related to the so-called biophilia concept (i.e., a preference for interacting in the natural environment as a consequence of our evolutionary development) and based on theories of restorative effects [ 32 ]. With the onset of the COVID-19 pandemic in 2020, society faced new situations, and many people faced forced isolation, which led to negative emotions of fear, disappointment, and insecurity. The survey [ 33 ] across the countries showed a positive influence of greenery and resulted in a shift of the participants’ perception about the beneficial contribution of plants to the emotional welfare of inhabitants. Nearly 40% of participants declared a stronger motivation for having a higher number of plants at home. It turned out that the presence of greenery in the interior reduced the level of stress and depression and increased positive mood during the COVID-19 confinement period. In recent years, the development and scientific interest in interior greenery has increased significantly. The interior greenery is not only represented by plants grown in pots but also by so-called green walls or living walls [ 34 ]. Today, there are many studies that define different systems and designs of these elements [ 34 – 37 ]. It is obvious that indoor greenery offers several benefits, such as producing oxygen through photosynthesis [ 38 ] and affecting the physical parameters of indoor air quality, mainly temperature and humidity [ 34 , 38 – 40 ], CO 2 concentration [ 41 ], and acoustics [ 39 ]. However, the use of green walls in the interior may lead to increased humidity, which can pose a risk associated with mold problems, especially in humid and hot climates [ 36 ]. A study conducted by Hollands and Korjenic [ 42 ] shows an improvement of hygrothermal comfort in schools and offices. In addition, this study shows that the improvement of hygrothermal comfort has significantly reduced the absence due to illness of employees and increased cost savings based on the lower absence rate. The study shows that the vertical indoor greenery has a potential to improve indirect economic effects in the context of reduced sick leave in offices. Although the interest of researchers in investigating the effect of green walls in the indoor environment is high, most studies focus on the effect in a hot climate during cooling season [ 43 ], while the effect during the heating season in a colder climate is not well-studied. As living walls, water features such as fountains and pools but also vertical water features are more and more commonly parts of building interiors, especially for their decorative character. However, compared to green walls, the effect of water elements on physical parameters of the indoor environment has not been sufficiently investigated [ 44 ]. The design of water elements in the interior may vary, either in shape or material. Water walls are most often used in the interior for the smaller space requirements required for their installation. In this case, water flows over the solid material and forms a thin film on it, which is in direct contact with the air, while water circulates in that system and its temperature is not adjusted. As in the case of outdoor water elements, internal water elements are used mainly in the context of evaporative cooling, because of which the air temperature decreases and water temperature increases [ 45 , 46 ]. The evaporation process Sustainability 2021,13, 11649 3 of 23 is also associated with a change in the state of humidity, which increases. This can cause unpleasant air conditions, especially in warm and humid climates [ 47 , 48 ]. It follows that the evaporative cooling potential of water walls is more suitable for hot and dry climates. On the other hand, there is an assumption that with the regulation of the temperature of the water flowing in the system, it is possible to use the water wall with greater flexibility and adapt its use to the state of the air in the indoor environment [ 49 ]. If the water in the system is cooled below the air dew point, condensation will occur, dehumidifying the air in the room [ 44 , 50 ]. Conversely, if the water in the system is heated and maintained at a stable temperature, which will be similar to the air temperature, evaporation will occur, which will increase the humidity, and at the same time, the air in the indoor environment will not be cooled [ 51 ]. A stable water temperature in the system also reduces the risk of Legionella bacteria occurrence, which increases with increasing water temperature [52]. This paper focuses on the effect of a living wall on air physical parameters in the indoor environment during the heating season in the city of Brno, the Czech Republic. Temperature and humidity were monitored in semi-open and closed spaces for one month in February 2021. The humidification capacity of a water wall with controlled water temperature was defined by an equation based on laboratory measurements. Subsequently, this equation was applied using the measured data obtained by monitoring the living wall in the closed space. In addition to the physical parameters of the indoor microclimate, water consumption during the selected period is also monitored. As the synergy of living and water walls in the interior has not been sufficiently researched so far, the presented paper fills the gap of knowledge. It aims to determine the efficiency of a green wall in different types of space as well as to define the area of the water wall for a specific size of space with respect to thermal comfort during the heating season in the city of Brno. 2. Materials and Methods 2.1. Research Methodology To determine the influence of the living and water wall on the physical parameters of the indoor environment (temperature and humidity), the experimental in situ verification of the green wall and the laboratory conditions for the water wall were chosen. In both cases, these were full-scale models. The effect of the living wall on the indoor environment was recorded during the heating period, specifically from 1 February to 1 March 2021. The heating season in the Czech Republic, according to government regulations, begins on 1 September, if the outdoor average air temperature drops below 13 ◦ C for two consecutive days and no further temperature rise is expected. To determine the distribution of humidity and temperature through the living wall, the boundary conditions were monitored and recorded in close proximity to the wall in the vertical direction. In addition to monitoring of the boundary conditions in the proximity of the living wall, boundary conditions were also recorded at the distance of two meters from the living wall. The effect of the water wall on air parameters was monitored at different boundary conditions in the climatic chamber. The obtained data were analyzed and then the humidification capacity of the water wall was determined, which is quantified by the general equation of evaporation rate and shows the dependence between the evaporation rate, air temperature, and relative humidity. The obtained equation was subsequently used to determine the interaction of green and water walls by virtual application in the building interiors. Measured boundary conditions from the experimental verification of the effect of the living wall on air and humidity temperature are used as input values (Figure 1). A total of three scenarios are created. In the case of Scenario 1, the influence of the living wall on physical parameters of the indoor microclimate (temperature and humidity) is monitored in a semi-open space without building modifications. In Scenario 2, the interior is modified, and a wooden structure with a cover foil is built to define the action area of the green wall. In Scenario 3, the synergy of water and living walls in the defined space is considered, and thus the water wall is implemented in the interior theoretically Sustainability 2021,13, 11649 4 of 23 using the determined equation from laboratory measurements and measured data from Scenario 2, specifically the data from the sensor located 2 m from the living wall. In addition to the influence of living and water walls on the indoor microclimate, the water consumption of both walls is determined as well. Figure 1. Research scheme. 2.2. Living Wall 2.2.1. Location The experimental living wall was built in July 2020 at the Institute of Building Structures, Faculty of Civil Engineering, Brno University of Technology. The historical building was built in the 19th century and is not insulated. The living wall is located on the third floor in the corridor tract (Figure 2), which is open from one side. In this space, there is a steel panel radiator, which is connected to the central heating system that works every working day. Experimental measurements were performed at the end of the second third of the heating season; the radiator in the corridor area has a constant heating power during the season, and as it was the same during the scenarios, its impact was neglect. The walls of the corridor and the ceiling are covered with lime–cement plaster; the floor is tiled with ceramic tiles with grout with a hydrophobic effect. The corridor is illuminated through a window with double-insulating glass oriented south-east and with dimensions of 2.05 ×2.65 m (w ×h) . The window was not opened during the test period. The space of the corridor is without mechanical ventilation; therefore, the humidity level could not be controlled and regulated before the start of experimental measurements, and the state of indoor air is mainly influenced by the state of exterior air. As can be seen from Figure 2, the corridor space is delimited mainly by the interior and thus there were minimal thermal fluctuations between the test room of the corridor and the rest of the interior. In the case when the space is closed (Scenarios 2 and 3), the area that is in contact with the exterior is 12% of the total area of the corridor space. Sustainability 2021,13, 11649 5 of 23 Figure 2. Section of floor plan of third floor of Faculty of Civil Engineering building with location of green wall. The city of Brno is located in the south-eastern part of the Czech Republic (coordinates: 49 ◦ 11 0 33 00 N, 16 ◦ 36 0 30 00 E). According to the World Map of Köppen–Geiger Climate Classification, the climate of Brno is the oceanic climate (Cfb) [ 53 , 54 ], which is characterized as mild with no dry season and with warm summers. The coldest months are December (long-term avg. temp. − 0.3 ◦ C), January (long-term avg. temp. − 1.7 ◦ C), and February with a long-term average temperature of 0.2 ◦ C. January and February are the months with the lowest amount of precipitation of 27 and 25 mm, respectively. Even though a long-term average relative humidity for January, February, and December is relatively high (84%, 79%, and 86%, respectively) [ 55 ], due to low temperatures, the humidity ratio is low, and after heating the air to the interior temperature, the relative humidity often drops to a low value [ 56 ], which may cause diseases or irritations of skin, eyes, and upper respiratory tracts [ 57 ]. Due to the common problem with low humidity during the heating season, the measurement of the effect of the living wall in the month of February was chosen, specifically in the period from 01.02. to 01.03.2021. Figure 3shows the average hourly weather data for February 2021 in Brno. The data are obtained from a professional weather station located in the campus of the Faculty of Civil Engineering, which records data in minute intervals [ 58 ]. During this period, the lowest average hourly temperature was − 11.0 ◦ C, which was measured on February 15th. The highest average hourly temperature was recorded on 26 February, specifically 13.1 ◦ C. The average temperature for this period was 0.25 ± 4.9 ◦ C, which approximately corresponds to the long-term average temperature for February in Brno. The relative humidity during the selected period ranged from 41.7% to 100%, and the average value was 91.9 ± 12.7%, which is a significantly higher value compared to the long-term average RH for the city of Brno. The average globe irradiance during this period was 68.74 W/m 2 with a maximum of 566 W/m 2 and the amount of precipitation was 30.5 mm. Sustainability 2021,13, 11649 6 of 23 Figure 3. Outdoor boundary conditions for all scenarios shown as hourly average values of weather data in city of Brno during the selected period of 01.02. − 01.03.2021 obtained from a professional weather station located in the campus of Faculty of Civil Engineering [ 58 ]: ( a ) temperature and relative humidity; (b) precipitation and solar irradiance. 2.2.2. Construction Process The dimensions of the living wall are 2.18 × 2.3 m (w × h); thus, the area of the living wall is 5.0 m 2 (Figure 4b). The lower edge of the living wall is 1.4 m from the floor and the upper edge is 0.1 m from the ceiling. The system solution of company FloraUrbanica [ 59 ] was used as the construction solution, which is characterized as a lego system—panels are vertically locked into each other. The first step was to install underlying plywood with a waterproof layer, which is anchored to a load-bearing wall. Subsequently, the panels were fixed to a wooden chipboard, a total of 13 rows, while, in one row, there were three panels with a capacity of six (left), three (middle), and six (right) flowerpots. The panels were connected in the vertical direction. These panels were made of polypropylene and aluminum, which ensures long life and 100% recyclability. Flowerpots, which are squareshaped with dimensions of 13 × 13 × 13 cm, were inserted in these panels; the total number of flowerpots was 195 (15 flowerpots in one row). The most-used plants were Philodendron Grand Brasil (approx. 20%), Philodendron Scandens (approx. 20%), Aglaonema Silver Queen (approx. 15%), Beaucarnea Recurvata (approx. 10%), or Monstera Obliqua and Deliciosa (approx. 5%) and others. A total of approximately 12 species of plants were used (Figure 4a). As a growing medium, the mineral hydroponic substrate with a grain fraction of size 3/8 was used. The main components of the hydroponic substrate were pumice stone (approx. 60%), zeolite granules, and lightweight expanded clay aggregate. Sustainability 2021,13, 11649 7 of 23 Figure 4. ( a ) Most frequently used plant species; ( b ) frontal view of experimental living wall; (c) detailed view of irrigation system. 2.2.3. Irrigation System The plants were grown with the use of a sub-irrigation system when the plant sucks water from the bottom of the panels. The water tank is stored in a cabinet under the living wall and consists of two plastic tanks (Figure 4c); the volume of each one is 25 L. The tanks are connected at the bottom by a pipe. A submersible pump is in one of the tanks; after it is switched on, the water is pumped into the upper part of the wall by the irrigation pipe. First, the water irrigates the plants located the highest and the excess water flows by gravity into the lower parts of the wall. At the end of the irrigation process, the excess water drains back into the plastic tank through the return pipes. The connecting pipe ensures that the water level is equal in both tanks after some time. Part of the irrigation system is a return pipe, with a total of five pipes—two for the panels with six flowerpots and one for the panel with three flowerpots. As already mentioned, the return pipe serves to supply excess water to the plastic tank. This system prevents the accumulation of water at the lower part of the wall as well as excessive water consumption as the excess water accumulates back in the water tank and is used for irrigation again. The water tank is connected to a source of drinking cold water via a supply pipe. Water is added to the plastic tank manually as appropriate. The pump is connected to a mobile application that ensures automatic irrigation, or remote start, if necessary. In the winter season, the frequency of the irrigation system starts is at least twice a week, or more often after visual inspections. The duration of the system irrigation is 30 min and is performed in the morning (7:30–8:00 a.m.). As noted earlier, the entire irrigation system is placed in a cabinet, which was made from birch as the final surface treatment. This solution and the choice of light colors of the surrounding walls emphasized the decorative character of the living wall even more. Sustainability 2021,13, 11649 8 of 23 2.2.4. Measuring Infrastructure To define the influence of the living wall on physical parameters of the indoor environment, Comet DigiL/M digital sensors were installed. The sensors record the air temperature and relative humidity; their specification is shown in Table 1. The three sensors (1A, 1B, and 1C) are located close to the living wall, specifically 200 mm from the panel along the vertical axis of the wall. These sensors are arranged in the vertical direction (each 575 mm), which made it possible to monitor the change in temperature and RH depending on the height. The position of the fourth sensor (2B) is oriented at the intersection of the horizontal and vertical axes of the living wall and is located 2000 mm from the sensor 1B. Figure 5shows the vertical and horizontal spatial arrangement of the sensors. Table 1. Specification of used sensors for recording of living wall influence on indoor microclimate. Parameter Device Range Deviation Air humidity Comet DigiL/M 0 to 100% RH ±1.8% RH (at nominal temperature +23 ◦C and RH 0–90%) temperature −10 to +60 ◦C±0.4 ◦C Data collection from sensors is realized by multiloggers Comet. The freely available Comet vision software was used for the communication and set of data loggers. Recording of measured parameters was performed in 5 min time steps. To monitor the water consumption of the living wall, a digital flow meter with the accuracy of 0.1 L was installed on the supply pipe to the water tank. Before irrigation, the water in the tanks is refilled to a pre-specified level. Subsequently, one hour after the end of the irrigation process, the water in tanks is replenished to the same level, and the amount of water consumed during irrigation is read from the flow meter. To determine the water consumption, this activity must be repeated after each irrigation. 1 1 (a) (b) Figure 5. Schematic view on living wall, irrigation system, and measuring infrastructure: (a) front view; (b) cross-section. Sustainability 2021,13, 11649 9 of 23 2.3. Water Wall 2.3.1. Laboratory Conditions and Water Wall Prototype Design To quantify the evaporation capacity of the water wall, the experimental verification under laboratory conditions was chosen, specifically in the climatic chamber (Figure 6a) with a floor area of 6.32 m 2 and height of 2.85 m. The climatic chamber is located in the laboratory of the Faculty of Civil Engineering, Technical University of Košice, and is characterized by its ability to set and maintain steady boundary conditions (temperature range from − 20 to +125 ◦ C, relative humidity from 20% to 95%) for the entire duration of the measurement. The walls are made from stainless steel, so the moisture buffer effect by the surrounding surface can be neglected and the clean humidification potential of the water wall can be determined. Sustainability 2021, 13, x FOR PEER REVIEW 9 of 23 2.3. Water Wall 2.3.1. Laboratory Conditions and Water Wall Prototype Design To quantify the evaporation capacity of the water wall, the experimental verification under laboratory conditions was chosen, specifically in the climatic chamber (Figure 6a) with a floor area of 6.32 m2 and height of 2.85 m. The climatic chamber is located in the laboratory of the Faculty of Civil Engineering, Technical University of Košice, and is characterized by its ability to set and maintain steady boundary conditions (temperature range from −20 to +125 °C, relative humidity from 20% to 95%) for the entire duration of the measurement. The walls are made from stainless steel, so the moisture buffer effect by the surrounding surface can be neglected and the clean humidification potential of the water wall can be determined. (a) (b) (c) (d) Figure 6. Experimental setup for determination of humidification capacity of water wall: (a) exterior view on climatic chamber; (b) design of experimental water wall prototype; (c) final experimental water wall prototype; (d) falling water film on water wall prototype. For the experimental verification, the full-scale water wall prototype was designed (Figure 6b) and built (Figure 6c). The water wall prototype consists of two collecting water tanks with a rectangular shape made of 6 mm thick polypropylene material. The water is pumped from the lower water tank to the upper water tank, in which the perforated pipe is located [60]. This ensures a fluent and continuous distribution of water throughout the tank. Subsequently, the water falls over the overflow edge made up of a glass pane, flows Figure 6. Experimental setup for determination of humidification capacity of water wall: ( a ) exterior view on climatic chamber; ( b ) design of experimental water wall prototype; ( c ) final experimental water wall prototype; ( d ) falling water film on water wall prototype. For the experimental verification, the full-scale water wall prototype was designed (Figure 6b) and built (Figure 6c). The water wall prototype consists of two collecting water tanks with a rectangular shape made of 6 mm thick polypropylene material. The water is pumped from the lower water tank to the upper water tank, in which the perforated pipe is located [ 60 ]. This ensures a fluent and continuous distribution of water throughout the tank. Subsequently, the water falls over the overflow edge made up of a glass pane, flows Sustainability 2021,13, 11649 16 of 23 Table 4. Boundary conditions measured evaporation rate, absolute difference, and percentage deviation between measured and calculated evaporation rate. Measurements 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Temperature (◦C) 19.2 ±0.1 19.2 ±0.8 20.7 ±0.7 21.2 ±1.6 21.7 ±0.1 21.8 ±0.3 22.1 ±0.3 23.2 ±0.5 23.7 ±1.4 24.1 ±0.1 24.3 ±0.7 25.8 ±0.1 27.4 ±0.3 28.3 ±0.7 Relative humidity (%) 56.6 ±2.6 42.4 ±4.3 41.0 ±4.0 36.4 ±3.3 54.4 ±2.1 38.8 ±3.7 39.2 ±3.9 45.9 ±2.9 34.8 ±3.3 49.7 ±2.0 37.8 ±4.0 48.4 ±2.1 31.3 ±2.7 30.0 ±2.3 Measurement: ER (g/h) 184.11 260.77 246.75 287.54 180.97 244.11 249.38 240.32 255.05 188.89 235.84 188.25 293.87 271.23 Equation: ER (g/h) 187.59 259.10 253.54 269.29 179.16 255.76 252.45 215.12 26424 191.46 249.33 194.18 274.65 281.22 Absolute difference 3.48 1.67 6.79 18.25 1.81 11.65 3.07 25.20 9.19 2.57 13.49 5.93 19.22 9.99 Percent deviation (%) 1.89 0.64 2.75 6.35 1.00 4.77 1.23 10.48 3.60 1.36 5.72 3.15 6.54 3.68 The determined equation obtained from experimental measurements can be used to calculate the humidifying effect for different boundary conditions, as the water element is intended to help to achieve an ideal level of humidity. The water wall has not been tested for higher humidity when its effect on the environment would be considered negative. Figure 12 shows the relative range of the evaporation rate and boundary conditions in which the results and determined equation still apply. The red line indicates the range of boundary conditions that were tested experimentally in the climate chamber. Figure 12. Evaporation rate of water wall with an area of 1 m 2 for the selected temperature and relative humidity using determined Equation (1). Scenario 3 In the case of a virtual water wall application, the same area of the water wall as the area of the living wall, i.e., 5 m 2 , is considered. For the virtual application of the water wall in space, the determined Equation (1) and the measured data from Sensor 2B of Scenario 2 are used. The humidity ratio is determined according to the relation: χ=0.622 RH ×pw00 p−RH ×pw00 (2) Sustainability 2021,13, 11649 17 of 23 where pw” is partial pressure of saturated water vapor, calculated on the basis of: pw00 =610.78 ×e17.269×T T+237.3 (3) To calculate the effect of the water wall in the space, the air volume of 61.3 m 3 and the air density of 1.2 kg/m 3 are considered. The mean calculated humidification capacity of the water wall is 1128.94 g/h, which caused an increase in the mean humidity ratio from 7.5 g/kg (Scenario 2) to 8.8 g/kg. The maximum and minimum humidity ratios are 10 and 7 g/kg, respectively. By applying the water wall, the mean relative humidity increased by 7.4% to 51.8%. The maximum and minimum relative humidity are 58.7% and 42%, respectively. Similarly to the previous scenarios, the data from 8:00 to 10:00 are not considered in the overall assessment. It can be seen in Figure 13 that relative humidity does not exceed 60%. In the case of Scenario 3, only the change of the water vapor content in the air by the action of the water wall in the interior is considered; the change in temperature by the action of the water wall is not considered, and for this reason it is not shown in Figure 13. The difference represents the increment caused by the action of the water wall. Figure 13. Course of selected physical parameters for Scenario 3, where sensor curve 2B shows measured data from Scenario 2. 3.3. Water Consumption During the selected period of 29 days, a total of 11 irrigation cycles of the living wall were performed, which is approximately one irrigation cycle every 3 days. The amount of water for individual cycles is not the same and varies in the range of 8.4 to 15.2 L. The average water consumption per irrigation cycle is 11.25 L. A total of 123.7 L of water was consumed, which represents 0.85 L/m 2 per day. In the case of a water wall, the water consumption is proportional to the amount of evaporated water. With a water wall area of Sustainability 2021,13, 11649 18 of 23 5 m 2 , using the Equation (1) and measured data from Scenario 2, the average amount of evaporated water per hour is 1128.98 g/h. In 14 days, 380.26 L would be consumed, which represents 5.42 L/m2per day. Previous studies have shown higher water consumption of green and living walls. Fernández-Cañero et al. [ 43 ] examined the water consumption of an indoor living wall for different types of substrates, and the study was performed experimentally in a warm climate. Their results show a different water consumption during June (the warmest period during the measurements) in the range of 3 to 5 L/m 2 per day, depending on the substrate used. A review of European living wall installations conducted by Gunawardena and Steemers [ 63 ] shows that a 6-day average water consumption during winter was in the range of 1.37–1.55 L/m2per day. In this case, the lower consumption may be caused not only by winter conditions but also by the irrigation system and the method of growing plants, which is described in Section 2.2.3. There is no waste of water during the irrigation process, and the excess water is drained back into the water tank. In the case of the water wall, the consumption is higher than in the living wall, but this ensured that the minimum relative humidity did not fall below 40%. 3.4. Comparison of Scenarios Achieving the required thermal comfort in the building is essential for meeting the needs of occupants and the satisfaction level of indoor environmental quality. Although the greater emphasis is placed on achieving a satisfactory air temperature [ 64 ], it is equally important to achieve a satisfactory indoor humidity level, which consumes about 10–15% of the total energy consumed by the building [ 65 ]. Low or high levels of humidity in the building are associated with various sick building symptoms, bacteria, fungi, and virus risk. The relative humidity must therefore be within a certain defined range to achieve a positive health effect. In 1985, Sterling et al. [ 66 ] defined the range between 40–60% as the optimal comfortable relative humidity. A regulation of Government of the Czech Republic No. 361/2007 Coll. [67] extends this range and considers relative humidity at work in the range of 30–70% to be satisfactory. The government regulation sets the conditions for health protection at work with minimal whole-body physical activity (office administrative work, work with PC, laboratory work, etc.) and orders the minimum workplace temperature to be 20 ◦ C, with the optimum temperature at 22 ◦ C. However, in some cases, even when the required level of humidity resulting from the government regulation was reached, the occupants felt dissatisfied with the humidity, which manifested itself as dry or sore throat and itching, burning, or irritation to the eyes [68]. The resulting measured and calculated values of physical parameters are evaluated based on the ASHRAE Standard 55-2010 [ 69 ] that specifies conditions for acceptable thermal comfort during the heating season. As the living wall is located at university premises, when defining the comfort zone, a metabolic rate of 1.1 met is applied, which corresponds to light physical work, such as computer work. Clothing insulation is set at 1.0 clo; this insulation level is typical for clothing worn when the outdoor environment is cool. Figure 14 shows individual points of the scenarios in relation to the thermal comfort zone according to the ASHRAE Standard 55. A total of 3696 points are evaluated for each scenario, which are obtained from sensor 2B for Scenarios 1 and 2 and calculated for Scenario 3, respectively. The evaluation does not take into account the values measured between 8:00 and 10:00 a.m. As can be seen from the graphical solution of the thermal comfort zone, most points belong to the area of the comfort zone according to the ASHRAE Standard 55-2010; specifically regarding Scenario 1, it is 98.6%; regarding Scenario 2, it is 99.8%; and regarding Scenario 3, it is 99.6% of the time. Thus, thermal comfort is unsatisfactory at a negligible level for all three scenarios. If the results of the relative humidity are evaluated based on the recommended range of 40–60%, Scenario 1 is completely unsatisfactory, and the level of relative humidity is always lower than 40%. By closing the space (Scenario 2), humidity is lower than 40% only 13.5% of the time. The presence of a water wall in the interior Sustainability 2021,13, 11649 19 of 23 (Scenario 3) eliminates this problem, and the relative humidity does not fall below 40%. At the same time, the recommended upper limit of 60% was not exceeded. The resulting values of relative humidity in Scenario 3 are not taken into account for the sorption capacity of the surrounding materials, and it can be assumed that in the real application of the water wall, the relative humidity would be even lower, and thus the water wall with the area of 5 m 2 is suitable for the selected room with the volume considered in this study. The assessment of the relative humidity level based on the regulation of the Government of the Czech Republic (range 30–70%) shows that Scenario 1 (semi-open space) does not meet this regulation 37.2% of the time. Scenarios 2 and 3 fully meet this regulation. As for the minimum temperature requirement based on the regulation of the Government of the Czech Republic, the scenarios fully meet this requirement, and the minimum air temperature is not lower than 20 ◦C. Figure 14. Displaying evaluated points for each scenario and graphic illustration of an acceptable range of temperature and humidity for spaces that meet criteria specified according to ASHRAE Standard 55-2010. 4. Conclusions and Outlook The presented case study deals with the combination of in situ measurement with the influence of the vegetation wall on the physical parameters of the air and the virtual application of the water wall based on laboratory measurements. As the vegetation wall was applied in a specific space of the historic building, it was not possible to regulate the initial boundary conditions; the given space had its specifics such as space geometry, orientation, windows, and surface materials. The obtained results show that for effective and comprehensive use of vegetation elements in the interior with the aim of a positive impact on the indoor microclimate parameters, it is necessary to consider their use concerning the indoor space. Because the performed in situ measurements had their limitations and variables that could not be removed and regulated, in terms of experimentation with water and vegetation elements, it seems reasonable that further research will be carried out in an artificially environment (test chamber), which should be characterized as follows: •the surface temperature of the surrounding surfaces is the same; • the sorption (desorption) capacity of the surrounding surfaces is known, and resp. testing is performed on sorption-inactive surfaces; •the exchange and parameters of the air supplied to the test room are known. The results obtained from future regulated and controlled measurements will be used to create a numerical model in a simulation tool, where it would be possible to evaluate various simulation scenarios. In addition to the standard physical and energy parameters, the requirements for the simulation software should include the possibility to specify the Sustainability 2021,13, 11649 20 of 23 sorption/desorption capacity of the surfaces and to consider the mass moisture of the embedded materials as an initial condition. Using validated numerical (simulation) experiments, it would be possible to determine: •the optimal ratio of room volume and water/vegetation element; •the impact of the presence of humans, animals, and their activities; •the influence of different external climatic parameters; •the influence of building envelope thermal quality; •the influence of HVAC system; and •the impact of moisture buffering effect and others. The presented paper was created during an exchange stay within the project CZ.02.2.69 /0.0/0.0/18_053/0016962 “International mobility of researchers at Brno University of Technology II”. Natural elements represented by living and water walls are a solid and important part of the indoor environment, where they have a positive effect on people 0 s well-being. Therefore, it is necessary to further develop and deepen this issue in terms of the impact on the physical parameters of the indoor environment. Author Contributions: Conceptualization, K.C. and D.B.; methodology, K.C. and M.V.; software, K.C., J.V. and O.N.; validation, K.C., M.V. and D.B.; formal analysis, K.C. and M.V.; investigation, K.C.; resources, K.C.; data curation, K.C.; writing—original draft preparation, K.C. and M.V.; writing— review and editing, K.C. and M.V.; visualization, K.C.; supervision, Z.V.; project administration, A.R., J.P. and Z.V.; funding acquisition, J.P. and Z.V. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: All data are presented in this article in the form of figures and tables. Acknowledgments: The authors are extremely grateful for the support of the Technology Agency of the Czech Republic FV40357 “Research and development of new building material consisting of a composite sandwich plate for vegetative vertical constructions at TOPWET company” and the Slovak Research and Development Agency APVV-18-0360 “Active hybrid infrastructure closer to a sponge city”. Conflicts of Interest: The authors declare no conflict of interest. References 1. Fong, K.C.; Hart, J.E.; James, P. A review of epidemiologic studies on greenness and health: Updated literature through 2017. Curr. Environ. Health Rep. 2018,5, 77–87. [CrossRef] 2. Nieuwenhuijsen, M.J.; Khreis, H.; Triguero-Mas, M.; Gascon, M.; Dadvand, P. Fifty shades of green: Pathway to healthy urban living. Epidemiology 2017,28, 63–71. [CrossRef] 3. 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