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Experimental studies of the thermo and humidity state of a new building facade insulation system based on panels with ventilated channels
Energy & Buildings 206 (2020) 109607
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Experimental studies of the thermo and humidity state of a new building facade insulation system based on panels with ventilated channels M.I. Nizovtsev∗, V.N. Letushko, V. Yu. Borodulin, A.N. Sterlyagov Kutateladze Institute of Thermophysics SB RAS, Acad. Lavrentyev Ave.1, Novosibirsk, 630090, Russia
a r t i c l e
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Article history: Received 22 April 2019 Revised 8 November 2019 Accepted 10 November 2019 Available online 11 November 2019 Keywords: Facade system Heat-insulated panel Ventilated channels Airflow Experiment Heat transfer Moisture transfer Relative humidity Vapor pressure
a b s t r a c t Laboratory and full-scale experiments were carried out with new facade systems with ventilated channels to remove excess moisture from the insulation material. The aim of the work was to study the effect of ventilated channels of facade panels on the moisture condition of the heat-insulation. In laboratory experiments, the effect of air velocity in ventilated channels on the heat-insulation moisture content at different indoor air humidity was investigated. The results of measurements of temperature and relative humidity of air in the panel and in the ventilated air channels at different humidity of the indoor air in the cold period of the year are given. It was found that even with a high humidity of the indoor air of about 70%, the relative humidity of the air in the material of insulation did not exceed 50%, which provided high heat-protected properties of the panels. Temperature stratification of 8–10 °С on height was recorded in the ventilated channels. It led to the appearance of free convective upward currents in the channels and intensification of the moisture removal from the insulation.
1. Introduction The outer layer of the facade of the building performs, in addition to the aesthetic function that determines the appearance of the building, also protective functions from rain, wind and solar radiation [1]. Modern architects seek to use ecological materials as the outer layer. Untreated wood is becoming increasingly popular as a facade cladding. The traditional facing material is brick. However, such materials degrade over time [2]. One of the main reasons of degradation of facing facade materials is weathering, as well as the growth of mold and alga [3,4]. Insufficient frost resistance of porous materials creates serious problems in cold climates [5]. Thin metal layers with various protective coatings are perspective for use as protection of traditional porous building materials. The outer metal layer reliably protects the building from wind and rain. However, if the outer layer is metal, then condensation and moisture accumulation problems may arise in the external building envelope. The system of ventilated facade allows solving the problem of excessive moisture accumulation. The literature uses the more general term Double-Skin Facade (DSF). The emergence of DSF refers to the beginning of the twen∗
Corresponding author. E-mail address: [email protected] (M.I. Nizovtsev).
https://doi.org/10.1016/j.enbuild.2019.109607 0378-7788/© 2019 Elsevier B.V. All rights reserved.
© 2019 Elsevier B.V. All rights reserved.
tieth century [6]. At present time, there is a tendency to their widespread using [7], so it is necessary to carry out theoretical and experimental studies of these facades to determine energy balances in applications. The European standard EN 13119: 2007 “Curtain Walling-Terminology” associates DSF with the existence of glass skins separated by a cavity which is not necessarily ventilated [8]. DSFs are made with natural or forced ventilation to prevent overheating. This motivated the creation of ventilated facades (VFs). According to the International Energy Agency [9], the first building with a ventilated facade was built in 1967 at the University of Cambridge. Later, ventilated facades with opaque outer layers were used, and the term “opaque ventilated facades” (OVFs) was attached to such facades. OVFs are less studied [10,11] than ordinary transparent ventilated facades [12]. A summary of information on the results of investigation of OVFs can be found in review [13]. The OVF system was originally developed in the countries of northern Europe to solve durability problems associated with protection from rain, wind and thermal fluctuations [14,15]. Depending on the execution of the outer layer, OVFs are divided into “open joints, discontinuous skin ventilated facades” (OJVFs) [10,17–19] and “closed joints, continues outer skin ventilated facades” (CJVFs) [16] (Fig. 1).
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Fig. 1. Outer skin types: a) open joints, discontinuous skin; b) closed joints, continues outer skin.
It is believed that the more openings on the outer skin of OJVF, the better the facade is ventilated and its overheating decreases [20,21]. Such facades are optimal for the southern regions. CJVFs are characterized by lower heat losses in winter, and they are preferable for regions with cold winters [19]. The effectiveness of the VF is determined by mixed convection due to solar radiation and wind action. In [20] it was concluded that on the upper floors of buildings the ventilation of the air gap VF is provided mainly by the wind and on the lower floors the ventilation is provided by the forces of buoyancy due to solar radiation. VF systems are used both in the construction of new buildings and in the reconstruction of old ones [21]. In many countries the problems of renovation of facades of buildings are quite actual [22,23]. This is associated with the gradual destruction of facades under the influence of environmental factors, and, on the other hand, with increasing requirements for reducing energy consump-
tion for heating and air conditioning of buildings. At the reconstruction of buildings there are problems of the maintaining permissible moisture content in the materials of building envelopes [24] but ventilated facades can effectively remove moisture. It should be noted a number of new solutions using VF was appeared in recent years. Such solutions include the use of phase change materials (PCM) in the air gaps of ventilated facades in order to cool a room during the summer day owing to a heat accumulator cooled at night [25]. Another new solution is the use VF panels with prefabricated air gaps [26]. This technology significantly reduces installation time and ensures high quality. The new facade system (Fig. 2) based on panels with ventilated channels and metal skin was described earlier in our article [27] and patent [28]. The facade system consists of heat-insulating panels with vertical ventilated channels (Fig. 2a). The panels are coated with an outer metal skin. Channels provide the removal of vaporous moisture from the insulation (Fig. 2b). Panels were mounted with horizontal ventilation slits. In [27] much attention is paid to the moisture content of the facade materials while using this system. The scientific literature on VF discusses issues related to the protective functions of ventilated facades from solar insolation heating [17,29], from wind and rain [1,11]. However а little attention is paid to other important function that is related to maintaining facade materials over the year in relatively dry condition. This function of the ventilated facade is especially important for regions with relatively low temperatures in winter. In these regions, during the cold season, the indoor partial pressure of water vapor is higher than outdoor. Due to the difference in the pressure, the vapor diffuses from the building to the outside through the porous materials of the exterior walls. In the process of moisture transfer, the vapor cools and can condense and accumulate in the materials in form of liquid or ice. The accumulation of moisture and the formation of ice in materials reduce their heat-shielding properties, leads to the formation of defects and the destruction of wall structures [30]. Ventilated facade systems increase the vapor permeability of the facade and prevent the accumulation of moisture in the exterior walls of buildings. This article presents the results of laboratory and full-scale experiments with new facade system for insulating buildings on the basis of panels with ventilated channels and an outer metal skin. The thermo and humidity state of the facade system depends on the air flow rate in the channels, which in turn is caused by many natural environmental factors. Under natural conditions, these factors cannot be regulated. In laboratory experiments, it is possible
Fig. 2. Façade system with ventilated channels. a) Exterior wall with facade system, b) Vapor removal scheme through ventilated channels.
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to vary the air flow rate from experiment to experiment, which makes it possible to determine its effect on the change in the thermo and humidity parameters inside the insulating materials. This explains the need for laboratory experiments. In laboratory experiments, the task was to show that an increase in speed in the ventilated channels of the panel leads to an intensification of moisture removal processes through the insulation layer. The purpose of full-scale studies was to experimentally verify the performance of ventilation of the panel heat-insulating layer through the ventilated channels of the proposed geometry and to ensure the relatively dry state of thermal insulation in the cold season. In the full-scale experiments, it was planned to identify the effect of solar radiation on the ventilation rate and moisture removal, since significant heating of the metal cladding located on the outside of the heat-insulation can enhance convective heat and mass transfer through the ventilated channels. 2. Experimental studies 2.1. Laboratory setup For researches of the operating regimes of panels with ventilated channels, a laboratory experimental setup was assembled. The scheme of the experimental setup is shown in Fig. 3. The experimental setup consists of a humidity chamber with dimensions of 335 × 10 0 0 × 40 0 0 mm, one side of the chamber is open. During experiments this side is being closed by the facade panel with ventilated channels, so that the ventilated chan-
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nels are directed vertically. The total thickness of the mineral wool insulation layer with a density of 90 kg/m3 in the panel was 80 mm. The thermal conductivity coefficient of the mineral wool is 0.04W/(m K), and the vapor permeability coefficient is 1.66 × 10−10 kg/(m s Pa). The ventilated channels with a cross section of 20 × 40 mm were located behind the thin metal skin. The distance between the channels was 65mm. The width of the panel was 335 mm, and the height was 10 0 0 mm. In the humidity chamber the air relative humidity was maintained using an ultrasonic humidifier. In experiments air coming from the pump was supplied into the ventilated channels at the bottom of the panel. Air flowrate through the channels was adjusted by changing the air velocity in the range from 0 to 0.4 m/s. An autonomous temperature and relative humidity sensors Eclerk-USB-RHT-1 were installed inside the mineral wool insulation layer of the panel and in one of the ventilated channels. The sensors provided temperature measurement with an absolute error of ± 1.0 °С and relative humidity with an error of ± 2.0%. The hardware resolution in temperature was 0.1 °С, and in relative humidity it was 0.1%. After experiments all information from the sensors was transferred to a PC. The layout of the sensors is shown in Fig. 4. Sensors No. 1, No. 3, No. 4, No. 5 were located in the mineral wool insulation of the panel. The dimensions of the sensor case were 2 × 4 × 5 mm; the dimensions of the sensor element were 2 × 3 mm. The sensors were mounted through holes with a diameter of 3 mm. The voids that formed during installation were filled with mineral wool.
Fig. 3. The scheme of the experimental setup: 1 – humidity chamber, 2 – panel with channels, 3 – ultrasonic humidifier, 4 – air pump, 5 – sensors, 6 – personal computer.
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Fig. 4. Sensor layout.
Fig. 5. Scheme of the positions of the sensor number 6.
Sensor No. 2 was located in a humidity chamber at a distance of 5mm from the thermal insulation of the panel at height of 480 mm. Sensor No. 6 could move along the height of the central ventilated channel. The scheme of the positions of the sensor No. 6 where measurements were made is shown in Fig. 5. 2.2. Full-scale experiment For long time experiments with ventilated channels under natural conditions, a panel with height of 1090 mm and 694 mm
width was taken. The thickness of the mineral wool layer with density of 90 kg/m3 was 160 mm. A layer of extruded polystyrene foam 20 mm thick was fixed on the inner side of the thermal insulation. This layer simulated the thermo and humidity properties of the construct layer of the wall. The thermal conductivity coefficient of extruded polystyrene foam is 0.034 W/(m K), and the vapor permeability coefficient is 3.9 × 10−12 kg/(m s Pa). Thus according to [31], the layer corresponds to the thermal resistance of brickwork from full-bodied clay brick with a thickness of 400mm and, more than 2 times, has a lower resistance to vapor permeability. The sensors Eclerk-USBRHT-1 were installed inside the mineral wool layer of the panel and in the ventilated channel of the panel. The layout of the sensors is shown in Fig. 6. In one of the central air channels five sensors were installed from No. 1–5 (top to bottom), four sensors were installed in mineral wool. They placed on the thickness from No. 7 to No. 10 (from the inner surface to the outer one). In addition, sensor No. 6 recorded the parameters of the indoor air, and sensor No. 11 recorded the parameters of the outdoor air. Temperature and relative humidity measurements were carried out by each of the sensors with an interval of 1 min between measurements and recorded in memory. Data from the sensor memory blocks were periodically transferred to a personal computer for further processing. A panel with sensors was installed instead of one of fragments of window on the western facade of the two-storied building of the laboratory building (Fig. 7). The outdoor air flow could freely enter to the channels through the bottom inlet and went out
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3. Results and discussion 3.1. Laboratory moisture measurements
Fig. 6. The layout of sensors in the panel for full-scale experiments.
through the top outlet. Thus, the operating of the facade panel on the outer wall of the western facade of the building in the climatic conditions of the city of Novosibirsk was modeled. The purpose of this series of experiments was to monitor the temperature and humidity of the mineral wool insulation layer of the panel and to verify the performance of ventilation of the panel heat insulating layer through the ventilated channels of the proposed geometry for maintaining the relatively dry state in the mineral wool in the cold season. Experiments were carried out in the cold season with high and low relative humidity of the indoor air.
Laboratory study of the humidity of panels with ventilated channels was performed by two series of experiments. Each laboratory experiment lasted at least 12 h. Data obtained in a stationary regime were used for further analysis. In all experiments, the air temperature in the humidity chamber, inside the panel and into ventilated channels had the same value 30 °С. Relative humidity of the air in the room ϕ was 45%. In the first series of experiments, the effect of opening the channels on the moisture transfer through the panel insulation layer was studied. The results of measurements of relative humidity are shown in Figs. 8 and 9. In the experiments the outlets of the channels were always open, but the inlets at the bottom of the panel could be open or closed. With the closed channels the relative humidity ϕ in the chamber was 89%. The relative humidity of the air in the central ventilated channel slightly changed with the height of the channel and it was on average 82% (Fig. 8a). The channel was practically not ventilated. When the channels were open, the relative humidity of the air in the chamber decreased to 85%. At the general decrease in the relative humidity inside the channel redistribution ϕ with height from 57% at the inlet to 75% at the outlet was observed (Fig. 8b). Such a distribution of relative humidity in the channel indicated the occurrence of a flow in the channel from the bottom to the top. The occurrence of the flow in the channel also led to a change in the distribution of relative humidity in the mineral wool in the cross section of the panel (Fig. 9). With the closed channels the relative humidity of the air in the chamber and in the mineral wool was practically same. With open channels a decrease in relative humidity in the direction from the chamber to the channel was observed in the cross section of the panel. This also indicated the presence of flow in the channel from bottom to top. In the second series of experiments the effect of air velocity in the ventilated channels on the change in relative humidity both in the air channels and in the panel was studied. During the second series of experiments, the air temperature at the inlet of the ventilated channels and in the chamber was 30 °C. Relative humidity
Fig. 7. View of the established sample of the panel with ventilated channels on the external wall; a) from the facade of the building; b) from inside the room.
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Fig. 8. Change of relative humidity along the height of the air channel: a) with closed air channels, b) with open air channels.
Fig. 9. Change of the relative humidity of the air in the cross section of the panel y/h = 0.5 (along line 2 in Fig. 10) when the channels are opened.
Fig. 11. The effect of air velocity in the air channels on the change in relative humidity in the cross section at y/ h = 0.5 along line 2 of Fig. 10.
at the inlet of the channels was 42%–45% and in the chamber the one was 78%–85%. Fig. 10 shown the relative humidity distribution on the horizontal section of the panel at the height of y/h = 0.5 along line 1 (the central line between the channels) and along line 2 (the center of the channel). In this case the air velocity in the channels was equal 0.2 m/s. In the experiments a decrease in the relative humidity on the thickness of the panel (from the chamber towards the channels) was observed. Along line 2 the drop of the relative humidity was larger than along line 1. As the air velocity in the air channels increased, the relative humidity drop across the panel thickness increased (Fig. 11). This indicates the intensification of moisture transfer. The dependence of the relative humidity of the thermal insulation on the air flow rate in the ventilated channels at the stationary regime is summarized by the following relation: Fig. 10. The relative humidity distribution in the horizontal section of the panel at y/h = 0.5 along lines 1 and 2.
ϕ = (78.2 − 5v ) − (18.6 + 17.7v )x/L[%],
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Fig. 12. Change in the air relative humidity along the channel height.
where v is the flow velocity in the channel, x is the coordinate according to Figs. 4 and 5, L is the thickness of the thermal insulation of the panel. As follows from the analysis, when the air velocity in the ventilated channels increased, the air relative humidity at the outlet decreased (Fig. 12). It provided a reduction in air humidity inside the panel. Fig. 13 shows the results comparison of the moisture balance. The vapor flowrate through the mineral wool and the amount of moisture removed through the ventilated channel were estimated at different air flowrates. Line (3) is an approximation of the results of calculations (1) and shows a monotonic increase in the mass flowrate of water vapor filtered through mineral wool with an increase in the air flowrate in the channels. The calculations were carried out according to the experimental values of relative humidity in mineral wool in the central horizontal section along thickness and the known vapor permeability coefficient 1.66 × 10−10 kg/(m s Pa). The average increase in the mass flowrate was about 0.2 mg/s for every 0.1 m/s increase in the air velocity. The change in the moisture content in the channel between
Fig. 13. Comparison of the mass flow rate of water vapor through the mineral wool (1) with a change in the content of water vapor between the outlet and inlet of the ventilated channel (2); 3, 4 – linear approximations of the corresponding data.
the outlet and the inlet (2) was approximated by a similar linear dependence (4) on the air velocity. The observed increase in the intensity of mass transfer through mineral wool with increasing flowrate of air was due to the intensification of mass transfer at the interface between the mineral wool and the air channel. The comparison shows satisfactory agreement between these two mass flowrates that indicates the correctness of the results. 3.2. Full-scale thermo and humidity measurements Experiments in condition at low air relative humidity in indoor were conducted in March 2018. This period is characterized by low indoor air relative humidity. The two-day interval from 0:00 on March 17 (regime 1) was selected for analysis due to stable weather conditions with clear sky. Experiments at high relative humidity of the indoor air which was maintained with an ultrasonic humidifier were carried out In
Fig. 14. Outdoor air parameters; a) regime 1, b) regime 2.
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Fig. 15. Indoor air parameters; a) regime 1, b) regime 2.
Fig. 16. Temperature distribution in the mineral wool panel; a) regime 1, b) regime 2. Locations of sensors from the inner surface to the outer one was denoted accordingly be numbers 7–10.
April 2018. For the analysis the two-day interval from 0:00 on April 5 (regime 2) was chosen. During the experiments, the southwest wind prevailed at a speed of 1–2 m/s. The daylight hours are shown in Fig. 14. The maximum insolation in regime 1 was 430 and 441 W/m2 at 16 h 30 min on March 17 and 18, respectively. The maximum insolation in regime 2 was 584 and 310 W/m2 at 17 h on April 5 and 6, respectively. Both selected intervals were accompanied by lowering the outdoor temperature at night (for the first regime to −20 °С and for the second regime to −10 °С) and increasing by 10–15 °С during daytime (Fig. 14). When the outdoor air temperature increased, its relative humidity decreased from 70% to 80% at night to 15%–20% during the day. For the first regime with low natural average relative humidity of the internal air of 8% the average temperature of the indoor air was 27 °С (Fig. 15a). For the second regime the average tempera-
ture of indoor air was 25 °С at high average relative humidity of 69% (Fig. 15b). The temperature change in different sections of the mineral wool panel is shown in Fig. 16, the numbers in the figure hereinafter correspond to the sensor positions in Fig. 6. According to the results of observations, the change in temperature inside the mineral wool panel for both regimes was cyclical with an increase in temperature during the daytime and a decrease in the nighttime. At the same time, the temperature inside the layer of mineral wool at each moment of time increased from the outer surface to the inner one. It should be noted that a significantly larger temperature change in the daytime of the outer layer of mineral wool was observed as compared with a change in the outside air temperature. This is associated with heating the outer metal layer of the panel and the adjacent layer of mineral wool by solar radiation at clear sky.
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Fig. 17. Temperature of the air in the ventilated channel; a) regime 1, b) regime 2. The sensors in the channel are location on top to the bottom accordingly numbers 1–5.
Fig. 18. Relative humidity of the air in the ventilated channel; a) regime 1, b) regime 2.
Fig. 17 shows the results of measurements of air temperature of the ventilated channel over time at different height. During the daytime from 15 to 18 h due to the solar heating the outer metal layer of the panel a significant temperature rise by 12–20 °С above the outdoor air temperature was observed in the ventilated channels. Inside the channels the difference in air temperature between inlet and outlet was 8–10 °С. Such a temperature difference should lead to the presence of a free convective air flow in the channels. As a result of the calculations for this flow, a speed range of 0.2– 0.3 m/s was obtained, which led the intensification of moisture removal from mineral wool, associated with an increase in speed in ventilated channels in the daytime. A decrease in humidity in mineral wool with an increase in speed in ventilated channels in this range was shown earlier in laboratory experiments.
At night with a cloudless sky, the air temperature in the ventilated channel was several degrees lower than the outdoor temperature due to external thermal radiation. This led to a descending flow in the channel which was much less intense. During the daytime a decrease in the air relative humidity was observed in the ventilated channel due to a significant increase in air temperature (Fig. 18). The partial pressures of water vapor in the ventilated channel, in the mineral wool and the indoor air for both regimes are determined by the temperature and relative humidity (Fig. 19). For clarity the figure shows the partial pressures, according to the indications of the edge sensors of the ventilated channel (5-bottom, 1-top) and mineral wool (7 is the inner layer, 10 is the outer layer). The changes in partial pressures obtained from the intermediate
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Fig. 19. Partial pressure of vapor in the mineral wool, in a ventilated channel and indoor air; a) regime 1, b) regime 2.
Fig. 20. Relative air humidity in the mineral wool; a) regime 1, b) regime 2.
sensors were located between the values for the edge sensors and are not shown in the figure. The partial pressure of water vapor in the room most of the observation time for regime 1 and all the time for regime 2 exceeded the partial pressure of water vapor in the mineral wool and the ventilated channel. This indicated the predominant movement of water vapor from the room to outdoor through the facade panel. To analyze the intensity of water vapor flow two areas can be distinguished: I – night and II – day (they are shown in the figure for the first day). Region I was characterized by either the absence or a relatively low drop in the partial vapor pressure between the mineral wool and the ventilated channel. This showed the low intensity of the vapor flow from the mineral wool. Area II demonstrated an increase in the temperature of the outer layer of mineral wool.
The increase was accompanied by a more rapid growth of the vapor pressure in the layer compared with an increase in the partial pressure in the ventilated channel. As result a more intense release of water vapor into the ventilated channels was occurred. At the same time, the vapor flow from the room to the mineral wool was reduced. Thus, in region II, an intense removal of moisture from the mineral wool was observed. Fig. 20 shows the results of measuring the relative humidity of the outdoor air and in the mineral wool. According to the measurement results, the relative humidity of the air in the mineral wool of the panel increased towards the outside and fluctuated during the day. With an increase in the relative humidity of the indoor air, an increase in the relative humidity of the air in the mineral wool was observed. However, even at high humidity of the indoor
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exceed 50%, which provided the panels with high heat-protection properties. An analysis of the heat-moisture state of mineral wool in a panel with ventilated channels in the cold season revealed two factors leading to additional intensification of moisture removal from the panel. In clear weather during the day, due to solar radiation, an increase in temperature was observed in the outer layer of the panel. This led to an increase in the pressure drop between the vapor in the mineral wool and in the ventilated channels, and as a result led to the intensification of moisture removal. Due to solar heating, the second factor was associated with an increase in temperature with the height of the channel. He created a convective flow of air, which also enhanced the removal of moisture from the panel in accordance with laboratory experiments. Laboratory and full-scale studies of the heat- and moisture state of the heat-insulating panel with ventilated channels confirmed the computational results [27] about that the developed design provides effective removal of moisture from the outer layer of the insulation. Comparison of the air humidity in the material with its permissible values showed that the heat-insulation layer of the facade with ventilated channels will be under normal operating conditions. Fig. 21. Thermo and moisture state of mineral wool: 1- measurement results in the center of the mineral wool layer in regime 1; 2 – limiting mould fungus formation curve.
Declaration of Competing Interest No conflict of interest.
air of about 70% (Fig. 20b), the relative humidity of the air in the mineral wool did not exceed 50%. This gave the panels high thermal protection properties. It should be noted that one of the conditions for using a facade system with ventilated channels is their ability to provide a normal thermo and humidity state in the heat-insulation material under a given climate. The implementation of this condition in the work was checked by comparing the air humidity in the material with its permissible value [32]. Fig. 21 shows that the results of the measurements of air relative humidity lie significantly below isopleth curve (2), which predicts of mould fungus formation on the surface and inside building component. Below the curve there is no biological activity expected on the mineral wool. This means that the mineral wool heat-insulation in this facade system will be in normal operating conditions. 4. Conclusions Experimental laboratory studies of moisture transfer through a heat-insulating panel with ventilated channels showed that with open channels due to the differential partial pressures of the vapor in mineral wool and in the channels, the vapor flow occurred that led to a decrease in the relative humidity in the thermal insulating material of the panel. When the air velocity in the channels was more than 0.1 m/s, which correspond to the actual air velocities in the ventilated channels of the facade system, a significant intensification of moisture removal from the panel was observed due to a decrease in the average relative humidity of the air in the ventilation channels. With an increase in air velocity in the channels from 0 m/s to 0.4 m/s, there was a decrease in humidity in the mineral wool with almost constant relative humidity of the indoor and outdoor air. As a result of the full-scale studies of heat and humidity processes in heat-insulating panels with ventilated channels in the cold period of the year it was established that an increase in the relative humidity of the air in the mineral wool was occurred with an increase in the relative humidity of the indoor air. However, even with a high relative humidity of the indoor air of about 70%, the relative humidity of the air in the mineral wool did not
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[16] M.Thebault, J. Reizes, S. Giroux–Julien, V. Timchenko, C. Ménézo, Impact of external temperature distribution on the convective mass flowrate in a vertical channel – a theoretical and experimental study, Int. J. Heat Mass Transf. 121 (2018) 1264–1272. [17] M.J. Suárez, C. Sanjuan, A.J. Gutiérrez, J. Pistono, E. Blanco, Energy evaluation of an horizontal open joint ventilated facade, Appl. Therm. Eng. 37 (2012) 302–313. [18] A.C. Dimoudi, A.V. Androutsopoulos, S.P. Lykoudis, Experimental study of the cooling performance of a ventilated wall, J. Build. Phys. 39 (2016) 297–320. [19] C. Sanjuan, M.N. Sánchez, M.R. Heras, E. Blanco, Experimental analysis of natural convection in open joint ventilated façades with 2 D PIV, Build. Environ. 46 (2011) 2314–2325. [20] E. Gratia, A. Herde, Natural ventilation in a double-skin facade, Energy Build. 36 (2004) 137–146. [21] M.A. Shameri, M.A. Alghoul, K. Sopian, M. Fauzi, M. Zain, O. Elayeb, Perspectives of double skin facade systems in buildings and energy saving, Renew. Sustain. Energy Rev. 15 (2011) 1468–1475. [22] L.L. Fleur, B. Moshfegh, P. Rohdin, Measured and predicted energy use and indoor climate before and after a major renovation of an apartment building in Sweden, Energy Build. 146 (2017) 98–110. [23] C. Alonso, I. Oteiza, J. Garcia-Navarro, F. Martin-Consuegra, Energy consumption to cool and heat experimental modules for the energy refurbishment of facades. Three case studies in Madrid, Energy Build. 126 (2016) 252– 262.
[24] D.I. Kolaitis, D.A.K. E.Malliotakis, I. Mandilaras, D.I. Katsourinis, M.A. Founti, Comparative assessment of internal and external thermal insulation systems for energy efficient retrofitting of residential buildings, Energy Build. 64 (2013) 123–131. [25] A. de Gracia, L. Navarro, A. Castell, L.F. Cabeza, Numerical study on the thermal performance of a ventilated facade with PCM, Appl. Therm. Eng. 61 (2013) 372–380. [26] T. Colinart, M. Bendouma, P. Glouannec, Building renovation with prefabricated ventilated façade element: a case study, Energy Build. 186 (2019) 221–229. [27] M.I. Nizovtsev, V.T. Belyi, A.N. Sterlygov, The facade system with ventilated channels for thermal insulation of newly constructed and renovated buildings, Energy Build. 75 (2014) 60–69. [28] Patent (RU) for Useful Model No. 94597, Wall panel for cladding and warming of building (May 27, 2010). [29] C. Suárez, P. Joubert, J.L. Molina, F.J. Sánchez, Heat transfer and mass flow correlations for ventilated facades, Energy Build. 43 (2011) 3696–3703. [30] F. Kong, H. Wang, Heat and mass coupled transfer combined with freezing process in building materials: modeling and experimental verification, Energy Build. 43 (2011) 2850–2859. [31] S. Pravil 50.13330. 2012, Thermal performance of the buildings (2012) (in Russian). [32] K. Sedlbauer, Prediction of Mould Fungus Formation on the Surface and Inside Building Component, Department of Building Physics, University of Stuttgart, Stuttgart, Germany, 2001.
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Energy & Buildings journal homepage: www.elsevier.com/locate/enbuild
Experimental studies of the thermo and humidity state of a new building facade insulation system based on panels with ventilated channels M.I. Nizovtsev∗, V.N. Letushko, V. Yu. Borodulin, A.N. Sterlyagov Kutateladze Institute of Thermophysics SB RAS, Acad. Lavrentyev Ave.1, Novosibirsk, 630090, Russia
a r t i c l e
i n f o
Article history: Received 22 April 2019 Revised 8 November 2019 Accepted 10 November 2019 Available online 11 November 2019 Keywords: Facade system Heat-insulated panel Ventilated channels Airflow Experiment Heat transfer Moisture transfer Relative humidity Vapor pressure
a b s t r a c t Laboratory and full-scale experiments were carried out with new facade systems with ventilated channels to remove excess moisture from the insulation material. The aim of the work was to study the effect of ventilated channels of facade panels on the moisture condition of the heat-insulation. In laboratory experiments, the effect of air velocity in ventilated channels on the heat-insulation moisture content at different indoor air humidity was investigated. The results of measurements of temperature and relative humidity of air in the panel and in the ventilated air channels at different humidity of the indoor air in the cold period of the year are given. It was found that even with a high humidity of the indoor air of about 70%, the relative humidity of the air in the material of insulation did not exceed 50%, which provided high heat-protected properties of the panels. Temperature stratification of 8–10 °С on height was recorded in the ventilated channels. It led to the appearance of free convective upward currents in the channels and intensification of the moisture removal from the insulation.
1. Introduction The outer layer of the facade of the building performs, in addition to the aesthetic function that determines the appearance of the building, also protective functions from rain, wind and solar radiation [1]. Modern architects seek to use ecological materials as the outer layer. Untreated wood is becoming increasingly popular as a facade cladding. The traditional facing material is brick. However, such materials degrade over time [2]. One of the main reasons of degradation of facing facade materials is weathering, as well as the growth of mold and alga [3,4]. Insufficient frost resistance of porous materials creates serious problems in cold climates [5]. Thin metal layers with various protective coatings are perspective for use as protection of traditional porous building materials. The outer metal layer reliably protects the building from wind and rain. However, if the outer layer is metal, then condensation and moisture accumulation problems may arise in the external building envelope. The system of ventilated facade allows solving the problem of excessive moisture accumulation. The literature uses the more general term Double-Skin Facade (DSF). The emergence of DSF refers to the beginning of the twen∗
Corresponding author. E-mail address: [email protected] (M.I. Nizovtsev).
https://doi.org/10.1016/j.enbuild.2019.109607 0378-7788/© 2019 Elsevier B.V. All rights reserved.
© 2019 Elsevier B.V. All rights reserved.
tieth century [6]. At present time, there is a tendency to their widespread using [7], so it is necessary to carry out theoretical and experimental studies of these facades to determine energy balances in applications. The European standard EN 13119: 2007 “Curtain Walling-Terminology” associates DSF with the existence of glass skins separated by a cavity which is not necessarily ventilated [8]. DSFs are made with natural or forced ventilation to prevent overheating. This motivated the creation of ventilated facades (VFs). According to the International Energy Agency [9], the first building with a ventilated facade was built in 1967 at the University of Cambridge. Later, ventilated facades with opaque outer layers were used, and the term “opaque ventilated facades” (OVFs) was attached to such facades. OVFs are less studied [10,11] than ordinary transparent ventilated facades [12]. A summary of information on the results of investigation of OVFs can be found in review [13]. The OVF system was originally developed in the countries of northern Europe to solve durability problems associated with protection from rain, wind and thermal fluctuations [14,15]. Depending on the execution of the outer layer, OVFs are divided into “open joints, discontinuous skin ventilated facades” (OJVFs) [10,17–19] and “closed joints, continues outer skin ventilated facades” (CJVFs) [16] (Fig. 1).
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Fig. 1. Outer skin types: a) open joints, discontinuous skin; b) closed joints, continues outer skin.
It is believed that the more openings on the outer skin of OJVF, the better the facade is ventilated and its overheating decreases [20,21]. Such facades are optimal for the southern regions. CJVFs are characterized by lower heat losses in winter, and they are preferable for regions with cold winters [19]. The effectiveness of the VF is determined by mixed convection due to solar radiation and wind action. In [20] it was concluded that on the upper floors of buildings the ventilation of the air gap VF is provided mainly by the wind and on the lower floors the ventilation is provided by the forces of buoyancy due to solar radiation. VF systems are used both in the construction of new buildings and in the reconstruction of old ones [21]. In many countries the problems of renovation of facades of buildings are quite actual [22,23]. This is associated with the gradual destruction of facades under the influence of environmental factors, and, on the other hand, with increasing requirements for reducing energy consump-
tion for heating and air conditioning of buildings. At the reconstruction of buildings there are problems of the maintaining permissible moisture content in the materials of building envelopes [24] but ventilated facades can effectively remove moisture. It should be noted a number of new solutions using VF was appeared in recent years. Such solutions include the use of phase change materials (PCM) in the air gaps of ventilated facades in order to cool a room during the summer day owing to a heat accumulator cooled at night [25]. Another new solution is the use VF panels with prefabricated air gaps [26]. This technology significantly reduces installation time and ensures high quality. The new facade system (Fig. 2) based on panels with ventilated channels and metal skin was described earlier in our article [27] and patent [28]. The facade system consists of heat-insulating panels with vertical ventilated channels (Fig. 2a). The panels are coated with an outer metal skin. Channels provide the removal of vaporous moisture from the insulation (Fig. 2b). Panels were mounted with horizontal ventilation slits. In [27] much attention is paid to the moisture content of the facade materials while using this system. The scientific literature on VF discusses issues related to the protective functions of ventilated facades from solar insolation heating [17,29], from wind and rain [1,11]. However а little attention is paid to other important function that is related to maintaining facade materials over the year in relatively dry condition. This function of the ventilated facade is especially important for regions with relatively low temperatures in winter. In these regions, during the cold season, the indoor partial pressure of water vapor is higher than outdoor. Due to the difference in the pressure, the vapor diffuses from the building to the outside through the porous materials of the exterior walls. In the process of moisture transfer, the vapor cools and can condense and accumulate in the materials in form of liquid or ice. The accumulation of moisture and the formation of ice in materials reduce their heat-shielding properties, leads to the formation of defects and the destruction of wall structures [30]. Ventilated facade systems increase the vapor permeability of the facade and prevent the accumulation of moisture in the exterior walls of buildings. This article presents the results of laboratory and full-scale experiments with new facade system for insulating buildings on the basis of panels with ventilated channels and an outer metal skin. The thermo and humidity state of the facade system depends on the air flow rate in the channels, which in turn is caused by many natural environmental factors. Under natural conditions, these factors cannot be regulated. In laboratory experiments, it is possible
Fig. 2. Façade system with ventilated channels. a) Exterior wall with facade system, b) Vapor removal scheme through ventilated channels.
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to vary the air flow rate from experiment to experiment, which makes it possible to determine its effect on the change in the thermo and humidity parameters inside the insulating materials. This explains the need for laboratory experiments. In laboratory experiments, the task was to show that an increase in speed in the ventilated channels of the panel leads to an intensification of moisture removal processes through the insulation layer. The purpose of full-scale studies was to experimentally verify the performance of ventilation of the panel heat-insulating layer through the ventilated channels of the proposed geometry and to ensure the relatively dry state of thermal insulation in the cold season. In the full-scale experiments, it was planned to identify the effect of solar radiation on the ventilation rate and moisture removal, since significant heating of the metal cladding located on the outside of the heat-insulation can enhance convective heat and mass transfer through the ventilated channels. 2. Experimental studies 2.1. Laboratory setup For researches of the operating regimes of panels with ventilated channels, a laboratory experimental setup was assembled. The scheme of the experimental setup is shown in Fig. 3. The experimental setup consists of a humidity chamber with dimensions of 335 × 10 0 0 × 40 0 0 mm, one side of the chamber is open. During experiments this side is being closed by the facade panel with ventilated channels, so that the ventilated chan-
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nels are directed vertically. The total thickness of the mineral wool insulation layer with a density of 90 kg/m3 in the panel was 80 mm. The thermal conductivity coefficient of the mineral wool is 0.04W/(m K), and the vapor permeability coefficient is 1.66 × 10−10 kg/(m s Pa). The ventilated channels with a cross section of 20 × 40 mm were located behind the thin metal skin. The distance between the channels was 65mm. The width of the panel was 335 mm, and the height was 10 0 0 mm. In the humidity chamber the air relative humidity was maintained using an ultrasonic humidifier. In experiments air coming from the pump was supplied into the ventilated channels at the bottom of the panel. Air flowrate through the channels was adjusted by changing the air velocity in the range from 0 to 0.4 m/s. An autonomous temperature and relative humidity sensors Eclerk-USB-RHT-1 were installed inside the mineral wool insulation layer of the panel and in one of the ventilated channels. The sensors provided temperature measurement with an absolute error of ± 1.0 °С and relative humidity with an error of ± 2.0%. The hardware resolution in temperature was 0.1 °С, and in relative humidity it was 0.1%. After experiments all information from the sensors was transferred to a PC. The layout of the sensors is shown in Fig. 4. Sensors No. 1, No. 3, No. 4, No. 5 were located in the mineral wool insulation of the panel. The dimensions of the sensor case were 2 × 4 × 5 mm; the dimensions of the sensor element were 2 × 3 mm. The sensors were mounted through holes with a diameter of 3 mm. The voids that formed during installation were filled with mineral wool.
Fig. 3. The scheme of the experimental setup: 1 – humidity chamber, 2 – panel with channels, 3 – ultrasonic humidifier, 4 – air pump, 5 – sensors, 6 – personal computer.
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Fig. 4. Sensor layout.
Fig. 5. Scheme of the positions of the sensor number 6.
Sensor No. 2 was located in a humidity chamber at a distance of 5mm from the thermal insulation of the panel at height of 480 mm. Sensor No. 6 could move along the height of the central ventilated channel. The scheme of the positions of the sensor No. 6 where measurements were made is shown in Fig. 5. 2.2. Full-scale experiment For long time experiments with ventilated channels under natural conditions, a panel with height of 1090 mm and 694 mm
width was taken. The thickness of the mineral wool layer with density of 90 kg/m3 was 160 mm. A layer of extruded polystyrene foam 20 mm thick was fixed on the inner side of the thermal insulation. This layer simulated the thermo and humidity properties of the construct layer of the wall. The thermal conductivity coefficient of extruded polystyrene foam is 0.034 W/(m K), and the vapor permeability coefficient is 3.9 × 10−12 kg/(m s Pa). Thus according to [31], the layer corresponds to the thermal resistance of brickwork from full-bodied clay brick with a thickness of 400mm and, more than 2 times, has a lower resistance to vapor permeability. The sensors Eclerk-USBRHT-1 were installed inside the mineral wool layer of the panel and in the ventilated channel of the panel. The layout of the sensors is shown in Fig. 6. In one of the central air channels five sensors were installed from No. 1–5 (top to bottom), four sensors were installed in mineral wool. They placed on the thickness from No. 7 to No. 10 (from the inner surface to the outer one). In addition, sensor No. 6 recorded the parameters of the indoor air, and sensor No. 11 recorded the parameters of the outdoor air. Temperature and relative humidity measurements were carried out by each of the sensors with an interval of 1 min between measurements and recorded in memory. Data from the sensor memory blocks were periodically transferred to a personal computer for further processing. A panel with sensors was installed instead of one of fragments of window on the western facade of the two-storied building of the laboratory building (Fig. 7). The outdoor air flow could freely enter to the channels through the bottom inlet and went out
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3. Results and discussion 3.1. Laboratory moisture measurements
Fig. 6. The layout of sensors in the panel for full-scale experiments.
through the top outlet. Thus, the operating of the facade panel on the outer wall of the western facade of the building in the climatic conditions of the city of Novosibirsk was modeled. The purpose of this series of experiments was to monitor the temperature and humidity of the mineral wool insulation layer of the panel and to verify the performance of ventilation of the panel heat insulating layer through the ventilated channels of the proposed geometry for maintaining the relatively dry state in the mineral wool in the cold season. Experiments were carried out in the cold season with high and low relative humidity of the indoor air.
Laboratory study of the humidity of panels with ventilated channels was performed by two series of experiments. Each laboratory experiment lasted at least 12 h. Data obtained in a stationary regime were used for further analysis. In all experiments, the air temperature in the humidity chamber, inside the panel and into ventilated channels had the same value 30 °С. Relative humidity of the air in the room ϕ was 45%. In the first series of experiments, the effect of opening the channels on the moisture transfer through the panel insulation layer was studied. The results of measurements of relative humidity are shown in Figs. 8 and 9. In the experiments the outlets of the channels were always open, but the inlets at the bottom of the panel could be open or closed. With the closed channels the relative humidity ϕ in the chamber was 89%. The relative humidity of the air in the central ventilated channel slightly changed with the height of the channel and it was on average 82% (Fig. 8a). The channel was practically not ventilated. When the channels were open, the relative humidity of the air in the chamber decreased to 85%. At the general decrease in the relative humidity inside the channel redistribution ϕ with height from 57% at the inlet to 75% at the outlet was observed (Fig. 8b). Such a distribution of relative humidity in the channel indicated the occurrence of a flow in the channel from the bottom to the top. The occurrence of the flow in the channel also led to a change in the distribution of relative humidity in the mineral wool in the cross section of the panel (Fig. 9). With the closed channels the relative humidity of the air in the chamber and in the mineral wool was practically same. With open channels a decrease in relative humidity in the direction from the chamber to the channel was observed in the cross section of the panel. This also indicated the presence of flow in the channel from bottom to top. In the second series of experiments the effect of air velocity in the ventilated channels on the change in relative humidity both in the air channels and in the panel was studied. During the second series of experiments, the air temperature at the inlet of the ventilated channels and in the chamber was 30 °C. Relative humidity
Fig. 7. View of the established sample of the panel with ventilated channels on the external wall; a) from the facade of the building; b) from inside the room.
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Fig. 8. Change of relative humidity along the height of the air channel: a) with closed air channels, b) with open air channels.
Fig. 9. Change of the relative humidity of the air in the cross section of the panel y/h = 0.5 (along line 2 in Fig. 10) when the channels are opened.
Fig. 11. The effect of air velocity in the air channels on the change in relative humidity in the cross section at y/ h = 0.5 along line 2 of Fig. 10.
at the inlet of the channels was 42%–45% and in the chamber the one was 78%–85%. Fig. 10 shown the relative humidity distribution on the horizontal section of the panel at the height of y/h = 0.5 along line 1 (the central line between the channels) and along line 2 (the center of the channel). In this case the air velocity in the channels was equal 0.2 m/s. In the experiments a decrease in the relative humidity on the thickness of the panel (from the chamber towards the channels) was observed. Along line 2 the drop of the relative humidity was larger than along line 1. As the air velocity in the air channels increased, the relative humidity drop across the panel thickness increased (Fig. 11). This indicates the intensification of moisture transfer. The dependence of the relative humidity of the thermal insulation on the air flow rate in the ventilated channels at the stationary regime is summarized by the following relation: Fig. 10. The relative humidity distribution in the horizontal section of the panel at y/h = 0.5 along lines 1 and 2.
ϕ = (78.2 − 5v ) − (18.6 + 17.7v )x/L[%],
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Fig. 12. Change in the air relative humidity along the channel height.
where v is the flow velocity in the channel, x is the coordinate according to Figs. 4 and 5, L is the thickness of the thermal insulation of the panel. As follows from the analysis, when the air velocity in the ventilated channels increased, the air relative humidity at the outlet decreased (Fig. 12). It provided a reduction in air humidity inside the panel. Fig. 13 shows the results comparison of the moisture balance. The vapor flowrate through the mineral wool and the amount of moisture removed through the ventilated channel were estimated at different air flowrates. Line (3) is an approximation of the results of calculations (1) and shows a monotonic increase in the mass flowrate of water vapor filtered through mineral wool with an increase in the air flowrate in the channels. The calculations were carried out according to the experimental values of relative humidity in mineral wool in the central horizontal section along thickness and the known vapor permeability coefficient 1.66 × 10−10 kg/(m s Pa). The average increase in the mass flowrate was about 0.2 mg/s for every 0.1 m/s increase in the air velocity. The change in the moisture content in the channel between
Fig. 13. Comparison of the mass flow rate of water vapor through the mineral wool (1) with a change in the content of water vapor between the outlet and inlet of the ventilated channel (2); 3, 4 – linear approximations of the corresponding data.
the outlet and the inlet (2) was approximated by a similar linear dependence (4) on the air velocity. The observed increase in the intensity of mass transfer through mineral wool with increasing flowrate of air was due to the intensification of mass transfer at the interface between the mineral wool and the air channel. The comparison shows satisfactory agreement between these two mass flowrates that indicates the correctness of the results. 3.2. Full-scale thermo and humidity measurements Experiments in condition at low air relative humidity in indoor were conducted in March 2018. This period is characterized by low indoor air relative humidity. The two-day interval from 0:00 on March 17 (regime 1) was selected for analysis due to stable weather conditions with clear sky. Experiments at high relative humidity of the indoor air which was maintained with an ultrasonic humidifier were carried out In
Fig. 14. Outdoor air parameters; a) regime 1, b) regime 2.
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Fig. 15. Indoor air parameters; a) regime 1, b) regime 2.
Fig. 16. Temperature distribution in the mineral wool panel; a) regime 1, b) regime 2. Locations of sensors from the inner surface to the outer one was denoted accordingly be numbers 7–10.
April 2018. For the analysis the two-day interval from 0:00 on April 5 (regime 2) was chosen. During the experiments, the southwest wind prevailed at a speed of 1–2 m/s. The daylight hours are shown in Fig. 14. The maximum insolation in regime 1 was 430 and 441 W/m2 at 16 h 30 min on March 17 and 18, respectively. The maximum insolation in regime 2 was 584 and 310 W/m2 at 17 h on April 5 and 6, respectively. Both selected intervals were accompanied by lowering the outdoor temperature at night (for the first regime to −20 °С and for the second regime to −10 °С) and increasing by 10–15 °С during daytime (Fig. 14). When the outdoor air temperature increased, its relative humidity decreased from 70% to 80% at night to 15%–20% during the day. For the first regime with low natural average relative humidity of the internal air of 8% the average temperature of the indoor air was 27 °С (Fig. 15a). For the second regime the average tempera-
ture of indoor air was 25 °С at high average relative humidity of 69% (Fig. 15b). The temperature change in different sections of the mineral wool panel is shown in Fig. 16, the numbers in the figure hereinafter correspond to the sensor positions in Fig. 6. According to the results of observations, the change in temperature inside the mineral wool panel for both regimes was cyclical with an increase in temperature during the daytime and a decrease in the nighttime. At the same time, the temperature inside the layer of mineral wool at each moment of time increased from the outer surface to the inner one. It should be noted that a significantly larger temperature change in the daytime of the outer layer of mineral wool was observed as compared with a change in the outside air temperature. This is associated with heating the outer metal layer of the panel and the adjacent layer of mineral wool by solar radiation at clear sky.
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Fig. 17. Temperature of the air in the ventilated channel; a) regime 1, b) regime 2. The sensors in the channel are location on top to the bottom accordingly numbers 1–5.
Fig. 18. Relative humidity of the air in the ventilated channel; a) regime 1, b) regime 2.
Fig. 17 shows the results of measurements of air temperature of the ventilated channel over time at different height. During the daytime from 15 to 18 h due to the solar heating the outer metal layer of the panel a significant temperature rise by 12–20 °С above the outdoor air temperature was observed in the ventilated channels. Inside the channels the difference in air temperature between inlet and outlet was 8–10 °С. Such a temperature difference should lead to the presence of a free convective air flow in the channels. As a result of the calculations for this flow, a speed range of 0.2– 0.3 m/s was obtained, which led the intensification of moisture removal from mineral wool, associated with an increase in speed in ventilated channels in the daytime. A decrease in humidity in mineral wool with an increase in speed in ventilated channels in this range was shown earlier in laboratory experiments.
At night with a cloudless sky, the air temperature in the ventilated channel was several degrees lower than the outdoor temperature due to external thermal radiation. This led to a descending flow in the channel which was much less intense. During the daytime a decrease in the air relative humidity was observed in the ventilated channel due to a significant increase in air temperature (Fig. 18). The partial pressures of water vapor in the ventilated channel, in the mineral wool and the indoor air for both regimes are determined by the temperature and relative humidity (Fig. 19). For clarity the figure shows the partial pressures, according to the indications of the edge sensors of the ventilated channel (5-bottom, 1-top) and mineral wool (7 is the inner layer, 10 is the outer layer). The changes in partial pressures obtained from the intermediate
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Fig. 19. Partial pressure of vapor in the mineral wool, in a ventilated channel and indoor air; a) regime 1, b) regime 2.
Fig. 20. Relative air humidity in the mineral wool; a) regime 1, b) regime 2.
sensors were located between the values for the edge sensors and are not shown in the figure. The partial pressure of water vapor in the room most of the observation time for regime 1 and all the time for regime 2 exceeded the partial pressure of water vapor in the mineral wool and the ventilated channel. This indicated the predominant movement of water vapor from the room to outdoor through the facade panel. To analyze the intensity of water vapor flow two areas can be distinguished: I – night and II – day (they are shown in the figure for the first day). Region I was characterized by either the absence or a relatively low drop in the partial vapor pressure between the mineral wool and the ventilated channel. This showed the low intensity of the vapor flow from the mineral wool. Area II demonstrated an increase in the temperature of the outer layer of mineral wool.
The increase was accompanied by a more rapid growth of the vapor pressure in the layer compared with an increase in the partial pressure in the ventilated channel. As result a more intense release of water vapor into the ventilated channels was occurred. At the same time, the vapor flow from the room to the mineral wool was reduced. Thus, in region II, an intense removal of moisture from the mineral wool was observed. Fig. 20 shows the results of measuring the relative humidity of the outdoor air and in the mineral wool. According to the measurement results, the relative humidity of the air in the mineral wool of the panel increased towards the outside and fluctuated during the day. With an increase in the relative humidity of the indoor air, an increase in the relative humidity of the air in the mineral wool was observed. However, even at high humidity of the indoor
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exceed 50%, which provided the panels with high heat-protection properties. An analysis of the heat-moisture state of mineral wool in a panel with ventilated channels in the cold season revealed two factors leading to additional intensification of moisture removal from the panel. In clear weather during the day, due to solar radiation, an increase in temperature was observed in the outer layer of the panel. This led to an increase in the pressure drop between the vapor in the mineral wool and in the ventilated channels, and as a result led to the intensification of moisture removal. Due to solar heating, the second factor was associated with an increase in temperature with the height of the channel. He created a convective flow of air, which also enhanced the removal of moisture from the panel in accordance with laboratory experiments. Laboratory and full-scale studies of the heat- and moisture state of the heat-insulating panel with ventilated channels confirmed the computational results [27] about that the developed design provides effective removal of moisture from the outer layer of the insulation. Comparison of the air humidity in the material with its permissible values showed that the heat-insulation layer of the facade with ventilated channels will be under normal operating conditions. Fig. 21. Thermo and moisture state of mineral wool: 1- measurement results in the center of the mineral wool layer in regime 1; 2 – limiting mould fungus formation curve.
Declaration of Competing Interest No conflict of interest.
air of about 70% (Fig. 20b), the relative humidity of the air in the mineral wool did not exceed 50%. This gave the panels high thermal protection properties. It should be noted that one of the conditions for using a facade system with ventilated channels is their ability to provide a normal thermo and humidity state in the heat-insulation material under a given climate. The implementation of this condition in the work was checked by comparing the air humidity in the material with its permissible value [32]. Fig. 21 shows that the results of the measurements of air relative humidity lie significantly below isopleth curve (2), which predicts of mould fungus formation on the surface and inside building component. Below the curve there is no biological activity expected on the mineral wool. This means that the mineral wool heat-insulation in this facade system will be in normal operating conditions. 4. Conclusions Experimental laboratory studies of moisture transfer through a heat-insulating panel with ventilated channels showed that with open channels due to the differential partial pressures of the vapor in mineral wool and in the channels, the vapor flow occurred that led to a decrease in the relative humidity in the thermal insulating material of the panel. When the air velocity in the channels was more than 0.1 m/s, which correspond to the actual air velocities in the ventilated channels of the facade system, a significant intensification of moisture removal from the panel was observed due to a decrease in the average relative humidity of the air in the ventilation channels. With an increase in air velocity in the channels from 0 m/s to 0.4 m/s, there was a decrease in humidity in the mineral wool with almost constant relative humidity of the indoor and outdoor air. As a result of the full-scale studies of heat and humidity processes in heat-insulating panels with ventilated channels in the cold period of the year it was established that an increase in the relative humidity of the air in the mineral wool was occurred with an increase in the relative humidity of the indoor air. However, even with a high relative humidity of the indoor air of about 70%, the relative humidity of the air in the mineral wool did not
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