Hygrothermal properties analysis of cross-laminated timber wall with internal and external insulation systems

Journal of Cleaner Production 231 (2019) 1353e1363

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Hygrothermal properties analysis of cross-laminated timber wall with internal and external insulation systems Hyun Mi Cho, Seunghwan Wi, Seong Jin Chang, Sumin Kim* Department of Architecture and Architectural Engineering, Yonsei University, Seoul, 03722, Republic of Korea

a r t i c l e i n f o

a b s t r a c t

Article history: Received 18 February 2019 Received in revised form 15 May 2019 Accepted 18 May 2019 Available online 25 May 2019

Environmental energy is being studied actively around the world due to the effects of climate change, global warming, and energy policies. Energy policies are being reinforced to reduce building energy consumption. Therefore, environmental-friendly and sustainable building materials have been used to reduce energy consumption. The cross-laminated timber (CLT) wall is an environmental-friendly material that stacks layers at right angles, and bonds them together to form large solid panels. However, there is no standard for CLT structure walls in Korea. This study focuses on analyzing the hygrothermal properties of the CLT wall by showing the water content of the CLT wall, mold growth risk of CLT by WUFI simulation, and energy load by DesignBuilder using the climatic conditions of Seoul, Korea. CLT walls Ext_EPS, Ext_FG, and Ext_EPSFG based on an external insulation system, and walls Int_EPS, Int_FG, and Int_EPSFG based on an internal insulation system, were prepared for simulation analysis. The total water content (TWC) of Wall Ext_EPSFG was measured to be 8.67 kg/m2, which was the lowest TWC. This indicates that the TWC of the external insulation system wall is lower than that of the internal insulation system wall. Furthermore, the water content (WC) of structure based on the external insulation system is lower than that based on the internal insulation system. This indicates that the WC of Wall Ext_FG, measured to be a maximum 8.69% of WC, is lower than Wall Int_EPS, measured to be a maximum 10.45% of WC. According to the risk of mold growth, this indicates that all of the CLT wall layers have low mould growth risk, and the maximum mould index of walls Ext_FG and Int_EPSFG was measured to be 0.019. As a result of the hygrothermal analysis in this paper, CLT walls based on an external insulation system are more suitable than the internal insulation system. Therefore, this study analyzed the energy consumption of CLT walls based on the external insulation system, which was found to be lower than the energy consumption of the internal insulation system walls. © 2019 Elsevier Ltd. All rights reserved.

Keywords: Cross-laminated timber (CLT) Hygrothermal performance Hygrothermal simulation WUFI Energy efficiency DesignBuilder simulation

1. Introduction Environmental energy is being studied actively around the world because of the effects of climate change and global warming, and energy policies and systems are being reinforced to reduce building energy consumption (Nik, 2017; Kang and Kim, 2016). The Paris Climate Accord Agreement in 2014, which includes 189 countries, has agreed on measures to reduce global environmental energy consumption, and the Korean government has also announced that it will reduce the nation's greenhouse gas emission by 37% by 2030. In addition, domestic energy-related standards will be strengthened from 2017 to the level of the passive house, and

* Corresponding author. E-mail address: [email protected] (S. Kim). https://doi.org/10.1016/j.jclepro.2019.05.197 0959-6526/© 2019 Elsevier Ltd. All rights reserved.

from 2025 these will be obliged to be at the zero energy house level. Korea's energy consumption trend (2005) is 55% in the industry sector, 21% in the transportation sector, and 23% in the building sector. In the long term, reducing building energy consumption is an important factor in improving energy efficiency, because as the country becomes more developed, the proportion of building energy consumption of total energy consumption increases (Lee and Choi, 2016; Chang et al., 2017a,b). Therefore, to reduce energy consumption in the building sector, environmentally friendly and sustainable building materials should be used. Wood is the most representative natural material, and has low carbon emissions of 15 kg/m3 and a high carbon storage of 250 kg/m3; thus, building energy consumption can be reduced by maximizing carbon storage and reducing carbon emissions (Woodism and Woodism city, 2017; AiXin et al., 2017; Seo et al., 2017) The manufacture of building materials requires enormous energy and compared to wood,

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aluminum requires 790 times, steel requires 190 times, and concrete requires 3.5 times the energy (“Korea Woodism-city Project Research Society”, 2017). A total of 231,972 buildings were constructed in Korea in 2016, of which 205,699 were reinforced concrete and steel structures, 10,198 were masonry and 14,945 were wooden buildings. Compared to the previous yearly rate of increase, reinforced concrete and steel frame construction showed þ2.7%, masonry showed 9.8% and wooden construction þ9.9%, and among construction projects in Korea, the wooden structure showed the greatest growth rate (Ridley et al., 2014). In Korea, forest area occupies 63.2% of the national land area, and the forestry ratio is ranked fourth in the OECD countries, following Finland (73.1%), Japan (68.5%) and Sweden (68.4%), so there is potential for development of the forestry industry (“Korea National Forestry Administration”, 2017). CLT is composed of layers of lumber that are stacked at right angles to each other, and bonded together to form large solid panels. CLT has a higher structural capacity than wood frame, and can form walls, floor slabs, and roofs, and is also a wood material that is suitable for modular, large-scale, and high-rise building construction (Pang et al., 2016; Alsayegh, 2012). However, there is no standard in Korea for the CLT structural wall, and since CLT is basically a wood material, hygrothermal performance analysis for the moisture damage of wall is required to guarantee long-term durability performance (Kalamees and Vinha, 2003; McClung et al., 2014; Lepage et al., 2012). Therefore, in this study, the wood frame wall layer was selected and evaluated, based on the domestic standard wood frame house design published by the Korea Rural Community. Hygrothermal behavior according to the location of the insulation material was analyzed and evaluated by €r - kinetic heat and the WUFI Pro 5.3 (W€ ame und Feuchte instationa moisture) simulation program according to the heat transmission coefficient of the insulation standard in current law of the domestic wall. Chang et al. analyzed the hygrothermal performance of the Korean wood frame structure wall that applies macro-packed phase change material (MPPCM) with n-octadecane using the WUFI program, and this study suggests that the MPPCM-applied wood frame wall can solve the problem of mold growth (Chang et al., 2017a,b). Chang et al. analyzed the hygrothermal performance of the standard wood frame structure wall of the Korea Rural Community according to the regional climate data of Korea using the WUFI simulation program, and this study confirms that the Total Water Content (TWC) of the wall in 2014 is lower than that of the wall in 2010 (Chang et al., 2016). Korjenic et al. describes the possible connection of both of the above mentioned modern technologies, and gives results of the research and development of both of the insulation materials based on natural fibers; in particular, technical hemp, flax, and jute and their application in buildings with plant facades and roofs (Korjenic et al., 2016). This study also mentions the hydrothermal behavior of the developed materials, including computational simulation of the behavior of the optimal hemp fiber based material after building into a structure with plant facade. Clung et al. shows that the WUFI program can predict the hygrothermal behavior at the actual construction design stage, by comparing the field-measured value and WUFI simulation value of the moisture content (MC) of each of five kinds of CLT (McClung et al., 2014). Therefore, it is appropriate to analyze the hygrothermal performance of the CLT frame wall by using the WUFI program. Pelaz et al. investigated the thermal behavior of the CLT building considering the material characteristics and structural design of the exterior of the wooden facade using radiata pine wood in the Basque country, and DesignBuilder simulation program was used to analyze the cooling and heating energy load of CLT structure (Pelaz et al., 2017). Through this paper, it was confirmed that the energy load obtained by measuring the real

conductivity of the CLT structure is 5.07% lower than that using the regulation conductivity parameters. Azadeh studied building energy optimization, and optimized the performance of sunlight screen based on Erwin Hauer's design using the DesignBuilder simulation. This study shows that optimized facing screens of (30 and 100) % window-to-wall (WINR) can reduce annual energy usage by (35 and 42) % (Azadeh, 2011). DesignBuilder operates on the Energy Plus platform, and contains advanced modeling tools in a user-friendly interface. It is a significant aid to architects by designating and evaluating the energy performance and carbon emissions of a building from the early design stage. It also visualizes solar shading, and investigates design alternatives to maximize thermal comfort, and the benefits of daylight and natural ventilation. For engineers, it is useful to model HVAC, daylight, airflow, cost, energy and carbon, and to optimize solutions to confront design aims, and to maximize the benefits for clients. DesignBuilder is useful for engineers to model HVAC, daylight, and airflow; to minimize energy consumption, carbon emissions and costs; and to optimize solutions to achieve design aims (Kirimtat et al., 2016). CLT is an environmentally sustainable building material and CLT construction is an innovative idea that not only reduces carbon emissions but also reduces building energy. However, the construction of CLT in Korea is not activated and the details of the wall for CLT architecture are not presented. Therefore, the purpose of this study is to determine the suitability of CLT building in Seoul, South Korea. Therefore, this study analyzed the hygrothermal behavior of CLT wall by showing the water content of CLT wall and mold growth risk of CLT material using the WUFI simulation program, and evaluated the energy load on the selected wall using the DesignBuilder simulation program and proposed CLT walls of the passive house that is suitable for the climate of Seoul in Korea. 2. Methodology In this section, CLT panels developed in Korea were used (Pang et al., 2016), and the properties of CLT panels which are needed for hygrothermal simulation analysiswere analyzed through laboratory tests. Hygrothermal analysis using WUFI simulation program and analysis water content and mould growth risk, and the energy load of CLT structure was evaluated through the DesignBuilder program. 2.1. Laboratory tests In order to analyze the hygrothermal behavior of buildings using WUFI simulation, various physical properties of the building materials constituting the structure are required. Generally, the bulk density, porosity, specific heat capacity, thermal conductivity, and water vapour resistance factor of building materials are used for heat transfer calculation and moisture transfer calculation (Fraunhofer, 2017) In this study, the bulk density, specific heat capacity, thermal conductivity, porosity, and water vapour resistance factor of CLT materials were measured, which values are basically necessary for the simulation of the thermal moisture of a building. 2.1.1. Porosity The porosity was measured by Porosimetry, which is a method of measuring the size, porosity, and apparent density of pores present on the surface of a sample by adsorbing mercury to the sample, and the porosity related equations were as follows (1):

D¼

4tcosq P

(1)

where, D is the diameter of sample pore, P is the pressure, t is the

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surface tension of mercury, and q is the contact angle between the pores of the sample and mercury.

permeability (kg/m2s), and da is the water vapour permeability of air with respect to partial vapour pressure.

2.1.2. Specific heat capacity Differential scanning calorimetry (DSC) was used to analyze the specific heat capacity. This uses a device that can measure the calorie value by comparison with the reference sample according to the phase change of the material, by heating the sample and the reference sample at a constant heating rate.

d¼

2.1.3. Thermal conductivity The thermal conductivity was measured by thermal conductivity analyzer (C-Therm Technologies Ltd.). In order to measure the thermal conductivity of dry material, CLT material was measured after drying at 60  C for 48 h (Wi et al., 2017). 2.1.4. Water vapour resistance factor Water vapour resistance factor (m, ) was calculated according to the dry cup test method of ISO 12572 hygrothermal performance of building materials and products - Determination of water vapour transmission properties (ISO, 2001) standard (ISO, 2001). The 100 mm  100 mm square CLT samples were stabilized in a constant temperature and humidity chamber set at a temperature of (23 ± 5)  C and a relative humidity of (50 ± 5) %, before starting the dry cup test. The mass of CLT was measured as the change was measured more than 3 times within 5% of the sample's own mass. The stabilized sample was combined with a cup filled with silica gel to prepare cup assembly, and the measurement was started. Fig. 1 shows that the silica gel inside the cup should be at least 15 mm thick, and the air gap between the silica gel and the CLT sample should be maintained at (15 ± 5) mm (Moon et al., 2012; Kang et al., 2018). The water vapour resistance factor was calculated according to Eqs. (2)e(4), based on ISO 12572, 2001:

m¼

da d

(2)

where, m is the water vapour resistance factor, d is the water vapour

G,d A,Dpa

(3)

where, G is the slope of the regression line between mass and time, excluding the earlier, non-linear, stage of the test, d is the thickness (m), A is the area of specimen (m2), and Dpa is the water vapour pressure difference across specimen (Pa).

da ¼

  0:083p0 T 1:81 Rv ,T,p 273

(4)

where, p0 is the standard barometric pressure ¼ 1013 (hPa), p is the average barometric pressure (hPa), T is the thermodynamic temperature (K), and Rv is the gas constant for water vapour ¼ 462 (Nm/(kg.K)). 2.2. Simulation 2.2.1. WUFI simulation program Simulation programs for hygrothermal analysis include WUFI €rme und Feuchte instationar) developed by the Fraunhofer (Wa Institute in Germany, which allows dynamic analysis of hygrothermal performance (Kang and Kim, 2016) The WUFI program analyzes the thermal and moisture environment of buildings based on DIN 4108 standard (DIN 4108, 2013). In this study, hygrothermal analysis was performed according to the layer composition of CLT wall through WUFI Pro 5.3 version, and the risk of mold growth was analyzed using WUFI Bio. The water content of the whole wall is calculated based on the analysis of the simulation results of at least 5 years. If the water content after 5 years is lower than the initial value, it can be judged as safe from the long-term moisture problem (Chang et al., 2017a,b). In general, if the water content is constant over many years, the wall has reached the stabilization stage of hygrothermal behavior. In the case of wood, ASHRAE Handbook 2005 Fundamentals Chapter 24 states that the risk of corrosion and defects increases if the moisture content of the mass exceeds 20% (Chapter 24, 2001). The risk of mould growth was assessed using the Lowest Isopleth for Mould growth (LIM) curve and the Mold Index provided by the WUFI program (M. Krus et al., 2007). 2.2.2. Used weather data Weather data is an essential variable required in thermal building simulation that is unique, and dependent on the location of the building. The climate data used in this simulation is based on the weather data of Seoul, Korea which is located at 37.34 N latitude and 126.58 E longitude. The weather data for the building thermal simulation is generated by the Passive House Institute Korea (Passive House Institute Korea, 2017). Hygrothermal performance in this study was set as the target for the wall installed to the north, and the indoor climate conditions were set at 20  C, and the relative humidity was set at EN13788 Humidity Class 3. Fig. 2 and Table 1 show the weather data.

Fig. 1. CUP test assembly.

2.2.3. Risk of mould growth LIM 1 is LIM B І (Biological recyclable materials), which refers to the curve when inorganic material is used as an interior finishing material and the mould index is presented as an indicator of mold germination status. Tables 2 and 3 show the germination status of the mold according to the numerical value (Valipour, 2014; Sedlbauer et al., 2001).

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Fig. 2. Weather data of Seoul, Korea.

Table 1 Weather data of Seoul, Korea. Temperature ( C)

Relative humidity (%)

Mean

Max.

12.6

35.0

Min. 13.7

Mean

Max.

60

100

Min. 19

Counter-radiation Sum (kWh/m2a)

Mean Cloud Index ()

Mean Wind Speed (m/s)

Normal Rain Sum (mm/a)

2761.2

0.68

2.68

1426

Table 2 Relationship between temperature and humidity for the initiation of mold growth. Temperature condition ( C)

Critical relative humidity (% RH)

0  T  20 20 < T  50 50 < T

0.00267T3þ0.160T2-3.13T þ 100.0 80 No growth is assumed

Table 3 Mold growth status of Mold Index. Mold Index

Mold growth status

0 1 2

No growth Slight mold growth observed by microscope General mold growth observed by microscope (more than 10% distribution) Slight mold growth observed with the naked eye More than 10% distribution of mold observed with the naked eye More than 50% distribution of mold 100% distribution

3 4 5 6

2.2.4. DesignBuilder The DesignBuilder runs the EnergyPlus platform, which includes advanced modeling tools with a user-friendly interface, and which is a convenient simulation program for designing and evaluating building energy performance and carbon emissions during the initial design phase for architects (Kirimtat et al., 2016). In order to analyze the heating and cooling energy load using DesignBuilder, the building was modeled using ‘Rural Forest-12-26-A’ type residence (except warehouse), which is the standard design drawing presented by the Korea Rural Community, as shown in Fig. 3. The entrance, boiler room, and utility room were set to unheated, the roof was interpreted as semi-unconditioned, and all rooms had the same wall configuration. Input values other than the specified value

were used by default in DesignBuilder. Tables 4 and 5 show the modeling data. 3. Results and discussion 3.1. Physical property of CLT The porosity through the porosimeter is 0.49 m3/m3, and the bulk density and specific heat capacity measured by DSC are 610 kg/ m3, 958 J/kgK, and specific heat capacity as shown in Fig. 4. The thermal conductivity of the dried CLT was 0.163 W/mK, and the Water vapour resistance factor of 630 was measured according to the ISO 12572 dry cup test. Table 6 shows the results of physical property analysis of CLT material. 3.2. Configuration of CLT wall assembly Since the details of the wall of the CLT frame structure are not established in Korea at present, the wall detail of the CLT frame structure is constructed through this study, and walls are proposed with hygrothermal performance that is suitable for the Seoul climate in Korea. Table 7 shows the configuration of each wall layer. Wall KW is the wall layer of the standard wood frame structure (2014) of rural residence proposed by the Korea Rural Community. Since there is no standard CLT wall configuration in Korea, the hygrothermal performance is analyzed by constructing the CLT wall based on the design of Wall KW. Wall KCLT changed the OSB material, which is the light-weight structure of Wall KW, into the CLT material whose physical properties were analyzed in this paper. Wall KW and Wall KCLT have the same configuration and properties of materials, except for CLT. Wall KW_OSB 120 changed the thickness of OSB, which is the structure of Wall KW, to 120 mm, which is the thickness of CLT, and analyzed the hygrothermal behavior according to thickness by comparing the Total Water Content (TWC)

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Table 5 Building modeling data. Heating & cooling setpoints

Heating: 20  C, RH 50%, Cooling: 26  C, RH 50%

Occupant schedule

00:00e08:00, 18:00e24:00 08:00e18:00 130 W/person (Factor: 0.9) 5.0 W/m2 3.0 W/m2 0.05 person/m2 0.5 ACH 10 L/sec$person Ideal Loads Air System Seoul, Korea (.epw)

Metabolic rate per person Lighting density Equipment gain Occupancy Airtightness Ventilation HVAC Climatic data

100% 30%

Fig. 3. Modeling of DesignBuilder simulation.

with Wall KCLT. Walls Ext_EPS, Ext_FG, and Ext_EPSFG are constructed of wall layers in accordance with the standard of energy saving design criteria of buildings (January 2016) proposed by the Ministry of Land, Infrastructure, and Transport. The heat transmission coefficient of Walls Ext_EPS, Ext_FG, and Ext_EPSFG is 0.21 W/m2K, and the hygrothermal behaviors were analyzed by different types of insulation materials. Ext_EPS consisted of EPS insulation of 139 mm thickness, Wall Ext_FG consisted of Fiberglass wool insulation of 123 mm thickness, and Ext_EPSFG consisted of Fiberglass wool insulation of 100 mm thickness and EPS insulation of 26 mm thickness. Walls Ext_EPS, Ext_FG, and Ext_EPSFG are designed as an external insulation system. Walls Int_EPS, Int_FG, and Int_EPSFG have the same insulation material as Walls Ext_EPS, Ext_FG, and Ext_EPSFG, respectively, and are designed as an internal insulation system; and these were compared to analyze the hygrothermal behavior according to the location of the insulation of wall and the heating and cooling energy consumption.

3.3. Measured TWC Fig. 5 represents the TWC of all walls. Although the TWC of Wall KW without CLT is the lowest, all walls are considered to have longterm moisture stability, considering that TWC is downward for 5 years. Wall KCLT has a maximum TWC of 10.39 kg/m2, indicating

Fig. 4. Specific heat capacity of CLT.

that the CLT application wall should be presented, instead of replacing only the structure with CLT in the general lightweight wood structure. In addition, the maximum TWC of Wall Ext_EPSFG is 8.67 kg/m2, which shows the lowest TWC value among CLT walls. Fig. 6 represents the TWC of Walls KW, KCLT, and KW_OSB120. The maximum TWC of Wall KW is 4.24 kg/m3, which is lower than that of Wall KCLT. However, the maximum TWC of Wall KW_OSB120 was 14.47 kg/m3 when the thickness of OSB, which is the structure of Wall KW, was changed to 120 mm, which is the same as CLT; and it was confirmed that it has higher moisture

Table 4 Materials of building modeling data. Materials Roof

Floor

Internal partition

Ceiling Door

Asphalt single Mortar Concrete EPS Gypsum board Leveling concrete EPS Concrete Aerated concrete Mortar Floor paper Mortar Concrete Mortar Gypsum board Timber door

Thickness (mm)

Thermal conductivity (W/m$K)

Density (kg/m3)

Specific heat capacity (J/kg$k)

3 30 200 110 12.5 50 70 200 110 30 3 18 200 18 12.5 45

0.040 1.400 1.950 0.036 0.180 1.950 0.036 1.950 0.200 1.400 0.072 1.400 1.950 1.400 0.160 0.150

1120 1920 2240 20 800 2240 20 2240 640 1920 480 1920 2240 1920 800 608

1260 900 900 1210 1090 900 1210 900 900 900 1380 900 900 900 1090 1630

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Table 6 Physical property of CLT. Materials Density (kg/m3) Porosity (m3/m3) Specific heat capacity (J/kgK) Thermal conductivity (W/mK) Water vapour resistance factor () Schematic CLT

602

0.49

958

0.163

content than Wall KCLT's maximum TWC of 10 kg/m3. This means that compared to the lightweight wood frame structural wall, the CLT wall is moisture stabilized in Seoul, Korea. The maximum and minimum values for the TWC for a year are shown in Table 8. In the case of the external insulation system, the minimum value of TWC is 6.41 kg/m3 and 6.42 kg/m3 lower than that of the internal insulation system. The maximum value of TWC is the Int_EPS of 8.01 kg/m3, Int_FG and Int_EPSFG of 7.99 kg/m3, which is lower than that of the external insulation system. 3.4. WC for each CLT of wall Fig. 7 shows the Water Content (WC) in CLT, which is the structure of CLT walls for 3 years. It can be concluded that the CLT of all walls has moisture stability, because all walls show a downward trend without exceeding WC 20%, which is the standard of ASHRAE Handbook 2005 Fundamentals Ch. 24. Compared with the location of the insulation, in Walls Ext_EPS, Ext_FG, and Ext_EPSFG, which are external insulation system, Wall Ext_EPSFG has a maximum WC of 8.67% for 3 years, and in Walls Int_EPS, Int_FG, and Int_EPSFG, which are internal insulation system, Wall Int_EPS has a maximum WC of 10.45%. Fig. 8 shows the WC during the summer period. The average precipitation in the summer period of Seoul is 309.4 mm, which is the highest in July of the year at 394.7 mm. Also during the summer period, the Int_EPS using the internal insulation system exhibits a maximum WC of 9.55%, and the Ext_EPSFG maximum of 8.67% in the external insulation system. Fig. 9 shows WC during the winter period. The winter in Seoul is a dry climate, so the WC of the CLT also shows a gradual decline. During the winter period, the internal insulation system showed higher WC than the external insulation system, and the walls using EPS and fiberglass wool insulation were (9.55 and 9.41) %, respectively. Among the extermal insulation system walls, Ext_FG has the maximum WC of 8.60% and the Ext_EPS of 7.54% in December. Comparing the WC between the external insulation systems during the winter period, fiber glass wool insulation has better long-term drying performance than EPS, considering that the WC of the wall using the fiberglass insulation is drastically lowered. As a result, it can be concluded that the CLT wall using external insulation system has better long-term drying capacity than the internal insulation system. The WC values for one year are shown in Table 8 and tend to be the same as for TWC. The maximum value of WC is about 57.85 kg/m3 for external insulation system and higher than that for internal insulation system. However, the minimum value of WC is three types of the external insulation system is about 50.5 kg/m3, which is lower than that of the internal insulation system. Lepage analyzed the initial WC of the CLT in the Canadian city using the WUFI simulation program used in this paper and analyzed the WC by CLT wall layer location. In Vancouver, Canada, the WC of the CLT wall was 57% and Ottawa was 12% (Lepage et al., 2012). Wang and Ge investigate the wetting and drying behavior of CLT walls using a Delphin simulation program. The WC was about 15% similar to the WC analyzed in this paper and showed slightly higher WC when there was rain leakage

630

(Wang and Ge, 2016). McClung et al. analyzed the hygrtothermal performance of five types of CLT walls and measured the WC of each CLT material. The measured WC showed about 15% toward the indoor (McClung et al., 2014). 3.5. Risk of mould growth Risk of mould growth was evaluated by LIM 1 line and mould index (Sedlbauer, 2001). Fig. 10 indicates the LIM 1 line of the wall. If the graph is drawn over the dotted curve, this means that mold is likely to occur. The graph shows the relative humidity (Y-axis) of the surface with time-dependent temperature change (X-axis), which gradually becomes colored in yellow depending on time. As a result, the CLT of all CLT walls has been found to be above the LIM 1 curve after 5 years, but the risk of mould growth is not high, due to the short time of the above graph. The mould index as shown in Fig. 11 and all CLT materials do not exceed mould index 0.020. Walls Ext_FG and Int_EPSFG show a maximum mold index of 0.019. In addition, the CLT of all walls shows a tendency to gradually decrease after a lapse of time, and after seven months, they show mould index 0, which confirms that the CLT of the wall structure has a low long-term risk of mould growth. Mould growth and mould index for one year are shown in Table 8 and the final mold growth after one year is 10e11 mm for the external insulation system and about 0.7 mm for the internal insulation system. After one year, the value of the mould index is similar to zero for both external and internal insulation systems, indicating that there is little risk of mould growth in the CLT material. 3.6. Energy consumption by insulation system Fig. 12 shows the cooling and heating energy consumption for 1 year as interpreted by the DesignBuilder simulation program. It can be seen that the CLT wall with external insulation is more energy efficient than the CLT wall with internal insulation. In addition, walls using EPS insulation show the maximum energy consumption irrespective of the insulation system, and walls using fiberglass wool insulation appear to be effective in reducing energy consumption. Table 9 shows energy consumption by type of insulation system and Int_EPS has the highest heating and cooling energy consumption of 7242.7 kWh, while Ext_FG has the lowest value among the 6 kinds of CLT walls, which is 7228.7 kWh. 3.7. Configuration of the energy-saving CLT walls The passive house was introduced by the Passive House Institute in Darmstadt, Germany. This concept has been leading the global construction concept for energy efficiency and pleasant living space. There were many requirements for the construction of the passive house, such as advanced building envelope insulation, HVAC system, and high air tightness levels (Kylili et al., 2017). Over the past 30 years, many studies related to the passive house have

Table 7 Configuration of wall layer. Wall

KW

KCLT

Ext_EPS

Ext_FG

Material

Bulk density (kg/m3)

Porosity (m3/ m3)

Heat capacity (J/kgK)

Thermal conductivity (W/mK)

Diffusion Resistance Factor (-)

Cement board Air layer Vapour retarder OSB Fiberglass EPS Vapour retarder Gypsum board

1130 1.3 130 630 30 30 130 850

0.48 0.999 0.001 0.6 0.99 0.95 0.001 0.65

840 1,000 2,300 1,500 840 1,500 2,300 850

0.255 0.23 2.3 0.13 0.035 0.04 2.3 0.2

28 0.38 100 650 1.3 50 100,000 8.3

Cement board Air layer Vapour retarder CLT Fiberglass EPS Vapour retarder Gypsum board

1130 1.3 130 602 30 30 130 850

0.48 0.999 0.001 0.49 0.99 0.95 0.001 0.65

840 1,000 2,300 958 840 1,500 2,300 850

0.255 0.23 2.3 0.163 0.035 0.04 2.3 0.2

28 0.38 100 630 1.3 50 100,000 8.3

Wood cladding Air layer Vapour retarder EPS Vapour retarder CLT Gypsum board

350 1.3 130 30 130 602 850

0.8 0.999 0.001 0.95 0.001 0.49 0.65

1,880 1,000 2,300 1,500 2,300 958 850

0.084 0.23 2.3 0.04 2.3 0.163 0.2

1963 0.38 100 50 100000 630 8.3

Wood cladding Air layer Vapour retarder Fiberglass Vapour retarder CLT Gypsum board

350 1.3 130 30 130 602 850

0.8 0.999 0.0001 0.99 0.001 0.49 0.65

1,880 1,000 2,300 840 2,300 958 850

0.084 0.23 2.3 0.035 2.3 0.163 0.2

1,963 0.38 100 1.3 100,000 630 8.3

U-value (W/m2K)

0.172

0.158

0.21

0.21

Assembly

Wall

Ext_ EPSFG

Int_ EPS

Int_ FG

Int_ EPSFG

Material

Bulk density (kg/m3)

Porosity (m3/ m3)

Heat capacity (J/kgK)

Thermal conductivity (W/mK)

Diffusion Resistance Factor (-)

Wood cladding Air layer Vapour retarder Fiberglass EPS Vapour retarder CLT Gypsum board

350 1.3 130 30 30 130 602 850

0.8 0.999 0.001 0.99 0.95 0.001 0.49 0.65

1,880 1,000 2,300 840 1,500 2,300 958 850

0.084 0.23 2.3 0.035 0.04 2.3 0.163 0.2

1,963 0.38 100 1.3 50 100,000 630 8.3

Wood cladding Air layer Vapour retarder CLT EPS Vapour retarder Gypsum board

350 1.3 130 602 30 130 850

0.8 0.999 0.001 0.49 0.95 0.001 0.65

1,880 1,000 2,300 958 1,500 2,300 850

0.084 0.23 2.3 0.163 0.04 2.3 0.2

1,963 0.38 100 630 50 100,000 8.3

Wood cladding Air layer Vapour retarder CLT Fiberglass Vapour retarder Gypsum board

350 1.3 130 602 30 130 850

0.8 0.999 0.001 0.49 0.99 0.001 0.65

1,880 1,000 2,300 958 840 2,300 850

0.084 0.23 2.3 0.163 0.035 2.3 0.2

1,963 0.38 100 630 1.3 100,000 8.3

Wood cladding Air layer Vapour retarder CLT EPS Fiberglass Vapour retarder Gypsum board

350 1.3 130 602 30 30 130 850

0.8 0.999 0.001 0.49 0.95 0.99 0.001 0.65

1,880 1,000 2,300 958 1,500 840 2,300 850

0.084 0.23 2.3 0.163 0.04 0.035 2.3 0.2

1,963 0.38 100 630 50 1.3 100,000 8.3

U-value (W/m2K)

0.21

0.158

0.21

0.21

Assembly

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Fig. 5. TWC of all walls.

Fig. 7. WC of CLT walls for 3 years.

Fig. 6. TWC of walls KW, KCLT, and KW_OSB120. Fig. 8. WC of CLT walls during summer.

Table 8 Summary of hygrothermal performance. Walls TWC (kg/m2) Max. value Min. value CLT material WC Max. value (kg/m3) Min. value (kg/m3) Max. value (%) Min. value (%) Mould risk Mould growth (mm) Mould index ()

Ext_EPS

Ext_FG

Ext_EPSFG

Int_EPS

Int_FG

Int_EPSFG

8.26 6.42

8.39 6.41

8.37 6.41

8.01 6.82

7.99 6.82

7.99 6.82

57.85 50.58 9.61 8.40

57.85 50.50 9.61 8.39

57.83 50.51 9.61 8.39

56.57 52.56 9.40 8.73

56.63 52.14 9.41 8.66

56.35 52.42 9.36 8.71

11.0 0.019

10.9 0.019

10.0 0.017

0.7 0.001

0.7 0.001

0.6 0.001

H.M. Cho et al. / Journal of Cleaner Production 231 (2019) 1353e1363

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insulation system are more moisture stabilized than internal insulation walls, and energy consumption can be saved. Therefore, this section suggests the energy saving type CLT walls using the external insulation system. In addition, a passive house level CLT wall layer was constructed, and compared with Walls Ext_EPS, Ext_FG, and Ext_EPSFG, to analyze the energy efficiency. If the CLT wall is changed to the passive house level, the heating and cooling energy consumption can be reduced by 3.56% in Wall Ext_EPS, 3.52% in Wall Ext_FG, and 3.53% in Wall Ext_EPSFG. Fig. 13 shows the passive house level CLT walls. Liu et al. analyzed the possibility of using CLT as an alternative building material for carbon and energy intensive building materials such as concrete, and found that CLT could save 36.4% of energy compared to concrete buildings (Liu et al., 2016). Khavari et al.

Fig. 9. WC of CLT walls during winter.

been conducted (Ridley et al., 2014; Georges et al., 2014). A passive house is a building that can be used for winter without a heating system. The goal of the passive house is to minimize the direct energy consumption of facilities, and to give the occupants a sense of thermal comfort through indirect methods. The ultimate goal is to apply direct facilities only to those that are absolutely necessary. The passive house is a result of research to provide the residents with the most comfortable living environment, and after confirming this, it shows the additional effect of energy saving. In addition, the heat insulation property is based on the thermal transmittance of 0.15 W/m2K or less for external walls and roofs, and glass and window frames having a thermal conductivity of 0.8 W/m2K or less. After analyzing the results of simulations, CLT walls with external

Fig. 10. LIM 1 curve of CLT walls.

Fig. 11. Mold index of CLT walls.

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Fig. 12. Energy consumption of CLT walls.

analyzed the energy consumption of the CLT building based on the EnergyPlus model and analyzed that the CLT building is more energy efficient in areas where heating energy is used heavily. For example, Duluth's total energy cost savings were 10%. Khavari et al. suggested that CLT could reduce internal heat loads (Khavari et al., 2016).

4. Conclusions Due to the effects of climate change, global warming, and energy policies and systems, environmental energy is being actively studied worldwide. These policies are being reinforced for the reduction of building energy consumption. Therefore, environmental-friendly and sustainable building materials have been used to reduce energy consumption. Wood is an environmental-friendly material that has low carbon emissions of 15 kg/m3 and a high carbon storage of 250 kg/m3. Those advantages

allow the building energy consumption to be lowered. CLT is a timber layer stacked at right angles, and bonded together to form large solid panels. CLT has a higher structural capacity compared with wood-based building materials, such as wood frame, floor slabs, and roofs. Therefore, it can be used for modular and high-rise building construction by wood. However, there is no standard for the CLT structure wall in Korea. This study focuses on analyzing the hygrothermal properties of the CLT wall by showing the water content of the CLT wall, mold growth risk of CLT by WUFI simulation, and energy load by DesignBuilder using the climatic conditions of Seoul, Korea. Walls Ext_EPS, Ext_FG, and Ext_EPSFG based on an external insulation system, and Walls Int_EPS, Int_FG, and Int_EPSFG based on an internal insulation system, were prepared for simulation analysis. The total water content (TWC) of Wall Ext_EPSFG was measured to be 8.67 kg/m2, which was the lowest TWC; also the TWC of the external insulation walls was lower than that of the internal insulation walls. Furthermore, the Water Content (WC) of the structure based on the external insulation system was lower than that of the internal insulation system. Int_EPS using the internal insulation system exhibits a maximum WC of 9.55% and the Ext_EPSFG a maximum of 8.67% in the external insulation system in summer, and during the winter period, the internal insulation system showed higher WC than the external insulation system, and the walls using EPS and fiberglass wool insulation were (9.55 and 9.41) %, respectively. Among the external insulation system walls, Ext_FG showed the maximum WC of 8.60% and the Ext_EPS of 7.54% in December. As a result, it can be concluded that the CLT wall using the external insulation system has better long-term drying capacity than the internal insulation system. According to the risk of mould growth, this indicates that all of the CLT Wall layers have low mould growth risk, and the maximum mold index of Wall Ext_FG and Wall Int_EPSFG was measured to be 0.019. Comparing the Energy consumption by insulation system, the CLT wall with external insulation is more energy efficient than the CLT wall with internal insulation. In addition, walls using EPS insulation show the maximum energy consumption irrespective of the insulation

Table 9 Comparison of energy consumption of insulation systems. Energy consumption (kWh)

Ext_EPS

Ext_FG

Ext_EPSFG

Int_EPS

Int_FG

Int_EPSFG

Heating Cooling Total energy

6561.3 674.8 7236.1

6554.0 674.8 7228.7

6555.2 674.7 7230.0

6565.8 676.9 7242.7

6558.9 677.2 7236.2

6563.1 676.9 7240.0

Fig. 13. Energy saving CLT walls based on the external insulation system.

H.M. Cho et al. / Journal of Cleaner Production 231 (2019) 1353e1363

system, and walls using fiberglass wool insulation appear to be effective in reducing energy consumption. As a result of simulations analysis, CLT walls based on the external insulation system are suitable, compared with those using the internal insulation system. Therefore, this study analyzed the Energy consumption of Walls Ext_EPS, Ext_FG, and Ext_EPSFG based on the external insulation system, and the energy consumption of the passive house Walls Ext_EPS, Ext_FG, and Ext_EPSFG were measured to show (3.56, 3.52, and 3.53) % energy savings, respectively. In conclusion, this study proposed a standard of the CLT Wall for the passive house, and further studies would be necessary, depending on the hygrothermal performance of the CLT wall under diverse climatic conditions. Acknowledgement This work was supported by the Korea Institute of Energy Technology Evaluation and Planning and the Ministry of Trade, Industry and Energy of the Republic of Korea (No. 20194010201850). This research was supported by the Yonsei University Research Fund of 2018 (2018-22-0193). References AiXin, G., HongQiang, Y., JiaXin, C., YinXing, H., 2017. Review of carbon storage function of harvested wood products and the potential of wood substitution in greenhouse gas mitigation. For. Policy Econ. 85, 192e200. https://doi.org/10. 1016/j.forpol.2017.08.007. AlSayegh, G., 2012. Hygrothermal Properties of Cross Laminated Timber and Moisture Response of Wood at High Relative Humidity. ProQuest Diss. Theses; Thesis (m.a.sc.)–carlet. Univ. (Canada), 52e01, p. 118. Azadeh, O., 2011. Design optimization of a contemporary high performance shading screen e integration of ‘form’ and simulation tools. Proc. Build. Simul. 2011 12th Conf. Int. Build. Perform. Simul. Assoc. 2491e2498. Chang, S.J., Kang, Y., Wi, S., Jeong, S.G., Kim, S., 2017. Hygrothermal performance improvement of the Korean wood frame walls using macro-packed phase change materials (MPPCM). Appl. Therm. Eng. 114, 457e465. https://doi.org/10. 1016/j.applthermaleng.2016.11.188. Chang, Seong Jin, Seunghwan, Wi, Lee, Jongki, Lee, Hwayoung, Cho, Hyunmi, Cho, K.S., 2017. Analysis of cooling and heating energy demands of wooden houses with cross-laminated timber (CLT) using domestic plywood as core materials. J. Korean Soc. Living Environ. Sys. 24, 752e759. https://doi.org/10. 21086/ksles.2017.12.24.6.752. Chapter 24, 2001. Thermal and moisture control in insulated assemblies - Applications. In: ASHRAE Handb. Liu, Y., Guo, H., Sun, C., Chang, W.-S., 2016. Assessing cross laminated timber (CLT) as an alternative material for mid-rise residential buildings in cold regions in Chinada life-cycle assessment approach. Sustainability 8, 1047. https://doi.org/ 10.3390/su8101047. Fraunhofer. WUFI Pro Germany: fraunhofer IBP. n.d., [WWW Document]. URL. https://wufi.de/en/software/wufi-pro/. Georges, L., Berner, M., Mathisen, H.M., 2014. Air heating of passive houses in cold climates: investigation using detailed dynamic simulations. Build. Environ. 74, 1e12. https://doi.org/10.1016/j.buildenv.2013.12.020. Chang, S., Kang, Y., Wi, S., Jeong, S.-G., Kim, S., 2016. Analysis of hygrothermal performance for standard wood-frame structures in Korea. Journal of the Korean Wood Science and Technology 44, 440e448. https://doi.org/10.5658/ WOOD.2016.44.3.440. Kalamees, T., Vinha, J., 2003. Hygrothermal Calculations and Laboratory Tests on Timber-Framed Wall Structures, Building and Environment. https://doi.org/10. 1016/S0360-1323(02)00207-X. Kang, Y., Kim, S., 2016. Evaluation of the hygrothermal performance by wall layer component of wooden houses using WUFI simulation program. Journal of the Korean Wood Science and Technology 44, 75e84. https://doi.org/10.5658/ WOOD.2016.44.1.75. Kang, Y., Chang, S.J., Kim, S., 2018. Hygrothermal behavior evaluation of walls improving heat and moisture performance on gypsum boards by adding porous

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