Simulation calculation and analysis of building energy consumption of multi-story glued laminated timber structures

Abstract

As the only renewable building material, wood has a strong carbon sequestration effect. Thus, timber structures have the natural advantages of saving energy and reducing emissions. Currently, the research objects of building energy consumption are rarely timber structures. To further control the operational energy consumption of timber structures, this paper takes six-story glued laminated timber beam-column frame and light wood-frame shear wall structures as the research objects. Building energy consumption research is conducted through testing the heat transfer coefficient of the envelope structure, air circulation ratio, and Building Information Modeling (BIM) technology on-site. The results show that the energy consumption of the building is consistent with the current energy consumption of small- and medium-sized office buildings, and the heat gain and loss of the building are mainly due to solar radiation and heat conduction of the envelope, respectively. The airtightness of the building has the greatest influence on the energy consumption of the building, and the type of building structure and window-to-wall ratio have little influence on the energy consumption of the building.

Full Article

Simulation Calculation and Analysis of Building Energy Consumption of Multi-Story Glued Laminated Timber Structures

Yuying Zou,^a Xiaoyu Gu,^a Patrick Adjei,^b Zheng Wang,^a,* and Yujie Huang ^c

As the only renewable building material, wood has a strong carbon sequestration effect. Thus, timber structures have the natural advantages of saving energy and reducing emissions. Currently, the research objects of building energy consumption are rarely timber structures. To further control the operational energy consumption of timber structures, this paper takes six-story glued laminated timber beam-column frame and light wood-frame shear wall structures as the research objects. Building energy consumption research is conducted through testing the heat transfer coefficient of the envelope structure, air circulation ratio, and Building Information Modeling (BIM) technology on-site. The results show that the energy consumption of the building is consistent with the current energy consumption of small- and medium-sized office buildings, and the heat gain and loss of the building are mainly due to solar radiation and heat conduction of the envelope, respectively. The airtightness of the building has the greatest influence on the energy consumption of the building, and the type of building structure and window-to-wall ratio have little influence on the energy consumption of the building.

DOI: 10.15376/biores.18.4.7391-7410

Keywords: Glued laminated timber structure; Heat transfer coefficient; Building airtightness; Building energy consumption; Simulation calculation and analysis

Contact information: a: College of Materials Science and Technology, Nanjing Forestry University, Nanjing 210037, China; b: College of Civil Engineering, Nanjing Forestry University, Nanjing 210037, China; c: College of Civil Engineering, Southeast University, Nanjing 210037, China;

* Corresponding author: wangzheng63258@163.com

INTRODUCTION

Wood is characterized by its strong carbon fixation capacity and good stiffness (Wang et al. 2014, 2015, 2016, 2018, 2019). Therefore, timber structures naturally have the advantages of being low-carbon and environmentally friendly (Lin et al. 2015; Zuo and Wang 2017; Geng 2018; Liu et al. 2022). However, the operational phase of a building is highly energy-intensive. Glued laminated timber structures are mostly used in public buildings, which have the second highest energy consumption and carbon emissions of all buildings in the operational phase (Leonel et al. 2022; Zhang et al. 2022a,b). Therefore, studying the operational energy consumption of glued laminated timber structures and its control within a reasonable range can successfully reduce the amount of energy consumption during the whole life cycle.

Building airtightness, as an important influencing factor of energy consumption in the operational phase of buildings, has been studied by many scholars. Many studies abroad have used a probabilistic approach to study architectural physics (Peng et al. 2018; Wang and Roger 2021, 2022). The two main methods for testing building airtightness internationally are the blower door method and the tracer gas method (Xiong et al. 2022). Through the use of these two testing methods to test the airtightness and permeability of residential buildings, it was found that factors such as the quality of the building and the sealing of ventilation places such as windows and doors, have a particular influence on the overall building airtightness (Kalamees 2007; Sfakianaki et al. 2008; Pan 2010; Ambrose and Syme 2017). Furthermore, by designing a prediction model to test the airtightness of the building, the airtightness in calculation results of energy consumption are reliable, provided that the requirements are met (Alfano et al. 2012; Feng et al. 2014; Šadauskienė et al. 2016). In contrast, fewer studies have been conducted to calculate the effect of building airtightness on energy consumption by building numerical models. In many research studies, numerical simulations have been used to calculate and analyze the energy consumption of residential buildings. The multi-objective optimization algorithm NSGA-II, DeST software, and CFD software have been used. It has been found that airtightness has a negative correlation with energy consumption for buildings (Zhang et al. 2016; Ma and Cong 2020; Cao et al. 2022; Lin and Song 2022). In heating and cooling, heat transfer and airtightness are important factors affecting energy consumption. Improvement of heat transfer efficiency can reduce energy consumption, while improvement of air tightness can avoid loss of heat or cold air. Therefore, the study and improvement of these two factors are important to increase the efficiency of energy utilization and reduce the cost. In previous studies, there have been many studies on the effects of heat transfer and air tightness on energy consumption. However, most of the studies have been conducted on concrete structures, steel structures, etc., and fewer studies have been conducted on wood-framed buildings.

There have been few simulations and studies on the energy consumption of timber structures worldwide and even fewer on public buildings. The boundary conditions for the study of building energy consumption are primarily determined by referring to the standard values defined in each country’s relevant standards. However, these standards involve the heat transfer coefficient of the envelope, building airtightness, and building operation time that cannot be quantified accurately. Fewer studies have been conducted on the airtightness aspects of wood-framed buildings, but their impact on building energy consumption has been significant. Therefore, this paper takes a six-story glued laminated timber beam-column frame and light wood-frame shear wall as the research objects. On-site measurements of the heat transfer coefficient of the envelope and air circulation ratio were conducted. Using the measured data and the BIM technology, the annual energy consumption of the building was simulated, the priority of its airtightness influencing factors were explored, and the accuracy of the simulation calculations was improved.

EXPERIMENTAL

Material and Methods

Test subjects

The research object of this paper is the Research and Development (R&D) center building of Shandong Dingchi Wood Industry Co. The building is a six-story glued laminated timber beam-column frame-light wood shear wall system building. Except for the stairwell wall, the rest of the wall is SPF specification lumber composition of the shear wall. The stairwell wall material is made of SPF specification lumber made of cross-laminated timber (CLT). The beams, columns and floor materials are SPF glued laminated timber with a longitudinal length of 66.9 m, a transverse width of 17.4 m, and a total height of 24.7 m. The floor area is 4778.5 m². The number of floors of the main structure of the building is part six and part four, as shown in Fig. 1. The building is located in Penglai City, Shandong Province, which is in a cold region according to Appendix A.0.3 of GB 50176-2016 (2016), as shown in Fig. 2. The detailed structural drawings of each part of the building are shown in Fig. 3.

Fig. 1. R&D center building exterior rendering               Fig. 2. Building location schematic

Because the heat transfer coefficient test needs to arrange sensors, and according to the requirements in JGJ/T 357-2015 (2015), the measured area should not be less than 1.2 m × 1.2 m to meet the test requirements and facilitate the test. The office on the south side of the first floor is selected as the test space, as shown in Fig. 4. A diagonal line indicates the tested wall in the right figure. The internal material parameters of each structure are shown in Table 1.

Fig. 4. Schematic diagram of heat transfer coefficient test area

Table 1. Material Parameter Table of Wall, Floor, and Roof of R&D Center Building

Test Equipment and Methods

Wall heat transfer coefficient testing equipment and method

The test instruments in this study are mainly an HT-1 field heat transfer coefficient tester, heat flow meter sensor, and Pt1000 temperature sensor from Beijing Borin Jiji Technology Co. Based on the heat flow meter method, regarding GB/T 34342-2017 (2017), JGJ/T 357-2015 (2015), and GB/T 23483-2009 (2009). The schematic layout of measurement points is shown in Fig. 5, and the test site is shown in Fig. 6.

Fig. 5. Schematic diagram of sensor positioning              Fig. 6. Sensor layout on site

Building airtightness testing equipment and methods

This test was performed using the fan pressure method as specified in GB/T 34010-2017 (2017). The test methods are mainly divided into two categories: the decompression method and the pressurization method. The test results obtained by the decompression method are generally slightly larger than those by the pressurization method. The higher the airtightness of the building, the smaller the difference between the results measured by the two methods.

Table 2. Building Airtightness Testing Equipment

When testing, all the external doors and windows of the tested space should be closed, and all the internal doors should be opened so that the pressure in the test space can be guaranteed to be relatively uniform. The excess holes in the air conditioner or walls should be sealed with suitable materials to prevent errors in the test results, as shown in Fig. 7. When measuring, the first step is to measure the net volume of the space to be measured, the indoor and outdoor temperature and humidity and the atmospheric pressure. According to the target pressure, the pressure inside the room is pressurized or depressurized. After the indoor pressure is relatively stable, the indoor pressure will be collected several times. The air leakage volume can be calculated based on the atmospheric pressure, indoor and outdoor temperature, humidity, and pressure difference. The number of air changes of the test object is obtained from the air leakage volume and the net volume of the room. The test schematic and the device diagram are shown in Fig. 8 and Fig. 9, respectively.

Fig. 7. Indoor hole blocking

Fig. 8. Schematic diagram of the building                 Fig. 9. Installation and connection of blower

The test equipment is located inside the building, so the wind speed outside the test space is 0 m/s. The indoor temperature is 26.8 °C, the outdoor temperature is 19.1 °C, and the atmospheric pressure is 1.025 × 105 Pa.

Modeling and parameter setting for building energy simulation calculation

In this paper, Revit software developed by Autodesk was used to establish a 3D parametric model and simulate the building energy consumption through Ecotect Analysis 2010, as shown in Fig. 10.

Fig. 10. Building simulation models

To study the influence of different structural types on the energy consumption of the building, the main structure was designed as a concrete structure and CLT structure, respectively, while keeping the floor plan and facade of the building unchanged to compare the change of energy consumption of the building. The structural outline of the existing building is shown in Fig. 4. The internal material parameters of each structural elements are shown in Table 1. The CLT and concrete structure wall, roof, and floor slab samples are shown in Figs. 11 and 12, respectively, and the internal material parameters are shown in Table 3 (Dong et al. 2019).

Fig. 11. CLT structural component details

Fig. 12. Details of concrete structural components

Table 3. CLT and Concrete Structure Exterior Wall, Floor, and Roof Material Parameter Table

This study simulates a full year of work time versus rest time and the enterprise adopts the model of a single break with regular rest on legal holidays, including 79 days of holidays and 286 days of working days.

Referring to GB55015-2021 (2021), the boundary conditions of each room are set differently according to the personnel density, working status, and lighting in different areas (Table 4). The presence of room personnel in the room at each time of the same day is shown in Table 5.

Table 4. Simulation Parameters of Internal Gains

Table 5. Hourly Rate of Room Personnel

The standard value of illumination range of 50 to 500 lx, the lighting power density of 2 to 8 W/m², and holiday time were set to the off state according to the various space and office staff work requirements. Lighting usage at various times during the working day on the same day, was as shown in Table 6.

Table 6. Lighting Usage Time

The indoor temperature was limited to 20 to 26 °C. When the temperature was below or above this range, the air conditioner would automatically start working for cooling or heating to ensure the comfort of the indoor staff. The air conditioner was set to be off during the holidays. Air conditioning is used during the hours shown in Table 7, and not during the hours not shown in the table.

Table 7. Air Conditioner Usage Time

The power density of electrical appliances was 10 to 15 W/m², and the lighting was turned off during holidays. According to different spaces and the operational needs of office workers, the usage of the appliance at various times during the 24-h period on the same working day is shown in Table 8.

Table 8. Use Time of Electrical Appliances

When the number of air changes increased from 0.5 to 5 h^-1, respectively, the change in building energy consumption was calculated again using 0.5 as the step length to investigate the impact of airtightness on building energy consumption.

This simulation used the Chinese meteorological database dedicated to Ecotect Analysis software. Because the data of Penglai city is not available in the database, the data of Qingdao city, which is the nearest typical meteorological year to Penglai city, was used as a substitute in the calculation.

RESULTS AND ANALYSIS

Wall Heat Transfer Coefficient Test

According to section 3.4 of GB 50176-2016 (2016), the thermal resistance R of a single homogeneous material is given as Eq. 1,

(1)

where R is the thermal resistance of the material layer (m²·K/W), δ is the thickness of the material layer (m), and λ is the thermal conductivity of the material (W/(m·K)).

The heat transfer resistance R₀ for heat transfer from the flat wall of the enclosure is given as Eq. 2,

(2)

where R₀ is the thermal resistance of the flat wall of the enclosure (m²·K/W), ∑R is the total thermal resistance of the internal layers of the enclosure (m²·K/W), R_i is the heat transfer resistance of the internal surface (m²·K/W), and R_e is the heat transfer resistance of the external surface (m²·K/W).

The heat transfer coefficient K of the flat wall of the enclosure structure is given as Eq. 3,

(3)

where in Eq. 3 K is the enclosure structure flat wall heat transfer coefficient (W/ (m²·K)).

Because the shear wall of light wood frame structure is constructed as a hollow wall, the insulation material is placed inside the wall, and the stud is in the same plane, so the heat transfer coefficient is inconsistent within each area of the wall. For this reason, the heat transfer coefficient of the wall, K, is taken as the weighted average of the percentage of the projected area and the heat transfer coefficient in the area of the studs and the percentage of the projected area and the heat transfer coefficient in the area of the insulation wool, i.e. (Dong and Li 2018) Eq. 4,

(4)

where K is the light wood structure shear wall average heat transfer coefficient (W/(m²·K)), S_S is the stud area percentage of projected (%), K_S is the stud area average heat transfer coefficient (W/(m²·K)), S_I is the insulation wool area projection area percentage (%), and K_I is the insulation wool area average heat transfer coefficient (W/(m²·K)).

From the data in Table 1, it is calculated that:

It follows theoretically that:

(5)

Taking measurement point 1 as an example, the temperature and heat flow curves are shown in Fig. 13. On 10.19, the outdoor temperature increased, so additional heating measures were taken indoors to ensure the temperature difference between the inside and outside surfaces of the walls.

Fig. 13. Heat transfer coefficient test value curve of envelope

The comparison between the test results of the heat transfer coefficient of the wall and the theoretical values are shown in Table 9.

Table 9. Comparison of Field Test Value and Theoretical Value of Heat Transfer Coefficient

The difference between the average value of the wall heat transfer coefficient test and the theoretical value was only 0.847%, which demonstrates that the test was accurate and the theoretical value was the same as the actual situation. Therefore, the wall meets the design requirements for the thermal performance of walls in cold regions of China, and the theoretical value can be substituted into the building energy simulation software to simulate the annual energy consumption of the building.

Building Airtightness Testing

The airtightness test results of the first-floor office in the entirely blocked state are plotted as a function, as shown in Fig. 14, and the related test results are shown in Table 10.

Fig. 14. Airtightness test function diagram of the first-floor office completely blocked state

Table 10. Test Results of the Complete Airtightness of the Office on the First Floor