Relative importance of certain factors affecting the thermal environment in subway stations based on field and orthogonal experiments
Introduction
The public area (including the concourse and platform) in subway stations located in cold-climate regions, where the average ambient temperature in the coldest month is below 0 °C (Deliège & Nicolay, 2016; Kottek, Grieser, Beck, Rudolf, & Rubel, 2006; Peel, Finlayson, & McMahon, 2007), generally have no heating systems during winter, as they are designed to only guarantee temporary comfort for passengers. Previous studies have found that passengers feel cool or slightly cool at these stations (Chen, 2018; Ordódy, 2000; Yang et al., 2008). As people are becoming increasingly accustomed to an ideal indoor environment, passengers have begun to desire a more comfortable thermal environment in subways. To improve the thermal environment (which is complex and sensitive to different factors), the key influencing factor must be identified.
Researchers have discussed the factors influencing subway stations from different perspectives, such as environmental parameters (Ordódy, 2000; Yang, Zang, & Gong, 2013), operating conditions (Ampofo, Maidment, & Missenden, 2004b; Guan, Liu, Zhang, & Xia, 2018; Guan, Zhang, & Liu, 2018; Liu, 2003; Yang et al., 2013;), and design parameters (Guan, Liu et al., 2018; Liu, Zhu, & Wang, 2017; Pope, Newman, & Henson, 2000; Wang, 2007).
However, the effects of the factors influencing the thermal environment in winter have not been analyzed, and efficient experimental design strategies have not been applied. A good design of experiments (DOE) approach can facilitate the efficient collection of valid statistical information. Previous studies have followed the one-factor-at-a-time (OFAT) method (Liu, Li, Yang, & Zhang, 2017; Liu, Zhu et al., 2017; Wang, 2007; Wang et al., 2011), which varies the levels of only one factor at a time while the other factors are fixed (Czitrom, 1999). The OFAT method is labor-intensive and time-consuming when several factors are considered. For multivariate research, DOE is more efficient, as the method simultaneously changes several factors and requires fewer resources (such as experiments and time). The effect estimates of each factor are also more precise (Min, 2001). Orthogonal experimental design is an efficient strategy that selects only a fraction of all possible trials, whereas full factorial design conducts trials for all combinations of levels across all factors. Orthogonal experimental design applies an orthogonal array to uniformly arrange experiments. Therefore, all factor settings and all pairs of settings are tested simultaneously. Then, combined with range analysis and analysis of variance (ANOVA), the results can be analyzed to rank the factors according to their degree of influence, thereby identifying the key influencing factor.
In this study, an orthogonal experimental design was employed to elucidate the relative importance of factors influencing the complex subway thermal environment in a cold-climate region during winter. A flowchart for identifying the key influencing factors of the subway thermal environment is shown in Fig. 1. Based on a preliminary analysis and on-site measurement results, temperature was employed as the subway thermal environment index. Then, using the IDA Tunnel software, orthogonal experiments were conducted, and the results were analyzed to identify the key influencing factors, providing new insights for targeted strategy proposals for improving the subway thermal environment.
Section snippets
Field measurements
Xi’an (33°29’–34°44’ N, 107°40’–109°49’ E) is the largest city in northwestern China (Cao et al., 2005), and has a cold climate (the average temperature in the coldest month is below 0 °C) under the Köppen climate classification. The subway in Xi’an uses air-conditioning system only in summer, and it relies on natural ventilation both in winter and transitional seasons. The temperature of the constant soil temperature layer is 16 °C (Ren et al., 2012).
A typical subway station on the Xi’an Metro
Field experiments
The variations in the relative humidity inside and outside of the Xi’an subway station on the test day are shown in Fig. 7. The relative humidity inside the station was approximately 20–40 %, and it decreased near 15:30 as the temperature increased at the station. According to the thermal comfort zone in winter (ASHRAE Insights, 2002; ASHRAE, 2017; Parker, 1972), comfortable relative humidity range is 30–60 %, and sometimes a little higher than 70 % or as low as 25 % is still acceptable (
Discussions
Orthogonal experiments were conducted using IDA Tunnel, and the results were analyzed to detect the degrees of effects of different factors, thereby identifying the key influencing factor. In IDA Tunnel (EQUA Simulation AB, 2016) used in this study, the heat gains from passengers are calculated by the heat dissipated from a passenger and the ridership in station. The thermal resistance of clothes and the activity of passengers are also considered. As passengers are usually dressed in clothes
Conclusions
This study applied orthogonal design to provide a comprehensive analysis of the influencing factors (two environmental influencing factors and four factors concerning operation conditions) of a subway thermal environment in cold regions during winter. The orthogonal experiments conducted were aided by on-site measurements and IDA Tunnel simulations. The results were analyzed using range analysis and ANOVA, and the main findings are summarized below.
- (1)
As determined from the range analysis and
Declaration of Competing Interest
The authors declare no conflict of interest.
Acknowledgments
This study was supported by the National Key R&D Program of China (No. 2019YFC0605105) and the project of Key Technology of Thermal Environment Control of Subway Station in Northern China. Furthermore, the authors wish to acknowledge the support of China Railway First Survey and Design Institute Group Ltd., for their support to field experiments and numerical modelling for the present work. We are also grateful to Zhixiang Cao for the valuable advice and assistance during writing this
References (49)
- et al.
Underground railway environment in the UK Part 1: Review of thermal comfort
Applied Thermal Engineering
(2004) - et al.
Underground railway environment in the UK: Part 3: Methods of delivering cooling
Applied Thermal Engineering
(2004) - et al.
Estimation of soil temperature profile in Hong Kong from climatic variables
Energy and Buildings
(2011) - et al.
Energy consumption of subway stations in China: Data and influencing factors
Sustainable Cities and Society
(2018) - et al.
Performance investigation of outdoor air supply and indoor environment related to energy consumption in two subway stations
Sustainable Cities and Society
(2018) - et al.
On the determination of the thermal comfort conditions of a metropolitan city underground railway
The Science of the Total Environment
(2016) - et al.
Simulation study on air leakage of platform screen doors in subway stations
Sustainable Cities and Society
(2018) - et al.
A study on underground tunnel ventilation for piston effects influenced by draught relief shaft in subway system
Applied Thermal Engineering
(2008) - et al.
Simulating air distribution and occupants’ thermal comfort of three ventilation schemes for subway platform
Building and Environment
(2017) - et al.
Sensitivity analysis on main design parameters of underground railway thermal environment
HV&AC
(2017)
Analyses of the improvement of subway station thermal environment in northern severe cold regions
Building and Environment
Thermal modeling and parametric analysis of underground rail systems
Energy Procedia
Measurements of temperature distribution in ground
Experimental Thermal and Fluid Science
STESS: Subway thermal environment simulation software
Sustainable Cities and Society
Optimization of biodiesel production from camelina oil using orthogonal experiment
Applied Energy
Research on airflow and energy performance in PBD, PSD and PBD-PSD-combined environment control systems in subway
Sustainable Cities and Society
Experimental and numerical investigation of braking energy on thermal environment of underground subway station in China’s northern severe cold regions
Energy
Energy performance investigation of an innovative environmental control system in subway station
Building and Environment
Ventilation for subway stations with adjustable platform doors created by train-induced unsteady airflow
Building and Environment
Train-induced unsteady airflow effect analysis on a subway station using field experiments and numerical modelling
Energy and Buildings
An orthogonal experimental study on solid fuel production from sewage sludge by employing steam explosion
Applied Energy
Quantifying colocalization by correlation: The Pearson correlation coefficient is superior to the Mander’s overlap coefficient
Cytometry Part A
ASHRAE handbook-fundamentals
Cited by (43)
Impact of NO<inf>2</inf> emissions from household heating systems with wall-mounted gas stoves on indoor and ambient air quality in Chinese urban areas
2024, Science of the Total EnvironmentA quantitative study of the factors influencing human evacuation from ships
2023, Ocean EngineeringAn efficient design method of indoor ventilation parameters for high-speed trains using improved proper orthogonal decomposition reconstruction
2023, Journal of Building Engineering