Research on Wind Environment Simulation in Five Types of “Gray Spaces” in Traditional Jiangnan Gardens, China

Abstract

“Gray space”, also known as transitional space, focuses on the connection and transition between indoor and outdoor spaces in architecture. With its unique diversity of forms and functional inclusiveness, gray space reasonably integrates architectural spaces’ hierarchical construction with innovative ecological energy-saving concepts. Existing research mainly analyzes and interprets the design techniques of gray space from a visual perception perspective but needs more analysis of classification and design interpretation of the gray spaces in traditional gardens based on climate adaptability. This paper studied the gray spaces in traditional Jiangnan gardens, summarizing five common types of gray space in architectural spaces and their responses to the climate. Subsequently, we selected a typical representative for each of the five types of spaces and used “height-to-depth ratio (HDR), open space ratio (OSR), and direction (DIR)” as variables to conduct wind environment simulations. The simulation results help to determine the optimal climate adaptability scheme for each type of space. Through this research on the gray spaces of traditional gardens, we aimed to contribute to the conservation and utilization of classical gardens from an ecological energy-saving perspective and also provide ideas for passive energy-saving design in small public spaces and garden landscape spaces.

1. Introduction

“Gray space” is a transitional space between indoors and outdoors, proposed by Kisho Kurokawa based on the ideas of “Rikyu Gray” in Japan. This spatial concept originates from the “Engawa” form in traditional Japanese architecture. This area functions as a mediator between the interior and exterior, incorporating elements of both without firmly dividing them [1]. In modern architecture, similar concepts to “gray space” are known as transitional spaces, buffer zones, or semi-outdoor spaces, which have significant impacts on the occupants’ experience and building energy consumption. These spaces act as “environmental bridges” between indoor and outdoor environments, helping to regulate temperature and improve overall comfort [2].

Despite their importance, much of the research on heat transfer has traditionally focused on human thermal comfort in indoor environments like offices and shopping malls, often under stable environmental conditions [3], such as the tropical climate countries in Southeast Asia [4,5]. Later in recent studies, the relevant research has begun to explore the potential energy savings achievable through the optimization of transitional spaces. For example, optimizing the thermal neutral temperature in these areas can lead to significant energy savings [6,7]. From the starting of the research foundation, the study of Chun et al. [8] has categorized transitional spaces into three types based on their proximity to interior spaces, providing a scientific theoretical stimulation based for the later study. Typically, these spaces generally contribute between 10 and 40 percent of the overall volume of various types of structures [9], with their energy consumption per unit area being three times that of indoor spaces [10], due to factors such as wind speed, wind direction, and the mean radiant temperature of the outdoor space [11,12,13,14]. An assessment of the microclimate of urban transitional spaces revealed that temperature fluctuations significantly influence the thermal scenario [15], a point that warrants emphasis. Controlling solar radiation is vital for comfort in the summer, while managing wind speed is more important in the winter [16]. The wind speed had a significant impact on thermal comfort during the summer; improving the wind environment can effectively enhance thermal comfort in a low-carbon manner [17]. Adjusting heating setpoints in winter can lead to substantial energy conservation [18]. There is a different spatial defining on gray space within traditional and modern transitional spaces [19].

In traditional architecture, gray spaces are often defined by their accessibility and artistic integrity, while modern designs emphasize multifunctionality and ecological sustainability. In relevant study on traditional architecture, natural ventilation can be understood as the formation of a low-carbon environment, and passive designs are widely discussed in the architectural design [20]. Referencing the past studies on traditional Chinese building, the spatial element in the Chinese Garden such as the corridor and courtyard are understood as the gray space of the architecture. The courtyard, being a fundamental bioclimatic strategy, was mentioned as a transitional space in the author’s research [21,22]. Abdulkareem [20] highlighted that the courtyard is a passive strategy for urban architectural design that can reduce the building’s energy consumption and enhance user comfort. In recent studies on traditional gardens and urban parks in the Jiangnan region, Xu et al. [23] analyzed the energy-saving potential of traditional gardens through field measurements and software simulations. Xiong et al. [24] redesigned the coverage and density of water bodies, trees, and buildings in the Lingering Garden to improve its microclimate and thermal comfort. Kong et al. [25] and Xu et al. [26] conducted case studies on the energy-saving effects and potential of green spaces and landscapes in modern urban parks. These studies primarily focus on green-energy-saving analysis and improvement of planning layouts from a macro perspective of garden and urban landscape composition.

However, this focus on aesthetics often overlooks the passive aspects of transitional spaces, particularly in terms of environmental factors like wind stimulation [27,28,29]. To address this gap, this paper studied wind stimulation in the gray spaces of Jiangnan gardens, considering spatial elements such as the pavilions, the corridors, the alleys, the courtyards, and the atriums as gray spaces. Among traditional research on wind stimulation, especially in landscape architecture, this study observed a perspective that has not been sufficiently addressed by other researchers. It provides a uniform discussion on comprehensive spatial structures in landscape architecture, an area still under explored in current research. By utilizing a unified simulation method, this study aims to provide basic insights into the wind environments of five common gray space prototypes in Jiangnan gardens, offering a series of foundational data that can further research into a deeper understanding in the future. This examination of the thermal performance of these spaces not only explores the potential for energy savings in different scales but also offers insight for landscape design regarding spatial type selection with different spatial characteristics. Despite advancements in the field, there remains a lack of comprehensive studies on the low-carbon, energy-saving design of transitional spaces in traditional Jiangnan gardens. By addressing this, this paper ultimately discusses how these gray spaces can be optimized and adapted in modern landscape design, enhancing their energy-saving effects and modern applicability.

2. Materials and Methods

2.1. Enclosure Interface Forms Shaping “Gray Spaces”

There has never been a clear definition of “gray space”. As shown in

Table 1. Five enclosure interface forms of gray spaces.

Without One Side Surface	Without Two Side Surface	Without Three Side Surface	Without Four Side Surface	Without the Top Surface

, “gray space” is an intermediate state between completely open outdoor and completely enclosed indoor spaces. Based on the degree of enclosure, “gray space” can be divided into five types of interface forms, shown in Table 1, in which the blue surface represents the open-up surface of the space. Corresponding to garden spaces, there are approximately five common types of spaces: pavilion space, corridor space, alley space, courtyard space, and atrium space. These spaces are primarily defined by varying degrees of enclosure, with each degree of enclosure contributing to distinct characteristics that collectively create a diverse and rich atmosphere within the traditional Jiangnan garden, especially in terms of ventilation, which plays a crucial role in shaping the overall experience.

2.1.1. Pavilion Space

Pavilion space is one of the most widely distributed space types in gardens. The most common form of pavilion space is open on all four sides, with only a roof and columns; however, there are also pavilions with one or several sides enclosed, such as semi-pavilions. The architectural layout of pavilions is diverse, with various shapes serving as nodal spaces in gardens that enhance the scenery and provide visitors with a place to admire the views and rest.

The four-sided open form of a pavilion, with only a roof, is very conducive to ventilation. In the Jiangnan region during summer, the high solar altitude angle allows the roof to block a significant amount of solar radiation. At the same time, the open design on all sides maximizes wind speed, providing a cooling effect in the summer. In winter, when the solar altitude angle is lower, more solar radiation can enter beneath the roof, offering warmth during sunny periods. Thus, pavilion space is suitable year-round, with particularly notable performance in the summer [27].

Pavilion spaces are generally small in volume, and their actual size often depends on the specific environment. Examples of pavilion spaces in traditional Jiangnan gardens include the 3 m² Shuxiao Pavilion in the Lingering Garden; the 8 m² Hefeng Simian Pavilion in the Humble Administrator’s Garden; and the Wuzhu Youju Pavilion in the Humble Administrator’s Garden, which exceeds 10 m². This study selected the Lüyi Pavilion in the Humble Administrator’s Garden as a prototype for spatial analysis. As shown in Figure 1, the Lüyi Pavilion has a square layout with sides measuring 2.77 m × 2.74 m and an eave height of 3.2 m, wherein its form is the most representative typical pavilion architecture in traditional Jiangnan gardens.

2.1.2. Corridor Space

Corridor space is the most common type of transportation linkage in gardens, typically consisting of a top interface and colonnades on both sides. Corridor space, unlike pavilion space, exhibits a wide range of shapes and orientations in gardens, exhibiting significant variations in length and form [28]. This is because in addition to providing transportation, they also meet the landscaping needs of the garden owner, serving purposes such as partitioning, enclosing, and providing places to pause and rest.

The forms of corridor space are diverse, with the most common being the “double-sided open corridor”, which is open on both sides. Moreover, we have “single-sided open corridors”, enclosing one side, and “warm corridors”, enclosing both sides (

Table 2. Three typical types of corridor space.

Single-Sided Open Corridor	Double-Sided Open Corridor	Warm Corridor

). Beyond these basic three types of enclosures, there are also “double corridors” with a wall in the middle, two-story corridor spaces, and corridors that adapt to changing terrain [29].

Due to minimal differences in wind environments between double-sided open corridor spaces and closer resemblance of warm corridor spaces to indoor conditions, these types are not considered in this study. This research focuses exclusively on single-sided open corridor spaces.

Compared to double-sided open corridor spaces, single-sided open corridor spaces have a wall on one side, which can block cold winds from that direction in winter. When the solar radiation angle is low, the wall can absorb some of the solar radiation and release energy through long-wave radiation. Therefore, with a reasonable orientation, single-sided open corridor spaces can create a relatively warm thermal environment during winter mornings or afternoons. In summer, the orientation of the wall and its angle to the prevailing wind direction significantly affect the thermal environment inside the space. When the wall direction has a small angle with the prevailing wind direction, the guiding effect of the wall increases the wind speed inside the space. The roof and one wall also block the intense solar radiation from entering space directly from noon to afternoon. Thus, by setting the orientation, wall placement, and height appropriately, single-sided open corridor spaces can create a favorable microclimate in summer. Consequently, single-sided open corridor spaces can adapt to both summer and winter conditions.

In traditional Jiangnan gardens, the dimensions of corridors typically have a net width of 1.2 m to 1.5 m, with columns spaced approximately 3 m apart and column heights around 2.5 m. As shown in Figure 2, this study selected the Xiao Feihong corridor in the Humble Administrator’s Garden as a case study since it has to most suitable environmental conditions and representative characteristics and dimensions within the corridors within the four traditional Jiangnan gardens. The Xiao Feihong corridor has a width of 1.6 m × 2.5 m and spans a length of 8.5 m across the water surface.

2.1.3. Alley Space

Alley space refers to a narrow walkway in gardens defined by walls on both sides and without a covering on top. The walls of an alley typically use the gable walls of buildings or standalone scenic walls, and they are generally quite tall, resulting in a strong sense of enclosure and directionality.

The elongated nature of alley spaces and the height of the walls make it difficult for solar radiation to penetrate into the space, providing a cool spatial experience during summer. Additionally, the well-defined orientation of alley spaces means that wind speed inside the alley is highly dependent on the angle between the alley’s direction and the external wind direction. When this angle is small, the wind speed inside the space increases significantly. Therefore, alley spaces are more suitable for summer, and an appropriate aspect ratio of height to width can minimize the amount of solar radiation entering the space. Furthermore, the design should aim to reduce the angle between the alley and the prevailing summer wind direction to enhance air circulation and create a cooler microclimate.

Alley spaces are commonly found at garden entrances. This study selected the original entrance alley in the Humble Administrator’s Garden as the research subject, which has typical characteristics of high depth-to-width ratio for alley spaces. As shown in Figure 3, the alley’s surrounding walls are 2.5 m high, with a walkway width of 3 m and a depth of 8.7 m [30].

2.1.4. Courtyard Space

In gardens, courtyard space refers to a semi-outdoor area enclosed on all four sides by buildings or walls and without a roof [31,32]. Due to its sufficient size, courtyard space can maximize solar radiation absorption. Additionally, the reflective radiation from hard paving makes the radiation levels in courtyard spaces much higher than in other gray space types. However, after sunset, the walls and hard paving release the accumulated heat, leading to poor thermal stability in courtyard spaces. Due to the open nature of courtyards, their heat absorption and dissipation are higher than in other space types. In terms of wind environment, courtyards lack directional guidance, resulting in a weaker correlation between wind speed and the space itself throughout the year. During winter, the higher thermal radiation in courtyards can create a warm feeling. Conversely, during summer, courtyards can feel relatively hot, with significant improvement only after sunset.

The size of courtyard spaces has no specific size limitations, generally depending on the size of the surrounding buildings. Typically, the courtyard spaces are in rectangular or square form, with an aspect ratio greater than 1. This study selected the entrance courtyard of the Lingering Garden as a case study. As shown in Figure 4, the entrance courtyard of the Lingering Garden has a planar dimension of 13 m × 10 m, with three sides enclosed by walls and one side by a building. The height of the enclosing walls is approximately 4 m [33].

2.1.5. Atrium Space

Atrium space is a special type of “courtyard space”, typically characterized by a small depth and walls that are taller than the depth. These spaces are commonly found in southern traditional dwellings and gardens [34]. Due to the height-to-depth ratio of the atrium spaces, they can generate strong convective winds. Convective winds cause hot air to rise and cool air to sink, making the atrium spaces significantly cooler than other areas and providing a refreshing and comfortable feeling during summer.

Unlike courtyards, although both regulate the microclimate of garden spaces, atriums differ significantly in design philosophy and usage purpose. Atrium spaces fundamentally emphasize ventilation rather than spatial usage [35], usually presented in smaller and more elongated forms. Therefore, the height-to-width ratio of the atrium spaces is generally less than 1. This study selected the atrium on the west side of Haitang Chunwu in the Humble Administrator’s Garden as a prototype. As shown in Figure 5, the atrium has a planar dimension of 3.5 m × 5 m, with two sides enclosed by walls and one side by a building, and the wall height is 3.5 m.

2.2. Simulation of Outdoor Wind Environment in “Gray Space”

2.2.1. Numerical Simulation Technology

To analyze the outdoor wind environment of five typical “gray spaces”, this study employed computational fluid dynamics (CFD) for numerical simulation. CFD is a numerical method that solves fluid dynamics equations to simulate airflow movements in different spaces [36,37,38]. This study utilized Ecotect software for numerical simulations, which can accurately simulate airflow under various environmental conditions [39].

We first constructed 3D models of five typical gray spaces in Ecotect and set the relevant climate and boundary conditions. The Ecotect software visually analyzes the wind environment for different types of gray spaces through precise wind speed and direction simulations. The parameters set in the Ecotect software are based on the climatic characteristics of Suzhou and have been adjusted multiple times to ensure the accuracy of the simulations. For example, the wind speed used in the simulations was 1.5 m/s, and the temperature was 30 °C. Considering the typical summer conditions in the Jiangnan region, we selected these parameters to reflect the microclimate characteristics of gray spaces in reality. The high consistency between the specified parameters and the actual environment ensures the reliability of the simulation results.

In Autodesk Ecotect Analysis 2011, the setting on environmental parameters such as geographical location and climate data are considered. Considering the research aims, assessing how spatial form affects the wind environment of the space, the simulation will primarily focus on wind speed. Air temperature and radiation will not be the main subjects of analysis in the simulation.

Shanghai was selected for climate data, referencing reliable sources like Energy Plus and Weather Atlas. Shown as Figure 6 and Figure 7 from Grasshopper Ladybug, the climate as a four-seasons region has a relatively moderate condition [40]. These data represent the weather conditions in four Chinese gardens located in Jiangnan region, having a subtropical monsoon climate. Air density was set at the typical value of 1.2 kg/m³ at sea level, and air viscosity at around 30 °C was 1.86 × 10⁻⁵. The average wind speed considered was 1.5 m/s at the height of human movement, and the temperature for July, representing summer, was 30 °C.

Figure 8 illustrates the variations in wind speed and temperature at different times of day during summer, aiming to analyze whether the wind speed can remain relatively stable under significant temperature changes in gray spaces. The blue solid line in the figure represents the changes in wind speed, showing that wind speed fluctuates slightly throughout the day. Specifically, the wind speed at 8:00 a.m. is 1.4 m/s, peaks at 1.5 m/s at noon, then decreases to 1.45 m/s at 4:00 p.m., and further drops to 1.35 m/s at 8:00 p.m. Although the wind speed experiences slight fluctuations throughout the day, the overall variation is minimal. This slight variation indicates that the gray space design can maintain relatively stable wind speed under different temperature conditions during a summer day. This stability is crucial for maintaining a comfortable microclimate environment.

Meanwhile, the red dashed line shows the temperature variations, revealing significant fluctuations in temperature throughout the day, gradually rising from 20 °C in the morning to 30 °C at noon, then gradually decreasing to 22 °C in the afternoon and evening. Despite the noticeable temperature changes, the variations in wind speed remain relatively small, further proving the effectiveness of gray spaces under different temperature conditions. By analyzing the changes in wind speed and temperature at different times of day, it is evident that the gray space design provides adequate thermal comfort under high-temperature conditions while maintaining a comfortable microclimate environment throughout the day under varying temperature conditions.

This analysis shows that despite significant temperature changes during a summer day, the wind speed in gray spaces remains relatively stable. This design strategy offers good comfort during the high temperatures at noon and avoids excessive wind chill effects after the evening temperature drops, maintaining a pleasant environment. In summary, the chart and analysis results validate the adaptability and stability of gray space design under different temperature conditions.

In this study, we focused the experimental period on the summer solstice, which has the highest radiation. The average temperature during summer is still acceptable, but its peak temperatures can occasionally reach around 37 °C in the Jiangnan region. In traditional Jiangnan gardens, the typical dimensions of common spaces, such as corridors, pavilions, and alleys, are user-friendly, integrating plantings and providing shade to users, which significantly improves the space. Therefore, in line with the research focus on the different enclosure interface forms of gray spaces and their impact on thermal comfort, we assumed radiation as not a primary focus in this study.

In the grid division stage, we used an unstructured grid to accommodate complex geometries. Higher grid density was applied in critical areas, such as space entrances and narrow passages, to capture subtle changes in airflow and heat transfer. We conducted a sensitivity analysis on different grid densities by comparing simulation results under various grid divisions to assess their impact on the final wind speed and temperature distribution.

Specifically, we performed simulations using three levels of grid density: coarse, medium, and refined.

Coarse grid: In the coarse grid division, the grid size in critical areas was approximately 0.5 m, while in other areas, it was 1.0 m. We primarily used this grid density for preliminary simulations to evaluate the model’s overall flow field distribution.

Medium grid: In the medium grid division, the grid size in critical areas was reduced to 0.3 m, while in other areas, it was 0.6 m. The simulation results at this density provided higher resolution than the coarse grid and were used to capture finer variations in wind speed.

Fine grid: In the final fine grid division, the grid size in critical areas was further reduced to 0.1 m, while in other areas, it ranged from 0.2 to 0.5 m. This grid density offered the highest simulation accuracy, ensuring precise capture of complex geometrical shapes.

The results indicated that the simulation results became more stable as grid density increased and differences gradually diminished. In the final selected grid scheme, the grid size in critical areas of each model was approximately 0.1 m, while in other areas, it ranged from 0.2 to 0.5 m. This selection balanced computational accuracy and efficiency, ensuring the stability and accuracy of the simulation results.

2.2.2. Parameter Variables and Simulation Methods

In Ecotect software, the setting on environmental parameters such as geographical location and climate data are considered. The air density is set to 1.2 kg/m³, air viscosity to 1.8 × 10⁻⁵, simulated wind speed to 1.5 m/s, and temperature to 30 °C.

The geometric variables affecting semi-outdoor spaces are typically determined by the height-to-depth ratio (HDR), spatial direction (DIR), and open space ratio (OSR) [41].

Table 3. Parameter variables of the five spatial prototypes.

Spatial Types	Parameter Variables
Pavilion space	HDR, OSR, DIR
Corridor space	HDR, DIR
Alley space	HDR, DIR
Courtyard space	HDR, OSR, DIR
Atrium space	HDR, OSR, DIR

lists the parameter variables affecting the outdoor wind environment of the five spatial prototypes. For the pavilion spaces, the courtyard spaces, and the atrium spaces, due to varying degrees of enclosure, it is necessary to consider their open space ratios. In contrast, for single-corridor spaces and alley spaces, where the enclosing boundaries are well-defined, the only variables affecting them are the height-to-depth ratio and spatial direction. Additionally, since the pavilion spaces, the courtyard spaces, and the atrium spaces are homogeneous and directionally non-specific, when all four sides of a pavilion space are open or all four sides of a courtyard and atrium space are enclosed, there is no directional distinction in the space. Thus, the only variable affecting these spaces is the height-to-depth ratio [42,43].

In the actual simulation process, we first established three-dimensional models based on typical cases of the five types of “gray spaces” found in real gardens. The pavilion spaces, the corridor spaces, the alley spaces, the courtyard spaces, and the atrium spaces were modeled according to their actual dimensions.

Secondly, to ensure calculation accuracy, we performed mesh discretization. The density and quality of the mesh directly affected the accuracy of the simulation results and computational efficiency. This study used an unstructured mesh with finer grids in critical areas.

Thirdly, boundary conditions were set according to the actual environment, including inlet wind speed, outlet conditions, and the roughness of the ground and building surfaces. This study was simulated under typical summer climate conditions, with an inlet wind speed of 1.5 m/s and a temperature of 30 °C.

Fourth, an appropriate turbulence model was selected for calculation. This study used the standard k-ε turbulence model, which effectively simulates turbulent characteristics in common building environments.

Finally, post-processing tools were used to analyze the simulation results; extract wind speed distributions under different height-to-depth ratios, open space ratios, and spatial directions; and perform comparative analysis of the results [44].

3. Quantitative Simulation Study of Five Types of Gray Spaces

3.1. Pavilion Space

3.1.1. Height-to-Depth Ratio (HDR)

For convenience in calculations, we rounded the scale of the pavilion space prototype to 3 m × 3 m × 3.6 m, with a height-to-depth ratio of 1.2. As shown in

Table 4. Schematic diagram of the 6 HDR conditions for the pavilion.

Schematic Illustration
HDR	0.7	0.8	0.9
Schematic Illustration
HDR	1	1.1	1.2

, assuming the side length of the pavilion was 3 m and the height ranged from 2.1 m to 3.6 m in 0.3 m increments, we obtained six different height-to-depth ratio conditions: 0.7, 0.8, 0.9, 1.0, 1.1, and 1.2.

As shown in

Table 5. Schematic diagram of the 6 HDR wind speed simulations for the pavilion.

Analysis Diagram
HDR	0.7	0.8	0.9
Analysis Diagram
HDR	1	1.1	1.2

, the pavilion space, with its four open sides and only the roof and columns as spatial elements, exhibited good ventilation performance. In the simulation, pavilions with different height-to-depth ratios (0.7, 0.8, 0.9, 1.0, 1.1, 1.2) showed variations in wind speed with changes in height-to-depth ratio. The simulation results indicate that as the height-to-depth ratio increased, the wind speed distribution inside the pavilion became more uniform, and the cooling effect became more pronounced. Especially in summer, a pavilion with a moderate height-to-depth ratio (e.g., 1.0) effectively enhances ventilation and reduces the perceived temperature. Specifically, the pavilion with a height-to-depth ratio of 1.0 had the best ventilation performance, with a wind speed of 1.5 m/s. The wind speeds for height-to-depth ratios of 0.7 and 1.2 were 1.3 m/s and 1.1 m/s, respectively, both lower than the wind speed at a ratio of 1.0. This indicates that a moderate height-to-depth ratio helps improve wind speed and enhances the cooling effect [45,46].

3.1.2. Open Space Ratio (OSR)

As shown in

Table 6. Schematic diagram of the 4 OSR conditions for the pavilion.

Schematic Illustration
OSR	1	0.75	0.5	0.25

, we classified the pavilion space’s open space ratio into four cases based on the degree of enclosure: 1, 0.75, 0.5, and 0.25. These correspond to common pavilion space forms: open on all four sides, enclosed on one side, enclosed on two sides, and enclosed on three sides. Based on the previous analysis of the impact of height-to-depth ratio on the wind environment, we selected a pavilion space with a height-to-width ratio of 1 as the prototype for the schematic diagrams of the open space ratios.

When the open space ratio is high, the pavilion space has a minimal obstructive effect on the wind, and the distance required for the wind speed to recover after passing through the pavilion is short; that is, the wind speed field returns to its initial level over a shorter distance. Conversely, when the open space ratio is low, the obstructive effect of the pavilion on the wind increases, and the distance required for the wind speed to recover after passing through the pavilion is longer; that is, the wind speed field takes a longer distance to return to its initial level.

Table 7. Schematic diagram of the 4 OSR wind speed simulations for the pavilion.

Analysis Diagram
OSR	1	0.75	0.5	0.25

shows the wind speed field distribution for the four open space ratio models. It can be seen that as the open space ratio decreased, the recovery distance of the wind speed field behind the pavilion gradually increased. This phenomenon indicates that with a lower open space ratio, the pavilion exerts a greater disturbance on the wind, affecting the wind flow path and speed, leading to a longer recovery distance of the wind speed behind the pavilion [47].

3.1.3. Spatial Direction (DIR)

In the simulation experiment on the impact of the pavilion’s spatial direction on the wind environment, as shown in

Table 8. Schematic diagram of the 4 DIR conditions for the pavilion.

Schematic Illustration
DIR	South	East	North	West

, we selected a pavilion space with an open space ratio of 0.75 as the spatial prototype and analyzed the wind environment from four directions: south, east, north, and west.

Through numerical simulation, the wind environment of pavilion spaces in different directions was analyzed. As shown in the illustrative result in

Table 9. Schematic diagram of the 6 DIR wind speed simulations for the pavilion.

Analysis Diagram
DIR	South	East	North	West

, the effect of different closed directions on the wind speed distribution inside the pavilion was significant. When the closed direction was perpendicular to the prevailing wind direction, the wind speed inside the pavilion was lower; when the closed direction was parallel to the prevailing wind direction, the wind speed inside the pavilion was higher. This indicates that setting the closed direction reasonably can effectively improve the wind environment inside the pavilion.

3.2. Corridor Space

3.2.1. Height-to-Depth Ratio (HDR)

The north side of the single-sided corridor space prototype is relatively open, with a corridor width of 1.6 m, a height of 2.5 m, and a length spanning 8.5 m across the water surface. It features typical height-to-width proportions of traditional garden corridor spaces and is situated in a relatively open location, making it suitable for research. As shown in

Table 10. Schematic diagram of the 6 HDR conditions for the single-sided corridor.

Schematic Illustration
HDR	1.2	1.4	1.6
Schematic Illustration
HDR	1.8	2.0	2.2

, assuming the corridor width is 1.6 m and the height ranges from 1.92 m to 3.52 m in 0.32 m increments, we obtained six different height-to-depth ratio conditions: 1.2, 1.4, 1.6, 1.8, 2, and 2.2.

As shown in

Table 11. Schematic diagram of the 6 HDR wind speed simulations for the single-sided corridor.

Analysis Diagram
HDR	1.2	1.4	1.6
Analysis Diagram
HDR	1.8	2.0	2.2

, the single-sided corridor space, due to having a wall on one side, provided better insulation compared to a double-sided open corridor during winter. In the simulation, as the height-to-depth ratio increased (1.2, 1.4, 1.6, 1.8, 2.0, 2.2), the wind speed distribution inside the corridor changed significantly. The single-sided corridor with a height-to-depth ratio of 1.6 had the highest wind speed at 1.45 m/s. For height-to-depth ratios of 1.2 and 2.2, the wind speeds were 1.26 m/s and 1.15 m/s, respectively. The single-sided open corridor, with properly designed wall orientation and height during summer, can create a favorable microclimate.

3.2.2. Spatial Direction (DIR)

Through the simulation of the wind environment for different height-to-depth ratios in the corridor space, we selected the single-sided open corridor space with a height-to-depth ratio of 1.6 as the spatial prototype. As shown in

Table 12. Schematic diagram of the 6 DIR conditions for the single-sided corridor.

Schematic Illustration
DIR	Southwest	South	Southeast

, when analyzing the spatial directions of the single-sided corridor space, we chose the southwest, south, and southeast directions for wind environment analysis.

As shown in

Table 13. Schematic diagram of the 3 DIR wind speed simulations for the single-sided corridor.

Analysis Diagram
DIR	Southwest	South	Southeast

, the numerical simulation analysis of the wind environment in the single-sided corridor space for different directions revealed that the wind speed was highest in the south direction, at 1.6 m/s. The wind speeds in the southwest and southeast directions were lower, at 1.4 m/s and 1.2 m/s, respectively. This indicates that the directional orientation of the single-sided corridor space had a significant impact on the wind environment, and a well-chosen direction can enhance ventilation within the corridor.

3.3. Alley Space

3.3.1. Height-to-Depth Ratio (HDR)

The entrance corridor of the Humble Administrator’s Garden features a typical height-to-depth ratio, with the surrounding walls standing at 2.5 m high, an alley width of 3 m, and a depth of 8.65 m, resulting in an initial height-to-depth ratio of approximately 0.8. As shown in

Table 14. Schematic diagram of the 6 HDR conditions for the alley space.

Schematic Illustration
HDR	0.7	0.8	0.9
Schematic Illustration
HDR	1	1.1	1.2

, assuming the corridor width is 3 m and the height varies from 2.1 m to 3.6 m in 0.3 m increments, we obtained six different height-to-depth ratio conditions: 0.7, 0.8, 0.9, 1.0, 1.1, and 1.2.

As shown in

Table 15. Schematic diagram of the 6 HDR wind speed simulations for the alley.

Analysis Diagram
HDR	0.7	0.8	0.9
Analysis Diagram
HDR	1	1.1	1.2

, the simulation results indicate that the height-to-depth ratio of the alley had a significant impact on wind speed. Alleys with a smaller height-to-depth ratio, due to their narrower angle, exhibited higher wind speeds and a more pronounced cooling effect. The corridor with a height-to-depth ratio of 0.8 had the highest wind speed, at 1.48 m/s. The wind speeds for height-to-depth ratios of 0.7 and 1.2 were 1.25 m/s and 1.36 m/s, respectively. The height-to-depth ratio of the alley had a notable effect on wind speed, with a moderate ratio helping to increase wind speed and enhance the cooling effect [48].

3.3.2. Spatial Direction (DIR)

When analyzing the spatial direction of the alley space, we first selected the corridor with a height-to-depth ratio of 0.8 as the spatial prototype. As shown in

Table 16. Schematic diagram of the 4 DIR conditions for the alley.

Schematic Illustration
DIR	West	Southwest	South	Southeast

, we selected the west, southwest, south, and southeast directions for numerical simulation and analysis of the wind environment in the corridor space under different directions.

As shown in

Table 17. Schematic diagram of the 4 DIR wind speed simulations for the alley.

Analysis Diagram
DIR	West	Southwest	South	Southeast

, the simulation results indicate that the wind speed in the alley space was highest in the south direction, at 1.5 m/s. The wind speeds in the west and southeast directions were lower, at 1.3 m/s and 1.1 m/s, respectively. These results suggest that the orientation of the alley space has a significant impact on wind speed, and selecting the appropriate direction can help optimize the wind environment within the space [49].

3.4. Courtyard Space

3.4.1. Height-to-Depth Ratio (HDR)

The entrance courtyard at the gate of the Lingering Garden has an area of 13 m × 10 m, with three sides enclosed by walls and one side by a building, and the height is not uniform. For ease of analysis, the model was simplified to 10 m × 10 m. As shown in

Table 18. Schematic diagram of the 6 HDR conditions for the four-sided enclosed courtyard.

Schematic Illustration
HDR	0.2	0.4	0.6
Schematic Illustration
HDR	0.8	1	1.2

, assuming the courtyard height is 4 m in the simulation, we varied the height from 2 m to 12 m in 2 m increments, resulting in six different height-to-depth ratio conditions: 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2.

The courtyard space is a four-sided enclosed, roofless semi-outdoor space. The simulation results shown in

Table 19. Schematic diagram of the 6 HDR wind speed simulations for the four-sided enclosed courtyard.

Analysis Diagram
HDR	0.2	0.4	0.6
Analysis Diagram
HDR	0.8	1	1.2

indicate that the height-to-depth ratio of the courtyard had a minimal impact on wind speed but significantly affected thermal radiation.

3.4.2. Spatial Direction (DIR)

As shown in

Table 20. Schematic diagram of the 4 DIR conditions for the three-sided enclosed courtyard.

Schematic Illustration
DIR	North	West	South	East

, for the numerical simulation and analysis of the wind environment in the courtyard space under different directions, we selected the courtyard with a height-to-width ratio of 0.4 as the spatial prototype and considered west, south, east, and north directions as the variables for spatial orientation.

As shown in

Table 21. Schematic diagram of the 4 DIR wind speed simulations for the three-sided enclosed courtyard.

Analysis Diagram
DIR	North	West	South	East

, the simulation results indicate that when the wind direction aligned with the direction of the opening, ventilation within the space was optimal, resulting in the highest average wind speed. Conversely, when the wind direction was perpendicular to the opening direction, higher wind speeds were observed along the sides.

3.5. Atrium Space

3.5.1. Height-to-Depth Ratio (HDR)

The original atrium measures 3.5 m × 5 m, with two sides enclosed by walls and one side by a building, with non-uniform height. As shown in

Table 22. Schematic diagram of the 6 HDR conditions for the four-sided enclosed atrium.

Schematic Illustration
HDR	0.8	1	1.2
Schematic Illustration
HDR	1.4	1.6	1.8

, for ease of analysis, we assumed the simulated atrium height was 3.5 m, varying the height from 2.7 m to 6.3 m in 0.6 m increments. This resulted in six different height-to-depth ratio conditions: 0.8, 1.0, 1.2, 1.4, 1.6, and 1.8.

As shown in

Table 23. Schematic diagram of 6 HDR wind speed simulations for the four-sided enclosed atrium.

Analysis Diagram
HDR	0.8	1	1.2

, the simulation results indicate that the atrium space with a moderate height-to-depth ratio (such as 1.2) exhibited good ventilation during the summer. The atrium with a height-to-depth ratio of 1.2 showed the highest wind speed, at 1.45 m/s. At height-to-depth ratios of 0.8 and 1.8, the wind speeds were 1.22 m/s and 1.24 m/s, respectively. Atrium spaces designed with a moderate height-to-depth ratio can effectively enhance ventilation and regulate microclimate during the summer [50].

3.5.2. Spatial Direction (DIR)

As shown in

Table 24. Schematic diagram of the 4 DIR conditions for the three-sided enclosed atrium.

Schematic Illustration
DIR	South	North	West	East

, for the analysis of the impact of spatial direction on wind speed in atrium spaces, we selected the most common configuration of three enclosed sides. The analysis was conducted on a three-sided enclosed atrium space with a height-to-depth ratio of 1.2.

As shown in

Table 25. Schematic diagram of the 4 DIR wind speed simulations for the three-sided enclosed atrium.

Analysis Diagram
DIR	South	North	West	East

, numerical simulation analysis of the wind speed distribution in the three-sided enclosed atrium space under the south, north, west, and east directions revealed that the atriums facing south and north had the best ventilation, with the highest average wind speed, which helps create a favorable microclimate. The ventilation effects in the west and east directions were relatively poor, with the lowest wind speed in the east direction due to the high resistance against the prevailing wind. Therefore, in atrium design, priority should be given to the south and north orientations to enhance ventilation and spatial comfort.

3.6. Validation

To enhance the reliability of the numerical simulation results, we also conducted field tests to verify the accuracy of the simulation outcomes. Specifically, we selected the typical Jiangnan region as the test site and performed comprehensive field measurements within gray spaces. The experimental plan consists of three steps: experiment setup and preparation, data collection, and data analysis.

Firstly, we selected prototypes of five types of gray spaces typical of the Jiangnan region to ensure they exhibited representative wind speed characteristics. Then, in each of the five experimental areas, we deployed multiple anemometers at different heights and positions to obtain the spatial distribution of wind speeds. The measurement period was set to be continuous for 48 h to cover various weather conditions and wind speed changes.

Figure 9 compares the measured and simulated data at different measurement points under five different simulation scenarios. Each chart illustrates the differences between the measured wind speed and the simulated wind speed.

• Pavilion Space (Figure 9a)
  Point Layout: The measurement points were distributed at the four corners inside the pavilion (P1, P2, P3, P4) to reflect the wind speed variations within the space. The measured data show that the wind speed was uniform across the four points. The simulated data were slightly higher than the measured values, but the overall trend was consistent. This result indicates that the numerical simulation can effectively capture the wind speed distribution within the space.
• Corridor Space (Figure 9b)
  The measurement points were arranged along the corridor length (P1, P2, P3, P4) to capture the variations in wind speed along the corridor direction. The measured data were slightly lower than the simulated data. The simulation results showed a slight increase in wind speed along the direction of the corridor, which was related to the geometric characteristics of the corridor and the simulation method used.
• Alley Space (Figure 9c)
  The measurement points were arranged along the length of the alleyway (P1, P2, P3, P4) to reflect the wind speed variations within the alleyway. The measured data were very close to the simulated data, and the simulation results accurately captured the wind speed variations within the alleyway, verifying the model’s reliability.
• Courtyard Space (Figure 9d)
  The measurement points were arranged at the four corners of the courtyard (P1, P2, P3, P4) to reflect the wind speed variations in different corners. The measured data were close to the simulated data, with the simulated values being slightly higher, but the difference was not significant. This result indicates that the simulation method can effectively reflect the wind speed distribution within the courtyard.
• Atrium Space (Figure 9e)
  The measurement points were set at the four corners of the atrium (P1, P2, P3, P4) to capture the wind speed variations. The simulated data were slightly higher than the measured data, but the trends were consistent, indicating that the simulation results were relatively accurate and suitable for analyzing the wind environment in the atrium.

These charts display the comparison between measured and simulated data for five different types of gray spaces, demonstrating the effectiveness and accuracy of numerical simulations while reflecting the wind speed distribution within different types of spaces.

Figure 9. Comparison charts of measured and simulated data for the five types of gray spaces. (a) Pavilion space; (b) corridor space; (c) alley space; (d) courtyard space; (e) atrium space.

Figure 9. Comparison charts of measured and simulated data for the five types of gray spaces. (a) Pavilion space; (b) corridor space; (c) alley space; (d) courtyard space; (e) atrium space.

4. Discussion

This study focused primarily on the microclimate characteristics of gray spaces within a specific area; therefore, location and climate conditions were not considered variables. A typical subtropical monsoon climate characterizes the study area in the Jiangnan region. Climate parameters such as temperature, humidity, and wind speed were set based on the actual climatic conditions of this region. These settings significantly impact the simulation results, as the hot and humid summer climate in Jiangnan directly affects the thermal and wind environments of gray spaces. The selected typical gray spaces in Jiangnan gardens, including pavilions, corridors, alleyways, courtyards, and atriums, exhibit different energy-saving effects in response to the summer climate. Open gray spaces, such as pavilions and corridors, fully utilize natural ventilation, reducing the temperature difference between the interior and exterior of buildings, enhancing comfort, and reducing energy consumption. Relatively enclosed gray spaces, such as atriums and alleyways, can effectively reduce heat accumulation through proper ventilation design.

Furthermore, since the study objects were clearly defined, the dimensions and spatial configurations were modeled based on the actual conditions of the existing gray spaces. Thus, the geometric dimensions of gray spaces, including height-to-depth ratio, width-to-height ratio, openness ratio, and orientation, directly determined their internal wind and thermal environments. The study results show that gray spaces with a moderate height-to-depth ratio had sound ventilation effects in summer, effectively optimizing the temperature difference between indoors and outdoors and the airflow distribution. Gray spaces with a high openness ratio improve air circulation but, in some cases, may lead to excessive ventilation, affecting comfort. The choice of orientation also significantly impacts wind speed and thermal comfort, with north- or south-facing designs optimizing the wind environment.

In summary, the simulation results directly reflect the performance of gray spaces under these specific regional and climatic conditions rather than the effects of broader climate and spatial dimension variables. This study provides a theoretical basis for optimizing gray space design for summer conditions through a detailed analysis of location, climate data, and gray space dimensions. When appropriately selected and optimized, these factors can effectively improve the microclimate environment in summer, enhancing thermal comfort and energy-saving effects. Future research can further explore the performance of these factors in other seasons and different geographical locations, providing more comprehensive guidance for the design and optimization of gray spaces.

Although this study conducted an in-depth analysis of the wind environment of gray spaces in traditional Jiangnan gardens under summer climate conditions using computational fluid dynamics (CFD) methods, it needs more consideration for optimizing gray spaces for winter. Winter’s climatic characteristics differ significantly from summer’s, especially in the Jiangnan region, where winter is cold and humid. Therefore, the design of gray spaces needs to consider reducing heat loss and improving thermal comfort.

In winter, controlling wind speed and utilizing solar radiation are particularly important. The optimization design of gray spaces in winter may require enhanced enclosure to reduce cold wind intrusion. At the same time, strategically placed openings and orientations can increase the use of solar radiation to enhance warmth. Compared to summer, the design of gray spaces in winter should focus more on insulation and wind protection. Increasing wall height or using insulating materials can effectively reduce heat loss for semi-open spaces like courtyards and atriums.

Another limitation of this study is the need for more air temperature analysis within the spaces. This limitation means the study did not consider the effects of solar radiation, radiative exchange with the atmosphere, radiative exchange between gray space surfaces, or the environment. As a result, it is impossible to accurately determine the actual thermal behavior of the gray spaces analyzed. Neglecting these radiative factors may lead to discrepancies between the simulation results and real-world conditions, particularly in evaluating thermal comfort and energy-saving effects.

Future research should explore optimization strategies for gray spaces in the Jiangnan region during winter, such as simulating the thermal conductivity of different enclosure forms and assessing the impact of adding insulation layers or adjusting the orientation of openings on the thermal comfort of gray spaces in winter. Additionally, future studies should incorporate the impact of solar radiation, considering the distribution and variation of radiant heat within gray spaces, especially under different materials and surface characteristics. For changes in air temperature within gray spaces, more sophisticated simulation methods or field measurements should be used to verify and adjust the simulation results to enhance their accuracy.

A more comprehensive study of the performance of gray spaces under different seasonal and climatic conditions, particularly in exploring winter optimization design and the impact of radiant heat, will provide more guidance for the energy-saving optimization of both traditional Jiangnan gardens and modern public spaces. Future research can also integrate other environmental factors, such as humidity and sunlight, to conduct a more thorough analysis of the thermal environment of gray spaces. This study will help provide a more systematic theoretical foundation and practical guidance for the year-round optimization design of gray spaces in the Jiangnan region.

5. Conclusions

Through the simulation analysis of five typical “gray spaces” in Traditional Jiangnan Gardens, this study identified the optimal configurations for these five space types during the summer (Table 26):

• The most suitable height-to-depth ratio for pavilion spaces is 1.0, at which wind speed is maximized, helping to create a cooler microclimate in summer. Additionally, appropriate open space ratio and spatial direction settings can significantly improve the wind environment and enhance spatial comfort. In winter, pavilion spaces can reduce heat loss from solar radiation through roof shading. During spring and autumn, pavilion spaces have good ventilation, making them suitable for comfortable outdoor activities.
• For single-sided open corridor spaces, a height-to-depth ratio of 1.6 is ideal for ventilation. Wind speed is highest when the corridor is oriented south, highlighting the importance of proper direction selection for improving corridor ventilation. In winter, the corridor spaces can absorb solar radiation through the walls, creating a warm environment. In spring and autumn, these spaces have moderate ventilation and sunshine, providing a comfortable transition area.
• For alley spaces, with a height-to-depth ratio of 0.8, such spaces are suitable for a cool microclimate in summer. Wind speed is highest when facing south, indicating that wind direction significantly influences the alley’s wind environment. With appropriate sheltering, alley areas can reduce the penetration of cold winds in winter. During spring and autumn, alley spaces offer good ventilation, making them comfortable walking passages.
• The height-to-depth ratio primarily impacts heat transfer in courtyard spaces, with minimal effect on wind speed. Proper orientation can greatly enhance the courtyard’s ventilation and temperature conditions. By improving the thermal radiation of hard surfaces and plants, courtyard spaces can be inviting throughout winter. In spring and fall, these areas provide a pleasant microclimate for various outdoor activities.
• Atrium spaces with a height-to-depth ratio of 1.2 have good ventilation in summer. When facing south and north directions, this provides the best ventilation and promotes a favorable microclimate. During winter, atrium spaces provide warmth through the thermal radiation of high walls. Conversely, in spring and autumn, atrium spaces offer moderate ventilation and temperature, providing a comfortable environment as a resting place.

This study used computational fluid dynamics (CFD) methods to simulate and analyze the wind environment of gray spaces in traditional Jiangnan gardens, providing theoretical support and technical guidance for the energy-efficient optimization design of gray spaces. It is hoped that these conclusions will offer valuable references for the preservation and modernization of traditional Jiangnan gardens and provide insights into passive energy-efficient design for small public spaces and landscape gardens.

Table 26. Optimal configurations for five space types.

“Gray Space” Types	Optimal HDR	Optimal DIR	Optimal OSR	Seasonal Suitability	Optimization Effect
Pavilion	1	Reasonable setting	1 (totally opened-up)	Cool in summer, comfortable in spring and autumn, and reduces heat loss in winter	Achieving maximum wind speed, creating a cool summer microclimate
Corridor	1.6	Facing south	N/A	Ventilation in summer, moderate spring and autumn, and absorption of solar radiation in winter	Achieving optimal ventilation effect
Alley	0.8	Facing south	N/A	Cool in summer, comfortable in spring and autumn, and less cold wind in winter	Achieving maximum wind speed, creating a cool summer microclimate
Courtyard	Minimal impact	Reasonable setting	Less affected	Ventilation in summer, moderate spring and autumn, and increased heat radiation in winter	Improving ventilation and thermal environment
Atrium	1.2	Facing south and north	N/A	Ventilation in summer, moderate in spring and autumn, and warmth in winter	Achieving good ventilation effect, forming a favorable microclimate environment.

Table 26. Optimal configurations for five space types.

“Gray Space” Types	Optimal HDR	Optimal DIR	Optimal OSR	Seasonal Suitability	Optimization Effect
Pavilion	1	Reasonable setting	1 (totally opened-up)	Cool in summer, comfortable in spring and autumn, and reduces heat loss in winter	Achieving maximum wind speed, creating a cool summer microclimate
Corridor	1.6	Facing south	N/A	Ventilation in summer, moderate spring and autumn, and absorption of solar radiation in winter	Achieving optimal ventilation effect
Alley	0.8	Facing south	N/A	Cool in summer, comfortable in spring and autumn, and less cold wind in winter	Achieving maximum wind speed, creating a cool summer microclimate
Courtyard	Minimal impact	Reasonable setting	Less affected	Ventilation in summer, moderate spring and autumn, and increased heat radiation in winter	Improving ventilation and thermal environment
Atrium	1.2	Facing south and north	N/A	Ventilation in summer, moderate in spring and autumn, and warmth in winter	Achieving good ventilation effect, forming a favorable microclimate environment.