1. Introduction
In recent years, the frequent occurrence of extreme cold weather has not only increased the energy consumption of building heating, but also seriously affected people’s work, life and physical health [
1]. According to the report of BBC NEWS, since 1 November 2016, extreme cold weather has occurred continuously in Italy, Poland, the Czech Republic, and other European countries, which has led to more than 20 deaths and the suspension of traffic and transport in most areas [
2]. Through studying the influence of cold weather on the death rate in European cities from 1990 to 2000, Analitis et al. found that for each 1 °C decrease in air temperature, the daily death rate increases 1.35%, and the prevalence rate of cardiovascular, respiratory and cerebrovascular diseases will increase by 1.72, 3.30 and 1.25%, respectively [
3]. The analysis results found by Healy et al. showed that measures such as improving the outdoor environment, enhancing housing insulation performance and increasing public health expenditure could effectively reduce the death rate in winter [
4].
Residential areas, as a city’s basic unit, have the closest connection with people’s living environment; the thermal environment of residential areas directly affects people’s physical and mental health, as well as human comfort sensation during outdoor activities [
5,
6]. The meteorological factors affecting outdoor human thermal sensation include wind velocity, air temperature and relative humidity, and so forth, of which the wind velocity plays a dominant role [
7]. Therefore, in the early stage of planning, the influence of the relevant factors of residential building layout on the outdoor wind environment and thermal comfort should be fully considered to create a comfortable human settlement environment [
8,
9,
10,
11]. In recent years, several researchers, through field measurement, wind tunnel tests and numerical simulation, have studied the relationship between the building layout factors (building density, floor area ratio, building height, building orientation, sky-view factor, etc.) and the outdoor wind environment, and obtained many corresponding results [
12,
13,
14].
Using field measured meteorological data on wind speed, air temperature, relative humidity and solar radiation in two pedestrian streets in Curitiba, Brazil, and in combination with a questionnaire survey, Krüger et al. [
15] carried out a multiple regression analysis regarding thermal sensation and measured meteorological data, and demonstrated the relationship between the sky-view factor and the thermal comfort of pedestrians. In a long-term study, Johansson et al. observed the thermal environment of two streets with different aspect ratios in Fitz, Morocco, and carried out an analysis of the thermal comfort using the physiologically equivalent temperature (PET) index. The results showed that for the street with an aspect ratio of 9.7, the annual mean wind velocity is 0.4 m/s, and the PET is stable at 23–28 °C in summer; while for the street with the aspect ratio of 0.6, the annual mean wind velocity is 0.8 m/s, and the PET is more than 40 °C in summer [
16].
Tsang et al. [
17] studied the pedestrian-level wind environment around high-rise buildings using wind tunnel tests, and the results showed that, for a single building, increasing the building width enlarges the area of low wind speed zones, and increasing building height is conducive to natural air ventilation at pedestrian level. However, increasing building height will lead to weak natural air ventilation when the buildings are separated by a distance less than half of the building width—the podiums will seriously impede natural air ventilation, and worsen the pedestrian comfort around buildings. Williams et al. [
18] carried out a large-scale wind tunnel test on the pedestrian-level wind environment of the central areas of Ottawa, Canada. They examined 16 prevailing wind directions and had 615 measuring points. The study results provide a significant reference for the future wind environment prediction and planning of the region.
Based on the renormalization group (RNG) k-epsilon turbulence model, Zhang et al. [
19] performed a simulation study on the wind environment of three different kinds of building layouts. Their results showed that a staggered building arrangement is helpful for air movement, and when the wind direction is S-N or SE-NW, the natural air ventilation is the most significant. Hong et al. [
20] carried out a numerical study on the outdoor wind environment and thermal comfort at pedestrian level for several different building layout patterns using the Simulation Platform for Outdoor Thermal Environment (SPOTE). Their results showed that the building layout patterns’ orientation with respect to wind has a significant effect on both the wind environment and thermal comfort, and when the longer facade of the building is parallel to the prevailing wind direction, the wind speed at the edges of the building increases. Carfan et al. [
21] studied the wind environment and thermal comfort in both a densely built district and a city park using ENVI-met software. They showed that the wind speed of the high building density area is lower, and the predicted mean vote (PMV) value of both study areas is nearly the same. Emmanuel et al. [
22] carried out the simulation study on the microclimate of the street canyons with different height-to-width ratio in Colombo, Sri Lanka, by ENVI-met, the results indicated that the air temperature and average radiation temperature decrease obviously, and the wind speed decreases distinctly with increasing height-to-width ratio.
The research above focuses mainly on the effect of relevant factors of building layout on the microclimate and pedestrian thermal comfort under dry heat and humid heat climate conditions; there is a lack of research on the winter outdoor wind environment under harsh climatic conditions in severe cold regions. At the same time, most of the study objects being relatively unitary, mainly concerning individual built cases, their results failed to accurately reflect the universal law of wind environment and pedestrian thermal comfort of residential areas. Furthermore, the results of some researches, because of a lack of a due consideration of actual planning and design requirements, are inapplicable to the actual urban construction projects.
Compared with field measurement and wind tunnel test, the numerical simulation, though taking less time, collects comprehensive experimental data, and in the meantime, the model parameters can be changed according to the experimental requirements. Therefore, it is more suitable for the study of many samples [
19].
As a main affecting factor of outdoor thermal environment, air temperature plays an important role in thermal comfort. However through the field measurements of the winter microclimate of residential areas in cold regions, it was found that the building layouts have little impact on air temperature, but have significant impacts on the outdoor wind environment [
23]. Furthermore, through the questionnaire surveys on winter outdoor thermal comfort, it was found that people are more sensitive to wind speed than air temperature, so the wind environment has more significant effects on human thermal comfort in winter of cold regions [
24]. This study focuses on analyzing the outdoor wind environment of residential areas in severe cold regions, so there is no excessive discussion about air temperature.
This paper aims to study the relation between the relevant factors of building layout of the residential areas in severe cold regions of China and mean wind velocity ratio at the pedestrian level. The winter outdoor wind environment of typical residential areas in Harbin are simulated by using ENVI-met software. By means of Pearson correlation analysis, scatter plots and linear-fit estimation, this paper conducts quantitative analysis on the relations between the multistory and high-rise residential areas’ building density, floor area ratio, wind projection angle (the wind projection angle of residential areas is the included angle between the prevailing wind direction and the residential area orientation, the residential area orientation defined in this paper is that of the majority buildings in the area), and average building height, with the mean pedestrian-level wind velocity ratio. Moreover, the effects of the relative position of high-rise buildings in multi-high-level mixed residential areas on the mean wind velocity ratio is investigated. Based on the above analysis, the most significant and suitable variables are chosen to establish the prediction model of the mean wind velocity ratio at the pedestrian level. It is expected that this study could provide guidance and evaluation basis for the layout planning of residential areas in severe cold regions.
4. Prediction Model Establishment
Through analysis on the relationships between the multistory and high-rise residential areas’ building density, floor area ratio, wind projection angle, and average building height, with the mean pedestrian-level wind velocity ratio, it can be found that the above building layout factors have little effect on the mean pedestrian-level wind velocity ratio in multistory residential areas. However, there exists significant linear correlations between both the building density and wind projection angle with the mean pedestrian-level wind velocity ratio, and a weak correlation between floor area ratio and the mean pedestrian-level wind velocity ratio in high-rise residential areas.
This paper analyzed a prediction model of the mean pedestrian-level wind velocity ratio in high-rise residential areas. A multiple linear regression is used in this paper to analyze the quantitative relations among the variables. Through collinearity diagnostics, floor area ratio is removed, and the most significant variables building density and wind projection angle are ultimately chosen as the independent variables.
In the regression analysis, the significance level was set to 0.05, and the total sample number was 60 (shown in
Table 3 and
Table 5). The regression equation was:
where VR
mv is the mean pedestrian-level wind velocity ratio of high-rise residential areas; λ
b is the building density of high-rise residential areas; and θ
bw is the wind projection angle of high-rise residential areas. The regression summary statistics are: R = 0.738; R
2 = 0.545; standard error of estimate: 0.08102; F = 34.163, and;
p = 0.000 < 0.005. The building density and wind projection angle of high-rise residential areas can explain 54.5% of the variation in the mean pedestrian-level wind velocity ratio by the model.
According to the Equation (1), when the building density of high-rise residential areas is held constant, the mean wind velocity ratio at pedestrian level will increase with an increase in the wind projection angle; when the wind projection angle in high-rise residential areas is held constant, the larger the building density, the lower the mean wind velocity ratio at pedestrian level becomes.
5. Conclusions
While previous researches focus mainly on the effect of relevant factors of building layout on the microclimate under dry heat and humid heat climate conditions, this paper, focusing on severe cold regions, studies the relationships between the mean wind velocity ratio at the pedestrian level and the residential areas’ building density, floor area ratio, wind projection angle, average building height, and high-rise buildings’ relative position, providing quantitative guidance for planning and evaluation for wind environment of residential areas. The conclusions are as follows:
The building density of high-rise residential buildings has a significant negative linear correlation with the mean wind velocity ratio at the pedestrian level; when the building density is 19.5–23.4%, the interaction will be more significant. The building density of multistory residential areas has no linear correlation with the mean pedestrian-level wind velocity ratio. When the floor area ratio of high-rise residential areas is 2.34–3.12, the mean wind velocity ratio at pedestrian level has no obvious variation trend, and when the floor area ratio is 3.63–3.99, the mean pedestrian-level wind velocity ratio decreases gradually as the floor area ratio increases. The floor area ratio of multistory residential areas shows no linear correlation with the mean pedestrian-level wind velocity ratio. The relation between the wind projection angle and the mean pedestrian-level wind velocity ratio in high-rise residential areas is a significant positive linear correlation, and when the wind projection angle is 0–67.5°, the trend becomes more obvious. The influence of wind projection angle in multistory residential areas on the mean wind velocity ratio at pedestrian level is small. With rising average building height in residential areas, the mean pedestrian-level wind velocity ratio presents a slow increasing trend, but the correlation between the both is weak. For multi-high-level mixed residential areas, the three relative positions of high-rise buildings on the upwind side, downwind side or on both sides, have little influence on the mean pedestrian-level wind velocity ratio, which has a maximal difference of only 0.04.
Taking the building density and wind projection angle as independent variables, and through multiple linear regression analysis, a prediction model of the mean pedestrian-level wind velocity ratio of high-rise residential areas can be obtained. This prediction model has a high goodness of fit and can explain 54.5% of the variation. This prediction model can provide an accurate quantitative evaluation of the wind environment in high-rise residential areas in severe cold regions.