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Case Report

Impact of Night Ventilation on Indoor Thermal Environment of Residential Buildings under the Dual Carbon Target: A Case Study of Xi’an

by
Hongyan Xiang
1 and
Jing Li
2,*
1
School of Architecture, Xi’an University of Architecture and Technology Huaqing College, Xi’an 710038, China
2
North China Municipal Engineering Design & Research Institute Co., Ltd., Tianjin 300074, China
*
Author to whom correspondence should be addressed.
Buildings 2024, 14(8), 2459; https://doi.org/10.3390/buildings14082459
Submission received: 19 July 2024 / Revised: 6 August 2024 / Accepted: 7 August 2024 / Published: 9 August 2024
(This article belongs to the Special Issue Existing Environment, Equipment, Materials and Technical Means for Buildings)
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Abstract

:
Effectively reducing the energy consumed by buildings under the dual carbon targets in China was our focus in this study. We used experimental methods to test and analyze the indoor air and average radiation temperatures in a specific apartment building in Xi’an. We compared the impact of night ventilation on the indoor thermal environment using the EnergyPlus software V9.5.0. The results showed that night ventilation is suitable for the typical summer temperatures in Xi’an when the daily temperature range is larger than 6 °C. Night ventilation technology can be used for 76 days from June to August, accounting for approximately 82.6% of this period. The indoor air and average radiation temperatures both decrease with the adoption of night ventilation, with these temperatures decreasing with an increase in the daily temperature range. When the daily temperature range increases from 3 °C to 15 °C, night ventilation can reduce the indoor average and radiation temperatures by a maximum of 1.07 and 0.47 °C, respectively, on typical meteorological days. When the daily temperature range is 15 °C, the maximum energy savings is 4.85 kWh/d, and the cost saving index for air conditioning operation is 0.065 CNY/(m2·d). With a daily temperature range of 3 °C, the air conditioning operating costs are reduced by 63.7%. Our study provides a reference for building energy conservation and the creation of comfortable indoor thermal environments under the dual carbon target: a carbon peak before 2030 and carbon neutrality before 2060.

1. Introduction

People spend approximately 80% to 90% of their time indoors [1]; therefore, maintaining a high indoor air quality is crucial. However, with the continuous increases in the air tightness of residential buildings [2], the use of decoration materials, and outdoor air pollution [3,4], the types and concentrations of indoor pollutants in residential buildings have substantially increased. Residents may thus suffer from “sick building syndrome” [5], which seriously endangers people’s physical and mental health [6]. As a result, increasing the energy efficiency and reducing the carbon emissions of residential buildings while ensuring indoor air quality and comfort has become a hot research topic.
Ventilation is one of the main methods used to reduce the indoor air pollution in residential buildings [7]. Night ventilation, as a passive energy-saving technology for buildings, improves the indoor thermal environment and effectively reduces building energy consumption [8,9,10]. Natural ventilation cooling at night specifically refers to the introduction of colder natural wind into the building at night, using the heat storage capacity of the enclosure components through the convective heat transfer of internal and external air. Excess indoor heat is removed, reducing the temperature of the indoor air and enclosure structures during the day. Night ventilation shortens the time air conditioning is needed during the day and improves the indoor air environment [9]. Therefore, studying the impact of different factors on the energy-saving and cooling effects of night ventilation and selecting appropriate parameters is important for the promotion and application of night ventilation technology.
Studies have been conducted on night ventilation [11,12,13,14,15] and cooling, starting in foreign countries in the mid-20th century [11]. The research on night ventilation in China started later [12], mainly focusing on natural, mechanical, and mixed ventilation [13]. The research can be divided into three main types: theoretical analysis, experimental testing, and numerical simulation [14]. Initially, studies on natural ventilation involved a combination of theoretical and experimental methods [15]. The building climate and related factors affecting the night ventilation cooling effect were studied through analyzing relevant mathematical theoretical models and experimental data. Then, the measured data and simulation results were verified and analyzed through establishing building ventilation models and changing the influencing parameters, which further expanded the knowledge of the factors influencing night ventilation technology.
The relevant literature has studied the efficiency of night ventilation in residential buildings [16], the thermal environment under night ventilation [17], and the impact of night ventilation on PCM performance [18]. It provides fundamental research for the application of night ventilation. The current studies have mainly focused on suitable locations for night ventilation [19], night ventilation-related parameters [20], ventilation strategies [21], heat storage enclosure structures [22], and phase change materials [23]. However, most studies have been conducted in nonresidential buildings due to the limitations of night ventilation technology in terms of indoor privacy and night-time operation time [24]. As no one typically works at night in office buildings, this provides suitable conditions for the application of natural ventilation at night and so applications for office buildings have been the aim of most night ventilation technologies. However, as people are present at night in residential buildings, their actions impact the effect of these technologies by being heat sources and through their breathing, moving, washing, and so on. Their actions all impact the indoor parameters that affect the efficacy of night-time ventilation. Moreover, room layout, decoration types, and human habits differ between apartment buildings and office buildings. Therefore, research on apartment buildings is required.
First, through policies that differ among local governments [25], the construction of facilities for employees has included the construction various types of apartment buildings, which are accounting for increasingly larger proportions of residential buildings. Second, these buildings are relatively densely packed with rooms, and the density of people creates a warm thermal environment [26]. The changes in the outdoor temperature that have occurred with global warming differ in different regions [3,27], as do people’s personal requirements, which requires studies on night ventilation in residential buildings.
Xi’an is located in the Guanzhong Basin, in the central part of the Weihe River Basin, between 107.40° E and 109.49° E and 33.42° N and 34.45° N. Xi’an is a city with a relatively high concentration of higher education institutions and research institutes in the western region, having the highest density of universities and the largest number of people attaining higher education in China. Xi’an has rich educational resources and holds an important position in the western region as well as in the country. Xi’an is one of the five major education and research centers in China. Therefore, we selected Xi’an as the study object. With the rise of the Silk Road and the active aim of meeting the two carbon goals of peaking carbon emissions before 2030 and achieving carbon neutrality before 2060 [28], the impacts of night ventilation on the energy-saving and cooling effects of residential buildings in Xi’an need to be explored.
This study focused on the practical problems mentioned above, and an apartment building in Xi’an was selected as the study object. The indoor air temperature, average radiation temperature, and energy consumption after night ventilation were studied in depth through a combination of experimental testing and analysis. Our study provides guidance for the application of natural ventilation at night to conserve energy and reduce the carbon emissions of the apartment buildings in the region, which is valuable for achieving the dual carbon goals.

2. Methods

2.1. Building Selection

A typical high-rise apartment building in Xi’an was selected for testing. The building was 99.66 m tall, 57.90 m long, and 18.60 m wide, with a floor height of 3.12 m and a total area of 35,850 square meters. The building had 30 floors above ground and 2 floors underground, facing north and south. The building is shown in Figure 1. The building was an apartment building, with 24 similar rooms on each floor. For the convenience and economy of testing, room 1705 on the 17th floor was selected for testing.

2.2. Testing Instruments

The specific information on the instruments used in this study is shown in Table 1. The experiment ran from 28 July to 15 August 2023.

2.3. Testing Requirements

The layout of the indoor measurement points was mainly determined based on the relevant specifications [29] and previous studies [30]. Eleven air temperature measurement points were arranged indoors, at a distance of 0.6 m from the floor in the north–south direction and 1.3 m from the wall. The measuring points were evenly arranged in the room, and the spacing between the measuring points remained the same. The layout of the indoor measurement points is shown in Figure 2.
The north–south length of the experimental room was 8.8 m, the east–west length was 4.2 m, and the height was 3.12 m. The north–south cross-sectional area was 13.10 square meters, and its volume was 99.09 cubic meters. To reduce the error of the measurement points, two groups were tested, and the average of the two groups was used for calculation. In addition, to ensure the accuracy of the experimental results and prevent people and heat dissipation from affecting the measurement parameters, ignoring the influence of the enclosure structure (wall and floor parameters), the experiment was conducted under conditions without people, lighting, and the operation of other equipment. Indoor heat was only dissipated by a ventilation fan, which was calculated using Equation (1) [31]:
Q = 1000 n 1 n 2 n 3 1 − η η N
where N is the installed power of the ventilation fan, kW; η is the efficiency of the ventilation fan; n 1 is the use coefficient, which generally ranges from 0.7 to 0.9; n 2 is the simultaneous use of coefficients, which generally ranges from 0.5 to 0.8; and n 3 is the load factor, which is generally 0.5 [32].
The heat balance equation for the room’s air was established, which was calculated as [33]
∑ k = 1 N i F k a k c [ t k ( n ) − t r ( n ) ] + [ q 1 c ( n ) − q 2 c ( n ) ] + L a ( n ) ( c ρ ) a [ t a ( n ) − t r ( n ) ] / 3.6 − H E S ( n ) = V ( c ρ ) r [ t r ( n ) − t r ( n − 1 ) ] / ( 3.6 × Δ τ )
where q 1 c ( n ) − n is the convective heat dissipation from lighting, sensible human body heat, and sensible equipment heat, W; q 2 c ( n ) − n is the sensible room heat consumed by the evaporation of water due to the absorption of room heat, W; L a ( n ) − n is the air infiltration rate, m3/h; ( c ρ ) a , V ( c ρ ) r is the specific heat capacity of outdoor and indoor air, kJ/m3; t k ( n ) − n is the surface temperature at time k, °C; t a ( n ) and t r ( n ) are the outdoor and indoor air temperatures, respectively, °C; F k is the area of the kth wall surface, m2; a k c is the convective heat transfer coefficient of the kth wall, W/m2·K; V is the room volume, m3; and H E S ( n ) − n is the sensible heat removed by the air conditioning system, W.

2.4. Parameter Selection

The specific heat transfer coefficients of the building envelope structure are shown in Table 2, which were calculated using the EnergyPlus building energy consumption simulation software.
The apartment building was ventilated from 22:00 to 7:00. When the outdoor air temperature was lower than the indoor air temperature, mechanical ventilation was used, and infiltration ventilation was used at the other times. Infiltration ventilation refers to ventilation carried out through the gaps between doors and windows. The mechanical and infiltration ventilation frequencies of the building were set to 10 times/h and 0.5 times/h, respectively [34]. Room 1705 was selected as the simulation object; the apartment had 2 people in each room, and the heat generated by the indoor equipment was 2 W/m2. The heat dissipation of the indoor lighting was 15 W, and the lighting use rate is 0.2 from 7:00 to 8:00, 0.1 from 8:00 to 8:30, 0.8 from 19:00 to 22:00, and 0.2 from 22:00 to 23:00. The period of night ventilation was from June to August, and the testing room was equipped with a split air conditioning system, with the COP set to 3.2.

2.5. Simulation

The simulation steps were as follows: First, we used the 3D modeling software Sketch UP 2022 to build a building model for simulation. Second, we imported the building model into EnergyPlus for parameter settings and simulation. Finally, through changing the settings of simulation parameters, simulation results under different conditions were obtained and analyzed.
EnergyPlus uses FORTRAN90 as the programming language. In the simulation process, information was input about the building (enclosure structure, HVAC system, and people). We selected the relevant output report forms and generated input data files (IDFs) based on user-defined parameters. The main EnergyPlus program used an input data file (IDF) and converted the relevant input data based on the input data definition file (IDF). The relevant subroutines (Get Input) in each module of the main program read the data corresponding to the module and then performed the corresponding operation process. Finally, the corresponding output files were generated according to the user requirements, which were then converted into spreadsheets or other forms.

2.6. Evaluation Indicators

The indoor air temperature and average radiation temperature were used as the indicators to evaluate the cooling effect of night ventilation, and the reduced building energy consumption (i.e., energy savings) was selected for evaluating the energy-saving effect of night ventilation.

3. Results and Discussion

3.1. Meteorological Conditions in Xi’an

Figure 3 shows the variations in the average, maximum, and daily minimum outdoor temperatures from June to August in Xi’an.
As shown in Figure 3, the trends in the maximum, minimum, and average outdoor daily temperatures in typical years in Xi’an are similar. Overall, the outdoor air temperature in Xi’an was relatively low in June and late August, whereas the dry bulb temperature in July and early August was relatively high, with a maximum temperature of 40.4 °C. The typical annual minimum outdoor temperature in Xi’an was within 15.3–30.7 °C, so night-time ventilation can be used to improve indoor thermal environments. Figure 4 shows the distribution of the average outdoor daily temperature and temperature range from June to August, which was obtained by analyzing the hourly meteorological data of typical years in Xi’an.
Figure 4 shows that the average daily temperature in Xi’an from June to August was 16.3 °C to 35.8 °C. The lowest average outdoor daily temperature on 4 June was 16.3 °C, and the highest outdoor daily average temperature on 24 July was 35.8 °C. More days in June to August had an average outdoor daily temperature range of 28 °C to 32 °C in Xi’an, for a maximum of 34 days. In addition, the daily temperature range in a typical year from June to August in Xi’an had an approximately normal distribution [35]. More days had a typical temperature range of 9–12 °C from June to August in Xi’an, for a maximum of 44 days. Xi’an is suitable for night ventilation when the daily temperature difference is more than 6 °C [36]. Therefore, from June to August, night ventilation technology can be used in the summer in Xi’an for 76 days, accounting for approximately 82.6% of the total number of days in this period. Using night ventilation shows considerable energy conservation and cooling potential.

3.2. Model Verification

Figure 3 and Figure 4 show that every day within June to August meets the requirements for regulating indoor thermal environment using night ventilation in Xi’an, and all days tested met the requirements. Considering the thermal storage performance of building envelope structures and the relatively high and low outdoor air temperature in early and late August, respectively, we selected a typical day for testing: 15 August. The simulated and measured indoor air temperatures are compared in Figure 5.
Figure 5 shows that the simulated indoor air temperature was consistent with the measured values, with a maximum error of 0.31 °C, a minimum error of 0.02 °C, and a relative error of −1.03% to 0.91%. The simulated temperature was lower than the measured value at night and higher than the measured value during the day. The reason for this may have been that the thermal storage performance of the furniture and decorative materials was not considered in the simulation [37], resulting in errors. This conclusion is consistent with those in the literature [33,38], verifying the correctness of our results. The experimental and simulation results are in relative agreement, within the allowable error range, effectively proving the correctness of the building model and simulation methods. In addition, comparing the results under different operating conditions using simulations indirectly provides the specific operating conditions that have been met, making the model more applicable to other conditions.

3.3. Impact of Daily Temperature Range on Indoor Air Quality

The daily temperature range is mostly in the range of 0–15 °C, according to the outdoor meteorological data of typical summers in Xi’an. Based on the actual situation for typical years in Xi’an, numerical simulations were conducted using five different daily temperature ranges: 3 °C, 6 °C, 9 °C, 12 °C, and 15 °C. Figure 6 shows the effect of night ventilation on indoor air temperature for different temperature ranges.
When the average daily outdoor temperature is the same, the indoor air temperature gradually decreases with the increase in the daily temperature range, and the decrease is larger during mechanical ventilation than during infiltration ventilation (Figure 6). When the daily temperature range is 3 °C, the average, highest, and lowest temperatures of the indoor air are 29.65 °C, 30.71 °C, and 28.34 °C, respectively. When the daily temperature range is 6 °C, 9 °C, 12 °C, and 15 °C, the average indoor temperature decreases by 0.26 °C, 0.55 °C, 0.80 °C, and 1.07 °C compared with when the daily temperature range is 3 °C; the highest temperatures decrease by 0.04 °C, 0.14 °C, 0.27 °C, and 0.33 °C, respectively; and the lowest temperature decreases by 0.45 °C, 1.17 °C, 1.77 °C, and 2.33 °C, respectively. When the indoor temperature is high and the daily temperature range is large, night ventilation can increase the time the indoor temperature is below 28 °C [38], which is more comfortable for sleep.
Figure 6 also shows that after the start of night-time ventilation, the indoor air temperature quickly drops because the ventilation fan brings cold outdoor air into the room, which thoroughly mixes with the indoor air. We found that the indoor air temperature substantially increased from 8:00 to 10:00. The mechanical ventilation ended at 8:00, so indoor ventilation relied solely on infiltration, so the heat was ineffectively dissipated. This conclusion is consistent with those in the literature [39], proving the correctness of our method. During infiltration ventilation, the indoor air temperature slightly decreases with the increase in the daily temperature range, and the reduction in the temperature peak is not notable. When the daily temperature range is 15 °C, the highest indoor temperature only decreases by 0.33 °C because when the daily average outdoor temperature is the same, although an increase in daily temperature range increases the cold storage capacity of the enclosure structure, the outdoor temperature is also higher during the day, resulting in an insignificant decrease in the indoor temperature.
In addition, decreases in indoor air temperature are related to the outdoor air temperature at night [40]. When the outdoor night air is cool, night-time ventilation can maintain the indoor air at a lower temperature, to ensure the thermal comfort of the human body and reduce the running time of fans or air conditioning.

3.4. Impact of Daily Temperature Range on Average Indoor Radiation Temperature

Figure 7 shows the effect of night ventilation on the average indoor radiation temperature for different temperature ranges.
As shown in Figure 7, when the average outdoor daily temperature is the same, as the daily temperature range increases, the average peak indoor radiation temperature decreases and the overall temperature decreases. When the daily temperature range is 3 °C, the average, highest, and lowest average radiation temperatures are 29.60 °C, 30.01 °C, and 29.29 °C, respectively. When the daily temperature range is 6 °C, 9 °C, 12 °C, and 15 °C, the average indoor radiation temperature decreases by 0.11 °C, 0.23 °C, 0.35 °C, and 0.47 °C, respectively, compared with when the daily temperature range is 3 °C. Although the average indoor radiation temperature during mechanical ventilation decreases more than during infiltration ventilation, the decrease is still relatively small compared with the indoor air temperature.
With the daily temperature range increases, the decrease and fluctuation in the average indoor radiation temperature are relatively small. When the daily temperature range is the same, the average indoor radiation temperature increases with the increase in the outdoor daily average temperature. In addition, the initial heat storage capacity of building envelope structures can affect the average indoor radiation temperature [41].

3.5. Impact of Daily Temperature Range on Building Energy Consumption

Figure 8 shows the reductions in air conditioning operation time with night ventilation for different daily temperature ranges.
Figure 8 shows that when the average outdoor daily temperature is high, the operating time of indoor air conditioning decreases with the increase in daily temperature difference. On 15 August, when the daily temperature range was 3 °C, the indoor air temperature was 28 °C, which is higher than the designed indoor temperature. Night ventilation reduced the air conditioning operation time by approximately 2.5 h. When the daily temperature range was 15 °C, night ventilation reduced the air conditioning operation duration by 10.58 h. Night ventilation under larger diurnal variations in temperature can effectively reduce the operating duration of indoor air conditioning. When the outdoor air is below 28 °C, mechanical ventilation throughout the day can meet the indoor human thermal comfort requirements without the need to turn on air conditioning [42]. However, the energy-saving effect is mainly limited by the duration of mechanical ventilation, which is mainly based on human behavior. When the daily variation in temperature is between 9 °C and 15 °C, the time that air conditioning is operated with reduced night ventilation increases with the increase in the daily temperature range. This is because the energy-saving effect is mainly limited by the cold storage capacity of the enclosure structure. This conclusion is consistent with that in the literature [43], which verifies the correctness of our findings. The temperature of the fresh air sent into the room at night gradually decreases, which increases the cold storage capacity of the enclosure structure and reduces the operating time of indoor air conditioning, thereby reducing energy consumption. Using the power listed for the ventilation fan, which was 33 W, the correlation coefficient was determined based on the results provided in the literature [33]; for an efficiency of 0.7, a use coefficient of 0.8, and a load coefficient of 0.5, the heat dissipation power of the ventilation fan was calculated as approximately 4.53 W. Figure 9 shows the variation in energy savings when using night ventilation for different daily variations in temperature.
Figure 9 shows that when the average outdoor daily temperature is the same, the energy savings increase with the increase in the daily temperature range. On 15 August, when the daily temperature range is 3 °C and 15 °C, the total energy consumption decreases by 1.76 kWh and 4.85 kWh, respectively, showing that night ventilation on days with large temperature ranges effectively reduces energy consumption. When the daily temperature difference is the same, the energy savings achieved with night ventilation do not increase with the increase in the average outdoor daily temperature. The energy savings are mainly caused by the cold energy stored in the enclosure structure with night ventilation. The total energy consumption substantially decreases on 15 August, partly due to the large initial heat storage capacity of the indoor enclosure structure, resulting in higher indoor temperatures, and partly as the outdoor temperature is relatively low. As such, night ventilation can reduce the indoor temperature and thus increase the cold storage capacity of the enclosure structure, effectively reducing the energy consumed by the air conditioning [44].
When the daily temperature variation increases from 3 °C to 6 °C, the energy savings increase by 1.82 kWh. When the daily temperature variation on 15 August is less than 3 °C, ventilation cannot lower the indoor air temperature below the designed temperature of 28 °C at night. Therefore, the operating duration of the air conditioner is not reduced: only the cold energy stored in the enclosure structure is used to reduce the energy consumed by the air conditioner the next day. Therefore, energy savings are not notable.
According to the electricity price standard in Xi’an, a fee is charged at a standard electricity price of 0.4983 CNY/kWh. For the room in this study, when the daily temperature difference is 15 °C, the electricity savings on 15 August is 2.42 CNY/d, and the air conditioning cost saved index is 0.065 CNY/(m2·d). Compared with a daily temperature difference of 3 °C, 63.7% of the air conditioning operating costs are saved. The high-rise apartment building has a total of 30 floors, with 24 identical rooms on each floor. If the energy savings for each room are the same and considering a daily temperature range of 15 °C, the daily electricity cost savings would be CNY 1742.4. Therefore, using night ventilation reduces building energy consumption and reduces electricity costs.

4. Conclusions

We studied the indoor air and average radiation temperatures inside an apartment building in Xi’an, and compared the impacts of night ventilation on the indoor thermal environment using the EnergyPlus software. Our preliminary conclusions are as follows:
  • The average daily temperature from June to August in Xi’an ranges from 16.3 °C to 35.8 °C. When the variation in the daily temperature in a typical summer in Xi’an is larger than 6 °C, ventilation can be conducted at night. Night ventilation can be used for 76 days in this period, accounting for approximately 82.6% of the period.
  • The indoor air and average radiation temperatures both decrease after adopting night ventilation and decrease with the increase in the daily temperature range. When the daily temperature range is 6 °C, 9 °C, 12 °C, and 15 °C, the average indoor temperature decreases by 0.26 °C, 0.55 °C, 0.80 °C, and 1.07 °C, respectively, compared with that for a daily temperature range of 3 °C. The highest temperatures decreased by 0.04 °C, 0.14 °C, 0.27 °C, and 0.33 °C, respectively; the lowest temperature decreased by 0.45 °C, 1.17 °C, 1.77 °C, and 2.33 °C, respectively.
  • When the daily temperature range increases, the peak average indoor radiation temperature decreases and the overall building temperature decreases. When the daily temperature difference is 6 °C, 9 °C, 12 °C, and 15 °C, the average indoor radiation temperature decreases by 0.11 °C, 0.23 °C, 0.35 °C, and 0.47 °C with the use of night-time ventilation, respectively, compared with that when the daily temperature range is 3 °C.
  • When the average daily outdoor temperature is high, the air conditioning system does not need to be operated for as long as the daily temperature range increases. When the daily temperature range is 15 °C, night ventilation reduces the time the air conditioning operates by 10.58 h. When the daily temperature range is 15 °C, the total energy consumption is reduced by 4.85 kWh, the electricity cost saved is 2.42 CNY/d, and the air conditioning operating cost saving index is 0.065 CNY/(m2·d). Compared with a daily temperature range of 3 °C, air conditioning operating costs are reduced by 63.7% with night ventilation. Our study provides a reference for building energy conservation and the creation of indoor thermal environments while meeting the dual carbon targets.
Night ventilation is also related to the local outdoor environment and the behavior of residents. The larger the outdoor temperature difference in the day, the more effective the night ventilation; however, the effects of night ventilation may vary with geographical environment. On this basis, resident-related factors should also be considered in the implementation of night ventilation, and personal behavior will be the main factor influencing the start and operation of night ventilation. Overall, more in-depth research is needed on night ventilation.

Author Contributions

Conceptualization, H.X.; methodology, J.L.; investigation, H.X.; data curation, J.L.; writing—original draft preparation, H.X. and J.L.; writing—review and editing, H.X. and J.L. All authors have read and agreed to the published version of the manuscript.

Funding

This study received no external funding.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

Author Jing Li was employed by the company North China Municipal Engineering Design & Research Institute Co., Ltd. The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Photograph of building selected for this study.
Figure 1. Photograph of building selected for this study.
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Figure 2. Layout of indoor measurement points.
Figure 2. Layout of indoor measurement points.
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Figure 3. Daily temperatures from June to August in typical years in Xi’an.
Figure 3. Daily temperatures from June to August in typical years in Xi’an.
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Figure 4. Average outdoor daily temperature variation and temperature range in Xi’an.
Figure 4. Average outdoor daily temperature variation and temperature range in Xi’an.
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Figure 5. Comparison of simulated and measured air temperature (relative humidity: 48~74%, solar radiation: 20.0~797.8 W/m2).
Figure 5. Comparison of simulated and measured air temperature (relative humidity: 48~74%, solar radiation: 20.0~797.8 W/m2).
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Figure 6. The variation in indoor air temperature for different daily temperature ranges.
Figure 6. The variation in indoor air temperature for different daily temperature ranges.
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Figure 7. The variation in average indoor radiation temperature for different daily temperature ranges.
Figure 7. The variation in average indoor radiation temperature for different daily temperature ranges.
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Figure 8. Night ventilation reduces air conditioning operation time.
Figure 8. Night ventilation reduces air conditioning operation time.
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Figure 9. Energy savings achieved with night ventilation.
Figure 9. Energy savings achieved with night ventilation.
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Table 1. The specific information of the instruments used in this study.
Table 1. The specific information of the instruments used in this study.
InstrumentManufacturerTest ContentRangeResolutionAccuracy
IAQ-Calc7525 indoor air quality detectorTSI Instrument Beijing Co., Ltd., Beijing, ChinaTemperature0~60 °C0.1 °C±0.6 °C
Relative humidity5~95% RH0.1% RH±3.0% RH
Vantage Pro2 Plus small weather stationShaanxi Furunke Electronic Technology Co., Ltd., Xi’an, ChinaTemperature−40~65 °C0.1 °C±0.5 °C
Relative humidity0~100% RH1% RH±3.0% RH
Wind speed1~67 m/s0.1 m/s±5%
Atmospheric pressure880~1080 hPa0.1 hPa±1 hPa
Table 2. The heat transfer coefficient of the building’s envelope structure [33].
Table 2. The heat transfer coefficient of the building’s envelope structure [33].
Enclosure StructureExterior WallInternal WallFloorRoofingOuter WindowDoor
Heat transfer coefficient
(W·m−2K−1)		0.691.523.10.432.11.5
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Xiang, H.; Li, J. Impact of Night Ventilation on Indoor Thermal Environment of Residential Buildings under the Dual Carbon Target: A Case Study of Xi’an. Buildings 2024, 14, 2459. https://doi.org/10.3390/buildings14082459

AMA Style

Xiang H, Li J. Impact of Night Ventilation on Indoor Thermal Environment of Residential Buildings under the Dual Carbon Target: A Case Study of Xi’an. Buildings. 2024; 14(8):2459. https://doi.org/10.3390/buildings14082459

Chicago/Turabian Style

Xiang, Hongyan, and Jing Li. 2024. "Impact of Night Ventilation on Indoor Thermal Environment of Residential Buildings under the Dual Carbon Target: A Case Study of Xi’an" Buildings 14, no. 8: 2459. https://doi.org/10.3390/buildings14082459

APA Style

Xiang, H., & Li, J. (2024). Impact of Night Ventilation on Indoor Thermal Environment of Residential Buildings under the Dual Carbon Target: A Case Study of Xi’an. Buildings, 14(8), 2459. https://doi.org/10.3390/buildings14082459

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