Severe Cold Zone Research Articles

Methods of determining thresholds of climate variables in building thermal design zoning in China

Climate variable thresholds (CVTs) are essential for building thermal design zoning (BTZ). However, the CVTs in the current BTZ are no longer suitable for developing the current building design. Therefore, the calculation method of bidirectional optimization zone index division standard is established: Forward optimization to obtain the outdoor threshold value that meets the indoor temperature calculation; Reverse optimization to obtain the distribution trend of the combined form of the envelope structure under the known indoor calculated temperature and outdoor climate conditions. According to the new calculation method, the outdoor heating threshold temperatures (OHTT) are adjusted from the original 5 °C–10 °C. In addition, CVTs are updated for significant subregions, such as: 1) the CVT for the hot summer and cold winter and hot summer and warm winter zone is calculated as 10 °C; 2) the CVT for severe cold (SCZ) and cold zones (CZ) is updated to −8 °C. These results will support the development of a BTZ and provide a scientific basis for reforming the heating method in China.

Thermal performance of solar ground source heat pump system for rural buildings in Chinese cold zone

In response to China's national policy of “achieving carbon peak by 2030 and carbon neutrality by 2060″, and to promote the heating system of rural buildings in China's severe cold zone. Two heating schemes of the GSHP (Ground Source Heat Pump) system and the SGSHP (Solar Ground Source Heat Pump) system are designed and simulated for a single rural residential building in Harbin city. The results present that the outlet temperature of buried pipe in SGSHP system is 13.86 % higher than that in GSHP system, and coefficient of performance (COP) correspondingly increases 9.2 %. There is a better comprehensive performance for the SGSHP system in cold climates. The standard coal consumption of SGSHP system is about 72.35 % less than that of biomass boiler system, showing a greater energy efficiency. Compared to the local conventional biomass boiler system, the dynamic cost payback period of the SGSHP system amounts to 11 years, while yielding a net present value (NPV) of 10,800 CNY throughout the project's life cycle. The emissions of CO2, SO2, and dust are reduced by 2617.13 kg, 19.38 kg, and 14.535 kg respectively. The results indicate a great overall performance of the SGSHP system for residential heating in the cold climate zone. This research offers an energy efficient and eco-friendly alternative for the space heating of Chinese rural buildings in cold climates.

Numerical study of the impact of make-up air in a residential kitchen on the heating and cooling demands of ULEBs

Ventilation significantly impacts energy consumption in ultra-low-energy buildings (ULEBs). However, in Chinese residential kitchens, the influence of mechanical ventilation formed by range hoods and make-up air systems on energy consumption has received limited attention. This study assesses the heating and cooling demands in ULEBs resulting from kitchen make-up air across different climate zones in China. The results reveal that in natural make-up air mode, there is a substantial rise in annual heating demand in cold and severe cold zones and a notable increase in annual cooling demand in hot summer and warm winter as well as hot summer and cold winter zones. Additionally, the natural make-up air mode often poses challenges in maintaining a satisfactory thermal environment in kitchens during both heating and cooling seasons. Conversely, the mechanical make-up air mode, especially with pretreatment of outdoor air to ensure thermal comfort in kitchens, significantly elevates both annual heating and cooling demands, making it hard for the building to meet the ULEB specifications, particularly in cold and severe cold zones. Furthermore, despite a generally small increase in annual cooling demand, the percentage rise in heating demand often exceeds the ULEB limits, ranging from 12.0% to 36.0%, depending on the climate zone.

A method for setting room temperature of district heating in northern China based on local thermal comfort

Currently, the district heating system in northern China primarily employs two types of terminals, namely radiators and radiant floors. The heating design temperature is set for the center of the room without considering local thermal comfort for individuals. As the real thermal environment within buildings is non-uniform, variations in thermal sensation across different parts of the body will affect whole-body thermal comfort. Therefore, it is crucial to prioritize local thermal comfort when setting room temperatures for heating purposes. In this study, we analyzed the data from the chamber experiments and Chinese Thermal Comfort Database, focusing on the district heating environments of residences, office buildings, and university classrooms in severe cold and cold zones. We developed a thermal sensation evaluation model for analyzing the most uncomfortable body part, investigated the lower limit of acceptable air temperature for this specific body part and inferred appropriate setpoint based on both this limit and head-ankle temperature difference. The results indicate that ankles are the most uncomfortable part with an estimated lower limit of acceptable air temperature at approximately 18 °C. Consequently, we recommend setting room temperatures of 20 °C for radiator heating (RH) and 19 °C for floor heating (FH) to ensure ankle thermal comfort. The findings of this study can provide theoretical basis for reasonable settings of heating room temperature for the aforementioned three types of buildings in northern China, thereby further achieving energy conservation.

Source tracing the bedroom bacteria across different climate zones in China during the heating season

Approximately 1/3 of people's time is spent in bedrooms. Regulating the health implications arising from the bedroom bacterial community demands an in-depth understanding of both the bacterial composition and the influential factors. This study employed high-throughput 16 S rRNA amplicon sequencing to characterize the bacterial community in 23 residential bedrooms across five climate zones in China. Our findings reveal that the bacterial richness and diversity were highest in the Hot-Summer-Cold-Winter (HSCW) zone, possibly due to its lowest indoor temperature during the heating season. Employing an advanced source tracing algorithm, we identified ventilation rate as the dominant factor affecting outdoor bacterial presence, with each additional air change per hour (ACH) increasing the outdoor bacterial abundance by 13.7 %. The integumentary system was the largest contributor to the occupant-associated bacteria, particularly in the residences located in the Severe Cold and Cold zones. Our study provides valuable insights into the diverse bacterial communities in residential bedrooms across various climate zones in China, elucidating the key factors and sources that contribute to shaping these complex microbial ecosystems.

Properly shortening design time scale of medium-deep borehole heat exchanger for high building heating performances with high computational efficiency

The medium-deep borehole heat exchanger (MDBHE) is a clean solution for building heating with renewable geothermal energy. The long-term performance evaluation with the design time scale same as the life span of the MDBHE is generally adopted by the MDBHE design for high heating performances. However, the long-term performance evaluation largely increases the computational load of the MDBHE design, resulting in practical inconvenience. This study proposes the idea that properly shortening the design time scale could maintain the information of the long-term performance evaluation for the MDBHE design with high heating performances while reducing the computational load. The idea is verified by the MDBHE design for building heating in the severe cold zone of China. The multiple design parameters of the MDBHE are simultaneously optimized considering climate change. The results show that under different geological conditions, economic conditions, and system safety requirements, compared with the life span of the MDBHE of 30–50 years, the design time scale properly shortened to 10 years achieves similar high heating performances regarding the energy consumption, cost, and system safety, and reduces the computational load by 66.1 %–79.3 %. This study contributes to high computational-efficient and high-performance design of the MDBHE for building heating.

Carbon reduction effectiveness and efficiency of earth-berming design for speed skating ovals

Earth-berming design is a common energy-saving practice for speed skating ovals. This study explores the impacts of different earth-berming conditions on the carbon emissions during the operation phase of the venue and evaluates the carbon reduction efficiency by taking into account the incremental carbon emissions caused by the excavation during the construction phase. In this study, three different climate zones were selected as the study environment to simulate the carbon reduction effect of two basic forms of mainstream-scaled speed skating ovals under various earth-berming conditions and to summarise the fitting equations of carbon reduction efficiency. The study found that the total annual carbon emissions (CE) of both forms are the lowest in the severe cold zone in general, and the decreased carbon (dCE) from the earthberming design positively correlates with the excavated volume (V) with a maximum value of 98.9tCO2e/y. Among all regions, the maximum dCE for all forms is highest in the severe cold zone, 5.1% and 9.8% more than that in the hot-summer-cold-winter zone, which has the worst performances. The carbon reduction efficiency of the earth-berming design was measured by critical gain time (T). The earth-berming covariates and T for both forms could be fitted by a quadratic equation, which showed that the larger the burial depth on the large-span space side of Form 1 compared to the auxiliary space side, the smaller the T-value, whereas the greater the V of Form 2, the smaller the T-value.

Effect of the spatial form of outpatient buildings on energy consumption in different climate zones in China.

Under the influence of global epidemics and the need for urban expansion, many outpatient buildings have been rapidly constructed, but the problem of high energy consumption has been neglected. There is a lack of research on the impact of outpatient building forms on energy consumption in different climate zones. Many studies have demonstrated that the energy consumption of a given building can be greatly reduced by adopting a reasonable spatial form design at the early stages of design. Therefore, if architects choose a reasonable spatial form, this could effectively reduce energy consumption. In this study, outpatient building cases in China were summarized, and three typical spatial forms were proposed: the centralized, corridor, and courtyard forms. The DesignBuilder tool was used to simulate and analyse the typical building energy consumption in different climate zones. The results showed that the corridor form (southwards) should be chosen in the severe cold zone, the centralized form (southwards) should be chosen in the cold zone and the hot summer and cold winter zone, the centralized form (northwards) should be chosen in the hot summer and warm winter zone, and the centralized or corridor form can be chosen in the warm zone. The results of this study could provide a reference for energy-efficient design of outpatient buildings in China and other regions with similar conditions and could help architects quickly select reasonable spatial forms at the early stages of design.

Feasibility of a medium-depth U-tube ground-source heat pump system in a severe cold zone in China

ABSTRACT In China, residential buildings have a high-volume ratio and density, which limit the amount of buried U-tube space available, thereby hindering the application of traditional ground-source heat pump systems (GSHPs). Due to the imbalance in heat transfer, the operating efficiency of GSHPs decreases annually in severe cold zones. To alleviate these issues, we assessed the feasibility of medium-depth U-tube GSHPs. An experimental platform in Fuxin City, China, was established, and a simulation model was designed with TRNSYS software. The area affected by the heating load was analyzed, and the proposed system was compared with solar-soil and medium-depth casing pipe GSHPs. The proposed system was found to be stable and efficient for long-term operations, delivering not only the lowest equivalent annual cost but also a 4.61% improvement in heating (compared to solar-soil GSHPs), an 81.54% improvement in cooling, and a 23.08% improvement in emission reductions (compared to medium-depth casing pipe GSHPs).The application of a special U-shaped pipe elbow and a dual-temperature switching valve allowed heat exchange conversion between the heating and cooling conditions. The results of the simulation model demonstrated that dual-temperature operation resulted in greater cooling performance and cheaper operating costs than did the single-temperature system.

Quantifying the effects of urban development intensity on the surface urban heat island across building climate zones

Urban heat island (UHI) has gradually been a critical issue in the context of global environmental change and regional sustainability. The urban development intensity (UDI) increases with rapid urbanization and exacerbates the UHI problem, but the effects and contributions of UDI on UHI remain unclear. Based on Landsat 8 satellite images, this study quantified the effects of UDI on surface UHI intensity (SUHII) in 20 important cities across 5 building climate zones of China by using regression analysis, correlation analysis and boosted regression tree (BRT), and analyzed their potential influence mechanisms. Results indicated that there was apparent spatial heterogeneity of SUHII in different building climate zones (ranging from 3.26 °C to 4.43 °C) and cities (ranging from 1.44 °C to 6.61 °C). The effect of UDI on SHUII in cities of north was stronger than that in south, the average R2 values of the UDI-SUHII relationship in severe cold zone and cold zone were higher than the other climate zones. Building density, as the most critical predictor of SUHII among UDI metrics in all cities, was significantly positively correlated with SUHII. The R2 values showed significant positive correlation with annual average sunshine duration and aridity, and significant negative correlation with annual average precipitation, humidity and soil clay content. Our findings can offer new insights and decision-support in climate-adapted urban planning and heat-related risk management across different building climate zones.

A systematic review on thermal environment and thermal comfort studies in Chinese residential buildings

Amid the backdrop of the energy crisis, thermal comfort is crucial to achieve energy savings. Residential buildings are characterized by a wide range of adaptive comfort opportunities. However, there has been a lack of systematic refinement and review of residential thermal comfort field studies in China to provide valuable recommendations for energy conservation. We systematically reviewed studies on thermal environment and thermal comfort in Chinese residential buildings published in peer-reviewed journals up to 2020. A total of 34 studies were deemed to have provided sufficient information on both the thermal environment and thermal comfort. We found that in winter, there were obvious differences between urban and rural dwellings in Severe Cold (SC) and Cold (C) zones, with regard to their indoor air temperature (urban: 19.8 ∼ 25.0 °C v.s. rural: 11.3 ∼ 17.8 °C) and neutral temperature (urban: 17.6 ∼ 25.1 °C v.s. rural: 11.9 ∼ 23.45 °C). While in summer, the indoor air temperature in urban dwellings were slightly lower than those in rural areas due to their prevalent use of air conditioner (urban: 26.1 ∼ 28.9 °C v.s. rural: 29.5 ∼ 34.9 °C). Indoor air temperature and neutral temperature varied considerably in different climate zones in winter. In SC zones, the indoor environment was overheated, which could lead to energy wastage and overheating discomfort for residents. Residents in Hot-Summer and Cold-Winter (HSCW) zone were the most tolerant to the variation of thermal environment (the median coefficient of MTS or TSV equation: SC: 0.18; C: 0.20; HSCW: 0.13; HSWW: 0.23).

Thermal performance study of multiple thermal insulating glazings with polycarbonate films as interval layers

With the development of global economy, the proportion of energy consumption in buildings is increasing to approximately 40% total energy consumption. The glazed window system, which is the weakest part in the building envelopes, remarkably contributes to energy loss. Scholars and manufacturers are constantly working to improve the thermal properties of glass, such as Low-E glass, aerogel glass, vacuum glass, and so on. However, the advanced glazing either shades the sunlight in winter, or is too expensive to be widely used. In this paper, polycarbonate films with high transparency are used as the interval layers of double glazing, which not only have better thermal properties and visible light transmittance in winter, but also are less expensive to be used. The structures and thermal properties of multiple thermal insulating glazing with polycarbonate films (MTIGP) are systematically investigated. The U-values of MTIGP can be achieved from 1.5 to 2.0 W/m2·K with high transmittance of visible light (Tvis, 60–70%), when compared with a typical Low-E double glazing system (U-value, around 2.0 W/m2·K; TVis, around 60%), even lower when argon (Ar) or krypton (Kr) is used instead of air. The Solar Heat Gain Coefficient (SHGC) of MTIGP is higher than that of a typical Low-E double glazing system, which means more sunlight transmitting into the glazing system in winter to keep the rooms warmer. MTIGP and double silver Low-E pane are simulated with EnergyPlus, the results shows that energy consumption of MTIGP is better than that of double silver Low-E pane. The developed glazing system is expected to be used in severe cold and cold climate zones to improve thermal insulation and sunlight transmittance to reduce energy consumption.

Effects of climate change on long-term building heating performance of medium-deep borehole heat exchanger coupled heat pump

The medium-deep borehole heat exchanger (MDBHE) coupled heat pump (HP) is a promising building heating solution for carbon reduction. Existing studies claim that the MDBHE-HP suffers a bottleneck challenge of long-term heating performance degradation because of the heating extraction attenuation of the MDBHE, which largely hinders the practical applications of the MDBHE-HP. This study innovatively proposes and justifies that climate change positively compromises the heating extraction attenuation of the MDBHE and significantly improves the long-term building heating performance of the MDBHE-HP. Climate change reduces the building heating load, which mitigates the heating extraction attenuation of the MDBHE, thereby reducing the unmet level of the building heating load. The mitigated heating extraction attenuation enhances the coefficient of performance of the MDBHE-HP, thereby reducing the heating energy consumption. Case studies of 30-year operation in the severe cold and cold zones of China with different geological conditions show that while the heating extraction attenuation of the MDBHE increases the heating energy consumption by 5.0% – 8.7%, climate change reduces the heating energy consumption by 9.2% – 17.0%. Moreover, climate change reduces the unmet level of the building heating load by 70.5% – 100%. Therefore, the positive effects of climate change on the long-term building heating performance of MDBHE-HP should be considered, which contributes to promoting the practical applications of the MDBHE-HP for low-carbon building heating.

Performance analysis of a novel solar assisted ground source heat pump water heating system with graded thermal energy storage

The solar assisted ground source heat pump system (SAGSHP) is recognized as an efficient, clean and economical renewable energy technology for hot water supply. However, in SAGSHP systems with an all-day hot water supply, the solar collectors can only heat the water tank with intense solar radiation, which wastes moderate and weak solar resources. In addition, as the SAGSHP system draws heat from the soil for a long time, the soil temperature around the borehole decreases, causing the performance of the GSHP to deteriorate. To solve the above problems, a SAGSHP system with graded thermal energy storage (SAGSHP-GTES) was proposed. This paper investigated the performance and feasibility of the SAGSHP-GTES system, using a case study of hot water supply in a campus dormitory in Changsha, China. Firstly, the drawbacks of solar energy utilization in the conventional SAGSHP system were analyzed. Then, the SAGSHP-GTES system was modeled by TRNSYS, and its operational performance was evaluated and compared with the conventional SAGSHP system. Finally, the feasibility and performance of the SAGSHP-GTES system in different climate zones of China were analyzed. The results showed that the conventional SAGSHP system had a poor solar energy utilization efficiency, with an average thermal efficiency of the SC (ηSC) of only around 19.4%. The long period of operation caused the soil temperature to drop from 18.1 °C to 2.78 °C, which led to a decrease in system efficiency and an increase in electricity consumption. By controlling the heat collection of the SC and the graded utilization of solar energy in the SAGSHP-GTES system, a high ηSC of around 42.7% was obtained, which improved the system efficiency while eliminating the problem of soil temperature drop. After 15 years of operation, the soil temperature increased from 18.1 °C to 19.9 °C, which led to an increase in the coefficient of performance of the system (COPsys) from 3.77 kW/kW to 3.84 kW/kW and COPGSHP from 3.45 kW/kW to 3.5 kW/kW, and a reduction in electricity consumption from 51,746 kWh to 50,735 kWh. In addition, the conventional SAGSHP system was not feasible in severe cold zones (Harbin) and cold zones (Beijing) of China, where soil temperatures fell below 0 °C and freezing of the circulating fluid occurred, while the SAGSHP-GTES system showed excellent performance in all climatic zones of China and is a feasible and efficient technology for hot water supply.

Research on Envelope Thermal Performance of Ultra-Low Energy Rural Residential Buildings in China

Rural energy consumption plays an important role in energy consumption due to the improvement of rural residents’ living quality requirements in China. Ultra-low energy rural residential buildings are proposed to decrease rural energy consumption. First of all, this paper aims to provide the definition of ultra-low energy rural residential buildings, which is to reduce 50% of the building energy consumption of the rural residential benchmark building according to the Chinese standard for energy efficiency of rural residential buildings. Secondly, this paper presents the heat transfer coefficients of building envelopes of ultra-low energy rural residential buildings in the severe cold zone, cold zone and hot summer and cold winter zone in China. Based on optimized design and simulation analysis, the heat transfer coefficients of building envelopes are determined by the construction cost, energy efficiency and retrofit feasibility. Thirdly, the suitable combination of a high-performance external wall and internal wall is recommended based on carbon emission and cost efficiency. As an achievement, a technical specification for ultra-low energy rural buildings has been proposed by the China Academy of Building Research. It is beneficial to design ultra-low energy rural residential buildings in China and other countries.

Research on indoor thermal comfort and energy consumption of zero energy wooden structure buildings in severe cold zone

Indoor thermal comfort level not only affects the indoor thermal environment but also affects building energy consumption. Generally speaking, the higher the thermal comfort of the building, the greater its energy consumption. Therefore, in severe cold zone with the most stringent thermal engineering standards in China, how to reduce building energy consumption while improving building thermal comfort is of great significant for the building in this region to achieve zero energy consumption. In order to achieve this research goal, this paper designs two kinds of wooden structure buildings with water-passing wall in severe cold zone. Through combination of simulation and scale model experiments, the performance of water-passing wall, thermal comfort performance of wooden structure building, and building energy consumption were studied. The research results indicate that the water-passing wall of the wooden structure building has good thermal stability and thermal insulation performance, which can isolate outdoor cold in winter. Moreover, due to the function of water-passing wall, the two kinds of wooden structure buildings have high thermal comfort levels throughout the year, with occupants feeling uncomfortable for no more than 6% of the year. It is compared with the energy consumption before the water supplying to the wall, the total energy consumption of the two kinds of wooden structure buildings were reduced by 44.3% and 46.2% respectively. Therefore, these two kinds of wooden structure building can pursue higher thermal comfort with lower energy consumption, it has high energy-saving benefits.

Thermal performance and thermal transmittance prediction of novel light-gauge steel-framed straw walls

Thermal bridges in light-gauge steel-framed exterior walls lead to more winter heat loss, summer heat gain, and building pathologies generated by moisture condensation and mould growth, which are unfavorable for building energy efficiency and service life of sheathing panels. A novel light-gauge steel-framed straw wall with a nonmetallic broken bridge layer was proposed, which consists of two sheathing panels on both sides of the wall, two frames, a middle sandwich layer, and two kinds of fasteners. The environmentally friendly straw boards including paper straw board (PSB) and wheat straw strand board (WSSB) were used as middle sandwich layer and exterior panel respectively. This study focuses on the thermal performance and the prediction method of thermal transmittance (Um-value) for such walls. Tests using the temperature control box-heat flux meter method were carried out for three representative walls with different configurations. Based on analyses of the temperature and heat flux density distributions, it is found that the broken bridge layer and the airspaces between the sheathing panel and the track or the bracing can effectively reduce the thermal bridge effect, with the relative effects less than 5%. Based on the test results of the Um-values, different wall configurations were matched with the feasible climate zones on the basis of energy efficiency design. After the validation by comparing with the test results in terms of temperature, heat flux density, and Um-value, the numerical study was carried out to broaden the feasible climate zones, and walls with improved configurations were proposed and analyzed. The results show that, by replacing the unventilated airspaces with the expanded polystyrene (EPS) boards, a maximum improvement in thermal performance reaches 74.89%. Thus, the feasible climate zones of the walls have been extended to the severe cold zone. Finally, a thermal transmittance prediction methodology based on the calculation method specified in European Standard EN ISO 6946-2017 in conjunction with the modified method considering thermal bridge effect was used to predict the Um-‍values of the improved walls. This study provides a new design strategy with nonmetallic broken bridge layer to reduce the unfavorable influence of thermal bridges in light-gauge steel-framed walls. Such a design strategy contributes to less energy consumption in addition to making full use of agricultural waste straw, which plays a positive role in the development of green buildings.

Climate Adaptability Analysis on the Shape of Outpatient Buildings for Different Climate Zones in China Based on Low-Energy Target

Under the impact of COVID-19 and the needs for urban expansion, a large number of outpatient buildings have been rapidly constructed, but the problem of high energy consumption has always been ignored. There is a lack of research on the adaptability of building shape in different climate zones. Many studies have shown that a reasonable shape in the early stage of design can significantly reduce the energy consumption of buildings. Therefore, it helps if architects quickly select a reasonable shape that can effectively reduce energy consumption. This study summarized a number of outpatient building cases in China and proposed three typical building shapes: centralized-type (Shape-1), corridor-type (Shape-2), and courtyard-type (Shape-3). The Design Builder tool was used to simulate and analyze the typical building energy consumption in different climate zones. The simulation results show that Shape-2 (angle: 0°) should be chosen in severe cold zone; Shape-1 (angle: 90°) should be chosen in cold zone; Shape-1 (angle: 0°) should be chosen in hot summer and cold winter zone; Shape-1 (angle: 60°) should be chosen in hot summer and warm winter zone; and Shape-1 or Shape-2 can be chosen in warm zone. The results of this study can provide suggestions for the energy saving design of outpatient buildings in China and other areas with similar conditions. The result can help architects make rapid shape selection in the early stage of design.

The characteristics of microorganisms in residence in summer and winter among different climate zones, China

<p indent="0mm">Indoor microbes have been listed in the category of indoor air pollutants by World Health Organization (WHO) in 1990. Exposure to a high concentration of airborne bioaerosol potentially causes adverse health effects, such as pneumonia, asthma, and allergies. People spend most of their time in residence in their life, so figuring out the characteristic of residential airborne microbes is very important for occupants’ health. However, previous studies mostly focused on indoor microorganisms in public buildings, while very little work has been done on the characteristics of indoor airborne bacteria and fungi in residence. In this study, we investigated the indoor airborne bacterial concentration, fungal concentration, and taxonomic diversity of residences in summer and winter among five different climate zones across China, as well as the community structure, and revealed the correlations between indoor airborne microbial characteristics (concentrations and taxonomic diversity) and geographical location by using polynomial fitting. Culturing and sequencing methods were combined in this study, for which we collected 376 culturable samples and 168 sequencing samples of bacteria and fungi each. We found the bacterial concentrations between summer and winter were significantly different in the hot summer &amp; cold winter climate zone and the hot summer &amp; warm winter climate zone, whereas there was no significant difference between different seasons among different climate zones for fungal concentrations. The bacterial concentrations in the hot summer &amp; cold winter zone (Nanjing, 875±553 CFU/m³) and hot summer &amp; warm winter (Shenzhen, 758±473 CFU/m³) were significantly higher than those in the other climate zones in summer (<italic>P </italic>&lt; 0.05); the lowest bacterial concentrations in winter were found in hot summer &amp; cold winter (Nanjing, 191±119 CFU/m³). For fungi, the highest concentrations were found in the severe cold climate zone (Harbin, 743±798 CFU/m³) and cold climate zone (Lhasa, 1369±1380 CFU/m³) in summer; while the highest was only found in the severe cold climate zone (Harbin, 654±493 CFU/m³) in winter. We also found that the bacterial diversity in the hot summer &amp; cold winter climate zone was significantly different between summer and winter; the fungi diversity in the hot summer &amp; cold winter climate zone and hot summer &amp; warm winter climate zones was significantly different between summer and winter. For bacteria, the lowest taxonomic diversity in summer was found in severe cold climate zone and the highest was found in hot summer &amp; cold winter climate zone; the lowest taxonomic diversity in winter was found in severe cold climate zone and hot summer &amp; cold winter climate zone. For fungi taxonomic diversity, the highest values were found in severe cold climate zone and hot summer &amp; cold winter climate zone in summer; the highest values were found in cold climate zone and hot summer &amp; warm winter climate zone in winter. We analyzed the community structure of bacteria and fungi at the phylum level. The TOP 4 bacterial species and TOP 3 fungal species between different climate zones in summer and winter were similar. The TOP 4 bacteria species in residences were <italic>Bacteroidetes</italic>, <italic>Proteobacteria</italic>, <italic>Firmicutes</italic>,<italic> </italic>and <italic>Actinobacteria</italic>. The TOP 3 fungi species were <italic>Ascomycota</italic>, <italic>Basidiomycota</italic>, and <italic>Zygomycota</italic>, except for Beijing, which is located in a cold climate zone. By analyzing the correlations between indoor microbial characteristics and geographical location, we found the variation of indoor microbial diversity with latitude was opposite in summer and winter. In summer, indoor bacterial concentrations and diversity first increased and then decreased with the increase of longitude, which was opposite to the trend of fungi. There was no correlation between winter bacterial concentrations and geographical location.

Comparison of airborne bacteria and fungi in different built environments in selected cities in five climate zones of China

Bioaerosols in different built environments and climate zones have unique effects on occupant health, which demands comparisons of their characteristics to make targeted control measures. This study investigated bioaerosol distribution in five different climate zones across China with four building types (n = 686 rooms). The results showed significant disparities in bioaerosol concentrations among various buildings and climate zones. The bacterial concentrations in residences (536 ± 647 CFU/m3) were significantly higher than in schools, offices, and hospitals owing to different built environments and human activities. The highest mean value of fungal concentration was found in schools (826 ± 955 CFU/m3) due to their greater landscaping area. The bacterial concentrations in the cold zone (307 ± 506 CFU/m3) and the hot summer and cold winter zone (214 ± 180 CFU/m3) were significantly lower than in the other three climate zones. The fungal concentrations in the severe cold zone (709 ± 900 CFU/m3) and the hot summer and warm winter zone (1094 ± 832 CFU/m3) were significantly higher than in the other three climate zones; the lower the indoor temperature (T) and the higher the air exchange rate, the lower the indoor airborne bacterial concentration; the lower the relative humidity (RH), the lower the indoor airborne fungi. In addition, a higher air exchange rate could also reduce the effect of occupant density on indoor bacterial concentration. The results of this study provide valuable data on bioaerosol profiles in various built environments and climate zones and highlight the significance of T, RH, and air exchange rate on indoor bioaerosol concentrations.