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The air infiltration rate of buildings strongly influences indoor environment and energy consumption. In this study, several traditional methods for determining the air infiltration rate were compared, and their accuracy in different scenarios was examined. Additionally, a method combining computational flow dynamics (CFD) with the Swami and Chandra (S-C) model was developed to predict the influence of the surrounding environment on the air infiltration rate. Two buildings in Dalian, China, were selected: one with a simple surrounding environment and the other with a complex surrounding environment; their air infiltration rates were measured. The test results were used to validate the accuracy of the air infiltration rate solution models in different urban environments. For the building with a simple environment, the difference between the simulation and experimental results was 0.86%–22.52%. For the building with a complex environment, this difference ranged from 17.42% to 159.28%. We found that most traditional models provide accurate results for buildings with simple surrounding and that the simulation results widely vary for buildings with complex surrounding. The results of the method of combining CFD with the S-C model were more accurate, and the relative error between the simulation and test results was 10.61%. The results indicate that the environment around the building should be fully considered when calculating the air infiltration rate. The results of this study can guide the application of methods of determining air infiltration rate. [ABSTRACT FROM AUTHOR]

Passive house standard buildings (PHSBs), characterized by exceptional airtightness, present a promising technology for attaining carbon neutrality by 2060. The level of building airtightness is closely associated with air infiltration, which significantly impacts building energy consumption. However, there has been insufficient analysis of air infiltration in highly airtight buildings across diverse climatic regions. The present study involves the numerical simulation of the air infiltration rate (AIR) in an airtight building under varying design conditions during winter and summer, followed by a comprehensive analysis of the corresponding energy demand associated with air infiltration. The simulation results indicate that the building's AIR ranges from 125 to 423 m3/h, with an average of 189 m3/h under summer design conditions, and from 40 to 344 m3/h, with an average of 198 m3/h under winter design conditions. The statistical findings demonstrate distinct distribution patterns for AIR and energy demand across various climatic regions, exhibiting significant variations in values. The discussion emphasizes the substantial heating load associated with air infiltration, even at a building airtightness level of 0.5 h−1, highlighting the necessity of considering its impact in the design of highly airtight buildings. Furthermore, it is recommended to establish specific airtightness limits for buildings in different climatic regions of China. This study offers theoretical guidance for the airtightness design of highly airtight buildings. [ABSTRACT FROM AUTHOR]

Heating and cooling in buildings accounts for over 20% of total energy consumption in China. Therefore, it is essential to understand the thermal requirements of building occupants when establishing building energy codes that would save energy while maintaining occupants' thermal comfort. This paper introduces the Chinese thermal comfort dataset, established by seven participating institutions under the leadership of Xi'an University of Architecture and Technology. The dataset comprises 41,977 sets of data collected from 49 cities across five climate zones in China over the past two decades. The raw data underwent careful quality control procedure, including systematic organization, to ensure its reliability. Each dataset contains environmental parameters, occupants' subjective responses, building information, and personal information. The dataset has been instrumental in the development of indoor thermal environment evaluation standards and energy codes in China. It can also have broader applications, such as contributing to the international thermal comfort dataset, modeling thermal comfort and adaptive behaviors, investigating regional differences in indoor thermal conditions, and examining occupants' thermal comfort responses. [ABSTRACT FROM AUTHOR]

To bring research and teaching together in engineering education, the term scholarship can be categorized into four types: research scholarship, applied research scholarship, integrative research scholarship, and teaching scholarship. Linking traditional research and classroom‐oriented teaching scholarship is a common and recurring challenge for many academics and active involvement in the latest research developments would directly improve the quality of teaching. In the case of research‐teaching of a heat transfer course, the teaching methodologies integrating academic research offer a great experience for students to learn various heat transfer concepts in a limited time frame. From the view of the research‐teaching nexus, analytical solving methods introduced in textbooks are reasonable ways to apply the integrated teaching strategies, which is highlighted by their fast results and versatility. Furthermore, a complete analytical solution to the subject matter could provide the fundamental knowledge necessary to comprehend the behavior of the associated thermal systems. This article demonstrates an analytical solution to the problem of heat and mass transfer for spherical particles in an airflow field. This investigation elucidates the basic principles in combination with advanced mathematical knowledge learned and its application to frontier research to improve the teaching of heat conduction and enhance the understanding of students at an undergraduate or graduate level. It greatly improves the engagement of students, promoting the theoretical concepts in engineering applications. The introduction of the latest developments in analytical solutions to teaching activities in the classroom will undoubtedly enhance the motivation and the horizon of students. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) methods are being increasingly used for predicting airflow fields around buildings, but personal computers can still take tens of hours to create a single design using traditional computing models. Considering both accuracy and efficiency, this study compared the performances of the conventional algorithm PIMPLE, fast fluid dynamics (FFD), semi-Lagrangian PISO (SLPISO), and implicit fast fluid dynamics (IFFD) in OpenFOAM for simulating wind flow around buildings. The effects of calculation parameters, including grid resolution, discrete-time step, and calculation time for these methods are analyzed. The results of the simulations are compared with wind tunnel tests. It is found that IFFD and FFD have the fastest calculation speeds, but also have the largest discrepancies with test data. The PIMPLE algorithm has the highest accuracy, but with the slowest calculation speed. The calculation speeds of the FFD, SLPISO, and IFFD models are 6.3, 3 and 13.3 times faster than the PIMPLE model, respectively. The calculation accuracy and speed of the SLPISO model are in between those of the IFFD, FFD and PIMPLE models. An appropriate algorithm for a project may be chosen based on the requirements of the project. [ABSTRACT FROM AUTHOR]

A fast thermal response numerical (TRN) approach for horizontal ground heat exchanger (HGHE) was developed and verified. The shape equivalence method was used to process the shapes of pipe cross section and elbows, reducing the meshing difficulty and the grid quantity of HGHE. A series of geometric equivalent quantization values were presented. Meanwhile, a semi-analytical equation was derived to reduce the sensitivity of the TRN model to the time step. The simulation results show the calculation speed of the TRN model is 38.98 times that of the Fluent model in the same case. Furthermore, long-term operations of HGHE were simulated, revealing that the soil around HGHE has good heat recovery capacity. [ABSTRACT FROM AUTHOR]

The pressure difference in buildings under natural state is usually below 10 Pa, and the air change rate at 50 Pa (ACH50) is often used to evaluate building airtightness. There is a dearth of research on air infiltration predictive model at different pressures in China. Moreover, the airflow coefficient (C), a key parameter for air infiltration, is necessary to determine ACH50. Based on prior experimental data, several methods including ordinary least squares (OLS), stepwise regression, partial least squares (PLS) and nonlinear fitting with independent variable screening methods, were employed to establish an airflow coefficient model. The determination coefficient (R2) and the variation coefficient of the root-mean-square error (CV(RMSE)) of these models were compared. The simulation results show that R2 of the airflow coefficient models for apartments and villas increased by a maximum of 25.9% and 2.3%, respectively, using PLS method. The improvement with nonlinear fitting was weaker. Based on K-P model, a conversion model between ACH50 and ACH4 was developed as an air infiltration predictive model under natural state. Blower door and tracer gas tests were conducted to verify the conversion model. The expected error was approximately 10%, which may be caused by measurement errors and shielding from surrounding obstructions. Further studies need to focus on obtaining more experimental data for building airtightness and developing a conversion model for high-rise residential buildings. [ABSTRACT FROM AUTHOR]

Combined district heating (DH) systems have at least one base load heat plant and several peak-shaving heat sources, which can be installed in the primary network or in the heating substations. This article studies the combined DH system with peak-shaving gas-fired boilers in heating substations, where the peak boilers can be connected to the heat exchangers in series or parallel mode. We analyze the thermal balances for these two connection modes and obtain the analytical operational regulation formulas for them. Then we study the operational methods for each connection mode, considering the heat distribution control strategies in both primary and secondary networks. Adopted control strategies are (1) variable temperature (VT) control, (2) variable flowrate (VF) control, and (3) variable temperature and flowrate (VT-VF) control. The combinations of these three strategies in primary and secondary networks are compared in terms of pumping energy consumption. The results indicate that operational strategies should be phased into different periods according to whether the peak heating is needed or not. In addition, the pumping energy consumption for the parallel connection mode is less than that that for the series connection mode with the same operational strategy, and the VF control strategy shows better energy saving potential. [ABSTRACT FROM AUTHOR]

The building energy consumption per unit area continuously decreases in recent years so that the ground-coupled heat pump system (GCHPS) with the horizontal ground heat exchanger (HGHE) no longer requires excessive underground area when they are applied to buildings. This phenomenon contributes to the popularity of the horizontal GCHPS. In this context, a simulation model of the horizontal GCHPS is developed to investigate their main design factors from the economic point of view. Taking the annual cost of GCHPS as the evaluation index, the orthogonal experiment design (OED) method and the analysis of variance (ANOVA) are applied to determine the influence degree of each factor on the economic aspects of the GCHPS. Then the control variable method is employed to analyze the effect of each factor on the performance and the economy of the GCHPS. The results of the present study show that the main affecting factors of the problem are the pipe length, pipe spacing, buried depth and pipe diameter of HGHE. Moreover, it is found that the flow rate of the heating medium has negligible impact on the HGHE. It is concluded that these factors in the order of importance are the pipe spacing, pipe diameter, pipe length, buried depth of the HGHE and the flow rate of the heating medium. Increasing the aforementioned parameters in accordance with the order of significance can improve the performance and reduce the operational expense of the horizontal GCHPS, but it increases the overall cost of the system. [ABSTRACT FROM AUTHOR]

The air-tightness performance of residential buildings in China is not fully investigated. This study intends to investigate the air-tightness performance of an ultra-low energy building in a cold area of China. The air-tightness of the building envelope was measured using blower door method and the whole year air infiltration of the building was simulated by a multi-zone network airflow model based on the air-tightness test results. A thermal infrared imager and a smoke pencil were used to find out the typical air leakage places in the building envelope. The leakage areas of the typical air leakage places are found by measuring the whole building and then sealing the corresponding component and determining the reduction in the building effective leakage area. Test results show that the air change rates of the building at the pressure difference of 50 Pa (ACH50) under the depressurization and pressurization modes are 0.5 and 0.49 h−1, respectively. Simulations show that the air change rate of building under the weather conditions of Dalian changes from 0 to 0.12 h−1with an average of 0.05 h−1. The typical air leakage places of the building were the reserved holes in the building envelope, the junctions of the windows with the walls, the deformation parts of the outer windows and doors, and the joints and vents that imprecisely sealed. The exhaust vents were found to be the most significant source of leakage among the tested typical air leakage places. [ABSTRACT FROM PUBLISHER]

This article describes the use of FLUENT software to simulate the heat transfer performance of U-tube heat exchangers in the ground source heap pump using the backfill materials of shape-stabilized phase change materials and crushed stone concrete. In this study, the shape-stabilized phase change material is a mixture of decanoic acid and lauric acid with the following mass concentration compositions: decanoic acid = 60%, silica = 10%, and expanded graphite = 6%. The mixture of shape-stabilized phase change material has a coefficient of thermal conductivity of 1.528 W/(m·K) and a latent heat of 109.2 kJ/kg. From the results of a 12-h simulation of the heat transfer dynamics, the heat exchange for a unit borehole depth of backfilling with shape-stabilized phase change material is 1.223 times the heat exchange for a unit borehole depth of backfilling with crushed stone concrete. In addition, the thermal influence radius of the backfill materials of shape-stabilized phase change material is 0.9 times of that of crushed stone concrete. As a result, under the same area of the buried pipes region, the shape-stabilized phase change material backfill can achieve a heat exchange 1.359 times that of crushed stone concrete backfill. Meanwhile, using shape-stabilized phase change material could contain the sustaining decline in coefficient of performance of heat pump at refrigerate condition to a certain extent and the appropriate physical parameters of phase change materials are also crucial. [ABSTRACT FROM PUBLISHER]

Chinese Kangs are widely used for home space heating in rural residences. However, the energy efficiency of a traditional Kang is less than 20%. Thus, the hot-wall Kang is gradually becoming popular in Jilin, Heilongjiang and Inner Mongolia of China because of its higher energy efficiency, comfortable indoor thermal environment and flexibility of application. The hot-wall Kang has three operation modes. The heat transfer model of Kang in previous studies was developed based on the three assumptions, which include the uniform Kang surface temperature, the neglect of the radiation effect of gas and the thermal storage of ash soil layer. However, the model of hot-wall Kang in this paper was improved with respect to the three assumptions, which were discussed in this paper. Then, the model was validated by experiments and applied to optimize the thermal performance of the hot-wall Kang. The results showed that the simulation results were in good agreement with the measurement results. Furthermore, based on the verified model, the better thickness and material of the cover board were found to be 0.06 m and foam concrete, respectively. [ABSTRACT FROM AUTHOR]

To examine thermal comfort and the corresponding physiological responses in non-uniform and dynamic indoor thermal environments, this article presents the investigation of thermal sensations and skin temperatures during step changes between the ambient environment and the workstation where local ventilation devices supplied air motion around the subjects’ heads. Twenty-three lab tests with human subjects were conducted to provide summer cooling in a controlled-environment chamber. Overall thermal sensations and skin temperatures were collected and analyzed. Data collected as subjects stepped between the ambient environment and the controlled-environment workstation displayed hysteresis and overshooting. That facial skin temperature correlates with thermal sensation provides a causal explanation of the overshooting and hysteresis. Further, the minimum change on facial skin temperature required to register a just-noticeable difference on thermal sensation was calculated to explore the correlation between facial skin temperature and overall thermal senation. In conclusion, thermal sensation data provide a sound quantifiable foundation for comfort-positive non-uniform indoor thermal environments. Facial skin temperature explains thermal sensation's changing characteristics during step changes in non-uniform thermal environments under varying local cooling methods. [ABSTRACT FROM PUBLISHER]

Chinese kangs are widely used by 175 million people for sleeping and home heating in rural Northern China. However, there are lack of some basic and critical studies on heat transfer and smoke flow characteristics of the kangs, which definitely hinder the development of Chinese kangs. This study presents an experimental assessment on a typically elevated Chinese kang. The heat gain, heat storage, and the heat release performance of the kang body are investigated, respectively, by combining the test data and theoretical analysis. The main results show that the smoke temperature at the inlet face of the kang flue varies within 250°C–600°C as the stove works for the most times. The smoke velocity in the kang flue is about 0.1 m/s–0.4 m/s, and the flow status is determined to be turbulent. The heat exchange between the smoke and the kang plates is mainly by natural convection. The surface temperature of the upper kang plate has significant temporal variation, and its distribution at the center part is reasonably uniform. The radiative heat from the kang plates plays a big role in the total heat release, accounting for 60.6% for the upper plate and 83.3% for the lower plate. [ABSTRACT FROM AUTHOR]

This study proposes to use gas-fired boilers as peak shaving heat sources in heating substations due to their capability to increase the reliability, flexibility and heat capacity without the need to change the district heating network (DHN). However, the design and operational requirements with different connection modes for this kind of DH system are still not clear. This paper presents a systematic study on this kind of DH system, analyzes the connection modes of series and parallel connections between the gas-fired boilers and the heat exchangers. For each connection mode, we figured out the thermal balances and obtained the design and operational parameters including the supply temperatures of the heat exchangers, gas-fired boilers and their variations under different network temperature levels and the base load ratios (β). Under the series connection mode, the design supply temperature of the heat exchangers has no relation with the design peak shaving flow ratio (ω′); it decreases linearly along with smaller β, and the decreasing slope is higher with bigger temperature difference (Δt) of the DHN. However, the design supply temperatures of gas-fired boilers increase linearly when β and/or ω′ are smaller, and the increasing speed is proportional to Δt. For the parallel connection mode, the design supply temperatures of the heat exchangers and gas-fired boilers are all affected by β, ω′ and Δt. The former decreases when β and/or ω′ are smaller, while the latter increases at the same time. Finally, the design peak shaving flow ratio ω′ are determined for the peak boilers with series and parallel connection modes. The study provides a theoretical basis for the design and operation of the DH system with peak heating boilers in substations in order to reach a lower investment and higher efficiency. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses the theme of the issue, topics discussed at the 8th International Cold Climate HVAC Conference 2015, heating and ventilation systems in cold climate.