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[Display omitted] • Definition and indicators of the local hotspots are clarified. • The main problems of weak airflow distribution are deeply analyzed. • Thermal management technologies are summarized by different scales for guidance. • Current limitations and future trend of hotspots elimination methods are discussed. The data centers consume a significant amount of energy, with cooling demand accounting for roughly 40% of the total energy usage. The primary reason for this is the presence of the local hotspots. To eliminate these hotspots, the standard approach is to lower the set point temperature of the whole computer room air conditioner (CRAC), resulting in overcooling and energy waste. This study provides an overview of the recent research on local hotspot management strategies, with a focus on the overheated servers as the most likely location of hotspots. To quantify the hotspots, this study provides a clear definition and summarizes the indicators from different aspects. It analyzes the correlation between the inlet and outlet air temperature and the overheating issues, which is often caused by high server loads or poor airflow distribution. And the most fundamental manifestation of the hotspots is hot air recirculation. This study analyzes potential solutions, such as optimizing airflow distribution and shortening the cold airflow path through design, control, and application. Additionally, the study discusses the limitations of the recent hotspots elimination research and proposes future perspectives. The aim of this review is to provide helpful knowledge on local hotspot elimination in the data centers, with consideration for integrated thermal and airflow distribution management strategies. The conclusion may assist in designing, operating, and retrofitting energy-efficient data centers in practice. [ABSTRACT FROM AUTHOR]

The falling-film technique is frequently applied in air-conditioning systems owing to its high energy efficiency. Circular tubes are typically used for falling-film evaporation, whereas other types of tubes, such as half-oval tubes, have rarely been investigated. This study aimed to examine the temporal and spatial distributions of a liquid film around a half-oval tube through experiments and numerical simulations. In the experiment, the film thickness over the half-oval tube was measured using a laser-induced fluorescence technique at wind speeds varying from 0 to 2 m/s and liquid Reynolds numbers ranging from 368 to 800. Meanwhile, transient simulation was utilised to assess the effect of tube type on the generation law and distribution characteristics of falling-film at length–width ratios (e) from 1 to 5. The modelling approach and numerical methods were validated using experimental results. Experimental results confirmed that airflow could evoke a shear force on the surface of liquid film to reduce and increase the film thickness in the 0.500–0.778 and 0.111–0.444 circumferential dimensionless location, respectively. The location of the axial minimum film thickness moved in opposite directions in the upper and lower parts. Meanwhile, the film thickness increased with the liquid Reynolds number, causing the thinnest point of liquid film to shift towards the liquid column. In contrast, a larger e accelerated the liquid film flow such that the film became thinner and the thinnest point of the liquid film moved away from the liquid column. The average film thickness of the four half-oval tubes was approximately 4.26–15.91% less than that of the circular tube. These results provide a reference for half-oval tubes used for falling-film evaporation in evaporative condensers. [ABSTRACT FROM AUTHOR]

• Wind towers incorporated to a greenhouse to provide wind driven natural ventilation. • Natural ventilation performance of the wind towers was assessed by CFD simulations. • CFD model was validated by flow visualization, point measurement, and PIV measurement. • At a wind speed of 3 m/s, the wind towers provided the recommended air change rate. • At a wind speed of 3 m/s, air velocity at crop height was within recommended values. In this study, the air change rate and airflow distribution inside a greenhouse equipped with wind towers were analyzed using Computational Fluid Dynamics (CFD) simulations, considering different wind speeds (1–5 m/s) and incident angles (0–45°). The validation methods included smoke visualization, hot wire velocity point measurements, and Particle Image Velocimetry (PIV) measurements. The visualized and simulated flow regimes exhibited fair agreement. The average discrepancy between the hot wire velocity point measurements and simulated results was about 7.96%. The predicted vector fields in the inlet and outlet wind towers demonstrated good qualitative agreement with the corresponding PIV measurements. The discrepancy between the predicted and measured maximum air velocity in the inlet tower was 15%, while it was 3% in the outlet wind tower. At an external wind speed of 3 m/s and normal incidence angle, the average velocity of the airflow entering the greenhouse was 0.65 m/s (about one air change per minute), while the average air velocity in the greenhouse was 0.44 m/s. The average air velocity inside the greenhouse at a crop height (1 m) ranged from 0.3 to 1.8 m/s, which is within the optimum range of recommended air velocities for greenhouses. [ABSTRACT FROM AUTHOR]

This paper investigated the cooling performance of a high-efficiency dew-point evaporative cooler with optimised air and water flow arrangement using the combined experimental and numerical simulation method. The experimental results showed that the wet-bulb efficiency of the dew-point evaporative cooler was increased by 29.3% and COP was increased by 34.6%, compared to the existing commercial dew point air cooler of the same capacity. An improved two-dimensional, multi-factor engaged numerical model which can scale up and optimize the size and capacity of the cooler was developed. The numerical predictions agreed well with the experimental results, indicating that the cooling rate of the dew-point evaporative cooler is influenced by the dew-point evaporative cooler structure. The cooling efficiency of the dew-point evaporative cooler with corrugated plates is more than 10% higher than with flat plates and the cooling efficiency of the dew-point evaporative cooler with the actual flow arrangement is only 62%–67% that of a dew-point evaporative cooler with an ideal counter-flow arrangement. The cooling efficiency can be improved by increasing the channel length and the air entrance length, and decreasing the channel width and channel gap within a reasonable range. [ABSTRACT FROM AUTHOR]

• A database covering three different localized airflow systems is built. • Eleven machine learning models are examined for individual thermal sensation prediction. • Air temperature is the major contributor to TSV using global sensitivity analysis. • The C5.0 model has better performance (82.3%) to predict TSV with 8 features. • Outcomes benefit for evaluation and application in buildings to energy savings. Although local air movement acts as a critical factor to enhance human thermal comfort and energy efficiency, the various factors influencing such movement have led to inconsistent publications on how to evaluate and design localised airflow systems in practice. This study aims to identify the main impacting factors for a localised airflow system and predict a cooling performance based on machine learning algorithms. Three typical localised airflow forms, i.e. an isothermal air supply (IASN), non-isothermal air supply (NIASN), and floor fan (FF), were deployed. The experiments were conducted under a variety of temperature/humidity/local air velocity conditions in a well-controlled climate chamber, and a database including 1305 original samples was built. The primary results indicated that a classification tree C5.0 model showed a better prediction performance (83.99%) for a localised airflow system, with 17 input parameters in the model. Through a sensitivity analysis, 8 feature variables were quantified as having significant main effect responses on subjects' thermal sensation votes (TSV), and three environmental factors (temperature, air velocity, and relative humidity) were identified as having the most significant effects. Using the 8 sensitive factors, the C5.0 model was modified with 82.30% accuracy for subject TSV prediction. A tree model demonstrating the decision rules in the C5.0 model was obtained, with air velocity (=0 m/s, >0 m/s) as the first feature variable and root node, and temperature (⩽28°C, >28°C) as the second feature variable and leaf node, respectively. The outcomes that provide the most influential variables and a machine learning model are beneficial for evaluating personal thermal comfort at individual levels and for guiding the application of a localised airflow system in buildings. [ABSTRACT FROM AUTHOR]

Highlights • A modular PCM-air heat exchanger for free cooling of buildings has been proposed. • Narrow air flow channels result in a higher cooling potential and a faster charging process. • Thermal comfort period provided by the system during the discharging phase is not affected by the air channels height. • Inlet air temperature and flow rate have a significant impact on the PCM charging and discharging performance. Abstract The use of phase change material (PCM) as energy storage of cooling during the night-time to be retrieved during the daytime is one of the sustainable strategies for cooling buildings. Application of this strategy in hot climates is scarce, and the majority of published work has been conducted in moderate and continental climates. Therefore, in the present work, a modular PCM-air heat exchanger appropriate for buildings application in hot-arid regions has been investigated, utilising commercial paraffin-based RT28HC PCM modules. The thermal performance of the proposed system has been investigated under various operating conditions for different PCM modules arrangements. The results confirmed that a compact TES unit with narrow air flow channels has a better thermal performance, resulting in 10–14% reduction in the charging time, whilst this has a negligible impact on the comfort time during the discharging period. The results have shown that the proposed system is capable of operating satisfactorily under hot-arid climate conditions, and substantial energy savings are achievable. [ABSTRACT FROM AUTHOR]

Abstract While vertical farming can promote sustainable living and mitigate urban heat island, vegetation could worsen the cross natural ventilation due to additional drag force on air flow. This study aims to investigate the impact of vertical farming on ventilation performance that is important to the thermal comfort especially at tropical/subtropical cities. The Computational Fluid Dynamics (CFD) simulation was first validated against the wind tunnel experiment in the street canyon with tree planting. The vegetable was modelled as porous medium in CFD simulation. In the parametric study, six configurations of facades module were investigated with respect to the vegetable block ratio, arrangement, and vegetable species. The results indicate that the natural ventilation performance is highly affected by the block ratio of vegetable. When three forth of the façade is covered by vegetable, i.e. block ratio of 0.75, the natural ventilation of the façade is very limited, with minimum leeward wind speed of 0.2m/s for incoming air flow of 2.0m/s. For the façade with a block ratio of 0.5, half of incoming air flow, i.e. minimum wind speed of 1.0m/s, can reach the near field downstream of the façade to promote indoor thermal comfort. Therefore, in the design process of the vertical farming, the block ratio of vegetable should be carefully determined regarding the ventilation performance. Furthermore, the natural ventilation with the same block ratio of vegetable could also be improved by appropriately modifying the vegetable arrangement and vegetable species. This study provides important understandings on vertical farming to enable architects to make the evidence-based decision in the architectural design. [ABSTRACT FROM AUTHOR]

Abstract To reduce the energy consumption for fresh air handling, a novel fresh air pre-handling system that fully exploits the shallow energy to precool and preheat fresh air is proposed in this study. The model of a typical all-air system with a pre-handling system is built on the TRNSYS platform. The energy saving potential of this fresh air pre-handling system is simulated based on the diverse climate of China. The results show that the ratios of the cumulated heat transfer capacity of the fresh air pre-handling system to the annual total of cooling and heating load range from 35% to 45% in the temperate zone and the subtropical zone, such as Shenyang, Beijing, and Shanghai, while the ratio in the tropical zone is approximately 10%. The energy saving rates are approximately 30% in most climate zones, but less than 5% in Guangzhou, the tropical climate zone. Moreover, the payback periods are within 4 years in the temperate and subtropical zones. However, the system is not economical in the tropical zone. All these results indicate that the fresh air pre-handling system with shallow geothermal energy is quite promising in most climate zones except in the hot summer and warm winter region with a tropical climate. [ABSTRACT FROM AUTHOR]

Highlights • Experimental tests of five IEC configurations are carried out. • Performance significantly depends on system configurations and water flow rate. • Highest effectiveness occurs in case of horizontal orientation of plates. • Lowest effectiveness occurs with water and secondary air supplied from the bottom. Abstract The indirect evaporative cooler (IEC) can be effectively used to increase energy efficiency and reduce energy consumption of HVAC systems. In particular, such system can be suitably adopted in data center applications, where the design indoor temperature can reach 45 °C, according to recent ASHRAE standards. It is well known that IEC performance can be significantly increased by an effective secondary air humidification process. In particular, the system should be designed in order to obtain an optimal water distribution on heat exchanger plates. In this paper, five different water nozzles and airflows arrangements of a IEC system based on a cross flow heat exchanger are experimentally investigated. The system is designed to have a limited water consumption (water to secondary air mass flow ratio between 1.4%–4%) and performance are measured in different operating conditions. Results show the highest wet bulb effectiveness (up to 82%–84% in the investigated conditions) is obtained in two configurations: (i) Horizontal orientation of heat exchanger plates; (ii) Vertical orientation of heat exchanger plates and water/secondary air supplied from the top. [ABSTRACT FROM AUTHOR]

Highlights • Influence of temperature fluctuations was examined in a human subjective experiment. • Generated airflows had distinct cooling effect on subjects. • Study indicates that sensation of draught was influenced by airflow temperature fluctuations. Abstract Besides air velocity, turbulence intensity and air temperature there are also other factors, which influence human thermal response to air movement. In this study, the impact of temperature fluctuations in airflow on human thermal sensation and perception of draught was examined. For the purposes of the study an air supply unit was designed for generating airflows with temperature fluctuations and used in a subjective experiment. The experimental study indicates that temperature fluctuations possibly influence the human perception of air movement with a distinct cooling effect. At high values of frequency and amplitude fluctuations a large discrepancy was found between predicted and measured values of draught discomfort. [ABSTRACT FROM AUTHOR]

Abstract Low temperature radiant heating systems are widely used in buildings being advantageous both from energy use and thermal comfort point of views. However, attention should be paid to asymmetric radiation especially in the case of wall heating. The aim of our research was to analyse the perception of thermal asymmetry in combination with different air velocities. A series of measurements were carried out in controlled environment involving 20 subjects (10 female, 10 male). It was shown that the thermal asymmetry is perceived at low air velocities, but increasing the air velocity to 0.1 m/s, 0.15 m/s or 0.2 m/s the perception of air movement overwrite the perception of thermal asymmetry. The heat removed by convection by the same air flow and air jet velocity was different for women and men group. The higher decrease of the skin temperature in case of women (around 2 K) leads to thermal sensation votes under −0.5 (even though the air and mean radiant temperature were 24 °C). The responses of women and men group regarding draught perception were different as well. [ABSTRACT FROM AUTHOR]

Highlights • The art on airflow distribution and management in data center is reviewed. • Experimental and numerical investigations of several typical cases are summed. • Energy efficiency of air distribution must be based on the reliability of data center. • HACS is a promising air management system due to its flexibility and extendability. • Improvement methods of vertical airflow uniformity needs to be developed. Abstract Rapid expansions of high-density data centers have been triggered worldwide owing to the high demand of cloud computing over the past decade. The airflow distribution and management have great association with the thermal performance of the typical underfloor air distribution (UFAD) data center. Therefore, numbers of configurations and methods have been proposed to improve the thermal performance of data centers with various operation conditions. This paper reviews the ventilation configurations of data center and presents the geometric effects of underfloor plenum on airflow. The experimental and numerical investigations on typical cases as well as the relevant parameters are also summed up. Various air management methods including cold aisle containment system(CACS), hot aisle containment system(HACS) and vertical exhausted duct system(VEDS) are analyzed on the benefits and limitations. Based on the enormous amount of research on the traditional UFAD system with hot aisle/cold aisle (HA/CA) arrangement, it can be concluded that the practices of data centers have a tendency of being more flexible and extendable, while the literature on the corresponding cases which applied HACS or other air distribution systems remains scarce. Moreover, beside the improvement of the airflow uniformity along the cold aisle, methods for enhancing the airflow uniformity along the height direction are also encouraged to be developed. [ABSTRACT FROM AUTHOR]

Highlights • A counter-flow heat pump driven liquid desiccant dehumidification system is tested. • There exists an optimal solution flow rate for the system and COP sys can be 6.5. • Appropriate air inlet parameters will have favorable effects on system performance. • Suitable supplementary water capacity is proposed to improve system performance. • COP sys of the new system can be 30% higher than the previous cross-flow system. Abstract A counter-flow heat pump driven liquid desiccant dehumidification (HPLD) system is considered as an energy-efficient approach for the humid air handling process, with advantages in terms of higher efficiency and simpler configuration. It is found that the adoption of a multi-stage heat pump cycle can improve the system performance, and then experimental tests for the system performance of the HPLD system with a two-stage heat pump cycle are investigated in the present study. The effects of solution flow rate, air inlet parameters including outdoor air and indoor exhaust air, and supplementary water capacity for the system on the system performance are elucidated according to the experimental results. It is found that the solution flow rate could affect the heat recovery performance between outdoor air and indoor exhaust air, and the performance of the heat pump. Thus, there exists an optimal solution flow rate for this counter-flow HPLD system, and the coefficient of performance of the system (COP sys) can be as high as 6.5 under the experimental condition. Besides, the increase of outdoor air inlet parameters and the decrease of indoor exhaust air inlet parameters with enough indoor exhaust air flow rate for the system have favorable effects on the system performance, due to the promotion to the heat recovery performance of the system. And more supplementary water capacity to remove the redundant heating capacity of the system would also improve the system performance mainly through lowering the condensing temperature. However, supplementary water capacity cannot be added too much for the system due to the dehumidification demand. Furthermore, the coefficient of performance of this counter-flow HPLD system is approximately 30% higher than that of a cross-flow HPLD system, handling more dehumidification demand. [ABSTRACT FROM AUTHOR]

Abstract In order to reduce the energy consumption for cooling in our buildings, the use of passive cooling solutions is necessary. One of these solutions is natural ventilative cooling, where airflows generated by single-sided natural ventilation, until today have mainly been calculated from the De Gids & Phaff equation in the European Standard EN 15242:2007. In the revised standard EN 16798-7:2017, a new version of the equation for single-sided natural ventilation is released. The work in this paper will compare the results from the new equation with earlier equations for single-sided ventilation and hold them up against wind-tunnel measurements, full-scale measurements and CONTAM calculations to clarify whether and why the new equation is to be preferred for future design solutions for single-sided natural ventilation and ventilative cooling. Due to the implementation in calculation standards and regulations, the new calculation model should underestimate rather than overestimate the airflow rates, so as to remain on the safe side when estimating ventilative cooling potential. The work in this paper concludes that the new simple direct calculation model in EN 16798-7:2017 predicts the airflows through windows in a more conservative way than earlier equations, by representing an average of the airflow rate in the building that is generally on the safe side. The accuracy of the EN 16798-7:2017 equation was found by comparison to wind tunnel measurements to be 29% but with underestimations in 88% of the cases investigated. For the CONTAM calculations, it was found that the use of the new EN 16798-7:2017 equation (with room based height for the stack effect) slightly underestimates the airflow rate as desired, as soon as the temperature difference across the opening is above 0°C. Based on the comparisons presented in this paper, the authors consider the new calculation model in EN 16798-7:2017 well suited for the use in calculation standards to integrate natural ventilative cooling effects from single-sided ventilation. [ABSTRACT FROM AUTHOR]

• A gray-box energy model for residential ACs is developed, calibrated, and validated. • State variables (evaporation and condensation temperatures) are keys in the model. • Heat transfer at condenser and evaporator correlate state variables to model inputs. • Seven performance properties functions are identified for model calibration. • The cooling capacity and electrical power input can be accurately predicted. Energy models for vapor compression refrigeration in residential air conditioners have been developed through white-box, gray-box, and black-box methods in decades. However, existing white-box and gray-box models require complicated equations with detailed geometries while black-box models require substantial experimental data. This paper aims to develop and validate a simple gray-box steady-state energy model without the need for detailed geometries, which can accurately predict the cooling capacity and electrical power input based on outdoor and indoor air conditions, and supply airflow rates. First three state variables, including the evaporation and condensation temperatures, and refrigerant mass flowrate, are applied to develop the energy model and are solved by three physical equations, including the energy conservations at the evaporator and condenser, and the refrigerant volume-mass flow correlation of the compressor. Secondly, seven performance property functions related to three state variables and three physical equations are identified and calibrated by simple temperature and power measurements. Finally, field experiments are conducted on a residential air conditioner to calibrate these performance property functions and validate the developed model. The validated results reveal the model can accurately predict the cooling capacity and electrical power input, with the normalized root mean square errors of 2.3% and 0.87% respectively. [ABSTRACT FROM AUTHOR]

Horizontal-arrangement parallel-path hybrid cooling towers (PPHCTs) are advantageous owing to their low construction cost, high cooling capacity, and broad application prospects. The dry and wet sections of these towers have separate air inlets but share the same air outlet, which is equipped with a fan. Air is delivered to the tower by the fan. The air flow distributions in the two sections mainly determine their respective cooling capacity and the entire tower cooling capacity. Traditional model usually adopted assumed or experimental air flow rate, which leads to low prediction efficiency. To solve this problem, in this study, an air distribution model considering fan performance curve and system resistance curve is proposed for calculating the exact air flow rate based on the configurations of the tower. In addition, the influence and contribution ratio of row numbers and transversal pitch in wet and dry sections on the air flow rate in each section is analyzed, which is beneficial for optimal design in the engineering application. Adding more rows or reducing the transversal pitch in the wet and dry sections increased the pressure drop on the same side, pressure drop on the other side, and overall pressure drop. Increasing the flow resistance coefficients in any of the wet or dry sections decreased the air flow rate on the same side and the overall air flow rate, while the air flow rate on the other side increased. The number of rows in the dry section significantly affected the air flow rate ratio between the dry and wet sections and the overall air flow rate. The contribution ratio of the number of rows in the dry section to the overall air flow rate was 76.75%, while to ratio of air flow rate between the dry and wet sections was 61.73%. The results of this study can be used for precise performance prediction and optimal design for the PPHCTs. [ABSTRACT FROM AUTHOR]

• To reflect the impact of indoor units on system performance, a novel index and model were proposed. • Simulation and experimental results validated the proposed performance model. • Proposed index was applied in a field test in an office and a residential building. In the context of a large market share, enhancing the actual performance of variable refrigerant flow (VRF) air-conditioning systems is of considerable importance. The operating states of indoor units (IUs) significantly influence the energy efficiency of a VRF system with multiple indoor terminals. Therefore, it is challenging to address accurate and concise representation of the operational characteristics of IUs for analyzing their impact on system performance. This study explored a novel performance index called capacity utilization rate (CUR) to illustrate the effect of IUs on system performance and developed a performance model based on this index. Simulation and experimental results demonstrated that energy efficiency and evaporating temperature decrease with a reduction in CUR under specific ambient temperatures and part-load rates. The proposed performance model was applied to real buildings in field tests to examine the operational characteristics of the VRF system. This research offers valuable insights for system design, performance simulation, and performance evaluation of VRF systems. [ABSTRACT FROM AUTHOR]

Row-based cooling has been recommended for cooling scenarios with high power densities. Existing studies on row-based cooling have mostly focused on good results, and the effectiveness and limitations of it need to be evaluated to optimize it. In this study, some airflow problems were observed by a field experiment for a data center with row-based cooling. Subsequently, a simulation corresponding to this data center was performed to fully learn and verify some airflow conditions below those expected, such as hot spots in some racks and vortex airflow, where the Supply Heat Index of modules 1 and 2 are 0.37 and 0.31. To further determine the airflow characteristics of row-based cooling, a comparative simulation of airflow distribution of row-based cooling and raised-floor cooling was performed. Finally, the effectiveness and limitations of row-based cooling were presented. The results showed that row-based cooling only decreases the Return Temperature Index by 0.4%. The limitations of it include vortex airflow, hot spots in head racks and adjacent racks of in-row coolers, and interaction between different modules; they are easy to occur in row-based cooling and some improvement suggestions are presented in future work. [ABSTRACT FROM AUTHOR]

An excellent way to obtain a detailed description of the air flows and temperature field in a zone is to perform accurate Computational Fluid Dynamics (CFD) simulations. Unfortunately, this is often prohibitive due to the powerful resources that are required, and the large computational times. As a consequence, several intermediate models between CFD and the standard well-mixed models have been proposed over the years. These are known as zonal models, and they aim at delivering sufficiently accurate predictions of the thermal comfort in a room, for long periods (months or even years), and with substantially shorter computational times. However, none of these models has yet been implemented in a building performance simulation (BPS) tool. In this work, we have developed and implemented a BLOCK zonal model [1,2] within the IDA ICE (BPS) software. A multi-node 1D model for the prediction of vertical temperature gradients is used, together with flow element theory and an appropriate algorithm for the estimation of view-factors in non-convex geometries with obstacles. The paper presents the theoretical background of the model along with advice on its range of applicability. Finally, the model is validated against several test cases, showing its suitability in predicting the thermal stratification. [ABSTRACT FROM AUTHOR]

• Confirms lack of maintenance for ventilation in French dwellings. • Assess the durability of humidity sensors in ventilation components. • Correlate maintenance level and limitation of airflows for ATDs. Humidity-based DCV systems have been widely used in France for 35 years and are considered as a reference system, including for low-energy residential buildings. The on-going "Performance 2" project delivers feedback from 13 years of on-site operation in twenty-two social housing apartments. The initial project was a large-scale monitoring on thirty new occupied apartments in two buildings in France equipped with this DCV system, which extended from 2007 to 2009. Thirteen years later the buildings are re-visited, and the monitoring system is turned back on with the intention to assess the ventilation system performance after a prolonged in-situ functioning period. Then, the components have been collected and tested in laboratory facilities: as collected, after cleaning, and finally after a light rehabilitation. Despite largely insufficient levels of maintenance, 100 % of the exhaust units and air inlets not purposely degraded by the occupant, still reacted as expected to humidity. A good relationship was found between the visual maintenance level and the limitation of maximum airflow for each Air Terminal Device (ATD): an average limitation of −10.6 m3/h has been evaluated for ATDs presenting a "Bad" level of maintenance whereas the average limitation was only −2.2 m3/h for ATDs showing a "Good" maintenance state. Finally, after cleaning and refurbishing, but without touching the hygroscopic sensor/actuator, the ATDs still meet the specifications and are very close to their original characteristics. [ABSTRACT FROM AUTHOR]

It was demonstrated in previous related experimental and modelling studies that an ASHP unit having a novel dual-fan outdoor coil (ASHP / DFOC) can help achieve evener frosting along airflow direction in the outdoor coil, leading to its better operating performances. To enable an ASHP / DFOC unit to efficiently operate at varying ambient conditions, an optimal control strategy for the experimental ASHP / DFOC unit was developed using a Generalized Regression Neural Network (GRNN) modelling approach, which is a variation to radial basis neural networks. A database for developing the GRNN model was established first, and a new coefficient of performance related index, which was the change rate of averaged COP (CRAC) was proposed after analysing the database. Then, based on the developed database and CRAC, a GRNN model was developed and validated, and then used to predict and search the optimal dual-fan operating modes when the experimental ASHP / DFOC unit was operated at different ambient air conditions. Finally, an optimal control strategy for the experimental ASHP / DFOC unit based on those identified optimal dual-fan operating modes was developed and experimentally validated. The experimental results demonstrated that the use of the developed optimal control strategy led to a higher heating efficiency, a longer frosting - defrosting duration and a fewer number of dual-fan switching for the experimental ASHP / DFOC unit, with its averaged COP improved by 9.9 % and 6.8 %, CRAC decreased by 17.1 % and 10.5 %, defrosting frequency reduced by 22.2 % and 12.5 %, and averaged frosting - defrosting duration extended by 32.8 % and 19.4 %, respectively, when compared to the use of traditional single-fan operating mode and a fixed dual-fan operating mode at varying ambient conditions. The study results can help achieve evener frosting of ASHPs with a higher operating efficiency and better feasibility at varying ambient conditions. [ABSTRACT FROM AUTHOR]

This study presents a holistic approach applied to assess the exploitation of renewable energy sources for design interventions in the early design phases in a consolidated urban environment. Concerning the cooling season, the approach implies set of environmental analyses focused on twofold assessments: (i) the use of renewable energy sources for active and passive strategies, (ii) the impact on outdoor thermal comfort of the technological solutions and cool materials installed on the buildings’ facades. From the definition of the local boundary conditions, preliminary climate analyses were conducted with dynamic simulation tools such as Ladybug and DIVA-for-Rhino , while numerical and computational fluid dynamic models, such as ENVI-met and OpenFOAM , were used to carry out microclimate and wind flow analyses. The approach is tested on two existing residential building blocks in a case study district in Bolzano (Italy). The assessment of several design interventions and building technological solutions have been studied: from the (i) addition of one-story volume on the existing buildings, to the (ii) creation of new green areas, and the (iii) installation of building integrated photovoltaic (BIPV), vertical greenery and double skin façade (DSF) systems on the building's façades. The results, divided into practice and policy implications, demonstrate that preliminary analyses play a relevant role to assess the exploitation of renewable energy sources to optimize the use of urban and building surfaces since the early design phases. High-albedo materials on the façades can counterbalance the loss of solar potential due to the overshadowing effect of the additional story. The combination of cool materials (e.g., white reflective plaster) and the increment of the buildings’ height could reduce by about 1°C the thermal discomfort registered during the high thermal peak during the day. Solar and urban airflow analyses allow optimizing the integration of BIPV in a DSF system; while the installation of green façade can reduce the air temperature locally by up to about 0.5°C. [ABSTRACT FROM AUTHOR]

Well-understanding indoor air movement with respect to openings in naturally-ventilated buildings is essential to provide healthy and comfortable indoor climate for livestock. This study investigated the effects of the sidewall opening configurations on internal airflow fields and air velocity characteristics within the animal occupied zone (AOZ). Eight cases with varied opening ratios and locations were tested under 8 m•s -1 free wind speed and wind direction perpendicular to the sidewalls. The ‘up-jet’ airflow pattern was observed when the opening ratio was no greater than 62.71% and the openings located beneath the eaves. Air went across the AOZ without circulating with the surrounding air when no sidewalls were installed below the AOZ height. Both air speed and turbulent kinetic energy increased when the opening was bigger with Pearson's correlation coefficients of 0.8 and 0.9 respectively, but the relationship between the opening size and the turbulence intensity was more complex. Uniform air speed distributions were observed in the AOZ with high sidewalls on bottom. By contrast, the air speed heterogeneity in the AOZ was found when sidewall heights were below the AOZ height. We conclude that care should be taken when using these kinds of opening configurations during extreme cold windy weather conditions. [ABSTRACT FROM AUTHOR]

In this paper we propose a novel and easily implementable model-based air balancing method for a ventilation system. The proposed method provides a well-defined form of balancing for a ventilation system, which can be effectively solved. The method follows three procedures: (i) mathematical modeling for duct system which is based on steady-state pressure balance; (ii) model parameters identification by supervised machine learning; (iii) determination of damper positions based on the model. The performance of this method is validated through testing in a duct testbed with five terminals. The results show that the final flow rates in all terminals match with the desired values with no more than 6.8% relative error. [ABSTRACT FROM AUTHOR]

Variable Air Volume (VAV) system is a typical time delay system with multiple variables, and it is difficult to build a dynamic response model for describing room temperature regulation process. This paper firstly proposes a novel model of dynamic response of room temperature based on the analytical solution of heat balance equation in VAV air conditioning zone. According to the solution, inertia time constant and magnification coefficient of room temperature response can be directly calculated by initial environmental parameters. The model is further extended to a Multi-Input Single-Output (MISO) model with airflow regulating actuators as input and room temperature as model output. Experimental studies are carried out to test practical supply airflow and room temperature response and corresponding model parameters are identified according to the measured data in the VAV experimental platform. The proposed identification method based on analytical solution is validated through simulation and compared with classical identification method. Results indicate that the proposed identification method could describe the room temperature dynamic characteristics of VAV system well, and it can be applied in control simulation and engineering application in future work. [ABSTRACT FROM AUTHOR]

In recent years, subway systems (rail transit) have become an increasingly significant means of urban transportation. Platform screen doors (PSDs) can play an important role in enhancing the thermal environment in subway stations. However, train-induced unsteady airflow results in unorganised ventilation at the entrances (supplying fresh air and causing heat exchange) and air infiltration at the PSDs (causing heat exchange) in subway stations with PSDs. In the present study, field experiments (in Xi'an, China) and numerical modelling were conducted to investigate the rate of air inflow at the entrances and the PSDs of subways. The accuracy of the model was verified using the results from field experiments. In addition, the effects of various factors such as the traffic density, the piston vent shaft at the station downstream location (PVSASDL), and the season were analysed. The simulation results showed that turning on the PVSASDL could reduce the rate of air inflow at the entrances to 29.2–93.8%, while that at the PSDs could be enhanced to 121.8–126.3% under different traffic densities. In addition, to explore appropriate control of the PVSASDL in winter, different outdoor temperatures were simulated for a traffic density of 12 pairs/hour. It was found that the temperature in the station could meet the standard requirements when outdoor temperatures were greater higher than −5   °C with either open or closed PVSASDL conditions. [ABSTRACT FROM AUTHOR]

Predicting the energy performance of household variable refrigerant flow (VRF) systems in the hot summer and cold winter (HSCW) region in China accurately is particularly challenging due to the frequent defrost operations of the VRF systems during winter. Hence, an improved energy model was developed to determine the energy performance of household VRF systems, taking into account the defrost operations. The energy model was validated by experiments and the energy performance of the VRF system for typical residential buildings in Chongqing, Changsha, Nanjing, and Shanghai was determined based on representative operation modes (full-time-full-space and part-time-part-space modes). The results indicate that the efficiency of the VRF system increases as the outdoor temperature decreases. However, the efficiency of the VRF system decreases as the part-load ratio decreases, which leads to variations in the cooling seasonal performance factor for the representative operation modes and cities. The heating seasonal performance factor is not only influenced by the outdoor temperature and part-load ratio distribution, but also defrost operations. Compared with the part-time-part-space mode of C1 and C2, the annual energy consumption for the C4 mode performs lower from 26.3% to 51.7% for typical residential buildings in the four representative cities. [ABSTRACT FROM AUTHOR]

Demand-controlled-ventilation (DCV) refers to a ventilation system with controlled air flow rate based on indoor air quality. DCV operates at reduced air flow rates during most of the operation time. Therefore, less energy is required for fan operation, compared to a constant-air-volume (CAV) ventilation system. Typically, DCV has a two-layer control with variable-air-volume (VAV) valves, and a fan speed control to maintain a constant-static-pressure in the duct system based on a pressure set point. However, this nominal design based fan pressure setpoint is higher than required when all VAV-valves are closed to a certain extent. Therefore, advanced pressure-reset (PR) control - resetting the pressure set point - potentially reduces fan energy use even further. This paper assesses the impact of fan control on both fan energy use and ventilation performance in DCV system of a densely occupied office. Results of a simulation model and realistic measurement setup are compared. The PR control, using air flow rate and VAV-valve position measurements as feedback, causes significantly reduction on fan energy use. These reductions compared to conventional DCV and CAV respectively, are approximately 10% and 72% in case of high occupancy and 50% and 93% in case of low occupancy. Largely, DCV with PR control is strongly considered, especially when occupancy is often expected to deviate significantly from the nominal conditions. Moreover, both simulations and measurements show that there is a clear trade-off between air flow rate deficit and fan energy use, when the fan energy use is lower, the air flow rate deficit is higher and vice versa. Furthermore, the results show that VAV-valve accuracy, characteristics and its lower operational limit hamper the ventilation system in achieving the predicted performance as in the simulation. [ABSTRACT FROM AUTHOR]

In this paper our objectives are to perform a numerical and experimental study of the velocity field in the area affected by a circular exhaust duct, to define the outline of flow separation area at its inlet, to come up with a reliable mathematical simulation of the separated flow at exhaust duct inlet, and to determine the effect of the duct inclination angle its serviced area. The stationary discrete vortex method has enabled development of an adequate and reliable technique for computation of separated flows at inlet of a local exhaust hood. We have studied airflow patterns around the exhaust duct using the discrete vortex method, CFD and natural experiment. Characteristic dimensions of the flow separation area at exhaust hood inlet have been determined with relation to the length and inclination angle of the hood. Shaping the exhaust duct to fit the resulting separation zone outline will enable savings of energy that would otherwise be wasted on overcoming local drag forces; furthermore, this will prevent escape of contaminants circulating in the separation area to the environment. Determining airflow velocity distribution patterns will facilitate the choice of the most efficient exhaust duct design to minimize the cost of contaminant removal. [ABSTRACT FROM AUTHOR]

Solar chimney has been primarily utilized for natural ventilation, but its application to smoke exhaustion was rarely explored. A 1:3 reduced-scale test platform with a dimension of 1.5 m × 1.5 m × 0.9 m (height) was used to optimize solar chimney under natural ventilation and smoke exhaustion, considering four influencing factors, including height of cavity inlet from the floor (0.2–0.8 m), cavity depth (2.5–17.5 cm), solar radiation (400–1200 W/m 2 ) and fire size (6.8–15.8 kW). Both natural ventilation and smoke exhaustion follow the same trend along the air inlet height and cavity depth, which confirms its viability on smoke exhaustion under fire condition without compromising the performance of natural ventilation. Experimental results suggested a chimney configuration of 0.5 m high air inlet and 12.5 cm cavity depth with optimized functions. External radiation shows obvious benefit on enhancing natural ventilation, while its influence on smoke exhaustion is limited. An empirical model was developed to predict the flow rate under normal and fire conditions. The outcomes of this study provide a technical guidance for the design of solar chimney under scenarios of both natural ventilation and smoke exhaustion. [ABSTRACT FROM AUTHOR]

Thermal comfort and emission efficiency are important factors when choosing heat emission systems in low energy buildings. In this study, we consider the context of northern low-energy buildings, and compare the three most popular heat emission systems: radiator, underfloor and air heating systems with upper distribution. With an analysis based on laboratory measurements performed in Tallinn, Estonia (Northern European climate), we determine the vertical temperature gradient and quantify heat emission losses in a typical low energy building with mechanical heat recovery ventilation. Compared to a reference ideal heater, ventilation-supplied air heating with upper distribution induced a vertical temperature gradient of about 1 K/m, which together with operative temperature variation increased the energy use by 9.9%. Regarding radiator and underfloor heating, the losses amounted instead to 2.3% and to 5.5%–7.9% respectively. Using our air and surface temperature measurements, we also verified experimentally the operative temperature variations previously determined for radiator and floor heating, and extended this concept to air heating. In conclusion, it is proposed to add operative temperature variation to the heat emission standard in order to enable fair comparison of heat emitters. Both vertical temperature gradient and operative temperature variations determined in this study provide a solid extension of the EN 15316-2:2017 methodology. [ABSTRACT FROM AUTHOR]

Large space building using side wall nozzle air-conditioning system may result in poor ventilation effectiveness for positions out of the reach of primary supply air. A secondary airflow device is proposed to be applied in such system to improve the uniformity of temperature and velocity distribution in the occupied zone under cooling condition. The characteristics of the secondary airflow device, including central-line velocity decay and jet trajectory model were investigated through experiments to provide fundamental data for the system design. The indoor thermal environment parameters were measured and compared between with and without the secondary airflow device system in a large space factory workshop conditioned by side wall air supply nozzles. Experimental results with the secondary airflow device showed that the vertical thermal stratification height slightly changed, with lower air temperature in unoccupied zone and higher temperature in occupied zone comparing to the cases without secondary airflow device. At occupied level, air diffusion performance index (ADPI) significantly improved, while the percentage dissatisfied (PD) due to draught decreased in the occupied zone. Air velocity uniformity at occupied level also significantly increased. The results of this study provide an exemplary reference for the design of the air distribution system in large-space buildings. [ABSTRACT FROM AUTHOR]

Experimental results of the airflow pattern for Active Chilled Beams (ACB) system are investigated in this paper, where the air velocity and turbulence intensity for the air jet near the ceiling are tested and recorded under both isothermal and non-isothermal conditions. Based on the results, the velocity profile along streamwise direction is found to be significant in analyzing air detachment from the ceiling. It is revealed that the Coandă effect can be enhanced by a high pressure drop of ACB terminal unit and impeded by the temperature difference between supply air and room air. The self-similarity for the air jet is observed to be feasible for a certain downstream distance where the vertical maximum velocity is within 1.25 slot heights. A comparison study has been conducted for two mathematical models describing the self-similarity with the experimental data. It turns out that Verhoff's model has an overall better performance than Schwarz and Cosart's model. The turbulence intensity, which tends to be larger for points with lower velocity, is higher in areas where the entrainment effect is stronger. [ABSTRACT FROM AUTHOR]

Though area in office buildings has expanded significantly in Hong Kong in the decade to 2013, increase in cooling energy use has been rather moderate. The factors and policy instruments that contributed to the impressive enhancement in energy usage efficiency are not available in published literature. Data of sixty-six office developments were examined to evaluate the role of policy instruments in bringing about the visible improvement. Numerical analyses reveal that use of chiller units with higher efficiency and fresh water cooling tower (FWCT) systems have contributed significantly to reduce cooling energy use of office space in Hong Kong. It is important to note that policies promulgated have played a key role in encouraging designers of office space to opt for energy efficient systems. The BEAM Plus certification for all public buildings has contributed the most (efficacy = 0.09) to the success in moderation of electricity consumption for cooling of office space. The FWCT scheme and the Building Energy Codes have had efficacies amounting to 0.076 and 0.026, respectively. Interestingly, the new OTTV requirement, used for regulation and monitoring of thermal performance of building envelopes, has had a negative rate of efficacy (0.018), implying that the government needs to review its appropriateness. [ABSTRACT FROM AUTHOR]

Previous studies have demonstrated a potential reduction in cooling load and improvement in comfort from the implementation of night ventilation. This paper describes the performance, in terms of indoor environmental conditions, of three buildings from both the U.S. and India that use night ventilation as their primary cooling method. The research methods used the following approach: (1) Assess the cooling strategy in relation to the adaptive comfort model; (2) Develop a hybrid model, using both first principle equations and the collected data, to predict the instantaneous air and mass temperatures within each building and use the model to assess performance of the cooling strategy; (3) Determine an optimized ventilation control strategy for each building to minimize energy and maintain comfortable temperatures. (4) Develop a statistical model using collected data to predict the window opening pattern for occupants of a building using natural night ventilation. The study yielded the following results: (1) The buildings in the mild climate are successfully keeping the indoor temperature low, but also tend to be overcooling; (2) The night ventilation strategy has very little impact on indoor conditions of the buildings in the mild climate; (3) The impact of night ventilation is less significant when there is low internal loads and heavy mass; (4) The building in the hot and humid climate is keeping the indoor temperature within the comfort bounds for 88% of the year; (5) The night ventilation strategy has advantageous impact on indoor conditons of the building in the hot and humid climate, but not enough to cool the space on its own; (6) Model predictive control has the potential to further improve the performance of night ventilation. (7) Window opening behavior for the building using natural night ventilation is most heavily dependent on indoor air temperature and mass temperature. [ABSTRACT FROM AUTHOR]

Due to vertically thermal stratification in indoor spaces, the cooling load calculation is always a challenge in the design of stratified air distribution systems (STRAD), which in turn is crucial to determine the supply air flow rate and the cooling load to be removed by the air conditioning system. In this paper, several cooling load calculation methods, developed in the past 20 years and focused on STRAD systems, were briefly reviewed. It attempts to clarify these methods in terms of their advantages, limitations and suitable ranges of applications. Furthermore, series of numerical simulations with a total number of 56 cases were conducted, and the applications of a novel cooling load calculation method in STRAD systems were investigated. The reliability of the method was validated for STRAD systems with separated locations of return and exhaust grilles, when adopted in three typical spaces with different building heights, namely a small office, a large terraced classroom and a terminal building. Databases of effective cooling load factors ( ECLF i ) for different heat sources distributed in the three spaces were obtained and presented, which can be conveniently used to calculate cooling loads. In addition, the influences of return grill height on the occupied zone cooling load as well as the energy saving potentials of STRAD systems were also clarified. The results presented in this paper are helpful for the design and optimization of STRAD systems. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive review of the open literature on motivations, methods and applications of linking stratified airflow simulation to building energy simulation (BES). First, we reviewed the motivations for coupling prediction models for building energy and indoor environment. This review classified various exchanged data in different applications as interface data and state data , and found that choosing different data sets may lead to varying performance of stability, convergence, and speed for the co-simulation. Second, our review shows that an external coupling scheme is substantially more popular in implementations of co-simulation than an internal coupling scheme. The external coupling is shown to be generally faster in computational speed, as well as easier to implement, maintain and expand than the internal coupling. Third, the external coupling can be carried out in different data synchronization schemes, including static coupling and dynamic coupling. In comparison, the static coupling that performs data exchange only once is computationally faster and more stable than the dynamic coupling. However, concerning accuracy, the dynamic coupling that requires multiple times of data exchange is more accurate than the static coupling. Furthermore, the review identified that the implementation of the external coupling can be achieved through customized interfaces, middleware, and standard interfaces. The customized interface is straightforward but may be limited to a specific coupling application. The middleware is versatile and user-friendly but usually limited in data synchronization schemes. The standard interface is versatile and promising, but may be difficult to implement. Current applications of the co-simulation are mainly energy performance evaluation and control studies. Finally, we discussed the limitations of the current research and provided an overview for future research. [ABSTRACT FROM AUTHOR]

In this contribution, a new model of switchable insulation element is introduced. This element essentially consists of a double glazing unit with a translucent insulating panel mounted inside. Switching of the U-value is achieved by control of an internal convective flow around the insulation panel. The element can be in an insulating state with a low U-value, or in a conducting state with a high U-value. First the new model of the element, based on numerous thermal, hydraulic and optical assumptions, is introduced. The airflow rate is calculated by balancing the pressure drops and the buoyancy driving force. The model is validated against U-value measurements, showing a reasonable accuracy. Finally, the model is used for a parametric analysis, where the influence of different thermophysical properties on the U-value and g-value of the element in insulating and conducting state is investigated. [ABSTRACT FROM AUTHOR]

A ground heat exchanger is the essential part of a ground source heat pump system. The soil temperature profile strongly influences soil properties and ground heat exchanger, which vary with time and space. The soil temperature profile is also a function of the heat transfer rate extracted from/or transferred to soil. Although there are several studies on the sizing and selection of ground heat exchangers, they either use the unchanged soil temperature obtained from meteorological data or do not run for long time periods to obtain a steady periodic soil temperature profile and, thus, over-predict the ground heat exchanger performance. The aim of this study is to obtain transient soil temperature profile of a parallel pipe horizontal ground heat exchanger by considering various system parameters with realistic boundary and operating conditions using meteorological and hourly building data. Experimental results have been obtained from a GSHP system established at Yıldız Technical University and compared with the results of numerical analysis. For a case study, the hourly required heating and cooling loads of a 200 m 2 office in Istanbul all year round are calculated by using HAP software. The fluid inlet temperatures equivalent to the hourly need for heating and cooling loads of office throughout the year have been simulated for a ten-year period in accordance with the different heat amounts extracted from soil or transferred to soil per unit pipe length. The effects of burial depth, pipe spacing and surface effects on soil temperature are also investigated. The horizontal and vertical temperature distribution in soil at the beginning, middle and end of heating and cooling seasons of first, fifth and tenth years are represented. Considering initial and operating costs, a reference function is defined as an optimization parameter. The effects of the increase rate in electricity prices, number of parallel pipes (NPT), burial depth, pipe spacing, pipe diameter and pipe length on reference function are investigated. [ABSTRACT FROM AUTHOR]

The transpired solar collector (TSC) is a low-cost technology for heating ventilation air for mainly for use in industrial and agricultural applications. Storing the excess energy generated during daytime in phase change material (PCM) could improve the economics of using TSCs. Since energy generated for storage could be increased by using a two-stage TSC (with a glazing) vs. a one-stage TSC, first, the thermal performance of the two configurations were compared. Then, performance of the PCM-based thermal energy storage (TES) unit coupled to a TSC was evaluated. At a suction velocity of 0.023 m/s, the one-stage TSC produced a 2 °C higher temperature rise and 8% higher efficiency than the two-stage TSC. The one-stage TSC was coupled to a TES unit packed with 80 kg of salt-hydrate type PCM (specific energy of ∼185 kJ/kg). When evaluated at four airflow rates, the TES unit stored between 76 and 107% of its theoretical heat storage capacity and provided tempered air 4 °C warmer than ambient air during nighttime. While residual energy (for daytime heating) increased with airflow rate, energy charged or discharged was unaffected. Over a week, the TSC-TEC stored 34% of the total useful energy produced for nighttime use, with a potential to displace 1.35 kg of liquefied natural gas. Replacing the expensive metal TSC with a perforated plastic TSC and a simpler TES design would improve the economics of storing solar energy for use after sundown. [ABSTRACT FROM AUTHOR]

The paper investigates whether air-water heat exchanger with longitudinal fins along the air flow direction are an appropriate means to reduce pressure loss in mechanical ventilation systems, compared to conventional heating coils. To answer this question, theoretical calculations regarding pressure loss and heat transfer are performed and the results are checked by measurements. It is found that a longitudinal fin heat exchanger with 30 radially arranged fins and an overall length of 830 mm transfers the same heat flow as a conventional heating coil (∅ 125). The pressure loss only adds up to about 60% to 70%, so a reduction of 30% to 40% can be achieved. Additionally it is expected, that the longitudinal fin heat exchanger is more suitable for efficient low temperature heating systems, because of the counter-current heat transfer. The disadvantage of its increased length can be compensated by integrating the longitudinal fin heat exchanger in a duct silencer, which is required anyway. Hence, the energy efficiency of mechanical ventilation system can be increased. [ABSTRACT FROM AUTHOR]

Knowing the pressure coefficient on building surfaces is important for the evaluation of wind loads and natural ventilation. The main objective of this paper is to present and to validate a computational modeling approach to accurately predict the mean wind pressure coefficient on the surfaces of flat-, gable- and hip-roofed rectangular buildings. This approach makes use of artificial neural network (ANN) to estimate the surface-average pressure coefficient for each wall and roof according to the building geometry and the wind angle. Three separate ANN models were developed, one for each roof type, and trained using an experimental database. Applied to a wide variety of buildings, the current ANN models were proved to be considerably more accurate than the commonly used parametric equations for the estimation of pressure coefficients. The proposed ANN-based methodology is as general and versatile as to be easily expanded to buildings with different shapes as well as to be coupled to building performance simulation and airflow network programs. [ABSTRACT FROM AUTHOR]

Floor swirl diffuser is one of the commonly used diffusers in underfloor air distribution (UFAD) system. Geometrical design of the floor swirl diffuser will affect the airflow pattern of the indoor environment. Thus, the purpose of this study is to examine the effect of geometrical design of a floor swirl diffuser on the aspects of airflow rate, number of diffuser blades, angle of attack of diffuser blades, and the grille thickness. Laboratory experiment was carried out to validate CFD simulation results. The results of this study have shown that diffuser blades have an important role in the airflow pattern. The grille thickness, which is required to withstand the impact and the load of human and furniture, needs to be minimized as the thickness is detrimental to the function of diffuser blades. Besides, airflow rate per diffuser is studied in UFAD system in order to achieve thermal stratification. The air throw is lower compared to a high angle of attack at the low angles of attack of 30° and 45°. The optimum number of diffuser blades to create the swirl effect is 18 blades with a free area of 18.86%. [ABSTRACT FROM AUTHOR]

In order to obtain satisfactory effect of air conditioning and ventilation, the floor–supply displacement ventilation has widely applied in many civil buildings. Swirl diffusers mounted on the floor are widely used to provide fresh air into the occupied zone in the floor–supply displacement ventilation system. This paper studied the air distribution performance of swirl diffuser by 2D-PIV (particle image velocimetry). The experiment was implemented in a full-scale room to achieve reliable data of swirl diffusers. Flow visualizations have been carried out to determine the shape of the swirl jet. The whole velocity field was measured by 2D-PIV system, which is very useful to analyze air distribution above the swirl diffuser. With the aid of the flow visualizations and PIV test technology, the macro and micro structure of the air flow above the swirl diffuser is specified in more detail. Moreover, the centerline velocity decay coefficient (K value) and entrainment ratio were obtained. The research work of this paper provides detailed experimental data of air flow above the swirl diffuser, which provide the reference for selection of air terminal devices and a basis for follow-up numerical simulation study. [ABSTRACT FROM AUTHOR]

Natural ventilation can provide building occupants with thermal comfort and a healthy indoor environment. Among all the design related parameters that affect ventilation performance, ventilation mode (i.e. single-sided and cross ventilation) is perhaps the main one. The current study uses full-scale in-situ measurements to investigate the effect of ventilation mode on thermal comfort and ventilation performance of a high-rise case study unit. Two modes of natural ventilation, single-sided and cross ventilation, are investigated. Air velocity, temperature and relative humidity were measured for both ventilation modes on two consecutive days in summer. Indoor thermal conditions were evaluated using the extended Predicted Mean Vote (PMV) and Standard Effective Temperature (SET*) comfort models. In addition, the relationship between reference wind speed and internal airflow, airflow distribution, and the effect of wind direction on internal airflow were investigated for both single-sided and cross ventilation. Finally, the implications of the research outcomes on natural ventilation design are discussed. Indoor thermal conditions were found to be within the comfort zone for more than 70% of the time under cross ventilation operation while single-sided ventilation provided adequate thermal conditions for only 1% of the time. Results from this study highlight a significantly better performance of cross ventilation over single-sided ventilation. [ABSTRACT FROM AUTHOR]

Transient high-temperature contaminated airflows generated during the pouring of high-temperature materials are widespread in Chinese industrial plants. In this study, the performance of both the local exhaust and the general exhaust with a constant flow rate to remove these transient contaminants was experimentally investigated, and the ventilation performance was compared between two local exhaust hoods. This study focused on the dispersion and removal characteristics of contaminant concentrations under the conditions of high-temperature airflows. The results showed that the cumulative contaminant concentration could be divided into four time slots and that there was a time lag between the cumulative concentration of the local and general exhaust. Additionally, the fitting formula of time-varying concentration decay was discussed to highlight the advantages of the designed hood performance. Finally, the dynamic evaluation index ( TCRR t ) for evaluating exhaust hoods on removing transient contaminants was proposed, and the connections between the proposed index and the traditional capture efficiency were illustrated. The minimu m TCRR t for the improved exhaust hood was invariably greater than that for the existing hood for each hood flow rate. This study demonstrates that increasing the containment volume of the exhaust hood can help to remove transient high-temperature contaminants in industrial plants. [ABSTRACT FROM AUTHOR]

A numerical model is developed for simulating a single or multi–story Double Skin Façade integrating Photovoltaics (DSF-PV). The DSF-PV can co-generate solar electricity and heat, while it also allows daylight to be transmitted to the interior space. The buoyancy-driven air flow inside the cavity may be assisted by a fan to cool down the photovoltaics while providing natural or hybrid ventilation to adjacent zones. Automated roller shades are also implemented in the model and help regulate heating and cooling loads but also control the daylight levels in the indoor space. A parametric analysis for different control strategies for the airflow within the cavity and the roller shading devices is performed with the purpose to apply the proposed methodology to minimize the heating and cooling demand of the DSF-PV system. In addition, a parametric analysis for different adjacent zones floor areas is performed. The simulations show that a DSF-PV system can supply approximately 120kWh/façade area/year covering the yearly electricity demand of the adjacent office if the floor area is approximately less than 3 times larger than the floor area. [ABSTRACT FROM AUTHOR]

Underfloor air distribution (UFAD) is an effective strategy to provide both ventilation and air conditioning for buildings. To predict indoor airflows and temperature distribution, zonal model has advantages over other methods such as multi-zone model and computational fluid dynamics (CFD) by considering the prediction accuracy and computational cost. In this work, a numerical algorithm for floor-mounted diffuser flows, which calculates the airflow mass conservation and energy conservation separately, was implemented in a newly developed zonal model computer program for UFAD application, based on the established zonal model-pressurized zonal model with air-diffuser (POMA). This computer program was validated by lab experiments under both natural convection condition and mechanical ventilation for a lab-scale mixing UFAD system. Comparisons of zonal model simulation results and experimental measurements for both temperature distributions and air flows in the lab room showed that the newly developed zonal model is a good tool for predicting the indoor thermal environment with UFAD system. [ABSTRACT FROM AUTHOR]

Measuring natural ventilation rates in buildings with large vents with high accuracy and precision is not straight forward due to high spatial and temporal variabilities in the velocity distribution. Simplification of airflow rate measurements are mostly effectuated by lowering sampling density. Different sampling densities were investigated for both direct and tracer gas methods and compared with a detailed direct measurement method were in a naturally ventilated animal mock-up building. The results obtained by the reference method indicated that using only sampling locations in the middle of the side openings overestimated the airflow rate. In view of wind variations, better accuracy, precision and lower coefficients of variation were obtained with a higher number of sampling locations. The coefficients of variation varied between 5% for the reference and 29% using only one sampling location in the side outlet. In the ridge opening, only one middle sampling location was sufficient for an accuracy of 2% and a precision of 3%. The indirect tracer gas method gave varying concentrations with high confidence intervals resulting in non-significantly different measurement results between the different sampling strategies. The pattern of sampling locations was found to be very important resulting in different accuracies for a given sampling density. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) modules installed on flat roof need to be cooled to improve the power conversion efficiency (PCE). The efficient use of natural wind for cooling is a low-cost alternative compared with the use of artificial cooling devices. In this study, a passive cooling scheme is proposed including components: curved eave and vortex generators (VGs) which is arranged on the roof to enhance the forced convective heat exchange and reduce temperature of rooftop PV module under prevailing wind conditions. The optimum arrangement of VGs was studied, temperature reduction and PCE of rooftop PV with the scheme were evaluated. The results show that the curved eaves installed on the flat-roof leading edge improved the convective heat exchange only in the airflow separation area. And the defect that surface convective heat exchange decreased along with the flow direction was improved when multi-row array VGs were arranged. The overall convective heat exchange on rooftop PV can be improved at a wide range of wind speed by scheme using curved eaves in combination with the symmetrically arranged VGs. After using the passive cooling scheme, the ratio of forced convective heat exchange on the rooftop PV upper surface to 60%, and the maximum temperature reduction is about 5.89 ℃, and PCE of PV is improved in summer. The low-cost passive cooling scheme proposed in this paper is expected to be applied to the new-built and reconstruction of flat-roof mounted PV system. [ABSTRACT FROM AUTHOR]