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The indoor thermal environment for the impinging jet ventilation combined with radiant ceiling(IJV/RC) air-conditioning system with different operating load conditions was simulated. The GA-BP neural network was applied to develop the predictive models between the operating performance(draught discomfort RPD, temperature difference between the head and ankle level Δt, air change efficiency eACE, and average temperature of operation ta) and design variables (supply temperature ts, supply velocity vs, chilled ceiling temperature tc, and room load Qc). The significance of each design variable on the studied operating performance was determined and ranked through correlation analysis. The results show that Δt decreases with the increase of vs, but the value of RPD increases accordingly. The increase of tc is helpful for the decrease of Δt and RPD, but the value of ta increases. The decrease of ta can be achieved by reducing ts, but the indoor air quality becomes worse. To achieve the goals of providing good indoor air quality and indoor thermal comfort, a multi-objective optimization for the IJV/RC was conducted by applying the improved particle swarm optimization(PSO) algorithm, and the optimal combinations of the studied design variables corresponding to the room loads were developed. The current results can provide theoretical guidance for the design and operation control for the IJV/RC system. [ABSTRACT FROM AUTHOR]

The matching relationship of operating parameters between the air supply and radiant systems has significant impact on the indoor thermal comfort and energy efficiency for combined air-conditioning system. The impinging jet ventilation (IJV) and chilled ceiling (CC) combined system (IJV/CC) overcomes the drawback of IJV which cannot be used in spaces with high cooling load. However, the matching relationship between the operating parameters of the IJV and CC are not clear due to limited research on IJV/CC at present. To ensure good thermal comfort and indoor air quality of the IJV/CC in an energy efficient way, this study mainly focuses on exploring the optimal combination of the operating parameters between the IJV and CC (including the supply temperature and supply velocity of IJV and internal surface temperature of CC (T c)). First, the indoor thermal environment for IJV/CC operating with different combinations of design parameters is simulated by CFD. Second, response surface methodology (RSM) is utilized to establish predictive models for various ventilation performance indicators by collecting the simulation results. Then, the optimal combinations of operating parameters between the IJV and CC are determined by using the technique of order preference by similarity to ideal solution (TOPSIS) coupled with the developed RSM models. Finally, control strategies for the IJV and CC are discussed and it suggests setting the value of T c in the range of 20–21 °C and a variable air volume system is preferred for the control of the air supply system to achieve efficient operation of IJV/CC. • Distributions of thermal environments for IJV/CC with high cooling loads are investigated. • Predictive models for various operation performance indicators of IJV/CC are established. • Matching relation between the IJV and CC are presented for efficient operation of IJV/CC. • The internal surface temperature of CC is suggested to set in the range of 20–21 °C. • A variable air volume system is preferred for the control of IJV. [ABSTRACT FROM AUTHOR]

Numerical simulations were conducted to investigate the effects of building height ratio (i.e., HR, the height ratio of the upstream building to the downstream building) on the air quality in buildings beside street canyons, and both regular and staggered canyons were considered for the simulations. The results show that the building height ratio affects not only the ventilation fluxes of the rooms in the downstream building but also the pollutant concentrations around the building. The parameter, outdoor effective source intensity of a room, is then proposed to calculate the amount of vehicular pollutants that enters into building rooms. Smaller value of this parameter indicates less pollutant enters the room. The numerical results reveal that HRs from 2/7 to 7/2 are the favorable height ratios for the regular canyons, as they obtain smaller values than the other cases. While HR values of 5/7, 7/7, and 7/5 are appropriate for staggered canyons. In addition, in terms of improving indoor air quality by natural ventilation, the staggered canyons with favorable HR are better than those of the regular canyons. [ABSTRACT FROM AUTHOR]

Impinging jet ventilation (IJV) is a new ventilation strategy for using in public and industrial buildings with large spaces. It combines advantages of both displacement ventilation (DV) and mixing ventilation (MV). Compared with DV and MV, however, there is a potential risk associated with the IJV system, i.e., particle resuspension from the floor due to the supply air, by which the high momentum jet is directed towards the floor. In the present study, particle concentrations under different supply airflow conditions were measured in an IJV room with indoor pollutant sources. The effect of supply airflow on the resuspension of the deposited particles and the critical supply velocities causing the resuspension for different supply heights and particle sizes were analyzed by using the measured data in a model IJV room. The results show that the critical supply velocity is increased with the increase of supply height and the decrease of particle diameter. Meanwhile, in practical applications, there is little risk of the significantly degrading IAQ induced by particle resuspension via supply airflow in an IJV room. Comparing the resuspension amount caused by the supply airflow of an IJV system with that caused by an occupant walking past, a sharp rise of supply velocity in a short time span in an IJV room will not result in significantly worse IAQ. [ABSTRACT FROM AUTHOR]

To explore the effect of traffic pollution on indoor air quality of naturally ventilated buildings in the vicinity of a street canyon, the wind flow and pollutant distributions in and around buildings with different window opening percentages (i.e. WOP, the percentage of the total window opening area to the total facade area) were investigated by three-dimensional numerical simulations. The numerical results show that the WOP changes the pressure distribution around the downstream building, which is due to the infiltration of air into the street canyon through the opening windows of both the upstream and downstream buildings. When the indoor air of the downstream building is supplied by the outdoor air from the street canyon, the ventilation flux will be increased with increasing WOP. If the indoor air is taken in from the leeward side of the downstream building, however, the trend of the ventilation flux is found reverse. The results also indicate that the effective source intensity, which is introduced to quantify the amount of traffic pollutant entering into buildings through unit ventilation area, decreases as the WOP increases. When the WOP reaches 10%, the averaged effective intensity is reduced by 30% compared to the reference case when all windows are closed. It means that if a naturally ventilated room in the downstream building has a fixed ventilated area over different seasons, the room will take in more pollutants from outdoors in winter than in other seasons. [ABSTRACT FROM AUTHOR]

Abstract: The time series of indoor and outdoor CO concentrations in natural ventilating rooms were monitored continuously and simultaneously in summer, and the relationships between indoor and outdoor CO concentrations at two sampling locations in the central area of Shanghai were examined and discussed. Linear regression analysis was employed to correlate indoor concentration levels with outdoor concentrations, and the diurnal cycles of the indoor and outdoor CO concentrations show positive correlations at both sampling sites. The monitoring data also indicate that the indoor to outdoor ratios of CO concentrations in the test natural ventilating rooms are less than but close to 1. In addition, a predicting model based on a mass balance assumption of indoor pollutants was applied for estimating the indoor CO concentrations by using the outdoor test data as inputs, resulting in good agreement with the test curves for the two sampling sites. [Copyright &y& Elsevier]

Abstract: Indoor air quality and pollutant dispersion in natural ventilation rooms have received considerable attention in recent years. In order to evaluate the pollutant concentration levels in the occupant zone in a displacement natural ventilation (DNV) room, the mathematical model in previous studies are employed and extended to estimate pollutant transportation in a DNV room with the consideration of both the incoming air concentration and indoor pollutant source, resulting in exponential type expressions in time for the concentration in the lower zone and the mean concentration in DNV rooms. The results show that for reducing the concentration in the lower zone to a certain value, the concentration of inflow air and indoor emission rate should be less than their critical values for a given effective opening area of the window. The effect of thermal radiation of the inner surface on the reduction of pollutant concentration in the upper zone is greater than that in the lower zone of a DNV room. In addition, the effective opening area of the window primarily influences the final concentration level in the DNV room, and only affects the decay rate of indoor pollutant concentration when the pollutant concentration of incoming air or the strength of the indoor source approach their critical values. [Copyright &y& Elsevier]

Abstract: A computer model for predicting aerosol dispersion in indoor spaces was validated with experimental data found in the literature. The validated model was used to explore the effect of the area or point source locations on aerosol particle transportation in ventilation rooms with rough surfaces. Two different ventilation strategies were studied: mixing ventilation (MV) and underfloor air distribution (UFAD) system. The simulation results show that in MV, the particle concentration and removal effectiveness are little dependent on the position of the pollutant sources. In UFAD, the source location has a strong impact on the distribution and removing of the contaminants. The particle removal performance strongly depends on the ventilation efficiency and the particle deposition loss in the room with rough surfaces. The important consideration in both the relative ventilation efficiency and the deposition rate is the relative position of the sources to the main airflow and the occupied zone in an UFAD room. [Copyright &y& Elsevier]

Thermal stratification is the key to improving energy efficiency and indoor air quality for impinging jet ventilation (IJV) system in cooling mode. However, unclear thermal stratification characteristics of IJV system can degrade the ventilation performance of the IJV. In the present study, the thermal stratification characteristics of an IJV is investigated by the validated simulation model for different supply air parameters and internal heat sources in interior zone of office buildings. The critical value of supply air parameters for the formation of thermal stratification is determined by thermal length scale, which considers the combined effect of inertial force and thermal buoyancy on the supply airflow. In addition, the cooling load in an IJV cooling room caused by the heat source intensity can be calculated directly and the heat source distribution is negligible. The results also indicate that the thermal stratification height (H) only depends on supply air parameters, while the temperature difference between head and ankle level (Δ T) is affected by both supply air parameters and cooling load. The predictive models of H and Δ T are obtained based on the simulation results, which could provide the theoretical basis for optimizing the design scheme of IJV system in interior zone of office buildings. • Thermal stratification (TS) of impinging jet ventilation for cooling is studied. • Critical value of supply air parameter (L m) is determined for the formation of TS. • Thermal stratification height H is mainly affected by L m but not cooling load (q). • Temperature difference between head and ankle (Δ T) is affected by both L m and q. • Predictive models of H and Δ T are obtained for design of impinging jet ventilation. [ABSTRACT FROM AUTHOR]

Impinging jet ventilation (IJV) system is believed to combines the advantages of good indoor air quality (IAQ) and high energy efficiency. However, there is few study about the optimization of multiple performance characteristics and the significance of design variables on the ventilation performance is not clear for IJV. This study addresses an approach based on Taguchi method with grey relational analysis for optimizing an IJV system with multiple performance characteristics (including draught discomfort (PD), temperature difference between the head and ankle level (Δ T), air change efficiency (ACE) and energy utilization coefficient (EUC)). The supply inlet height, supply velocity, supply temperature and return outlet height are selected as factors that affecting the ventilation performance of IJV and L 9 (43) orthogonal array is employed to design the experiments. First, the optimal combinations for PD, Δ T , ACE and EUC are determined separately by Taguchi method coupled with numerical simulations and the significance of the studied factors in promoting each evaluation index is revealed and ranked through main effect analysis and ANOVA. Second, the optimal combination of design variables corresponding to the best overall performance for IJV is determined by converting multi-objective into a single-objective according to Taguchi-based grey relational analysis. Then the important factors influencing the overall performance is ranked and the heights of supply inlet and return device are found to be significant factors in improving the overall performance. Finally, a confirmatory test is conducted to verify the improvement of performance characteristics and satisfactory results are obtained. • A multi-objective optimization study for impinging jet ventilation (IJV) is conducted. • Thermal comfort, indoor air quality and energy efficiency are considered together. • Significance of factors influencing the overall performance of IJV is revealed. • An optimal combination of design variables is obtained for the best performance. [ABSTRACT FROM AUTHOR]

For impinging jet ventilation (IJV) system, the energy efficiency is believed to be further improved by splitting the return vent from the exhaust device. However, how to properly set the return devices of IJV is unclear when it comes to a comprehensive consideration of the thermal comfort, indoor air quality (IAQ) and energy efficiency. In the present study, numerical simulations are performed to determine the thermal comfort indices (draught comfort (PD) and temperature gradient between the head and ankle levels (Δ T)), IAQ indices (air change efficiency (ACE) and contaminant removal efficiency (ε)) and energy efficiency index (η) for an IJV system with return outlet height (H) ranged from the ceiling to the floor level. The technique for order preferences by similarity to an ideal solution (TOPSIS) method is employed to determine the optimal return vent height by considering these performance evaluation indices simultaneously. The results indicate that when the H increases, the values of Δ T and η decrease, while the values of PD, ACE and ε increase. An optimal range of H (1.2–1.5 m above the floor) is recommended for the best overall performance of IJV. Moreover, a comprehensive graph of H is displayed in this paper, which could provide directions for optimizing the positions of exhaust and return devices. Image 1 • Impinging jet ventilation (IJV) with separate exhaust and return devices is studied. • Thermal comfort, indoor air quality and energy efficiency are considered together. • Short-circuit flow phenomenon of supply cold air might be occurred in the IJV. • An optimal return vent height (H) range for IJV is achieved by using TOPSIS method. [ABSTRACT FROM AUTHOR]

• Conduct a comprehensive review on the studies related to energy, thermal comfort and indoor air quality performance of underground buildings. • Reveal that numerical simulation is mostly used for energy study, while field experiment is primarily for indoor environment quality which need more attentions for underground buildings. • Finite difference method is the most adopted prediction method for underground building energy use in which the ground coupled heat transfer scheme requires further improvement. Underground spaces have received increasing attention in the past decades owing to the growing urban land scarcity. Underground spaces can have a variety of functions such as storage, shelter, and civic infrastructures, while underground buildings for human activities have gained less attention mostly due to the challenges in creating suitable living and working environments. With the attempt to design a healthy, comfortable and energy efficient underground building, this paper conducts a comprehensive review on the studies related to energy, thermal comfort and indoor air quality performances of underground buildings, ranging from prediction methods to influential factors to improving solutions. The review reveals that numerical simulation is mostly used to study underground building energy performance while field experimentation is primarily employed for investigating underground building indoor environment quality performance. Finite difference method is found to be the most adopted numerical method to predict the energy performance of underground buildings. Inherent uncertainty issues in ground coupled heat transfer still need to be improved to reflect more physics and balance prediction accuracy with computational cost. Further research is more necessary and crucial in the field of indoor environment quality performance than energy efficiency performance for underground buildings. [ABSTRACT FROM AUTHOR]

Numerical simulations are performed to predict the spatial distributions of indoor gaseous contaminant and aerosol particles (represented by the CO 2 produced by human respiration and the resuspended 2.5 μm particles caused by occupants' walking, respectively) concentration in a large-height space equipped with impinging jet ventilation (IJV) and mixing ventilation (MV) systems in heating modes. The local age of air, contaminant concentration of the breathing zone and ventilation efficiency for the removal of contaminants are compared between the IJV and MV rooms for both the constant volume (CAV) and variable volume (VAV) systems with different outdoor temperatures. The numerical results indicate that the mean age of air in the breathing zone of IJV is about 37–47% less than that of MV due to the different airflow patterns. Both the CO 2 and 2.5 μm particles distribute uniformly in the IJV room for the CAV and VAV systems, but the CO 2 is mainly distributed in the middle region of the room height and the 2.5 μm particles concentrate at the floor level away from the exterior wall in the studied MV room, which results in the contaminant concentrations of the breathing zone in most studied cases of IJV being lower than those in MV. The results also show that the ventilation efficiency in the IJV is higher than that in the MV with the same supply and exhaust configurations of this study, suggesting that the former is more advantageous in providing good indoor air quality (IAQ) than the latter. Image 1 • Indoor air quality in the impinging jet ventilation (IJV) heating room is studied. • IJV is compared with the mixing ventilation (MV) system under the same conditions. • Dispersions of both gaseous contaminant and particle are simulated for IJV and MV. • Mean age of air in the breathing zone in IJV is 37–47% less than that in MV. • Ventilation efficiency for the removal of contaminants is higher in IJV than in MV. [ABSTRACT FROM AUTHOR]

Numerical simulations are conducted to model the transient development of the buoyancy-driven natural ventilation. The simulations are compared with experimental data and theoretical predictions in the literature to validate the numerical model. The airflow behavior of three cases, i.e., the initial indoor temperature is equal to, higher and lower than the outdoor temperature, were analyzed by the numerical results, respectively. The results show that transient flow development of the last case is relatively complex in naturally ventilated rooms with inner heat sources due to the transformation from downward ventilation to upward ventilation. Vent area, heat source power and vertical position of the source are the main factors affecting the airflow rate, vertical temperature difference in the occupied zone and indoor thermal comfort, while the vent shape and the horizontal position of heat source on the floor seem to have marginal influence on the transient natural ventilation. In addition, initial indoor temperature is also a crucial factor influencing the establishment of steady state of the transient ventilation besides the vent and heat source characteristics. [ABSTRACT FROM AUTHOR]

Abstract: Heat gains in commercial buildings in China are rather large compared to those of other public buildings, for occupant densities are usually high in such buildings. To match the requirements for both indoor environment and building energy conservation, ventilation systems, either mechanical ventilation, i.e., ventilating cooling (VC) or air-conditioning cooling (AC) systems, play important roles in maintaining good indoor air quality and thermal comfort. As the time durations for cooling and heating of AC systems in such buildings are different from other types of public buildings, temperature ranges for the application of different ventilation strategies all year round were obtained by using the local meteorological records in the present study. The results show that the time period in a whole year can be divided into five ranges according to the four outdoor critical temperatures for the operation of VC and AC systems with a heat recovery ventilator (HRV). The critical temperatures are mainly influenced by local climatic characteristics, occupant density, and pressure drop of the ventilation system, etc. Furthermore, energy effectiveness by employing different ventilation modes in commercial buildings with large internal gains was discussed and compared for four cities located in four different climatic zones of China. [Copyright &y& Elsevier]

Abstract: The indoor temperature and humidity of four cities which are located in different climatic zones in China were monitored continuously in summer. The results show that the indoor air temperatures varied in narrow bands in the cities and the indoor thermal conditions were far from the ASHRAE 55-92 summer comfort zone during most of the measuring period. The indoor thermal environment of naturally ventilated rooms of residential buildings in the four cities was evaluated by using the predicted mean vote (PMV) model and the adaptive comfort model (ACM). The difference of thermal satisfaction between the two results was analyzed and discussed, and the potential of energy conservation was estimated by applying the ACM. The results show that even if energy consumption of dehumidification under humid climatic conditions is taken into consideration, when ACM is employed to optimize the operative temperature of the ventilation systems with the occupants maintaining control of the indoor thermal environment, the potential of energy conservation can be roughly more than 20% over the whole summer season in the four cities. [Copyright &y& Elsevier]