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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]

Excessive temperature stratification and draught are two prominent drawbacks for impinging jet ventilation (IJV). Using IJV together with ductless personalized ventilation (DPV) (i.e., IJV + DPV) has been proved to be an effective way to reduce temperature stratification, but the draught rate around occupant would be increased. In the current work, an in-depth study on the characteristics of indoor local thermal comfort for IJV + DPV operating with different scenarios is done. Predictive models for the local thermal comfort indicators are developed to optimize the operating parameters (including supply velocity of IJV (V s) and intake airflow rate of DPV (D f)) with different room cooling loads (Q). The results show that the application of IJV can be extended to spaces with high cooling loads (e.g., larger than 60 W/m2) by using together with DPV, but the risk of thermal discomfort increases. To avoid local thermal discomfort, the combination relationship between V s and D f should be properly matched and this relation becomes more stricter with the increase of Q. It also obtains that the maximum cooling load that IJV + DPV can eliminate is less than 170 W/m2. At last, to ensure the IJV + DPV create a good local thermal comfort environment, design chart about the feasible ranges of V s and D f are established for different values of Q. On the whole, the current study not only can provide a basis for the application of IJV + DPV in spaces with high cooling load, but also can provide theoretical guidance for the operation control and optimization design of the IJV + DPV. • Impinging jet ventilation (IJV) coupled with ductless personalized ventilation (DPV) can be used in high cooling load space. • There exists a risk of thermal discomfort for IJV combined with DPV (i.e., IJV + DPV). • Predictive models for thermal comfort indicators are developed for IJV + DPV. • Feasibility of IJV + DPV operating with different cooling loads is discussed. • Design chart for IJV + DPV is presented for achieving good thermal comfort. [ABSTRACT FROM AUTHOR]

Impinging jet ventilation (IJV) is believed to create good indoor thermal comfort and air quality (IAQ) in an energy efficient way. However, since there is little discussion about the relationship between its heating performance and airflow patterns, operation control of ventilation parameters (e.g., supply temperature, airflow rate, discharge height and nozzle shape) is not clear. To achieve a good heating performance for IJV, operation conditions are optimized by using data-driven model coupled with technique of order preference by similarity to ideal solution (TOPSIS). Draught discomfort (PD), air change efficiency (ACE) and energy utilization coefficient (EUC) are modeled as performance indicators. First, response surface methodology (RSM) and artificial neural network (ANN) are employed to establish predictive models for the performance indicators, a comparison between the two methods are then performed from prediction error analysis. It shows that both RSM and ANN can predict the ACE and EUC well, but compared to ANN, RSM is less reliable in estimating PD and may fall into the risk of misjudging comfort level. Then, the ANN is used together with the TOPSIS to optimize the IJV for heating and a square nozzle is better preferred among the studied nozzle shapes. Moreover, optimal conditions of supply parameters are determined and verified for different nozzle characteristics. Overall, the current results not only can provide reference for the design and operation control of ventilation parameters of IJV for heating, but also contribute to the practical applications of ANN in different ventilation scenarios. • RSM and ANN methods are used for modeling the thermal environment of IJV for heating. • Prediction accuracy between RSM and ANN for the same performance indicator is compared. • A multiple-criteria optimization study for IJV is conducted by ANN-based TOPSIS method. • Optimal conditions of ventilation parameters are obtained for the best performance. [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]

A validated analytical model is proposed to quickly calculate the transient indoor air temperature and wall temperature by using Laplace transformation and the method of constant variation. The analytical model is further combined with predicted mean vote (PMV) model to evaluate the indoor thermal environment. The quantitative influence of occupants' ventilation behavior (OVB) during the off-periods on indoor thermal comfort is studied for an intermittent heating (IH) room in the whole heating season. The results indicate that the OVB during the off-periods of IH system can significantly reduce the indoor thermal comfort level during the heating periods. The predictive model of minimum PMV during the heating periods is thus determined to provide a theoretical basis for balancing the OVB during the non-heating periods and indoor thermal comfort during the heating periods. In addition, considering the occupants who have the need for both ventilation and indoor thermal comfort, preheating may be a solution while the heating energy consumption will be increased. The increasing rate of heating energy consumption is approximately 32.5%–74.9%. To reduce the extra heating energy consumption caused by the preheating, occupants need to limit the OVB during the non-heating periods of IH system. • Indoor thermal environment (ITE) is studied in intermittent heating buildings. • ITE is studied for occupant ventilation behavior during non-heating period (OVBNH). • OVBNH can significantly affect indoor thermal comfort during heating period (ITCH). • Preheating may be an effective solution to meet the need for both OVBNH and ITCH. • The extra heating energy consumption caused by preheating is around 32.5%–74.9%. [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 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: 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]

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]