The Experts below are selected from a list of 3111 Experts worldwide ranked by ideXlab platform
Zhang Lin - One of the best experts on this subject based on the ideXlab platform.
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Equivalent room air temperature based cooling load estimation method for stratum Ventilation and Displacement Ventilation
Building and Environment, 2019Co-Authors: Sheng Zhang, Yong Cheng, Chao Huan, Zhang LinAbstract:Abstract Cooling load estimation is the base for the design and control of the air conditioning system. The indoor air temperature stratification of stratum Ventilation and Displacement Ventilation contributes to the energy saving, but challenges the cooling load estimation. The existing building simulation tools are generally equipped with only the fully mixed air model and ignore the indoor air temperature stratification. This study proposes an equivalent room air temperature based cooling load estimation method to enable the fully mixed air model to accurately estimate the cooling load of stratum Ventilation and Displacement Ventilation. The equivalent room air temperature is the air temperature with which the fully mixed air model can produce the same cooling load as that of stratum Ventilation/Displacement Ventilation. The equivalent room air temperature is modelled as a function of the supply air temperature, supply airflow rate and room air temperature of stratum Ventilation/Displacement Ventilation using response surface methodology. Case studies using the experimentally validated multi-node models are conducted to demonstrate the effectiveness of the proposed method. The mean absolute errors in the cooling load estimation by the proposed method for the constant-air-volume system and the variable-air-volume system are 0.02% and 5.78% respectively under stratum Ventilation, and 0.07% and 4.78% respectively under Displacement Ventilation. Compared with the conventional method, the proposed method improves the accuracy in the cooling load estimation by 70.92%–99.94%.
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heat removal efficiency based multi node model for both stratum Ventilation and Displacement Ventilation
Building and Environment, 2018Co-Authors: Sheng Zhang, Yong Cheng, Chao Huan, Zhang LinAbstract:Abstract The non-uniform distribution of vertical air temperature helps stratum Ventilation and Displacement Ventilation to save energy compared with mixing Ventilation. To reasonably predict the vertical distribution of the non-uniform air temperature, the multi-node (nodal) model requires an in-depth understanding of the airflow pattern and is specific for different designs of Ventilation, which challenges engineers/designers in practice. To be more practical, this study proposes a heat removal efficiency (HRE) based multi-node model. The proposed model employs HRE to conveniently represent the airflow pattern, requiring little understanding of the airflow pattern. Moreover, the proposed model is general for both stratum Ventilation and Displacement Ventilation, and flexible to include heating/cooling devices. Experimental case studies show that compared with the conventional model, the proposed model is more accurate and robust. The proposed model reduces the overall mean absolute error in the temperature predictions of the nodes of the air and inner surfaces of the enclosure by 0.1 ° C (from 0.94 ° C to 0.84 ° C) for stratum Ventilation, and by 0.08 ° C (from 0.33 ° C to 0.25 ° C) for Displacement Ventilation with floor heating; and reduces the associated overall standard deviation of errors by 0.14 ° C (from 0.55 ° C to 0.41 ° C) and 0.02 ° C (from 0.19 ° C to 0.17 ° C) respectively. Benefiting from its convenience, generality, flexibility, accuracy and robustness, the proposed model is practical and would contribute to the practical applications of the energy-efficient stratum/Displacement Ventilation strategies.
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Application potential of solar air-conditioning systems for Displacement Ventilation
Energy and Buildings, 2011Co-Authors: K.f. Fong, Zhang Lin, C.k. Lee, Tin-tai Chow, L.s. ChanAbstract:Abstract Solar air-conditioning can have higher application potential for buildings through the strategy of high temperature cooling. In recent years, Displacement Ventilation (DV), which makes use of the indoor rising plumes from the internal heat gains, provides a more effective supply air option than the traditional mixing Ventilation (MV) in terms of both thermal comfort and indoor air quality. As it is possible to raise the supply air temperature to 19 °C for DV, it would enhance the competitive edge of the solar air-conditioning against the conventional vapour compression refrigeration. Through dynamic simulation, a solar-desiccant-cooling Displacement Ventilation system (SDC_DV) was developed for full-fresh-air provision, while a solar-hybrid-desiccant-cooling Displacement Ventilation system (SHDC_DV) for return air arrangement. The latter was further hybridized with absorption chiller (AB) to become SHDCAB_DV, or adsorption chiller (AD) to be SHDCAD_DV, in order to be wholly energized by the solar thermal gain. Benchmarked with the conventional system using MV, the SDC_DV had 43.3% saving in year-round primary energy consumption for a typical office in the subtropical climate; the SHDCAB_DV had 49.5% saving, and the SHDCAD_DV had 18.3% saving. Compared with their MV counterparts, the SDC_DV, the SHDCAB_DV and the SHDCAD_DV could have 42.4%, 21.9% and 30.3% saving respectively.
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Numerical Investigation of Indoor Aerosol Particle Dispersion under Stratum Ventilation and under Displacement Ventilation
Indoor and Built Environment, 2009Co-Authors: Lin Tian, Zhang Lin, Qiuwang Wang, Jing LiuAbstract:Particle dispersion in a room under stratum Ventilation and under Displacement Ventilation have been investigated by numerical simulation. In addition, an experiment was carried out involving the newer stratum Ventilation. The agreements between simulated velocity, temperature by the RNG k-" turbulent model and the measured data were quite good. A discrete trajectory model was adopted to simulate the particle movement in a room. The results showed that the flow patterns created by different Ventilation modes have great influence on the fates of particles. The particle concentrations for the entire room and for the breathing zone under stratum Ventilation are less than that under Displacement Ventilation, which implies that the risk of particle inhalation under stratum Ventilation is less than that under Displacement Ventilation. The deposited particle mass on room walls and furniture surfaces under stratum Ventilation is greater than that under Displacement Ventilation. The particle mass deposited on the floor plays an important role in the process of particle deposition. The mass of particles that escaped under stratum Ventilation was less than that under Displacement Ventilation. Moreover, the influence of particle diameter on particle dispersion is also considered in the present paper.
A H Taki - One of the best experts on this subject based on the ideXlab platform.
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designing for thermal comfort in combined chilled ceiling Displacement Ventilation environments
1998Co-Authors: Dennis L Loveday, Ken Parsons, Simon Hodder, L.d. Jeal, A H TakiAbstract:This paper presents general guidance on designing for thermal comfort in combined chilled ceiling/Displacement Ventilation environments. Thermal comfort measurements involving 184 human subjects were carried out in a laboratory-based test room, constructed to resemble a normal office and equipped with a combined chilled ceiling and wall-mounted Displacement Ventilation system. Room characterization tests revealed that the chilled ceiling has a detrimental effect upon Displacement flow, suppressing the stratified boundary layer at ceiling temperatures of 18 C--21 C and destroying Displacement flow all together at low ceiling temperatures (14 C--16 C). Reduction in ceiling temperature was found to increase local air velocities at heights of 0.1 m and 1.1 m above the floor, showing further evidence of mixing, though there was an insignificant effect on local discomfort due to draft, as measured by subjective responses and by draft rating assessment. ISO Standard 7730 (1995) is shown to be valid, without modification, for predicting the thermal comfort of sedentary occupants performing office work in combined chilled ceiling/Displacement Ventilation environments. The vertical radiant asymmetry induced by a cooled ceiling does not significantly affect the thermal comfort of desk-seated occupants; this, together with relative humidity, is shown to require no additional comfort-related design limitations beyondmore » those already in the literature and beyond the prevention of ceiling surface condensation.« less
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Designing for thermal comfort in combined chilled ceiling/Displacement Ventilation environments
1998Co-Authors: Dennis L Loveday, Ken Parsons, Simon Hodder, L.d. Jeal, A H TakiAbstract:This paper presents general guidance on designing for thermal comfort in combined chilled ceiling/Displacement Ventilation environments. Thermal comfort measurements involving 184 human subjects were carried out in a laboratory-based test room, constructed to resemble a normal office and equipped with a combined chilled ceiling and wall-mounted Displacement Ventilation system. Room characterization tests revealed that the chilled ceiling has a detrimental effect upon Displacement flow, suppressing the stratified boundary layer at ceiling temperatures of 18 C--21 C and destroying Displacement flow all together at low ceiling temperatures (14 C--16 C). Reduction in ceiling temperature was found to increase local air velocities at heights of 0.1 m and 1.1 m above the floor, showing further evidence of mixing, though there was an insignificant effect on local discomfort due to draft, as measured by subjective responses and by draft rating assessment. ISO Standard 7730 (1995) is shown to be valid, without modification, for predicting the thermal comfort of sedentary occupants performing office work in combined chilled ceiling/Displacement Ventilation environments. The vertical radiant asymmetry induced by a cooled ceiling does not significantly affect the thermal comfort of desk-seated occupants; this, together with relative humidity, is shown to require no additional comfort-related design limitations beyondmore » those already in the literature and beyond the prevention of ceiling surface condensation.« less
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thermal comfort in chilled ceiling and Displacement Ventilation environments vertical radiant temperature asymmetry effects
Energy and Buildings, 1998Co-Authors: Simon Hodder, Ken Parsons, Dennis L Loveday, A H TakiAbstract:Abstract The paper presents some of the findings from a broader investigation aimed at determining thermal comfort design conditions for combined chilled ceiling/Displacement Ventilation environments. A typical chilled ceiling/Displacement Ventilation office has been created within a laboratory test room, in which the ceiling temperature can be varied over a range of typical operating values; the thermal comfort of eight female test subjects was then measured in the test room over the range of ceiling temperatures. Vertical radiant temperature asymmetry was found to have an insignificant effect on the overall thermal comfort of the seated occupants for the typical range of ceiling temperatures that would be encountered in practice in such combination environments. There was a slight trend for the reported sensation of ‘freshness’ to increase as ceiling temperature was reduced though this requires further study. It is concluded that existing guidance regarding toleration of radiant asymmetry is valid for thermal comfort design of chilled ceiling/Displacement Ventilation environments
Qingyan Chen - One of the best experts on this subject based on the ideXlab platform.
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Floor-supply Displacement Ventilation for workshops
Building and Environment, 2007Co-Authors: Josephine Lau, Qingyan ChenAbstract:Abstract This paper reported the investigation of the performance of floor-supply Displacement Ventilation with swirl diffusers or perforated panels under a high cooling load (nearly 90 W/m 2 ). The experiment was carried out in a full-scale environmental chamber to obtain reliable data on the floor-supply Displacement Ventilation for the validation of a computational-fluid-dynamics (CFD) program. Numerical simulations using CFD program were to evaluate the performance of the system for a large workshop. The impacts of several parameters, such as the air change rate, number of diffusers, diffuser location, occupant location, furniture arrangement, partition location, and arrangement of exhausts, on the indoor environment were investigated based on the thermal comfort level and indoor air quality. This study ranked the impacts of these parameters on indoor environment.
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Energy analysis for workshops with floor–supply Displacement Ventilation under the U.S. climates
Energy and Buildings, 2006Co-Authors: Josephine Lau, Qingyan ChenAbstract:Abstract Many studies have shown that floor–supply Displacement Ventilation systems are better than mixing Ventilation systems. The benefits include indoor air quality, thermal comfort and reduced energy use. The energy benefits depend on the climate conditions. This research compared the energy use of a floor–supply Displacement Ventilation system in a large industrial workshop with that of a mixing Ventilation system for five U.S. climate regions. It was found that the energy use and the system performance vary with the locations. The Displacement Ventilation system may use more fan and boiler energy but less chiller energy than the mixing Ventilation system. The total energy used is slightly less with Displacement Ventilation, although the Ventilation rate was increased in order to handle the high cooling loads found in U.S. buildings. Thus, the Displacement Ventilation system can save some energy in cooling mode. However, Displacement Ventilation system has a lower capacity of dehumidification. This system alone, thus, is not suggested for use in humid regions.
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energy analysis for workshops with floor supply Displacement Ventilation under the u s climates
Energy and Buildings, 2006Co-Authors: Josephine Lau, Qingyan ChenAbstract:Abstract Many studies have shown that floor–supply Displacement Ventilation systems are better than mixing Ventilation systems. The benefits include indoor air quality, thermal comfort and reduced energy use. The energy benefits depend on the climate conditions. This research compared the energy use of a floor–supply Displacement Ventilation system in a large industrial workshop with that of a mixing Ventilation system for five U.S. climate regions. It was found that the energy use and the system performance vary with the locations. The Displacement Ventilation system may use more fan and boiler energy but less chiller energy than the mixing Ventilation system. The total energy used is slightly less with Displacement Ventilation, although the Ventilation rate was increased in order to handle the high cooling loads found in U.S. buildings. Thus, the Displacement Ventilation system can save some energy in cooling mode. However, Displacement Ventilation system has a lower capacity of dehumidification. This system alone, thus, is not suggested for use in humid regions.
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Floor-Supply Displacement Ventilation in a Small Office
Indoor and Built Environment, 2003Co-Authors: Nobukazu Kobayashi, Qingyan ChenAbstract:This paper presents a study of the performance of a floor-supply Displacement Ventilation system using computational fluid dynamics (CFD). The experiment was carried out in a full-scale environmental chamber with a floor-supply system to obtain reliable flow information for the validation of a CFD program. The validated program was used further to evaluate the performance of the floor-supply Displacement Ventilation system with different air change rates, diffuser numbers, furniture arrangement, and cooling loads. The evaluation criteria are thermal comfort level and indoor air quality.
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performance evaluation and design guidelines for Displacement Ventilation
空気調和・衛生工学, 1999Co-Authors: X. Yuan, Qingyan Chen, Leon R. GlicksmanAbstract:This paper evaluates the performance of traditional Displacement Ventilation systems for small offices, large offices with partitions, classrooms, and industrial workshops under US thermal and flow boundary conditions, such as a high cooling load. With proper design, Displacement Ventilation can maintain a thermally comfortable environment that has a low air velocity, a small temperature difference between the head and foot level, and a low percentage of dissatisfied people. Compared with conventional mixing Ventilation, Displacement Ventilation may provide better indoor air quality in the occupied zone when the contaminant sources are associated with the heat sources. The mean age of air is younger, and the Ventilation effectiveness is higher. Based on results from Scandinavian countries and the authors' investigation of US buildings, this paper presents guidelines for designing Displacement Ventilation in the US.
Jelena Srebric - One of the best experts on this subject based on the ideXlab platform.
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contaminant dispersion with personal Displacement Ventilation part i base case study
Building and Environment, 2009Co-Authors: Xudong Yang, Caiqing Yang, Jelena SrebricAbstract:Abstract Personal Displacement Ventilation (PDV) is a new Ventilation concept that combines the positive features of Displacement Ventilation with those of task conditioning or personalized Ventilation. PDV is expected to create a micro-environment around an occupant to control the environment individually. In this study, a base PDV case with a contaminant source at different locations was modeled for contaminant dispersion in a full-scale chamber. Computational fluid dynamics (CFD) was used to simulate the indoor airflow and pollutant transport, and the simulation results were validated against the experimental data. The contaminant concentration field for three different contaminant source locations was analyzed. Based on our results, it seems that this kind of PDV system cannot create the expected “micro-environment” to avoid the disturbance of the outside airflow. Further studies on how to improve the PDV performance are given in the companion paper.
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CONTAMINANT DISPERSION IN PERSONAL Displacement Ventilation
2007Co-Authors: Caiqing Yang, Xudong Yang, Jelena SrebricAbstract:Personal Displacement Ventilation (PDV) is a new Ventilation concept that intends to combine the positive features of Displacement Ventilation with those of task conditioning or personalized Ventilation. PDV is expected to create a micro-environment around the occupant to control the environment individually. In this study, a PDV with a contaminant source at different locations was modeled for contaminant dispersion in a full scale chamber. Computational fluid dynamics (CFD) was used to simulate the indoor airflow and pollutant transport, and the simulation results were validated against the experimental data. The contaminant concentration field for three different contaminant source locations was analyzed. It seems that this kind of PDV system cannot create the expected “micro-environment” to avoid the disturbance of the outside airflow. Further studies are needed to examine the conditions where PDV could perform better.
Simon Hodder - One of the best experts on this subject based on the ideXlab platform.
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designing for thermal comfort in combined chilled ceiling Displacement Ventilation environments
1998Co-Authors: Dennis L Loveday, Ken Parsons, Simon Hodder, L.d. Jeal, A H TakiAbstract:This paper presents general guidance on designing for thermal comfort in combined chilled ceiling/Displacement Ventilation environments. Thermal comfort measurements involving 184 human subjects were carried out in a laboratory-based test room, constructed to resemble a normal office and equipped with a combined chilled ceiling and wall-mounted Displacement Ventilation system. Room characterization tests revealed that the chilled ceiling has a detrimental effect upon Displacement flow, suppressing the stratified boundary layer at ceiling temperatures of 18 C--21 C and destroying Displacement flow all together at low ceiling temperatures (14 C--16 C). Reduction in ceiling temperature was found to increase local air velocities at heights of 0.1 m and 1.1 m above the floor, showing further evidence of mixing, though there was an insignificant effect on local discomfort due to draft, as measured by subjective responses and by draft rating assessment. ISO Standard 7730 (1995) is shown to be valid, without modification, for predicting the thermal comfort of sedentary occupants performing office work in combined chilled ceiling/Displacement Ventilation environments. The vertical radiant asymmetry induced by a cooled ceiling does not significantly affect the thermal comfort of desk-seated occupants; this, together with relative humidity, is shown to require no additional comfort-related design limitations beyondmore » those already in the literature and beyond the prevention of ceiling surface condensation.« less
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Designing for thermal comfort in combined chilled ceiling/Displacement Ventilation environments
1998Co-Authors: Dennis L Loveday, Ken Parsons, Simon Hodder, L.d. Jeal, A H TakiAbstract:This paper presents general guidance on designing for thermal comfort in combined chilled ceiling/Displacement Ventilation environments. Thermal comfort measurements involving 184 human subjects were carried out in a laboratory-based test room, constructed to resemble a normal office and equipped with a combined chilled ceiling and wall-mounted Displacement Ventilation system. Room characterization tests revealed that the chilled ceiling has a detrimental effect upon Displacement flow, suppressing the stratified boundary layer at ceiling temperatures of 18 C--21 C and destroying Displacement flow all together at low ceiling temperatures (14 C--16 C). Reduction in ceiling temperature was found to increase local air velocities at heights of 0.1 m and 1.1 m above the floor, showing further evidence of mixing, though there was an insignificant effect on local discomfort due to draft, as measured by subjective responses and by draft rating assessment. ISO Standard 7730 (1995) is shown to be valid, without modification, for predicting the thermal comfort of sedentary occupants performing office work in combined chilled ceiling/Displacement Ventilation environments. The vertical radiant asymmetry induced by a cooled ceiling does not significantly affect the thermal comfort of desk-seated occupants; this, together with relative humidity, is shown to require no additional comfort-related design limitations beyondmore » those already in the literature and beyond the prevention of ceiling surface condensation.« less
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thermal comfort in chilled ceiling and Displacement Ventilation environments vertical radiant temperature asymmetry effects
Energy and Buildings, 1998Co-Authors: Simon Hodder, Ken Parsons, Dennis L Loveday, A H TakiAbstract:Abstract The paper presents some of the findings from a broader investigation aimed at determining thermal comfort design conditions for combined chilled ceiling/Displacement Ventilation environments. A typical chilled ceiling/Displacement Ventilation office has been created within a laboratory test room, in which the ceiling temperature can be varied over a range of typical operating values; the thermal comfort of eight female test subjects was then measured in the test room over the range of ceiling temperatures. Vertical radiant temperature asymmetry was found to have an insignificant effect on the overall thermal comfort of the seated occupants for the typical range of ceiling temperatures that would be encountered in practice in such combination environments. There was a slight trend for the reported sensation of ‘freshness’ to increase as ceiling temperature was reduced though this requires further study. It is concluded that existing guidance regarding toleration of radiant asymmetry is valid for thermal comfort design of chilled ceiling/Displacement Ventilation environments