The stabilities of the complexes of three pyridine-like ligands with M(II)(ATP)^(2-) and M(II)(M=Ni,Co)were studied by spectrophotometry and by comparing the stability constants of the ternary complexes with these of ...The stabilities of the complexes of three pyridine-like ligands with M(II)(ATP)^(2-) and M(II)(M=Ni,Co)were studied by spectrophotometry and by comparing the stability constants of the ternary complexes with these of the binary complexes.A stacking interaction between the pyridine ring and the purine ring of ATP is indicated.The general existence of the stacking interaction encourages us to interpret the antitumor mechanism of a new class of antitumor drugs.展开更多
Stack effect is a dominant driving force for building natural ventilation.Analytical models were developed for the evaluation of stack effect in a shaft,accounting for the heat transfer from shaft interior boundaries....Stack effect is a dominant driving force for building natural ventilation.Analytical models were developed for the evaluation of stack effect in a shaft,accounting for the heat transfer from shaft interior boundaries.Both the conditions with constant heat flux from boundaries to the airflow and the ones with constant boundary temperature were considered.The prediction capabilities of these analytical models were evaluated by using large eddy simulation(LES) for a hypothetical shaft.The results show that there are fairly good agreements between the predictions of the analytical models and the LES predictions in mass flow rate,vertical temperatures profile and pressure difference as well.Both the results of analytical models and LES show that the neutral plane could locate higher than one half of the shaft height when the upper opening area is identical with the lower opening area.Further,it is also shown that the analytical models perform better than KLOTE's model does in the mass flow rate prediction.展开更多
After comparing the mechanism of tilted plume under stack effect with that of spill plume,the tilted plume model induced by stack effect in a vertical shaft is developed simply based on the theoretical results and a s...After comparing the mechanism of tilted plume under stack effect with that of spill plume,the tilted plume model induced by stack effect in a vertical shaft is developed simply based on the theoretical results and a series of full-scale tests. It is shown that the two sides of plume are symmetrical and have an accordant regulation that the plume radius has a linear relation to the height z. The profile of fire plume under stack effect is similar to the windblown flame in wind tunnel,and the range of flame deflection angle is about from 50 to 60 degree.展开更多
Higher-s dielectric LaLuO3, deposited by molecular beam deposition, with TiN as gate stack is integrated into high-mobility Si/SiGe/SOI quantum-well p-type metal-oxide-semiconduetor field effect transistors. Threshold...Higher-s dielectric LaLuO3, deposited by molecular beam deposition, with TiN as gate stack is integrated into high-mobility Si/SiGe/SOI quantum-well p-type metal-oxide-semiconduetor field effect transistors. Threshold voltage shift and capacitance equivalent thickness shrink are observed, resulting from oxygen scavenging effect in LaLuO3 with ti-rich TiN after high temperature annealing. The mechanism of oxygen scavenging and its potential for resistive memory applications are analyzed and discussed.展开更多
Protonated tetraphenylporphine（H2TPP） J-aggregates were prepared by aggregation on the liquid-air interface. Using FTIR spectroscopy, the authors observed the infrared absorption spectra of H2TPP and its J-aggregate...Protonated tetraphenylporphine（H2TPP） J-aggregates were prepared by aggregation on the liquid-air interface. Using FTIR spectroscopy, the authors observed the infrared absorption spectra of H2TPP and its J-aggregates. The IR spectra of H2TPP J-aggregates show significant changes compared with that of HETPP monomer. Intensity changes（e.g., strong enhancement of the in-plane vibronic mode and weakening of the out-of-plane vibronic mode of phenyl and porphyrin skeletal） were interpreted on the basis of stacking effects. Observation of the same type of bands collapse into single band was explained by the increase in the symmetry of H2TPP molecules. And the new bands at 1635 and 3407 cm^-1 indicate the aggregates containing a large amount of bound water.展开更多
Transistor aging has become the most important factor affecting the integrated circuit reliability.There is detection error caused by stacking effect in the stability checker in the previous respective aging sensors.A...Transistor aging has become the most important factor affecting the integrated circuit reliability.There is detection error caused by stacking effect in the stability checker in the previous respective aging sensors.An improved prediction aging sensor scheme is proposed using symmetrical NOR gate.Simulation experiments show the improved method eliminates prediction error caused by stacking effect.Layout area overhead is 4.65%and 7.06%compared to two respective sensor structures.展开更多
It is necessary to understand the features of air pressure in a drainage stack of a high-rise building for properly designing and operating a drainage system. This paper presents a mathematical model for predicting th...It is necessary to understand the features of air pressure in a drainage stack of a high-rise building for properly designing and operating a drainage system. This paper presents a mathematical model for predicting the stack performance. A step function is used to describe the effect of the air entrainment caused by the water discharged from branch pipes. An additional source term is introduced to reflect the gas-liquid interphase interaction （GLII） and stack base effect. The drainage stack is divided into upper and base parts. The air pressure in the upper part is predicted by a total variation diminishing （TVD） scheme, while in the base part, it is predicted by a characteristic line method （CLM）. The predicted results are compared with the data measured in a real-scale high- rise test building. It is found that the additional source term in the present model is effective. It intensively influences the air pressure distribution in the stack. The air pressure is also sensitive to the velocity-adjusting parameter （VAP）, the branch pipe air entrainment, and the conditions on the stack bottom.展开更多
Accurate energy demand simulation in high-rise buildings requires evaluating the impact of stack-induced infiltration.This study introduces a simplified method for calculating infiltration loads by predicting the neut...Accurate energy demand simulation in high-rise buildings requires evaluating the impact of stack-induced infiltration.This study introduces a simplified method for calculating infiltration loads by predicting the neutral pressure level(NPL)based on key architectural and atmospheric data.The NPL location of the elevator shaft was determined through a mass balance approach by simplifying a multi-zone building to a single zone group on each floor.Based on the predicted NPL,the stack-induced pressure distribution was calculated to estimate the building’s infiltration rates.The method focuses exclusively on airflow driven by the stack effect,making it especially suitable for mid-and high-rise buildings where vertical airflow dominates.Case studies revealed significant variations in heating and cooling loads—up to 55%—due to differences in shaft planning,such as the number of vertical zones and service zone configuration.These findings underscore the importance of incorporating the vertical shaft plan into energy simulation.The proposed method provides comprehensive insights into the infiltration profiles by floor and can serve as a basis for developing strategies to manage load imbalances between floors.展开更多
Leakage current of CMOS circuit increases dramatically with the technologyscaling down and has become a critical issue of high performance system. Subthreshold, gate andreverse biased junction band-to-band tunneling (...Leakage current of CMOS circuit increases dramatically with the technologyscaling down and has become a critical issue of high performance system. Subthreshold, gate andreverse biased junction band-to-band tunneling (BTBT) leakages are considered three maindeterminants of total leakage current. Up to now, how to accurately estimate leakage current oflarge-scale circuits within endurable time remains unsolved, even though accurate leakage modelshave been widely discussed. In this paper, the authors first dip into the stack effect of CMOStechnology and propose a new simple gate-level leakage current model. Then, a table-lookup basedtotal leakage current simulator is built up according to the model. To validate the simulator,accurate leakage current is simulated at circuit level using popular simulator HSPICE forcomparison. Some further studies such as maximum leakage current estimation, minimum leakage currentgeneration and a high-level average leakage current macromodel are introduced in detail.Experiments on ISCAS85 and ISCAS89 benchmarks demonstrate that the two proposed leakage currentestimation methods are very accurate and efficient.展开更多
Indoor air dynamics and quality in high density residential buildings can be complex as it is affected by both building parameters,pollution sources,and outdoor meteorological conditions.The present study used CONTAM ...Indoor air dynamics and quality in high density residential buildings can be complex as it is affected by both building parameters,pollution sources,and outdoor meteorological conditions.The present study used CONTAM simulations to investigate the intra-building transport and concentration of an inert pollutant continuously emitted from an underground garage of a 15-floor building under moderate Mediterranean weather.The effects of outdoor meteorological conditions(air temperature,wind speed and direction)on indoor distribution of the emitted pollutant was tested under constant conditions.The importance of using actual transient meteorological data and the impact of their temporal resolution on calculated concentrations and exposure levels were also investigated.Vertical profiles of air exchange rate(AER)and CO concentration were shown to be sensitive to indoor-outdoor temperature difference,which controls the extent of the stack effect and its importance relative to wind effect.Even under constant conditions,transient mode simulations revealed that the time needed for pollutant distribution to reach steady state can be quite long(>24h in some cases).The temporal resolution(Ih vs.8h)of the meteorological data input was also found to impact calculated exposure levels,in an extent that varied with time,meteorological conditions and apartment position.展开更多
A major roadblock in achieving substantial building energy reduction is the low performance of old buildings that account for a significant portion of the building energy consumption.Finding low-cost energy retrofit s...A major roadblock in achieving substantial building energy reduction is the low performance of old buildings that account for a significant portion of the building energy consumption.Finding low-cost energy retrofit solutions that do not disrupt occupants’daily life during the retrofitting is the key to successful building energy retrofit initiatives.In this paper,a novel and low-cost exterior wall retrofitting solution is introduced,and its performance in reducing space cooling load was quantitatively evaluated to demonstrate its feasibility and effectiveness.The primary goal of this paper is to provide a quantitative assessment of the cooling-energy savings potential by using the proposed new wall system.The intended retrofitting targets are the large amount of existing cavity-wall buildings located in hot climate regions.The quantification of the before-after heat-flux reduction was conducted through a 3-dimensional steady-state low turbulence computational fluid dynamics(CFD)model,which is validated by benchmarking its prediction against the published experimental case results.The outcomes of the investigation suggest that this simple low-cost solution has great potentials in reducing buildings’summer cooling load in hot climate regions.The applicability of this solution is not limited to retrofitting existing buildings.New energy-efficient building designs can also adopt this solution in their envelope systems.展开更多
Multiple clusters of coronavirus disease 2019(COVID-19)in Hong Kong have involved vertical transmissions in residential buildings,wherein the flats of confirmed cases were often vertically aligned.Data on the building...Multiple clusters of coronavirus disease 2019(COVID-19)in Hong Kong have involved vertical transmissions in residential buildings,wherein the flats of confirmed cases were often vertically aligned.Data on the buildings and cases associated with 19 such clusters were retrieved and compared with the corresponding data on the entirety of Hong Kong region.Vertical transmissions usually occurred in old high-rise buildings with small flat areas and low estate prices during winter.In addition,infection occurred frequently among the elderly and among upstairs neighbours of index cases.Virus-laden aerosols may have been transmitted between flats mostly via shared drainpipes,and the vertical distribution of the confirmed cases in a building varied by its drainage system design.For buildings with their entire drainpipes installed indoors,both the upstairs and downstairs neighbours of the index case flats could be infected.By comparison,buildings with their drainage stacks installed outdoors had lower infection risks and demonstrated a clearer pattern of vertical transmission:most infected cases resided upstairs from the index case flats,indicating that the virus spread could be dominated by the stack effect.This study provides valuable data and analysis for developing epidemic control strategies for residential buildings.展开更多
Tall buildings in cold climates have unique challenges in maintaining indoor air quality due to stack effect.During the heating season,interior air buoyancy creates large pressure differentials in vertical shafts that...Tall buildings in cold climates have unique challenges in maintaining indoor air quality due to stack effect.During the heating season,interior air buoyancy creates large pressure differentials in vertical shafts that can drive airflow from lower floors into upper floors.This pressure differential can result in the spread of contaminants throughout a building.Most recently,concern over COVID-19 has increased attention to the potential spread of airborne diseases in densely populated buildings.For many multi-unit residential buildings,suite ventilation has traditionally relied upon fresh air supplied through a mechanically pressurized corridor.In cold climates,large pressure differentials created by stack-effect can reduce the effectiveness of this approach.Multizone and CFD simulations are employed to analyze airflow and contaminant spread due to stack effect.Simulations are conducted on an idealized model of a 10-storey building using a range of experimentally derived airtightness parameters.Simulations demonstrate stack effect can reduce corridor ventilation to suites and even reverse the airflow for leakier buildings.Reduced airflow to suites can result in the accumulation of contaminants.Reversal of the airflow can allow contaminants from a suite to spread throughout the building.Contaminant spread is illustrated as a function of mechanical ventilation,building airtightness,and ambient temperatures.Strategies to reduce the influence of stack effect on mechanically pressurized corridors are discussed.展开更多
To investigate the effect of tunnel slope on hot gas movement and smoke distribution in a slopping tunnel fire,a series of tunnel fire models are built by fire dynamics simulator(FDS),with a slope varies from 0 to 10%...To investigate the effect of tunnel slope on hot gas movement and smoke distribution in a slopping tunnel fire,a series of tunnel fire models are built by fire dynamics simulator(FDS),with a slope varies from 0 to 10%.Parameters such as ceiling temperature and airflow velocity are measured.The results indicate that the relationship between smoke back-layering length and tunnel slope can be described as an exponential function.The smoke temperature at the downstream exit first increased and then decreased with a higher slope.The airflow velocity at downstream outlet increased nonlinearity when tunnel slope was less than 8%.In the slope tunnel,the fire smoke spread process can be divided into three stages.Fire smoke spreads upstream to the peak distance,subsequently,the upstream smoke layer decreases gradually,the tunnel fire reaches a quasi-steady state.The backflow characteristics of smoke in sloped tunnels are coupled with the downstream length and outlet smoke temperature.In the initial stage of a slope tunnel fire,smoke spreads upstream for a long distance,endangering human health.展开更多
The R-value is defined as,“a measure of the resistance of an insulating or building material to heat flow,expressed as R-11,R-20,and so on;the higher the number,the greater the resistance to heat flow(Random House,20...The R-value is defined as,“a measure of the resistance of an insulating or building material to heat flow,expressed as R-11,R-20,and so on;the higher the number,the greater the resistance to heat flow(Random House,2016).”The first thermodynamic principle violated by the R-value is the singular use of the word heat flow.Heat flow,or transfer,occurs in three distinct ways;conduction,convection,and radiation.The R-value test will only measure a bulk insulations resistance to conductive heat transfer.This type of heat flow is almost undetectable in the built environment,regardless of climate or season-resulting in the R-value myth.In winter,the stack effect will cause convective flows through the home as warm air under pressure rises and escapes through the top,requiring an equal amount of cold replacement air to infiltrate at the bottom.On hot sunny days,the exterior of the home absorbs long wave ultra violet(UV)rays from the sun and reemits this radiant heat energy into the residence.The thermodynamics of an occupied structure under varying atmospheric conditions is not well understood,leading to major inefficiencies.The goal of this conceptual study is to reveal the shortcomings of current insulation practices at the residential level,conceptualize a series of related issues for future study and develop a preliminary methodological concept for resolutions to the problems identified.Conclusions indicate that further research needs to be dedicated to replacing the R-value rule with a realistic metric that considers the efficiency,health,and safety of the entire building.展开更多
Sustainability on a residential renovation can be difficult to achieve.As this project was a complete gut renovation and two small additions,which included a new third story space,roof,and a rear addition,it was easy ...Sustainability on a residential renovation can be difficult to achieve.As this project was a complete gut renovation and two small additions,which included a new third story space,roof,and a rear addition,it was easy to investigate a wide variety of sustainable options.The building envelope was improved,interior aspects modified,and the energy generation systems explored and selected to all work in unison to enhance the end result of the project.In order to measure the degree of sustainability,ODG wanted to use a residential design rating system.At the time this house was designed there were few recognized residential rating systems available and none appeared to be as stringent and broad reaching as the LEED Commercial Rating system.ODG used the LEED 2.2 rating system as a guideline.When this project began,LEED for Homes had not yet been developed.The Hilltop Residence project sought to infuse an existing residence with the following qualities:cost effective technology,a“not to exceed”budget,a 75-year life cycle,the client’s aesthetics,functional living,sustainable design,and allow for productive healthy residents.ODG used the LEED categories of Sustainable Sites,Water Efficiency,Materials&Resources,Energy&Atmosphere,and Indoor Air Quality.The sustainable goals that were met affect both the building and the site.The home was designed to use rapidly renewable materials,use less water,conserve energy,generate its own electricity,automate the mechanical house processes,and reduce stormwater runoff.The renovated home conserved existing material and used new materials that are rapidly renewable.By designing to a 75-year life cycle,materials selected were either rapidly renewable or incredibly durable.Buildings designed for longer lifespans are inherently sustainable because their components will not need to be replaced as often.The reduction of operating and maintenance costs will pass savings directly to the client,providing a return on investment for the costs of the renovation and addition.By increasing the native vegetation,the site reduced runoff from the roof and decreased the amount of water being added to the storm sewer system.These goals,once realized and incorporated into the redesign of the townhome provide a clean,healthy indoor environment and highlight a residence with a climate responsive design and conservation practices.展开更多
基金Supported by the National Natural Science Foundation of Chinathe Doctoral Program Foundation of Institution of High Education the Research Foundation of State Key Laboratory of Coordination Chemistry,Nanjing University.
文摘The stabilities of the complexes of three pyridine-like ligands with M(II)(ATP)^(2-) and M(II)(M=Ni,Co)were studied by spectrophotometry and by comparing the stability constants of the ternary complexes with these of the binary complexes.A stacking interaction between the pyridine ring and the purine ring of ATP is indicated.The general existence of the stacking interaction encourages us to interpret the antitumor mechanism of a new class of antitumor drugs.
基金Project(50838009) supported by the National Natural Science Foundation of ChinaProject(2010DFA72740-03) supported by the National Key Technology Research and Development Program of China
文摘Stack effect is a dominant driving force for building natural ventilation.Analytical models were developed for the evaluation of stack effect in a shaft,accounting for the heat transfer from shaft interior boundaries.Both the conditions with constant heat flux from boundaries to the airflow and the ones with constant boundary temperature were considered.The prediction capabilities of these analytical models were evaluated by using large eddy simulation(LES) for a hypothetical shaft.The results show that there are fairly good agreements between the predictions of the analytical models and the LES predictions in mass flow rate,vertical temperatures profile and pressure difference as well.Both the results of analytical models and LES show that the neutral plane could locate higher than one half of the shaft height when the upper opening area is identical with the lower opening area.Further,it is also shown that the analytical models perform better than KLOTE's model does in the mass flow rate prediction.
基金supported by the National Key Project of Scientific and Technical Supporting Programs Funded by Ministry of Science &Technology of China ( Grant No: 2006BAJ13B03)the RGCCERG Grant #CityU1253/04E from Hong Kong Re-search Grant Council, HKSAR
文摘After comparing the mechanism of tilted plume under stack effect with that of spill plume,the tilted plume model induced by stack effect in a vertical shaft is developed simply based on the theoretical results and a series of full-scale tests. It is shown that the two sides of plume are symmetrical and have an accordant regulation that the plume radius has a linear relation to the height z. The profile of fire plume under stack effect is similar to the windblown flame in wind tunnel,and the range of flame deflection angle is about from 50 to 60 degree.
基金Supported by the National Natural Science Foundation of China under Grant No 61306126
文摘Higher-s dielectric LaLuO3, deposited by molecular beam deposition, with TiN as gate stack is integrated into high-mobility Si/SiGe/SOI quantum-well p-type metal-oxide-semiconduetor field effect transistors. Threshold voltage shift and capacitance equivalent thickness shrink are observed, resulting from oxygen scavenging effect in LaLuO3 with ti-rich TiN after high temperature annealing. The mechanism of oxygen scavenging and its potential for resistive memory applications are analyzed and discussed.
基金Supported by the National Natural Science Foundation of China(No.10774057).
文摘Protonated tetraphenylporphine（H2TPP） J-aggregates were prepared by aggregation on the liquid-air interface. Using FTIR spectroscopy, the authors observed the infrared absorption spectra of H2TPP and its J-aggregates. The IR spectra of H2TPP J-aggregates show significant changes compared with that of HETPP monomer. Intensity changes（e.g., strong enhancement of the in-plane vibronic mode and weakening of the out-of-plane vibronic mode of phenyl and porphyrin skeletal） were interpreted on the basis of stacking effects. Observation of the same type of bands collapse into single band was explained by the increase in the symmetry of H2TPP molecules. And the new bands at 1635 and 3407 cm^-1 indicate the aggregates containing a large amount of bound water.
基金Supported by the National Natural Science Foundation of China(Nos.6127403661371025+1 种基金61106038)Fund of Ministry of Education of China(No.20110111120012)
文摘Transistor aging has become the most important factor affecting the integrated circuit reliability.There is detection error caused by stacking effect in the stability checker in the previous respective aging sensors.An improved prediction aging sensor scheme is proposed using symmetrical NOR gate.Simulation experiments show the improved method eliminates prediction error caused by stacking effect.Layout area overhead is 4.65%and 7.06%compared to two respective sensor structures.
基金Project supported by the National Natural Science Foundation of China (No. 10972212)
文摘It is necessary to understand the features of air pressure in a drainage stack of a high-rise building for properly designing and operating a drainage system. This paper presents a mathematical model for predicting the stack performance. A step function is used to describe the effect of the air entrainment caused by the water discharged from branch pipes. An additional source term is introduced to reflect the gas-liquid interphase interaction （GLII） and stack base effect. The drainage stack is divided into upper and base parts. The air pressure in the upper part is predicted by a total variation diminishing （TVD） scheme, while in the base part, it is predicted by a characteristic line method （CLM）. The predicted results are compared with the data measured in a real-scale high- rise test building. It is found that the additional source term in the present model is effective. It intensively influences the air pressure distribution in the stack. The air pressure is also sensitive to the velocity-adjusting parameter （VAP）, the branch pipe air entrainment, and the conditions on the stack bottom.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(2020R1A2C3013676).
文摘Accurate energy demand simulation in high-rise buildings requires evaluating the impact of stack-induced infiltration.This study introduces a simplified method for calculating infiltration loads by predicting the neutral pressure level(NPL)based on key architectural and atmospheric data.The NPL location of the elevator shaft was determined through a mass balance approach by simplifying a multi-zone building to a single zone group on each floor.Based on the predicted NPL,the stack-induced pressure distribution was calculated to estimate the building’s infiltration rates.The method focuses exclusively on airflow driven by the stack effect,making it especially suitable for mid-and high-rise buildings where vertical airflow dominates.Case studies revealed significant variations in heating and cooling loads—up to 55%—due to differences in shaft planning,such as the number of vertical zones and service zone configuration.These findings underscore the importance of incorporating the vertical shaft plan into energy simulation.The proposed method provides comprehensive insights into the infiltration profiles by floor and can serve as a basis for developing strategies to manage load imbalances between floors.
文摘Leakage current of CMOS circuit increases dramatically with the technologyscaling down and has become a critical issue of high performance system. Subthreshold, gate andreverse biased junction band-to-band tunneling (BTBT) leakages are considered three maindeterminants of total leakage current. Up to now, how to accurately estimate leakage current oflarge-scale circuits within endurable time remains unsolved, even though accurate leakage modelshave been widely discussed. In this paper, the authors first dip into the stack effect of CMOStechnology and propose a new simple gate-level leakage current model. Then, a table-lookup basedtotal leakage current simulator is built up according to the model. To validate the simulator,accurate leakage current is simulated at circuit level using popular simulator HSPICE forcomparison. Some further studies such as maximum leakage current estimation, minimum leakage currentgeneration and a high-level average leakage current macromodel are introduced in detail.Experiments on ISCAS85 and ISCAS89 benchmarks demonstrate that the two proposed leakage currentestimation methods are very accurate and efficient.
文摘Indoor air dynamics and quality in high density residential buildings can be complex as it is affected by both building parameters,pollution sources,and outdoor meteorological conditions.The present study used CONTAM simulations to investigate the intra-building transport and concentration of an inert pollutant continuously emitted from an underground garage of a 15-floor building under moderate Mediterranean weather.The effects of outdoor meteorological conditions(air temperature,wind speed and direction)on indoor distribution of the emitted pollutant was tested under constant conditions.The importance of using actual transient meteorological data and the impact of their temporal resolution on calculated concentrations and exposure levels were also investigated.Vertical profiles of air exchange rate(AER)and CO concentration were shown to be sensitive to indoor-outdoor temperature difference,which controls the extent of the stack effect and its importance relative to wind effect.Even under constant conditions,transient mode simulations revealed that the time needed for pollutant distribution to reach steady state can be quite long(>24h in some cases).The temporal resolution(Ih vs.8h)of the meteorological data input was also found to impact calculated exposure levels,in an extent that varied with time,meteorological conditions and apartment position.
文摘A major roadblock in achieving substantial building energy reduction is the low performance of old buildings that account for a significant portion of the building energy consumption.Finding low-cost energy retrofit solutions that do not disrupt occupants’daily life during the retrofitting is the key to successful building energy retrofit initiatives.In this paper,a novel and low-cost exterior wall retrofitting solution is introduced,and its performance in reducing space cooling load was quantitatively evaluated to demonstrate its feasibility and effectiveness.The primary goal of this paper is to provide a quantitative assessment of the cooling-energy savings potential by using the proposed new wall system.The intended retrofitting targets are the large amount of existing cavity-wall buildings located in hot climate regions.The quantification of the before-after heat-flux reduction was conducted through a 3-dimensional steady-state low turbulence computational fluid dynamics(CFD)model,which is validated by benchmarking its prediction against the published experimental case results.The outcomes of the investigation suggest that this simple low-cost solution has great potentials in reducing buildings’summer cooling load in hot climate regions.The applicability of this solution is not limited to retrofitting existing buildings.New energy-efficient building designs can also adopt this solution in their envelope systems.
基金supported by the Research Grants Council of Hong Kong's Collaborative Research Fund,Hong Kong SAR[No.C7025-16G].
文摘Multiple clusters of coronavirus disease 2019(COVID-19)in Hong Kong have involved vertical transmissions in residential buildings,wherein the flats of confirmed cases were often vertically aligned.Data on the buildings and cases associated with 19 such clusters were retrieved and compared with the corresponding data on the entirety of Hong Kong region.Vertical transmissions usually occurred in old high-rise buildings with small flat areas and low estate prices during winter.In addition,infection occurred frequently among the elderly and among upstairs neighbours of index cases.Virus-laden aerosols may have been transmitted between flats mostly via shared drainpipes,and the vertical distribution of the confirmed cases in a building varied by its drainage system design.For buildings with their entire drainpipes installed indoors,both the upstairs and downstairs neighbours of the index case flats could be infected.By comparison,buildings with their drainage stacks installed outdoors had lower infection risks and demonstrated a clearer pattern of vertical transmission:most infected cases resided upstairs from the index case flats,indicating that the virus spread could be dominated by the stack effect.This study provides valuable data and analysis for developing epidemic control strategies for residential buildings.
基金supported by the Natural Sciences and Engineering Research Council of Canada[NSERC DG 2016-04176].
文摘Tall buildings in cold climates have unique challenges in maintaining indoor air quality due to stack effect.During the heating season,interior air buoyancy creates large pressure differentials in vertical shafts that can drive airflow from lower floors into upper floors.This pressure differential can result in the spread of contaminants throughout a building.Most recently,concern over COVID-19 has increased attention to the potential spread of airborne diseases in densely populated buildings.For many multi-unit residential buildings,suite ventilation has traditionally relied upon fresh air supplied through a mechanically pressurized corridor.In cold climates,large pressure differentials created by stack-effect can reduce the effectiveness of this approach.Multizone and CFD simulations are employed to analyze airflow and contaminant spread due to stack effect.Simulations are conducted on an idealized model of a 10-storey building using a range of experimentally derived airtightness parameters.Simulations demonstrate stack effect can reduce corridor ventilation to suites and even reverse the airflow for leakier buildings.Reduced airflow to suites can result in the accumulation of contaminants.Reversal of the airflow can allow contaminants from a suite to spread throughout the building.Contaminant spread is illustrated as a function of mechanical ventilation,building airtightness,and ambient temperatures.Strategies to reduce the influence of stack effect on mechanically pressurized corridors are discussed.
基金National Nature Science Funds of China[No.52106185]Fellowship of China Postdoctoral Science Founda-tion[No.2021M693042].
文摘To investigate the effect of tunnel slope on hot gas movement and smoke distribution in a slopping tunnel fire,a series of tunnel fire models are built by fire dynamics simulator(FDS),with a slope varies from 0 to 10%.Parameters such as ceiling temperature and airflow velocity are measured.The results indicate that the relationship between smoke back-layering length and tunnel slope can be described as an exponential function.The smoke temperature at the downstream exit first increased and then decreased with a higher slope.The airflow velocity at downstream outlet increased nonlinearity when tunnel slope was less than 8%.In the slope tunnel,the fire smoke spread process can be divided into three stages.Fire smoke spreads upstream to the peak distance,subsequently,the upstream smoke layer decreases gradually,the tunnel fire reaches a quasi-steady state.The backflow characteristics of smoke in sloped tunnels are coupled with the downstream length and outlet smoke temperature.In the initial stage of a slope tunnel fire,smoke spreads upstream for a long distance,endangering human health.
文摘The R-value is defined as,“a measure of the resistance of an insulating or building material to heat flow,expressed as R-11,R-20,and so on;the higher the number,the greater the resistance to heat flow(Random House,2016).”The first thermodynamic principle violated by the R-value is the singular use of the word heat flow.Heat flow,or transfer,occurs in three distinct ways;conduction,convection,and radiation.The R-value test will only measure a bulk insulations resistance to conductive heat transfer.This type of heat flow is almost undetectable in the built environment,regardless of climate or season-resulting in the R-value myth.In winter,the stack effect will cause convective flows through the home as warm air under pressure rises and escapes through the top,requiring an equal amount of cold replacement air to infiltrate at the bottom.On hot sunny days,the exterior of the home absorbs long wave ultra violet(UV)rays from the sun and reemits this radiant heat energy into the residence.The thermodynamics of an occupied structure under varying atmospheric conditions is not well understood,leading to major inefficiencies.The goal of this conceptual study is to reveal the shortcomings of current insulation practices at the residential level,conceptualize a series of related issues for future study and develop a preliminary methodological concept for resolutions to the problems identified.Conclusions indicate that further research needs to be dedicated to replacing the R-value rule with a realistic metric that considers the efficiency,health,and safety of the entire building.
文摘Sustainability on a residential renovation can be difficult to achieve.As this project was a complete gut renovation and two small additions,which included a new third story space,roof,and a rear addition,it was easy to investigate a wide variety of sustainable options.The building envelope was improved,interior aspects modified,and the energy generation systems explored and selected to all work in unison to enhance the end result of the project.In order to measure the degree of sustainability,ODG wanted to use a residential design rating system.At the time this house was designed there were few recognized residential rating systems available and none appeared to be as stringent and broad reaching as the LEED Commercial Rating system.ODG used the LEED 2.2 rating system as a guideline.When this project began,LEED for Homes had not yet been developed.The Hilltop Residence project sought to infuse an existing residence with the following qualities:cost effective technology,a“not to exceed”budget,a 75-year life cycle,the client’s aesthetics,functional living,sustainable design,and allow for productive healthy residents.ODG used the LEED categories of Sustainable Sites,Water Efficiency,Materials&Resources,Energy&Atmosphere,and Indoor Air Quality.The sustainable goals that were met affect both the building and the site.The home was designed to use rapidly renewable materials,use less water,conserve energy,generate its own electricity,automate the mechanical house processes,and reduce stormwater runoff.The renovated home conserved existing material and used new materials that are rapidly renewable.By designing to a 75-year life cycle,materials selected were either rapidly renewable or incredibly durable.Buildings designed for longer lifespans are inherently sustainable because their components will not need to be replaced as often.The reduction of operating and maintenance costs will pass savings directly to the client,providing a return on investment for the costs of the renovation and addition.By increasing the native vegetation,the site reduced runoff from the roof and decreased the amount of water being added to the storm sewer system.These goals,once realized and incorporated into the redesign of the townhome provide a clean,healthy indoor environment and highlight a residence with a climate responsive design and conservation practices.
