On the competition between lateral convection and upward displacement in a multi-zone naturally ventilated space

AbstractWe consider the flow which develops when two separate spaces maintained at different temperatures, both in excess of the exterior temperature, are connected through high and low level openings to a central atrium in which there is negligible heat load but which can naturally ventilate through high and low level openings to the exterior. We show that with a small temperature contrast between the spaces or large openings from the atrium to the exterior, upflow displacement ventilation develops in each of the spaces, with air entering from the atrium at low level and exiting at high level. However, with a larger temperature contrast between the spaces or small openings between the atrium and the exterior, a convective circulation develops between the spaces, with upflow in the warmer space and downflow in the colder space. Exterior air, which may enter the atrium at low level, flows into the warmer space along with the air from the colder space. At high level, air flows back into the atrium from the warmer space, and then either vents from the building or flows into the colder space. In this convection dominated flow regime, the colder space is a net heat sink, whereas with the upward displacement ventilation, this space acts as a net heat source. This can have significant implications for energy usage and on the build up of contaminants in each of the spaces. We also show that in both steady flow regimes, the air at mid-level in the atrium is unventilated and stagnant. We discuss the relevance of our model for controlled natural ventilation in large public buildings such as shopping malls where individual shops often maintain temperatures independently of the central atrium-space.

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Displacement ventilation: a viable ventilation strategy for makeshift hospitals and public buildings to contain COVID-19 and other airborne diseases

Royal Society Open Science ◽

10.1098/rsos.200680 ◽

2020 ◽

Vol 7 (9) ◽

pp. 200680

Author(s):

Rajesh K. Bhagat ◽

P. F. Linden

Keyword(s):

Negative Pressure ◽

Natural Ventilation ◽

Public Spaces ◽

Positive Pressure ◽

Air Conditioner ◽

Displacement Ventilation ◽

Link Type ◽

Building Ventilation ◽

High Level ◽

General Wards

The SARS-CoV-2 virus has so far infected more than 31 million people around the world, and its impact is being felt by all. Patients with diseases such as COVID-19 should ideally be treated in negative pressure isolation rooms. However, due to the overwhelming demand for hospital beds, patients have been treated in general wards, hospital corridors and makeshift hospitals. Adequate building ventilation in hospitals and public spaces is a crucial factor to contain the disease (Escombe et al. 2007 PLoS Med. 4 ; Escombe et al. 2019 BMC Infect. Dis. 19 , 88 ( doi:10.1186/s12879-019-3717-9 ); Morawska & Milton 2020 Clin. Infect. Dis . ciaa939. ( doi:10.1093/cid/ciaa939 )), to exit lockdown safely, and reduce the chance of subsequent waves of outbreaks. A recently reported air-conditioner-induced COVID-19 outbreak caused by an asymptomatic patient, in a restaurant in Guangzhou, China (Lu et al. 2020 Emerg. Infect. Dis. 26 ) exposes our vulnerability to future outbreaks linked to ventilation in public spaces. We argue that displacement ventilation (either mechanical or natural ventilation), where air intakes are at low level and extracts are at high level, is a viable alternative to negative pressure isolation rooms, which are often not available on site in hospital wards and makeshift hospitals. Displacement ventilation produces negative pressure at the occupant level, which draws fresh air from outdoors, and positive pressure near the ceiling, which expels the hot and contaminated air out. We acknowledge that, in both developed and developing countries, many modern large structures lack the openings required for natural ventilation. This lack of openings can be supplemented by installing extract fans. We have also discussed and addressed the issue of the ‘lock-up effect’. We provide guidelines for such mechanically assisted, naturally ventilated makeshift hospitals.

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Unbalanced exchange flow and its implications for the night cooling of buildings by displacement ventilation

Environmental Fluid Mechanics ◽

10.1007/s10652-021-09785-7 ◽

2021 ◽

Author(s):

Nick Wise ◽

Gary Hunt

Keyword(s):

Theoretical Model ◽

Low Energy ◽

Exchange Flow ◽

Displacement Ventilation ◽

Excess Heat ◽

Low Level ◽

Cooling Strategy ◽

Rate Of Cooling ◽

Flow Changes ◽

High Level

AbstractPassive ventilation of buildings at night forms an essential part of a low-energy cooling strategy, enabling excess heat that has accumulated during the day to self-purge and be replaced with cooler night air. Instrumental to the success of a purge are the locations and areas of ventilation openings, and openings positioned at low and at high levels are a common choice as there is then the expectation that a buoyancy-driven displacement flow will establish and persist. Desirable for their efficiency, displacement flows guide excess heat out through high-level openings and cooler air in through low-level openings. Herein we show that displacement flow cannot be maintained for the full duration of a purge. Instead, the flow must transition to an ‘unbalanced exchange flow’, whereby the cool inflow of air at low level is maintained but there is now a warm outflow and a cool inflow occurring simultaneously at the high-level opening. The internal redistribution of heat caused by this exchange alters the rate at which heat is self-purged and the time thought necessary to complete a purge. We develop a theoretical model that captures and predicts these behaviours. Our approach is distinct from all others which assume that a displacement flow will persist throughout the purge. Based on this enhanced understanding, and specifically that the transition to unbalanced exchange flow changes the rate of cooling and resultant emptying times, we anticipate that practitioners will be better placed to design passive systems that meet their target specifications for cooling.

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Displacement ventilation: a viable ventilation strategy for makeshift hospitals and public buildings to contain Covid-19 and other airborne diseases

10.1101/2020.04.22.20075648 ◽

2020 ◽

Cited By ~ 1

Author(s):

Rajesh K. Bhagat ◽

P. F. Linden

Keyword(s):

Negative Pressure ◽

Natural Ventilation ◽

Public Spaces ◽

Positive Pressure ◽

Air Conditioner ◽

Displacement Ventilation ◽

Public Buildings ◽

Building Ventilation ◽

High Level ◽

General Wards

AbstractThe SARS-CoV-2 virus has so far infected more than 2.4 million people around the world, and its impact is being felt by all. Patients with airborne diseases such as Covid-19 should ideally be treated in negative pressure isolation rooms. However, due to the overwhelming demand for hospital beds, patients are being treated in general wards, hospital corridors, and makeshift hospitals. Adequate building ventilation in hospitals and public spaces is a crucial factor to contain the disease1,2, to exit the current lockdown situation, and reduce the chance of subsequent waves of outbreaks. Lu et al. 3 reported an air-conditioner induced Covid-19 outbreak, by an asymptomatic patient, in a restaurant in Guangzhou, China, which exposes our vulnerability to future outbreaks linked to ventilation in public spaces. We demonstrate that displacement ventilation (either mechanical or natural ventilation), where air intakes are at low level and extracts are at high level, is a viable alternative to negative pressure isolation rooms, which are often not available on site in hospital wards and makeshift hospitals. Displacement ventilation produces negative pressure at the occupant level, which draws fresh air from outdoor, and positive pressure near the ceiling, which expels the hot and contaminated air out. We acknowledge that, in both developed and developing countries, many modern large structures lack the openings required for natural ventilation. This lack of openings can be supplemented by installing extract fans. We provide guidelines for such mechanically assisted-naturally ventilated makeshift hospitals, and public spaces such as supermarkets and essential public buildings.

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On the effect of distributed cooling in natural ventilation

Journal of Fluid Mechanics ◽

10.1017/s0022112007009809 ◽

2008 ◽

Vol 600 ◽

pp. 1-17 ◽

Cited By ~ 6

Author(s):

S. R. LIVERMORE ◽

A. W. WOODS

Keyword(s):

Heat Source ◽

Laboratory Experiments ◽

Natural Ventilation ◽

Lower Layer ◽

Heated Plate ◽

Distributed Source ◽

Low Level ◽

High Level ◽

Enclosed Space

We examine the natural ventilation flows which develop when a low-level heat source interacts with a distributed zone of cooling at high level in an enclosed space. We develop some new analogue laboratory experiments in which we use a saline plume to model a localized heat source and a heated plate to model a distributed source of cooling. The experiments show that in a building with a low-level point source of heating, a two-layer steady stratification develops in which the depth of the lower layer decreases as the intensity of the cooling at the ceiling increases. We develop a theoretical model which accounts for the penetrative entrainment across the interface associated with the convection in the upper layer. We show that this becomes more dominant as the cooling increases and eventually the room becomes well-mixed. We discuss the role of such distributed cooling on the design of natural ventilation and its ability to provide sufficient flow and adequate temperature control.

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Teknik Data Mining Dalam Clustering Produksi Susu Segar Di Indonesia Dengan Algoritma K-Means

BRAHMANA: Jurnal Penerapan Kecerdasan Buatan ◽

10.30645/brahmana.v1i1.5 ◽

2019 ◽

Vol 1 (1) ◽

pp. 31-39

Author(s):

Ilham Safitra Damanik ◽

Sundari Retno Andani ◽

Dedi Sehendro

Keyword(s):

Data Mining ◽

Milk Production ◽

Clustering Algorithm ◽

Clustering Method ◽

Data Mining Techniques ◽

Low Level ◽

Fresh Milk ◽

Nutritional Needs ◽

High Level ◽

Level Cluster

Milk is an important intake to meet nutritional needs. Both consumed by children, and adults. Indonesia has many producers of fresh milk, but it is not sufficient for national milk needs. Data mining is a science in the field of computers that is widely used in research. one of the data mining techniques is Clustering. Clustering is a method by grouping data. The Clustering method will be more optimal if you use a lot of data. Data to be used are provincial data in Indonesia from 2000 to 2017 obtained from the Central Statistics Agency. The results of this study are in Clusters based on 2 milk-producing groups, namely high-dairy producers and low-milk producing regions. From 27 data on fresh milk production in Indonesia, two high-level provinces can be obtained, namely: West Java and East Java. And 25 others were added in 7 provinces which did not follow the calculation of the K-Means Clustering Algorithm, including in the low level cluster.

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Determinants of Abuse of the Bodies of the Dead

Rossijskoe Pravo. Obrazovanie, Praktika, Nauka ◽

10.34076/2410-2709-2019-4-71-77 ◽

2019 ◽

pp. 71-77

Author(s):

Margarita Khomyakova

Keyword(s):

Low Income ◽

Criminal Code ◽

Value Judgments ◽

Legal Norms ◽

Low Level ◽

Medical Institutions ◽

Specific Object ◽

The Subject ◽

The Dead ◽

High Level

The author analyzes definitions of the concepts of determinants of crime given by various scientists and offers her definition. In this study, determinants of crime are understood as a set of its causes, the circumstances that contribute committing them, as well as the dynamics of crime. It is noted that the Russian legislator in Article 244 of the Criminal Code defines the object of this criminal assault as public morality. Despite the use of evaluative concepts both in the disposition of this norm and in determining the specific object of a given crime, the position of criminologists is unequivocal: crimes of this kind are immoral and are in irreconcilable conflict with generally accepted moral and legal norms. In the paper, some views are considered with regard to making value judgments which could hardly apply to legal norms. According to the author, the reasons for abuse of the bodies of the dead include economic problems of the subject of a crime, a low level of culture and legal awareness; this list is not exhaustive. The main circumstances that contribute committing abuse of the bodies of the dead and their burial places are the following: low income and unemployment, low level of criminological prevention, poor maintenance and protection of medical institutions and cemeteries due to underperformance of state and municipal bodies. The list of circumstances is also open-ended. Due to some factors, including a high level of latency, it is not possible to reflect the dynamics of such crimes objectively. At the same time, identification of the determinants of abuse of the bodies of the dead will reduce the number of such crimes.

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EXPRESS: Marketers Project Their Personal Preferences onto Consumers: Overcoming the Threat of Egocentric Decision Making

Journal of Marketing Research ◽

10.1177/0022243721998378 ◽

2021 ◽

pp. 002224372199837

Author(s):

Walter Herzog ◽

Johannes D. Hattula ◽

Darren W. Dahl

Keyword(s):

Decision Making ◽

Consumer Preferences ◽

Research Question ◽

Pilot Studies ◽

Low Level ◽

Marketing Managers ◽

False Consensus Effect ◽

False Consensus ◽

High Level

This research explores how marketing managers can avoid the so-called false consensus effect—the egocentric tendency to project personal preferences onto consumers. Two pilot studies were conducted to provide evidence for the managerial importance of this research question and to explore how marketing managers attempt to avoid false consensus effects in practice. The results suggest that the debiasing tactic most frequently used by marketers is to suppress their personal preferences when predicting consumer preferences. Four subsequent studies show that, ironically, this debiasing tactic can backfire and increase managers’ susceptibility to the false consensus effect. Specifically, the results suggest that these backfire effects are most likely to occur for managers with a low level of preference certainty. In contrast, the results imply that preference suppression does not backfire but instead decreases false consensus effects for managers with a high level of preference certainty. Finally, the studies explore the mechanism behind these results and show how managers can ultimately avoid false consensus effects—regardless of their level of preference certainty and without risking backfire effects.

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Exploring The Effect of Visual Information Degradation on Human Perception and Performance In A Human-Telerobot System

Proceedings of the Human Factors and Ergonomics Society Annual Meeting ◽

10.1177/1071181320641310 ◽

2020 ◽

Vol 64 (1) ◽

pp. 1302-1307

Author(s):

Richard Stone ◽

Minglu Wang ◽

Thomas Schnieders ◽

Esraa Abdelall

Keyword(s):

Visual Information ◽

Human Perception ◽

Low Level ◽

Hit Rate ◽

Word Level ◽

Level Of Automation ◽

Significant Difference ◽

Human Operators ◽

And Performance ◽

High Level

Human-robotic interaction system are increasingly becoming integrated into industrial, commercial and emergency service agencies. It is critical that human operators understand and trust automation when these systems support and even make important decisions. The following study focused on human-in-loop telerobotic system performing a reconnaissance operation. Twenty-four subjects were divided into groups based on level of automation (Low-Level Automation (LLA), and High-Level Automation (HLA)). Results indicated a significant difference between low and high word level of control in hit rate when permanent error occurred. In the LLA group, the type of error had a significant effect on the hit rate. In general, the high level of automation was better than the low level of automation, especially if it was more reliable, suggesting that subjects in the HLA group could rely on the automatic implementation to perform the task more effectively and more accurately.

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