Natural ventilation of buildings theory measurement and design pdf
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- Ventilation (architecture)
- Natural Ventilation of Buildings - Ebook
- Natural Ventilation of Buildings (eBook, PDF)
Ventilation is the intentional introduction of outdoor air into a space. Ventilation is mainly used to control indoor air quality by diluting and displacing indoor pollutants; it can also be used to control indoor temperature, humidity, and air motion to benefit thermal comfort , satisfaction with other aspects of indoor environment, or other objectives.
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Institutional transmission of airborne infections such as tuberculosis TB is an important public health problem, especially in resource-limited settings where protective measures such as negative-pressure isolation rooms are difficult to implement.
Natural ventilation may offer a low-cost alternative. Our objective was to investigate the rates, determinants, and effects of natural ventilation in health care settings.
In these hospitals 70 naturally ventilated clinical rooms where infectious patients are likely to be encountered were studied. These included respiratory isolation rooms, TB wards, respiratory wards, general medical wards, outpatient consulting rooms, waiting rooms, and emergency departments.
These rooms were compared with 12 mechanically ventilated negative-pressure respiratory isolation rooms built post Ventilation was measured using a carbon dioxide tracer gas technique in experiments. Architectural and environmental variables were measured. For each experiment, infection risk was estimated for TB exposure using the Wells-Riley model of airborne infection.
Opening windows and doors maximises natural ventilation so that the risk of airborne contagion is much lower than with costly, maintenance-requiring mechanical ventilation systems. Old-fashioned clinical areas with high ceilings and large windows provide greatest protection. Natural ventilation costs little and is maintenance free, and is particularly suited to limited-resource settings and tropical climates, where the burden of TB and institutional TB transmission is highest.
In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion. PLoS Med 4 2 : e This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
These funding agencies had no involvement in the conduct or publication of this research. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. Tuberculosis TB is a major cause of ill health and death worldwide, with around one-third of the world's population infected with the bacterium that causes it Mycobacterium tuberculosis.
One person with active tuberculosis can go on to infect many others; the bacterium is passed in tiny liquid droplets that are produced when someone with active disease coughs, sneezes, spits, or speaks. The risk of tuberculosis being transmitted in hospital settings is particularly high, because people with tuberculosis are often in close contact with very many other people. Currently, most guidelines recommend that the risk of transmission be controlled in certain areas where TB is more likely by making sure that the air in rooms is changed with fresh air between six and 12 times an hour.
Air changes can be achieved with simple measures such as opening windows and doors, or by installing mechanical equipment that forces air changes and also keeps the air pressure in an isolation room lower than that outside it. In many parts of the world, hospitals do not have equipment even for simple air conditioning, let alone the special equipment needed for forcing high air changes in isolation rooms and wards.
Instead they rely on opening windows and doors in order to reduce the transmission of TB, and this is called natural ventilation. However, it is not clear whether these sorts of measures are adequate for controlling TB transmission. It is important to find out what sorts of systems work best at controlling TB in the real world, so that hospitals and wards can be designed appropriately, within available resources.
This study was based in Lima, Peru's capital city. The researchers studied a variety of rooms, including tuberculosis wards and respiratory isolation rooms, in the city's hospitals. Rooms which had only natural measures for encouraging airflow were compared with mechanically ventilated, negative pressure rooms, which were built much more recently. A comparison was also done between rooms in old hospitals that were naturally ventilated with rooms in newer hospitals that were also naturally ventilated.
The researchers used a particular method to measure the number of air changes per hour within each room, and based on this they estimated the risk of a person with TB infecting others using a method called the Wells-Riley equation. The results showed that natural ventilation provided surprisingly high rates of air exchange, with an average of 28 air changes per hour.
Hospitals over 50 years old, which generally had large windows and high ceilings, had the highest ventilation, with an average of 40 air changes per hour. This rate compared with 17 air changes per hour in naturally ventilated rooms in modern hospitals, which tended to have lower ceilings and smaller windows.
The rooms with modern mechanical ventilation were supposed to have 12 air changes per hour but in reality this was not achieved, as the systems were not maintained properly. These findings suggest that natural methods of encouraging airflow e. Some aspects of the design of wards in old hospitals such as large windows and high ceilings are also likely to achieve better airflow and reduce the risk of infection.
In poor countries, where mechanical ventilation systems might be too expensive to install and maintain properly, rooms that are designed to naturally achieve good airflow might be the best choice. Another advantage of natural ventilation is that it is not restricted by cost to just high-risk areas, and can therefore be used in many different parts of the hospital, including emergency departments, outpatient departments, and waiting rooms, and it is here that many infectious patients are to be found.
Infections transmitted by the airborne route are leading causes of morbidity and mortality worldwide, with tuberculosis TB alone causing 1. Outbreaks occur in prisons [ 2 , 3 ], homeless shelters [ 4 , 5 ], and schools [ 6 ], but it is health care facilities that may pose the greatest risk from airborne contagion by congregating infectious and susceptible individuals, resulting in frequent airborne nosocomial transmission [ 7 — 11 ].
This public health problem is exacerbated by HIV infection, which increases both susceptibility and hospitalisation. In industrialised nations, optimal care for patients at risk of transmitting airborne infections includes isolation in mechanically ventilated negative-pressure rooms. Staff and visitors wear particulate respirators, and dilutional ventilation with uncontaminated air provides additional protection from disease transmission when patients generate infectious aerosols by coughing.
Ventilation is usually measured in air changes per hour ACH , with guidelines recommending 6—12 ACH for the control of TB transmission in high-risk health care settings [ 12 ]. However, focusing on ACH alone may be misleading [ 13 ], because the absolute ventilation of a room per occupant is a major determinant of contagion in models of airborne infection, such as the Wells-Riley equation [ 14 ].
Protection against the transmission of airborne infection is increased by maximising absolute ventilation per occupant, which may be achieved by increasing the number of ACH or by increasing the room volume per occupant for a given rate of air exchange.
Dilutional ventilation with fresh air becomes critical for airborne infection control whenever infectious and susceptible people share air space without the use of particulate respirators, such as in waiting rooms, outpatient clinics, emergency departments, shared wards, and investigation suites.
These spaces are often ventilated at levels well below those recommended for the control of TB transmission. Furthermore, most airborne infections such as TB occur in the developing world where isolation facilities are sparse, effective mechanical ventilation is often too costly to install or maintain, respirator use is infrequent, and wards and waiting areas are frequently overcrowded.
Consequently, transmission of airborne infections to staff, relatives, and other patients is even more common in the developing world, where health care facilities may disseminate the very infections they are attempting to control. In resource-limited settings lacking negative-pressure respiratory isolation, natural ventilation by opening windows is recommended for the control of nosocomial TB [ 15 ], but the rates and determinants of natural ventilation in health care facilities have not been defined.
We therefore measured ventilation in a variety of hospital wards and clinics where infectious patients are likely to be encountered. We investigated the determinants of natural ventilation, and used mathematical modelling to evaluate the effect of natural ventilation on airborne TB transmission.
Ventilation was measured in experiments in 70 naturally ventilated rooms in eight hospitals in Lima, Peru. Direction of airflow was assessed using smoke tubes.
ACH were measured using a tracer gas concentration-decay technique [ 16 ]. With all windows and doors closed, carbon dioxide CO 2 was released and mixed well with room air using large fans to create a spatially uniform CO 2 concentration in the room. Fans were then switched off so as not to interfere with natural ventilation air currents. Depending on room size, after 5—15 min, windows and doors were opened, either simultaneously or sequentially. ACH were calculated as the gradient of the straight line through the natural logarithm of CO 2 concentration plotted against time in hours [ 16 ].
Exposure duration was 24 h, and susceptible individuals were assumed to be unprotected by particulate respirators. All statistical analyses were performed with Stata v. Determinants of ventilation and infection risk were first assessed by univariate regression. Three separate dependent variables were evaluated. Two were measures of ventilation. The third dependent variable was an estimate of TB transmission risk for exposure to patients producing 13 infectious quanta per hour as detailed in the preceding paragraph.
For all regressions dependent variables were normalised by log 10 -transformation, and a generalised estimating equation [ 20 ] was used to fit clustering of observations within rooms. Changes in CO 2 concentration were measured in each room. A characteristic pattern was observed of slow CO 2 concentration-decay with windows and doors closed, which markedly increased on opening windows and doors.
Figure 1 shows a typical concentration-decay curve, demonstrating the rapid increase in carbon dioxide removal by ventilation when windows and doors were opened. Such data was obtained for all rooms measured. The corresponding ACH were 28 versus 12 versus 1. After windows and doors were opened, CO 2 concentrations fell rapidly, indicating a calculated ventilation rate of 12 ACH. Repeated experiments of this type defined the effect of architectural and environmental variables on natural ventilation.
Opening increasing numbers of windows and doors increased ventilation. This is demonstrated in Figure 2 and Table 1 where absolute ventilation is shown for naturally ventilated rooms with windows and doors closed; partially open i. The lowest versus the upper three quartiles of wind speed combined are shown in Figure 2 and demonstrate the increase in natural ventilation with increasing wind speed and the rates of natural ventilation achieved even on relatively still days.
Figure 2 also shows the absolute ventilation calculated for the 12 mechanically ventilated respiratory isolation rooms in the study, assuming they were ventilated at the 12 ACH according to guidelines for high-risk areas [ 12 ]. The effect of partial and complete window opening and wind speed on natural ventilation is shown, compared with mechanically ventilated negative-pressure respiratory isolation rooms.
The triplet of bars on the left of the graph represents absolute ventilation measured in naturally ventilated clinical rooms on days when wind speed was within the lowest quartile i.
The triplet of bars in the centre of the graph represents absolute ventilation at wind speeds in the upper three quartiles combined i. The single bar on the right of the graph represents absolute ventilation in mechanically ventilated negative-pressure respiratory isolation wards at 12 ACH.
The corresponding median ACH for the seven bars from left to right are: 1. Old-fashioned facilities built pre had greater natural ventilation than more modern rooms built — Compared with the modern naturally ventilated facilities, these pre facilities were larger 85 m 3 versus 60 m 3 , with higher ceilings 4.
Ventilation and protection against airborne infection is shown for pre versus modern — naturally ventilated facilities versus mechanically ventilated negative-pressure respiratory isolation rooms. Data are shown for 64 naturally ventilated rooms with windows and doors fully open the remaining six naturally ventilated rooms had windows that could not be fully opened. Figure 4 shows modelling of airborne TB transmission risk over time for pre versus modern naturally ventilated facilities versus mechanically ventilated respiratory isolation rooms at 12 ACH.
Three different scenarios of increasing source infectiousness were investigated and demonstrate that the protective effect of ventilation diminishes as the infectiousness of the source increases. Figure 4 also demonstrates that the model predicts that all exposed susceptible persons eventually become infected when duration of exposure increases sufficiently.
The estimated risk of TB infection over time for exposure to three TB source cases of different infectiousness is shown for pre naturally ventilated facilities dotted lines versus modern — naturally ventilated facilities dashed lines versus mechanically ventilated negative-pressure isolation facilities at 12 ACH continuous lines.
Median values for all measures of absolute ventilation for each category of naturally ventilated room with all windows and doors open have been used in the model. Smoke tube testing in each room demonstrated the direction of airflow through doors or windows during experiments.
These patterns reflected the position of a room and its windows and doors in relation to the prevailing wind in Lima. The mechanically ventilated facility delivered less than half the number of ACH recommended when measured unpublished data. On inspection, air extraction and supply fans were unprotected by filters, motors were poorly maintained, and fan blades were corroded and clogged with deposits. Therefore, to improve external validity, values of 12 ACH and corresponding calculated values for absolute ventilation were substituted for all comparisons between mechanical and natural ventilation.
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: Due to the presence of high temperature and humidity in the sub-tropical climate like Phuentsholing, residents are forced to use electro mechanical ventilation increasing the energy consumption by a building. Phenomena such as global warming, population growth and longing for luxury living are the key reasons for an increase in energy demand.
Jetzt bewerten Jetzt bewerten. Natural ventilation is considered a prerequisite for sustainablebuildings and is therefore in line with current trends in theconstruction industry. The design of naturally ventilated buildingsis more difficult and carries greater risk than those that aremechanically ventilated. A successful result relies increasingly ona good understanding of the abilities and limitations of thetheoretical and experimental procedures that are used for design. There are two ways to naturally ventilate a building: winddriven ventilation and stack ventilation. The majority of buildingsemploying natural …mehr.
The design of naturally ventilated buildings is more difficult and carries greater risk than Natural Ventilation of Buildings: Theory, Measurement and Design.
Natural Ventilation of Buildings - Ebook
NCBI Bookshelf. Geneva: World Health Organization; Ventilation moves outdoor air into a building or a room, and distributes the air within the building or room. There are three methods that may be used to ventilate a building: natural, mechanical and hybrid mixed-mode ventilation.
Natural ventilation is considered a prerequisite for sustainable buildings and is therefore in line with current trends in the construction industry. The design of naturally ventilated buildings is more difficult and carries greater risk than those that are mechanically ventilated. A successful result relies increasingly on a good understanding of the abilities and limitations of the theoretical and experimental procedures that are used for design. There are two ways to naturally ventilate a building: wind driven ventilation and stack ventilation. The majority of buildings employing natural ventilation rely primarily on wind driven ventilation, but the most efficient design should implement both types.
Institutional transmission of airborne infections such as tuberculosis TB is an important public health problem, especially in resource-limited settings where protective measures such as negative-pressure isolation rooms are difficult to implement. Natural ventilation may offer a low-cost alternative. Our objective was to investigate the rates, determinants, and effects of natural ventilation in health care settings. In these hospitals 70 naturally ventilated clinical rooms where infectious patients are likely to be encountered were studied.
Natural Ventilation of Buildings (eBook, PDF)
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI:
Discharge coefficients C D are key input data in the evaluation of energy performance of naturally ventilated buildings. Such buildings are characterized by large openings windows, grills, vents for which accurate experimental data are rarely available in the literature or from manufacturers. In order to contribute with an experimental method for assessment and with new C D values from windows typically found in Brazil and Germany, this paper describes a set of experiments assessing the discharge coefficient of these windows for cross-ventilation. Experiments were carried out based on the standard BS EN set-up in a wind-tunnel with full-scale models. The investigated sample also comprised windows whose C D values were known for the validation of the method. Results for known windows are in line with previous work.
Natural Ventilation of Buildings: Theory, Measurement and Design comprehensively explains the fundamentals of the theory and measurement of natural.
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