Ventilation rate

Design dampers so that system will handle the minimum safe ventilation rate at maximum damper throttling... 

At times the ventilation rate becomes very low. Such a lack of air motion usually occurs in the weak pressure gradient near the center of an anticy-... 

Overcrowding issues should be noted. Future occupant density is estimated when the ventilation system for a building is designed. When the actual number of occupants approaches or exceeds this occupant design capacity, managers may find that lAQ complaints increase. At that point, the outdoor air ventilation rate will have to be increased. However, the ventilation and cooling systems may not have sufficient capacity to handle the increased loads from the current use of the space. 

Ventilation quantities Compare outdoor air quantities to the building design goal and local and State building codes and make adjustments as necessary. It is also informative to see how your ventilation rate compares to ASHRAE 62-1989, because that guideline was developed with the goal of preventing lAQ problems. 

If there is substantial airflow through the pathway, the peppermint oil odor could be diluted so that it is imperceptible. Tracer gases such as sulfur hexafluoride (SF ) can provide qualitative and quantitative information on pollutant pathways and ventilation rates. Use of tracer gases to obtain quantitative results requires considerable technical expertise. If it appears that a sophisticated study of pathways (or ventilation rates) is required, you need to use trained investigators. 

When you have pursued source control options and have increased ventilation rates and efficiency to the limits of your expertise, you must decide how important it is to pursue the problem further. If you have made several unsuccessful efforts to control a problem, then it may be advisable to seek outside assistance. The problem is probably fairly complex, and it may occur only intermittendy or cross the borders that divide traditional fields of knowledge. It is even possible that poor indoor air quality is not the actual cause of the complaints. Bringing in a new perspective at this point can be very effective. 

Ventilation Rate The rate at which indoor air enters and leaves a building. Expressed in one of two ways the number of changes of outdoor air per unit of time (air changes per hour, or "ACH") or the rate at which a volume of outdoor air enters per unit of time (cubic feet per minute, or "cfm"). 

Typical for normal quiet breathing is approximately 6-8 L/miii. In extreme circumstances, individuals can live for brief periods with minute ventilation rates as low as 1-2 Umin or as high as 300 L/min. Table 5.6 shows the dependence of on Vq, V-p, and / for a given. ... 

This section will describe general features of airflow patterns and then present information on the dimensions and locations of recirculating (stagnant) zones around the building envelope, which determine wind pressures and contaminant dilution. This knowledge allows one to select the locations of stacks and air intakes and to calculate infiltration and natural ventilation rates. 

This is the usual method of ventilation in domestic dwellings and many small office buildings and workshops. New standards, however, require buildings to have set ventilation rates, which require mechanical ventilation systems. However, as covered later, use is made of natural ventilation to control the air-change rate, regardless of the external conditions. This approach is not practical for industrial applications. 

Capture efficiency can also be measured by first estimating workspace emission rates and local exhaust emissions. The local exhaust emission rate equals the duct concentration (mass/volume) multiplied by the duct flow rate (volume/time). The workspace emission rates can be calculated using appropriate mass balance models and measured ventilation rates and workspace concentrations. Capture efficiency is the ratio of duct emission rate to total emission rate (duct plus workspace). ... 

Table 10.13 gives recommended ventilation rates for Germany. ... 

A dilution ventilation rate of at least 6 air changes per hour (ach) is recommended, with 12 or more ach recommended for new construction or renovation. This may not provide sufficient dilution to allow workers to enter without respiratory protection, but it is considered a feasible dilution rate that will reduce the risk of infection for those workers who must enter the room with respiratory protection. Dilution also reduces the contaminant concentration and therefore the risk when temporary leakage from the room occurs such as when doors are opened or closed. 

Nevertheless, in many cases, mean wind velocities can be assumed. In ventilation-system reliability studies, e.g., where minimum ventilation rates are to be determined, a calm situation with little wind must be assumed anyhow, and the need for accurate wind pressure coefficient data is not so obvious. 

Ventilation rate The actual mechanical or natural air change rate within a space, expressed in L/s or air changes per hour. The supply air may be all fresh air, or a mixture of fresh and recirculated air. 

In addition, they are usually constructed without isolation valves on the fuel supply lines. As a result the final connection in the pipework cannot be leak-tested. In practice, it is tested as far as possible at the manufacturer s works but often not leak-tested on-site. Reference 32 reviews the fuel leaks that have occurred, including a major explosion at a CCGT plant in England in 1996 due to the explosion of a leak of naphtha from a pipe joint. One man was seriously injured, and a 600-m chamber was lifted off its foundations. The reference also reviews the precautions that should be taken. They include. selecting a site where noise reduction is not required or can be achieved w ithout enclosure. If enclosure is essential, then a high ventilation rate is needed it is often designed to keep the turbine cool and is far too low to disperse gas leaks. Care must be taken to avoid stagnant pockets. 

Identifying specific quantified building ventilation rates can be difficult due to the number of non-linear parallel paths that may have to be simultaneously considered. 

When both wind and temperature difference act on ventilation openings, the result is very complex, but a reasonable approximation of flow rate is made by taking the higher of the two individual flow rates. This means that we can, for ventilation design purposes, generally ignore wind effects and design on temperature difference only, since wind effects can be assumed only to increase the ventilation rate. 

General ventilation is designed to keep air temperatures within a few degrees Centigrade of the outside shade temperature over the majority of the floor area. The ventilation rate required, which is not directly related to the space floor area or volume, is calculated from the formula ... 

In factories, air movement can be generated by unsophisticated equipment, since there is generally reasonable scope for equipment location and noise levels are often not critical. In offices and public spaces, the space, esthetic, noise and air movement criteria tend to be much tighter, and additional natural ventilation above that already provided by windows is normally impractical. The ventilation rate needed can still be calculated using equation (28.6),... 

The starting point for design of a dilution ventilation scheme is normally a hygiene survey in which levels of pollutants and the ventilation rate are measured under worst conditions. The required ventilation rate is then calculated by ratio of level of contamination measured and required, where... 

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