Natural ventilation defined

The use of a natural ventilation system assumes temperature stratification throughout the room height. Air close to heat sources is heated and rises as a thermal plume (Fig. 7.105). Part of this heated air is evacuated through air outlets in the upper zone, and part of it remains in the upper zone, in the so-called heat cushion. The separation level between the upper and lower zones is defined in terms of the equality of and G, which are the airflow rate in thermal plumes above heat sources and the airflow supplied to the occupied zone, respectively. It is assumed that the air temperature in the lower zone is equal to that in the occupied zone, and that the air temperature in the upper zone is equal to that of the evacuated air,... 

In an actual design, thermal modeling (Section 11.3) for diffetent seasoii-s will come fitst to. set tempetatute boundary conditions. Multizone aitflow simulation (Section 11.4) will follow to define ventilation needs in each zone. For large enclosed space.s, for natural ventilation, and for a variety of other special problems, CFD (Section 11.2) and integrated modeling (Section 11..S) are applied. 

I FIGURE I (.49 In thermal models, the ventilation airflow rates are input parameters in airflow models, on the other hand, room air tmiperatures must be defined In the output. Since natural ventilation airflows and room air temperatures are interdependent, both parameters must be intcgratly considered in the solution process. This is possible only by an integration of the natural airflow model into the thermal model. 

Measurements of ETS characteristics in a large, naturally ventilated university club showed that at most times when the number of smokers was small (less than ten), the smoke concentration decreased rapidly with time and the ETS peak was not detectable even 10-15 min after a cigarette had been smoked [53]. However, when the number of smokers was large, for example, during a rock concert, the ETS concentration in the room was very high, up to 5x10 particles cm and was characterised by the stable, well-defined broad peak. 

A confined space can be defined as any space of an enclosed nature which has limited means of access and egress, restricted natural ventilation and is not intended for continual occupancy by persons. It is, therefore, any space which, by virtue of its enclosed nature, presents a reasonably foreseeable specified risk of serious injury. 

I he origins of the above two errors are chfferent in cause and nature. A sim ple example is, when the mass of a weight is less than its nominal value, a systematic error occurs, which is constant in absolute value and sign. This is a pure systematic error. A ventilation-related example is, when the instrument faaor of a Pitot-static tube, which defines the relationship between the measured pressure difference and the velocity, is incorrect, a systematic error occurs. On the other hand, if a Pitot-static tube is positioned manually in a duct in such a way that the tube tip is randomly on either side of the intended measurement point, a random error occurs. This way, different phenomena create different ty pes of error. I he (total) error of measurement usually is a combination of the above two types. 

It is useful to define the disease category in order to predict the natural history and specific intervention. It is well known that patients with primarily restrictive disorders can have both inspiratory and expiratory muscle weakness, and apart from noninvasive ventilation (NIV), they also need cough assistance (4,5). On the other hand, patients with obstructive disorders rarely need mechanical expiratory aids except when they have a severe infectious exacerbation at which time difficulties in clearing copious secretions can occur (4,6,7). 

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