Stratification Strategy

A similar temperature and contaminant distribution throughout the room is reached with stratification as with a piston. The driving forces of the two strategies are, however, completely different and the distribution of parameters is in practice different. Typical schemes for the vertical distribution of temperature and contaminants are presented in Fig. 8.11. While in the piston strateg) the uniform flow pattern is created by the supply air, in stratification it is caused only by the density differences inside the room, i.e., the room airflows are controlled by the buoyancy forces. As a result, the contaminant removal and temperature effectiveness are more modest than with the piston air conditioning strategy. 

Advantages include low concentration in the ventilated zone can be achieved and relatively high contaminant removal and temperature effectiveness. However, the srratificacion strategy is sensitive to disturbances and stagnant areas with high 

Vertical temperature and contaminant distribution within the stratification strategy, typical schemes. To is supply air temperature, T is the temperature at the floor level, Tj Is room temperature, Cq and Q are contaminant concentrations in supply and room air above the stratification height, and y, is the stratification height 

In the stratification strategy the supply air is used to substitute the outgoing air from the ventilated (in most cases occupied) zone, thus preventing circulation patterns between the zones. The supply air has to be distributed in such a way that the buoyancy flows are not disturbed. Exhaust air openings are to be located downstream in order to avoid reverse currents within the room. The location of the contaminant sources and the heat sources causing density differences must be the same in order to carry out the contaminants with equal or higher density than air. 

Srratification is a desirable strategy to provide efficient room air condi-noning with much less effort than using the piston strategy. Its mam application in room air conditioning is the thermal replacement method. However, it can also be applied for contaminants without any thermal buoyancy sources that have different density from the room air. Examples of different air distribution methods to create thetma teplacement are presented in Fig. 8.12. 

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In the stratification strategy with a replacing air distribution in the lower zone, the height of the boundary layer between the lower and upper zones can be determined with the criteria of the contaminant interfacial level.This level, where the air mass flow in the plumes is equal to the air mass flow of the supply air, IS presented in Fig. 8,4. In this ideal case the wait and air temperatures are equal on the interfacial level. In practical cases they are not usually equal and the buoyancy flows on the walls will raise the level and decrease the gradient. 

Bach et al., Pozin, and Shilkrot and Zhivov - present two-zone models for mixing, zoning, and stratification strategies with different air distribution methods. 

Mundt presents a two-zone model for the calculation of temperature gradient within a stratification strategy. 

During summer. Fig. S. 6a, there is a need for cooling in the occupied zone (area up to 2 m from the floor level) rhus it is desirable to apply the stratification strategy with vertical temperature and contaminant stratification in the hall in order ro save cooling energy costs. This can be done, for example, by using a low-impulse air supply with the devices at the floor level. 

It the main reason for the stratification strategy is contaminant control in [he occupied zone, the same strategy should be applied in winter conditions, too. Thus, the selected hearing method has to fulfill two requirements to siip-pttrt the creation of the vertical stratification and not to create disturbing airflows into the hall. In this case one option would be the floor heating method see Fig. 8.16c. Additionally, one should consider the prevention of boundary layer flows along the outer walls using, for example, passive methods. -... 

Zonal models can be applied for each room air conditioning strategy (see Section 8.6), but they are mostly used in stratification and zoning strategies with different air distribution methods (see Section 8.7). 

Two-zone models are especially useful for stratification and zoning strategies because of the typical vertical accumulation of heat, contaminants, or water vapor within these strategies. The level of the boundary between the lower and the upper zone is usually determined on the level of the highest temperature or/and concentration gradient. 

Sections 8.7.3 and 8.7.4 give examples of the calculation of two-zone air flow and contaminant flow models applied to stratification and zoning strategies. 

The application of the strategies in system selection can be illustrated by using a simple example. Let us think about an industrial hail with some internal heat sources but without any remarkable internal movement that would disturb the stratification. 

Stratification is not specific to FEP - it is a universal strategy that improves the efficiency of many other methods for calculating free energies. Not surprisingly, we will return to this strategy several times, in particular in Chaps. 3 and 6. 

Andresen D, Steinbeck G, Bruggemann T, et al. Risk stratification following myocardial infarction in the thrombolytic era a two-step strategy using noninvasive and invasive methods. J Am Coll Cardiol. Jan... 

Stratification markers allow prediction of the response to a medication strategy [NQOl genotype in adenocarcinoma of upper gastrointestinal tract (Sarbia et al., 2003)]. 

INTRODUCTION 14 PESTICIDE CATEGORIES 15 PESTICIDE HANDLERS 15 Agricultural Pesticide Handlers 15 Tasks Performed by an Individual 16 Factors Affecting Exposure 16 Residential and Institutional Pesticide Handlers 18 Families of Pesticide Handlers 19 STUDY DESIGN CONSIDERATIONS 20 Worker Stratification 21 Routes of Exposure 21 Respiratory Exposure 21 Dermal Exposure 21 Sampling Strategy Selection 21 Statistical Analysis 22 PROTECTION OF HUMAN SUBJECTS 22 PESTICIDE EXPOSURE MONITORING METHODS 23 Passive Dosimetry 23... 

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