Air distribution methods

Typical application (example of a general room air distribution method)... 

The need for the implementation of target levels for air quality in industrial work rooms stems from different concerns. In addition to technological factors, the systematic design methodology, life cycle assessment, advances in air distribution methods, and increased integration with the process and... 

In rooms where energy is introduced primarily by supply air jets, air distribution methods are referred to as mixing type. With a perfect mixing-type air distribution, airflow pattern and air velocity at any point in the room are... 

Current mixing-type air distribution methods typically consider ventilation of the occupied zone with jets intercepting its upper boundary (e.g.. Fig. 7.6l2, c). Also, the occupied zone can be ventilated by the reverse flow produced as the supply jet degrades above the occupied zone level (Fig. 7.6h]. Mixing-type air distribution methods include air supply with jets projected vertically downward, inclined jets, jets directed vertically upward, and horizontal jets along room surfaces. 

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). 

In the zoning strategy the height of the boundary between lower and upper zones should be determined with the criteria of the air distribution method and devices. The lower zone should be defined high enough to get nearly all the induction air of the supply air devices from the controlied zone, as shown in Fig. 8.5. 

The flow rate of the plume through the zone boundary depends on the plume strength and vertical temperature gradient. In the case of a zoning strategy, the plume flow rate may also depend on the air distribution method and device because of the interaction between the plume and the supply air.-... 

The turbulent mixing between the zones depends on the air distribution method and device. "" ... 

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

Sandberg et al. present a two-zone model for a zoning strategy and active displacement air distribution method. 

A clear classification of the ideal strategies will help the evaluation of the present room air distribution methods in different operating conditions. It also creates a solid base for the development and promotion of new innovations in the field. 

Air distribution methods Exhaust methods Heating methods Cooling methods... 

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. 

However, the use of other room air distribution methods together with certain exhaust, heating, and cooling methods will also lead (intentionally or unintentionally) to the application of the mixing air conditioning strategy. Some examples are shown in Fig. 8.15. 

The choice of room airflow pattern and air supply method is subject to study in each separate case. Table 8.9 presents, however, some guidelines for air distribution methods most commonly applied for various cases. 

IHIII TABLE 8.9 Guidelines for Selection of Air Distribution Method... 

The plume airflows (q ) are determined as described in Section 7.5. The turbulent mixing iqi,) between zones and the penetration of the plume airflows iq, h,n) through the supply airflow patterns must be determined specially for the air distribution method and devices used as well as the locations of plumes and supply air devices. 

The air distribution method and dimensioning of the air supply devices are important factors in determining the accumuiation of hear and contaminants. Examples of this are presented in Section 8.4. After the behavior of the air distribution method and devices are known, the characteristic effects ot the other airflow elements can be calculated. 

Measured results of effectiveness and turbulent mixing are presented In literature by Bach (several air distribution methods) and Hagstrom et al. (mixing air distribution methods in zoning strategy).A typical example of an air distribution method and device in the zoning strategy is the so-called active displacement method, which is based on a nozzle duct device. ... 

K. Hagstrom, A. Zhivov, K. Siren, and L. L. Christianson, The influence of heat and contaminant source non-uniformity on the performance of three different room air distribution methods. ASHRAE Transactions, 1999, 2, 105. 

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