Mixing Strategy

8.6.6.1Description

The aim of the mixing air conditioning strategy is to provide uniform con ­ditions throughout the air-conditioned room.

The contaminant removal and temperature effectiveness in the mixing strategy are equal to 1. In practical installations incomplete mixing in the room and unfavorable temperature gradient and location of the exhaust open­ings in relation to air supply may, however, cause short-circuiting of the sup­ply air into the exhaust openings and the efficiency may remain below’ 1.

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Mixing Strategy

Ib) Inclined jets air supply

подпись: ib) inclined jets air supply

(c) Activent air supply

подпись: (c) activent air supply/ V ‘ ‘ rv

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Id) Jet-supported lowimpulse (e) Vortex air supply if) Horizontal zoning with

Curtain curtain

FIGURE 8.13 Examples of air distribution and exhaust methods for the zoning strategy

8.6.6.2Advantages and Disadvantages

Using the mixing strategy, stagnant areas with high local concentrations and unfavorable thermal gradients can be avoided during the hearing period. At the same time, it has low contaminant removal and temperature effective­ness and its high air velocity may cause drafts.

8.6.6.3Design Criteria

Air jets are used to create enough air movement inside the room to circu­late and mix the whole room air. This strategy is often called dilution ventila­tion as the contaminants created inside the room are mixed into the whole room volume thus reducing the local peak concentrations.

8.6.6.4Application

The room airflows are controlled mainly by the supply or/and circula­tion air jets using, for example, concentrated jets, ceiling air supply, or high­impulse nozzle systems. Examples of different methods are illustrated in Fig. 8.14.

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.

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(<j) Ceiling air supply (b) Concentrated air supply (c) Air supply with directing

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FIGURE 8.14 Examples of air distribution and exhaust methods for the mixing strategy.

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(a) Replacing air distribution: [b] Replacing air distribution: (r) Replacing air distribution:

Cooled ceiling recirculating fan heaters governing local exhaust

FIGURE 8.1S Examples of systems resulting in the mixing strategy despite the selected air distribution method.

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