Application of the Strategy in System Selection

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

During summer, Fig. 8.16a, there is a need for cooling in the occupied zone (area up to 2 m from the floor level); thus it is desirable to apply the stratification strategy with vertical temperature and contaminant stratification in the hall in order to save cooling energy costs. This can be done, for exam­ple, by using a low-impulse air supply with the devices at the floor level.

During winter additional heating is needed in the occupied zone due to the heat losses. The selection of the heating method depends on the selected air conditioning strategy for the heating season. In order to save heating en­ergy costs the exhaust air temperature should not exceed the temperature in the occupied zone. Thus, the desired strategy would be the mixing strategy. An appropriate heating method for that purpose would be, for example, an air and recirculation method with fan heaters located close to the ceiling; see Fig. 8.16b.

Application of the Strategy in System Selection

(a) Summer:

Stratification methods * Low-impulse air supply

(/)) Winter:

Mixing methods * Low-impulse air supply ” Recirculating fan heaters

(c) Winter:

Stratification methods

* Low-impulse air supply

* Floor heating

FIGURE 8.16 Application of the strategy in system selection examples.

It the main reason for the stratification strategy is contaminant control in the occupied zone, the same strategy should be applied in winter conditions, too. Thus, the selected heating method has to fulfill two requirements: to sup­port 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.12

To conclude the example: A different air conditioning strategy can and sometimes should be selected for different seasons or operating conditions. The strategy can be changed by using combinations of available methods.