Example

11.3.6.1 Building

The building is an industrial laundry with high thermal loads, ventilated naturally or by hybrid ventilation. The laundry cleans, among other things, hospital textiles; thus, high hygienic standards are required. Three different levels of internal thermal loads were assumed (60, 100, 160 W/m2) for the simulations.

11.3.6.2 Problem

For a representative summer case, the outdoor air exchange and the room air temperatures in various zones are to be determined.

I 1.3.6.3 Approach

For the calculations, several software tools were used. The natural ventilation and the thermal behavior were computed using the dynamic building and system simulation program TRNSYS.16 In TRNSYS, the natural airflows were modeled as power-law functions, basically considering stack effects. These functions were established using the COMIS17 model. Also, the influence of the design and the insect screens on the flow resistance of the openings was carefully considered. The example is documented in more detail in Breer and Dorer.1*

Space Load Factor

Outside air entering the space through openings near the ground spreads over the floor and absorbs energy from the floor surface. The resulting air temperature increase leads to buoyancy and forces the air up into the upper hall zone. This results in a temperature stratification in the hall. Due to this vertical temperature gradient, the air in the occupied zone does not reach the exhaust air temperature 0exilJUS( (see Fig. 11.37).

Example

This has a positive effect on thermal comfort, particularly in the summer period. The thermal space load factor N, is used to quantitatively characterize this effect (0out, outside air temperature; 0^, air temperature at working space level; 0exhamt’ exhaust air temperature):

— ?ssi—GJuiL- (11.17)

Exhaust ~ out

Soil Temperature

In many industrial halls, conduction into the ground is a major factor for heat loss. Therefore, an adequate modeling of the floor slab and the underlying, thermally active, soil is very crucial for reliable simulation results. In this case, the soil model in the TRNSYS model was established using results from an additionally performed finite-element program analysis.

11.3.6.4 Results

Primary results of the simulation are the room air temperatures, the air change rates, and the space load factors (Figs. 11.38 to 11.40).

A space load factor = 0.75 results for the important period of May — September. This corresponds very well with standard values given in VD1.19

During the summer period, high peak temperatures can be observed, which can be slightly reduced by using larger openings.

I 1.3.6.5 Conclusion

The study shows that in this particular case a natural ventilation system is a suitable and ecological possibility to remove the high internal thermal loads. Accurate information on the internal loads and the ventilation openings is crucial for the results of the thermal simulation.

Example