Cases without Moisture Source

Case of natural convection: case N10

In case N10, natural convection was created inside the test room. This was done by raising the temperature outside the room from 12°C to 42°C, while 24 hours later it was again lowered to 12°C. The response of the test room was monitored, while no air was supplied into the room. The mean convective heat transfer coefficient used in the simulation study were the ones measured by Togari et al. [66]: it is 3.5 W/m² at the vertical walls and glazing, and 2.3 and 4.6 W/m2 K at the floor and ceiling, respectively.

Figure 5.28 depicts results of the air temperature for the first nine hours when outdoor temperature was raised from 12 to 42°C; respectively at 1:00, 2:00, 3:00, 4:00, 5:00, 7:00 and 9:00. The simulated results were compared to the measurements in the test room and to the calculations performed by Togari et al. with the simplified model. Out of Figure 5.28, it can be concluded that the temperatures found by the coupled BES-zonal model were in good agreement with the measurements. Differences between the simulated results and the results presented by Togari et al., can be subscribed to differences in interior surface temperature leading to a difference in mass flows (Figure 5.29 right).

Figure 5.29 (left) shows simulated interior surface temperature and measured interior surface temperatures, which are used by Togari et al. as boundary condition, after two hours as measurements at that time were provided in the paper. The simulated surface temperature of the glass surface was underpredicted for the three lowest layers (RMS = 1.25°C). This deviation has no effect on the flow rate calculation. Because for the glass surface, there was no airflow back to the layer (min = 0), only the value of mout determines the upward current (mm). In the original model, the value for mout is independent of the surface temperature and therefore, the difference in simulated interior surface temperature has no influence on the wall current. The surface temperature for the insulated walls were in good agreement with the measured wall

surface temperatures (RMS = 0.53°C). However, small deviations were observed leading to a difference in the value for the mass flows (min, mm and mc) and thus layer temperatures.

Figure 5.28: The temperature for the first nine hours while heating outside the chamber. Comparison between the measured values and the values calculated by the thermal-zonal model in TRNSYS. Root

mean square errors are provided together with the time step.

Figure 5.29: Left: Interior surface temperature for the insulated wall and the glass surface. Comparison between the measured values and the simulated values by TRNSYS. Right: Values the mass flow [kg/hr]

from the layer to the wall current and between the layers. Comparison between the calculated values by Togari et al. and by the coupled BES-zonal model .

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measured coupled BES-thermal zonal model Model Togari

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MODELLING INDOOR CLIMATE IN TALL BUILDINGS 155

Case of forced convection (implementation of a jet): case H100

In case H100, the outside temperature of the test room was kept between 11°C and 12°C. Hot air was supplied to the test room at 0h00. The temperature of the supplied air was 40,7°C and the supply air volume was 150m³/h. The convective heat transfer coefficients used in the simulation study were the ones measured by Togari et al. [66]. It is 3.5 W/m²K at the insulated walls, and 2.3 and 9.3 W/m2 K at the floor and ceiling, respectively. At the glass surface, the convective heat transfer coefficient for the uppermost layer is 9.3W/m²K, for the other layers it is 5.8W/m²K.

Characteristics of the jet and supply were not described for the experiment.

Figure 5.30 shows the measured air temperatures and the air temperatures calculated by the thermal-zonal model and by the simplified model of Togari et al. [66]. The coupled zonal model achieved in predicting the temperature profile during heating with a heated jet flow. Differences between the simulated results and the results presented by Togari et al. have mainly two causes.

Figure 5.30: The progress of the temperature in case of hot air supply condition (jet).

Firstly, the difference in interior surface temperature leads to a difference in current flows. Figure 5.31 (left) shows simulated interior surface temperature and measured interior surface temperatures, which are used by Togari et al. as boundary condition, after two hours of heating.

Measurements at other times were not presented. Glass and wall temperatures were in good agreement with the measured values. As visualized in Figure 5.31 (right), the simulated surface temperature of the interior surfaces were underpredicted, leading to other values for the backflow from the current to the layer (min).

Secondly, because the characteristics of the real jet and the implemented jet model used by Togari et al. were not described, typical values for the characteristics from literature were used.

For the spreading a value of 0.151*s(x) was used (Table 5.5). As a result, other values were found for the flow rate of the jet. Compared to the values presented in the paper for the entrained air flow, significantly lower values were obtained (red numbers in Figure 5.31 (right)). However, since

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measured Coupled BES-thermal zonal model Model Togari

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there was no measurement of these flow rates, it was assumed that the stated values for the jet flow rate are the theoretical values and that these were not validated. To have an idea of the importance of the value of these flow rates, the case study was also calculated with values for the flow rate that approach the values presented in the paper. To do so, the spreading was increased to 0.195*s(x). As a result, higher values for the indoor air were obtained (Figure 5.32) and the indoor air temperature was overestimated.

Figure 5.31: Left: Interior surface temperature for the insulated wall and the glass surface. Comparison between the measured values and the simulated values by TRNSYS. Right: Values of the mass flow from

the layer to the wall current , by the jet (values left outside wall) and between the layers. Comparison between the calculated values by Togari et al. and by the coupled BES-zonal model .

Figure 5.32: The progress of the temperature in case of hot air supply condition (jet) with two different values for the spreading.

measured Coupled BES-thermal zonal model "Spread angle jet increased"

5.4.4 Issues Using the Coupled Zonal Model Starting from Outside Boundary