## 5. Drought Rate Evaluation Discussion
### DR Evaluation Based on the Measurement Data  
The measured \(DR\) time evolution curves plotted in Figure 10 represent data at four measurement points, processed with three different averaging procedures. The \(DR\) values are calculated using three moving intervals: the period of one minute, \(<\)\(DR\)\(>_{60\;\mathrm{s}}\); the period of three minutes, \(<\)\(DR\)\(>_{180\;\mathrm{s}}\), that corresponds to the practical procedure for evaluation of \(DR\) in ventilated spaces presented in [36]; and the period of fifteen minutes, \(<\)\(DR\)\(>_{900\;\mathrm{s}}\), which is in coherence with the experimental protocol, reported in [25]. The data processing started at the instant of \(t=1020\) s (the blue dashed lines in Figure 4) that corresponds to the beginning of the temperature quasi-steady-state phase. At all \(z\) levels considered, the time-averaged \(DR\) varies in time. The \(DR\) evolution reproduces to some extent the unsteady velocity behavior, presented previously in Figures 4 and 6: characteristic periods of 200-300 s are registered for the two quantities. It is evident that the \(DR\) assessment depends much on the averaging period. Remarkably that for the longest averaging period of 900 s, the time-averaged \(DR\) values also change in time significantly, see the red curve, especially at \(z=0.6\) m (Figure 10b) and \(z=1.7\) m (Figure 10d).  
In addition to the time evolution curves, Figure 11 presents the integral range of the \(DR\) time variation: for three intervals of averaging (60 s, 180 s, 900 s) the minimum, maximum, and median values over the thermal quasi-steady-state period are given. With the increase in the averaging interval, the range of \(DR\) variation becomes narrower. The minimum value grows up, the maximum value decreases, while the mean and the median values remain almost the same for the whole temperature quasi-steady-state period. At each level, the difference between the maximum \(DR\) and minimum \(DR\) is the lowest for the 900 s long interval; this difference varies from one point to another: at \(z=1.7\) m this  
Figure 10: Time evolution of \(DR\) at four monitoring points: (**a**) \(z=0.1\) m, (**b**) \(z=0.6\) m, (**c**) \(z=1.1\) m, and (**d**) \(z=1.7\) m (data for \(\theta=25^{\circ}\), case #1).  
difference is 23.6%, at \(z=1.1\) m it is 9.1%, at \(z=0.6\) m it is 19.8%, and at \(z=0.1\) m it is 6.8%. For the three intervals of assessment, the maximum difference between the \(DR\) median values is observed at \(z=1.7\) m, where the median value of \(<\)\(DR\)\(>_{60\) s is 2.0% lower than that of \(<\)\(DR\)\(>_{900\) s.  
The conclusion is that it is necessary to pay much attention to the measurement period for a reliable \(DR\) estimation. If the median values from a set of numerous measurements are used, the \(DR\) assessment interval for the room under consideration could be 180 s long since median values for \(<\)\(DR\)\(>_{180\) s and \(<\)\(DR\)\(>_{900\) s are practically equal. However, for the practical categorization of the room, it is insufficient, as a single measurement of 180 s long could be performed during a high-\(DR\) or low-\(DR\) period and the input used for categorization would be far from the median. The recommendation for the averaging period choice is that the range of variation of \(DR\), i.e., the difference between the maximum and the minimum \(<\)\(DR\)\(>\) values, for the sufficient averaging period, must be lower than 10% of the median value. Note that among the four points under consideration, at two points this condition is not fulfilled even for the longest period of 900 s (see Figure 11c,d).