# Improvement of the Chimney Effect in Stack Ventilation
## 3 Measurement Setup and Equipment
In this measurement campaign, the thermo-anemometers LB-801A and LB-801C were installed in a double-sensor configuration. Both thermo-anemometers were based on a hot-wire concept. The first thermo-anemometer LB-801A worked in an analog mode and measured low velocity. The sensor could measure the indoor convection air velocity between 0.05-10 m/s with the accuracy of \(\pm\)0.05 m/s. The second thermo-anemometer LB-801C worked in a digital mode and was used to detect airflow direction. The airflow direction detection function was designed by a modification of the LB-801C sensor. The sensor was modified by closing its airflow channel from one side and re-calibrating its characteristics for two opposite flow directions. The new characteristics were recorded in its EEPROM memory. Both sensors were installed as an integrated measurement point. The measurement data management software LBX 2012 registered the flow direction and air velocity. All sensors were calibrated by the LAB-EL Laboratory in Poland before their installation and commissioning. The sensors were confirmed by means of suitable calibration certificates. Before the start of the measurements, there were several days of testing. The sensors used in the experiment are presented in Table 3.  
Measurement of the wind velocity around the test building showed that weak winds prevailed during the tests, as the average wind velocity did not exceed 0.8 m/s. The maximum velocity during the measurements was 6.4 m/s and the minimum velocity was 0 m/s (Figure 8a). In the area of the test building, the dominant wind direction was north N (58%). A detailed wind rose with an average percentage of wind direction for the measured value is shown in (Figure 8b). As the research was carried out from August to November, most of the measured radiation intensity during the day exceeded the value of 100 [W/m\({}^{2}\)]. The measured intensity of solar radiation presented in (Figure 9) refers to the value of total solar radiation on the horizontal surface. Based on the measured values of solar radiation intensity from the NR LITE2 m (Kipp&Zonen), total solar radiation intensity Ic was obtained [15; 16]. Figure 8: Information about wind: (**a**) wind velocity, (**b**) wind direction. Figure 9: Total solar radiation during the experiment. There is uncontrolled and unintentional airflow in buildings due to wind and density differences. This phenomenon is called air infiltration. Infiltration occurs in window gaps and microcracks in the building envelope. The airflow through windows, openings and gaps in the building envelope is the result of the sum of the pressure drops due to the wind and the temperature difference at the point of flow. In an isolated ventilation system, based on experimental tests, the value of uncontrolled airflow caused by infiltration was checked. To describe the infiltration, we need to know air density in the building test. So, during the experimental tests, the ventilation air density in the analyzed room was checked (Figure 10). The average value of the ventilation air density in the analyzed room was 1.191 [kg/m\({}^{3}\)]. Knowing the measurement of air velocity at the inlet to the room and at the outlet from the ventilation duct, we can determine the amount of infiltration air based on the mass balance. The general equations governing the mass conservation in each zone can be written as follows:  
\[\frac{d\rho_{i}V}{dt}=\rho_{inlet}\Big{(}A_{eff\ inlet}\ U_{inlet}\Big{)}+\rho_ {outlet}\Big{(}A_{eff\ outlet}\ U_{outlet}\Big{)}+\rho_{leak}q_{leak}=0 \tag{2}\]  
where \(\frac{d\rho_{i}}{dt}\) is the air density change of the indoor air during the time step \(dt\), \(\rho_{inlet}\) is the air density in the inlet gap, \(A_{eff\ inlet}\ U_{inlet}\) is the volumetric flow rate in the inlet, \(\rho_{outlet}\) is the air density of indoor airflow in the outlet, \(A_{eff\ outlet}\ U_{outlet}\) is the volumetric flow rate in the outlet, \(\rho_{leak}\) is the air density of leakage and \(q_{leak}\) is the flow rate of leakage.