Experimental Evaluation of Impinging Jet Ventilation in an Office Environment : Indoor air quality, thermal comfort and airborne contaminants spread risk assessment

Sammanfattning

Ventilation strategy affects not only the amount of air supplied to a room, but also how fresh air, heat and contaminants are distributed within the occupied zone. This thesis experimentally compared the indoor environmental performance of an office equipped with Impinging Jet Ventilation (IJV) and an office with conventional mixing ventilation (CMV). The focus was on indoor air quality, thermal comfort, vertical stratification and indirect indications of airborne contaminant distribution under realistic office conditions. Measurements of air temperature, CO2 concentration and relative humidity were carried out from 3 March to 7 April 2026. In both offices, sensors were placed at 0.1 m, 0.6 m, 1.1 m and 1.7 m above floor level; in the IJV office, an additional sensor was placed at 3.02 m. The analysis compared full-period and working-hour data, with particular attention to vertical temperature gradients, vertical CO2 differences and daily variation at seated breathing height. Spot measurements of local air velocity and supply duct velocity were also used to estimate the IJV supply airflow, Reynolds number and draught rate. The results showed that the IJV office had lower working-hour CO2 concentration than the CMV office at all common measurement heights. At 1.1 m, the working-hour mean CO2 concentration, calculated from weekday measurements between 08:00 and 17:00 during the measurement period, was 469 ppm in the IJV office and 586 ppm in the CMV office. CO2 exceedance above 800 ppm was almost absent in the IJV office during working hours, while it occurred more frequently in the CMV office. When the temperature profiles were expressed relative to 0.1 m, both offices showed almost the same temperature increase up to 1.1 m, while the IJV office showed a slightly larger increase up to 1.7 m. The mean vertical temperature differences remained clearly below 3 °C. The estimated draught rate at the most critical measured point was 6.9 %, indicating no major draught problem at that position. Overall, the findings suggest that IJV may provide more favorable indoor air quality indicators than conventional mixing ventilation in a real office setting, while the measured relative temperature gradients and local draught-rate estimate did not indicate a major comfort problem. However, the results should be interpreted carefully, since the study was limited to two real offices and the measured differences may also have been influenced by radiator settings, room conditions, occupancy, window operation and internal heat loads.