Due to the global spread of diseases and epidemics, the need to maintain a clean indoor atmosphere has received increasing attention in recent years. Therefore, there will be a need to clearly estimate and define the areas that affect human exposure to pollutants, taking into account the occupied density, which is the primary importance of this research. The capacity of the chilled ceiling combined with mixing ventilation and personal ventilation systems has been studied and compared to the chilled ceiling with mixing ventilation in terms of mean air age, temperature distribution, CO2 concentration, and thermal efficiency, with the best flow rate of the proposed system considering the occupied density in a thermally insulated office room experimentally in the climate of Iraq (Hilla, a hot and dry climate). Twelve tests were performed for four different cooling loads with cooled ceilings (0%, 0.25%, 50%, and 80%), at a constant supply air flow rate with two PV airflow modifiers for three cases. As the cooling load treated by a chilled ceiling increased, the average air temperature increased with height in all cases. The lowest values of average air age appeared in the occupied area in the case of a chilled ceiling with mixing ventilation. This study shows that the chilled ceiling combined with a mixing ventilation and personal ventilation system with a flow rate of 7.5 L/s provides thermal comfort and higher air quality in the occupied area. based on the values of air exchange efficiency and occupants’ air exchange efficiency. As a result, a flow rate of 7.5 L/s is the best option for protecting occupants from direct pollution in the breathing zone and in the surrounding microclimate, because the lower the ventilation rate, the less air is changed for occupants.

The ability of the chilled ceiling combined with mixing ventilation and personal ventilation system (CC/MVPV) to provide comfort and protect occupants from negative pollutants in an office room in Iraq City-Hilla climate (hot and dry climate) was studied considering the occupied density. A transient 3D computational fluid dynamics (CFD) model was used to evaluate the mean air life, temperature distribution, carbon dioxide concentration and thermal efficiency with the best flow rate of the proposed system and compared with the mixing ventilation and chilled ceiling (CCMV) by using AIRPAK software. Three tests were conducted for three different cooling load cases treated with (25, 50, and 80%) cooled ceiling with a total cooling load of (14.8, 29.6, 47.4) W/m 2 of floor area. The chilled ceiling surface temperature ranged between (23, 21.39, 19)℃ and the mixing ventilation supply air temperature (19, 21, 23)℃ at a constant supply air flow rate (46 L/s) with two PV air flow rate (5 l/s, 7.5 l/s), room air temperature (25℃). It was discovered that by using a (CC/MVPV) system with an air flow rate (7.5 L/sec), the air quality in the breathing area can be improved based on the values of air exchange efficiency (ɳa) and air distribution performance index (ADPI), which are (72%, 89.9) respectively, the efficiency of air exchange (ɳD) when the visiting person (the person standing) stays in the room for an one hour, one and half hour , two hours by (99%, 96%, 94%), so we notice the longer he stays, the less the air change for the passengers due to the low ventilation rate.