Assessment of ventilation systems efficiency in office buildings, related to indoor volatile organic compound concentrations

The objective of this study is to develop an approach concerning the integration of volatile organic compounds (VOCs) emissions due to office equipment in computational fluid dynamics (CFD) simulations, in order to assess the indoor air quality (IAQ) in offices. The transport and diffusion phenomena of VOCs are taking into account in the CFD model by means of conservation equations of the mass fraction, written for each VOC that is intended to be considered in the simulation. These equations are added to the basic equations describing turbulent confined non-isothermal flows (conservation of mass, momentum, energy, and turbulent quantities) in CFD modelling. On the other hand, these equations should include source terms of mass for each VOC that is planned to be taken into account in the model. The values of these source terms are specified in the model according to experimental data available in the literature. The numerical model is applied in this study for a small office, taking into account two ventilation systems: conventional mixing ventilation system and displacement ventilation system. The simulations are carried out for low air flow rates with different air supply temperatures. Concerning the sources of VOCs in terms of electronic devices, the office is supposed to be equipped with 4 computers, 4 monitors, and 4 laser printers. The assessment of IAQ in the office is accomplished by taking into account in the CFD model the indoor levels of the following five VOCs: benzaldehyde, ethylbenzene, o-xylene, styrene, and toluene. The CFD model proposed in this study allows achieving values of VOCs concentrations throughout the entire indoor environment in a particularly comprehensive manner. Consequently, results are presented in terms of benzaldehyde, ethylbenzene, o-xylene, styrene, and toluene concentration contours in the office. The results show that the estimated VOCs concentration levels due to office equipment are far below the set threshold limit values, both in the case of mixing ventilation and displacement ventilation, despite low ventilation rates taken into account. However, it should be remembered that the results are based only on VOCs emissions due to electronic devices, VOCs generated from other indoor sources have not been taken into consideration during the simulations. On the other hand, the numerical description of VOCs sources for CFD modelling developed in this work may be easily extended for other indoor VOCs sources. Finally, the numerical approach proposed in this study can lead to relevant IAQ analyses, being an appropriate alternative to experimental investigations, challenging to carry out in situ.