Combined impacts of the ceiling radiant cooling and ventilation on dispersion and deposition of indoor airborne particles

Abstract

• Integrated ventilation-cooling effects on indoor particle dispersion are evaluated. • The CRCP surface temperature is a dominant parameter in particle deposition rate. • Particle decay rate in the up-supply ventilation is faster than down-supply one. • Particle decay is associated to temperature difference between CRCP and walls. • Concentration in breathing zone diminishes by decreasing temperature of CRCP. The present study investigates the integrated effects of the ceiling radiant cooling and ventilation on dispersion and deposition of indoor airborne particles. Five groups of particles with different sizes, ranging from 0.1 to 10 µm, are selected to be injected inside a ventilated space equipped with the ceiling radiant cooling panel (CRCP). Two ventilation strategies under different air change rates are considered, namely up-supply and down-supply ventilations. The conjugate heat transfer between the CRCP and indoor air is examined for different inlet temperatures of the chilled water. An Eulerian-Lagrangian CFD model is developed and validated by experimental data in order to predict the turbulent airflow characteristics and thermal performance of the CRCP system as well as the transient particle trajectories. The results indicate that the particle decay rate is associated with the temperature difference between the CRCP surface and surrounding walls. A sensitivity analysis on the results shows that the surface temperature of CRCP in both ventilation methods is a more effective parameter in particle deposition rate, compared to the inlet air velocity; a 40% augmentation of the ventilation rate leads to 2.6% increase in particle decay rate, whereas the same alteration in inlet water temperature of the CRCP results in 7.3% enhancement of the decay rate. It is shown that while the particle decay rate in up-supply ventilation is faster than down-supply one, the down-supply mode removes higher number of particles, for a given ventilation rate. Furthermore, it is shown that the particle concentration in breathing zone diminishes by decreasing the temperature of radiant cooling panel. Findings of the present study are expected to provide insights into future design of the ventilation and ceiling radiant cooling system for a better indoor air quality.