Influence of the optical and geometrical properties of indoor environments for the thermal performances of chilled ceilings

The sizing of radiant ceilings for cooling applications requires the correct evaluation of the dynamic removal thermal loads in indoor environments. The evaluation of thermal power removed by convection, infrared radiation and direct absorption of solar radiation incident on ceiling surface, called direct water load (DWL), for systems with low thermal inertia (chilled ceilings or ceilings made by capillary pipes) has to be carried out. The latter contribution must be evaluated in an accurate way because it is not a thermal load for indoor environment and strongly modifies the thermal balance in the air-conditioned volume. In order to evaluate DWL, a parametric study developed as a function of the main optical and geometrical characteristics of the cavity has been carried out with TRNSYS code. The development of a case study has highlighted the dynamic aspects of the several contributions involved in the thermal loads removal. The obtained results have allowed the definition of a new calculation methodology to evaluate the effective solar radiation absorbed by the cavity and, subsequently, to determine the fraction of solar radiation incident on ceiling surface and removed by DWL. Its evaluation has allowed estimation of the DWL incidence on the sizing procedure of light radiant ceiling for cooling applications.