Impact of Solar Heat Gain on Radiant Floor Cooling System Design
Radiant floor cooling systems are increasingly being used in transition spaces with large glazed surfaces, such as atria, airports, and perimeter areas. For these cases, the cooling capacity can increase significantly according to the scientific literature. However, current design standards and test methods provide only limited guidance on sizing of radiant floor cooling systems and their associated air systems in the presence of solar radiation. The goals of this study are to 1) review current radiant surface cooling capacity estimation approaches; and 2) evaluate the impact of solar heat gain on radiant floor cooling capacity. Sensitivity simulation studies were conducted to investigate the influence of window-to-wall ratio, orientation, building aspect ratio, shading options, and floor material shortwave absorptivity. Review of current radiant system design standards showed that existing radiant cooling capacity estimation methods are insufficient when the system is exposed to solar radiation because shortwave radiation generated by lighting and solar are not considered. Radiant cooling capacity ratio (RCCR), defined as the ratio of the EnergyPlus simulated radiant cooling capacity to the values calculated using ASHRAE Handbooks (2012) and ISO 11855 (2012) methods, were reported to gauge the impact of solar radiation. The simulation results showed that 1) the median of the RCCRISO is 1.7 and 1.3 for RCCRASHRAE, and the enhancement is attributed to shortwave radiation (both direct and diffuse) absorption; 2) RCCR is most sensitive to shading options and slightly sensitive to shortwave absorptivity of the floor surface material.