Comparison of Zone Cooling Load for Radiant and All-Air Conditioning Systems

By actively cooling down one or more surfaces in a space, water-based embedded surface cooling (radiant) systems remove heat both by convection and radiation. Therefore, unlike the case of well-mixed air distribution systems where the cooling load is purely convective, the cooling load for radiant systems is comprised of both convective and radiant components. However, in current practice, the same design cooling load calculation methods for the radiant systems are used as the convection based air systems. The purpose of this energy simulation study was to investigate if there are differences in peak zone cooling load and 24-hour total zone cooling energy generated by all-air distribution systems in comparison to radiant cooling systems. Sensitivity studies were performed for different load and boundary conditions. Simulation results show that total zone cooling energy for the radiant cooling systems studied can be 2.7-6.5% higher than the all-air systems, and peak zone cooling load can be in the range of 10-40% higher depending on the load conditions. Future research is needed to assess the implications for design guidelines. In general, even if the total zone level cooling energy may be slightly higher for the radiant systems, there are verified advantages of using hydronic-based radiant systems such as improved plant side equipment efficiency with warmer cold water temperature, possibility of night pre-cooling and utilization of natural cooling resource, and energy efficiency in transporting heat with water compared to air. All of these factors combine to produce better overall energy performance in radiant cooling systems.