Cooling load comparison of rooms conditioned with radiant cooling panels and all-air HVAC systems (ASHRAE RP 1729)

Radiant cooling systems have the potential for efficient chiller operation by using a higher chilled water temperature when compared to all-air systems. This affects the system efficiency, but it is not clear how the cooling load for these two systems is different. The present experimental study investigates differences between (i) room cooling load and (ii) overall heat transfer for (a) radiant and (b) all-air systems. It compares the thermal performance of these two systems for identical rooms considering different heat gains: (1) solar heat gain, (2) internal convective gains, and (3) internal radiative gains. Results show that for the same indoor air temperature the peak load is slightly higher for radiant systems (10% or smaller), regardless of the type of space heat gain. When considering thermal sensation, the performance of the two systems can be compared instead at the same operative temperature. The results also show that the cooling load for a radiant system depends greatly on the temperature control strategy (air vs operative temperatures). When operative temperature is used for the system control, the design load for radiant panels is almost the same as that of all-air systems, regardless of the type of the dominant space heat gain.