All-air vs. radiant cooling systems: Analysis of design and operation factors that impact building cooling loads (ASHRAE RP 1729)

Abstract

When compared to all-air systems, radiant cooling systems can improve chiller efficiency by using a higher refrigerant evaporation temperature. However, the details on differences in heat transfer and building cooling load between all-air and radiant systems are not well defined. This study uses experimental data and numerical modeling to examine the dynamics of cooling load and overall heat transfer for both radiant panel and all-air systems under various operating conditions. This study investigates the effect of: (a) heat gains (transmitted solar, internal radiative, convective), (b) set-point temperature control (air vs operative), (c) building thermal mass, (d) air circulation and surface convection, (e) panel surface area, (f) radiant system configuration (ceiling vs floor panels), and (g) intermittent system operation on the space cooling load of radiant cooling panels. Results show that for the same set-point air temperature radiant systems have slightly larger peak load than an all-air system regardless of dominant heat gain type. When considering set-point, control by operative temperature provides better performance for radiant systems. When air mixing and convection are enhanced, radiant panels allow for operational cost savings for space cooling as well as shifting building peak load to off-peak hours.