Rethinking Radiant Comfort

In a warming world, staying cool will require thinking outside the air-based comfort box. Radiant cooling and personal comfort systems allow air temperature setpoints to be increased, but current comfort standards fall short of fully elucidating that full potential. Historically, radiant cooling capacity has been limited by condensation risk from the direct contact of radiant panels with humid air, and have unavoidably needed to be coupled with air conditioning. Our recent studies and experimental systems demonstrate a way to decouple the risks of radiant panels using IR transparent membranes that protect sub-dewpoint non-condensing radiant cooling surfaces. This photonically enables radiant cooling while mitigating condensation and preventing convection and condensation issues around the panel as demonstrated in our 'Cold Tube' test bed. These nonstandard conditions have helped us uncover and address discrepancies between mean radiant temperature (MRT) field measurements and simulation. In order to describe the potential comfort zone differently from that which is commonly mapped on the psychrometric chart from standard comfort ranges, we present a new comfort mapping framework that allows radiation or natural ventilation to be selected as setpoints. We have discovered that calculations supporting much higher potential separation of MRT from air temperature are incorrectly calculated by current black globe correction methodologies. We demonstrate systematic error in MRT measurements using black globes. This has misinformed radiant comfort understanding, and we show here how it could systematically biased ASHRAE thermal comfort database measurements. Together, these findings help advance the field's understanding of radiant comfort, demonstrating the acceptability of comfort conditions with high (>30 °C) air temperature and low (<24°C) mean radiant temperatures. We conclude with new deductions from these models, tools, and experiments including how operative temperature misguidedly increases temperature with higher air speeds incorrectly associating warming with higher air speeds, how radiant to convective ratios of heat transfer are affected by air movement and more importantly how radiant cooling positively reinforces its relative effect while radiant heating negatively does and increases susceptibility to draft, and finally how radiant affects are highly spatialized independent of common practice of defining thermal zones with room volumes. From this evidence, we conclude that there are significant alternative conceptual frameworks not dependent on temperature proxies that can more accurately define comfort.