Center for the Built Environment

Radiant system design standards and guidebooks classify radiant systems as a function of their structure and geometry. We assume that design approaches, testing methods, and control strategies of radiant systems can be more clearly described and classified based on thermal parameters. We calculated using computational fluid dynamics method the thermal time con-stants for 66 radiant system cases. We found pipe spacing, thickness and material properties of structural layer have a significant impact on time constant, while operative temperature, water temperature and water flow regime do not. We found time constants of radiant ceiling panels vary between 30-91 s; for embedded surface systems between 0.25-3.5 h; for thermally activated building systems with pipes embedded in the massive concrete slabs, between 2.4-7.7 h; and for capillary pipes embedded in a layer at the inner surface, between 0.1-0.6 h. A preliminary radiant system classification scheme based on thermal time constant is proposed.