Dynamic performance of water-based radiant floors during start-up and high-intensity solar radiation

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In this paper, two typical types of radiant floors are examined: concrete core radiant floors and light radiant floors. Their variant dynamic behaviors during intermittent operation are illustrated, and the impact of transient solar radiation is determined through numerical calculation. The concept of the time constant is used to estimate quantitatively the thermal inertia of the different types of radiant floors, especially the response time in the start-up period of the cooling/heating systems. The response time of the concrete core radiant floor is estimated to be 1–3h, and that of the light floor is estimated to be 10–20min; these values are consistent with the actual cool-down/heat-up times. When exposed to solar radiation, the cooling capacity of the radiant floors is much higher compared to applications without solar radiation. To estimate the real-time floor surface temperature and cooling capacity with transient solar radiation for both design and operation, a simple calculation method based on thermal capacity of the radiant floor is introduced, and the results accord well with the numerical calculation results. And the dynamic equivalent heat resistance is defined to reflect the thermal behavior of radiant floor with transient solar radiation. In addition, the heat extraction by chilled water in the radiant floor is distinct from the heat absorbed at the floor surface due to the heat storage of the radiant floor, which is also estimated by simple calculation.