Radiant floor heating has received increasing attention due to its diverse advantages, especially the energy saving as compared to the conventional dwelling heating system. This paper presents a numerical investigation of airflow and heat transfer in the slot-vented room with the radiant floor heating unit. Combination of fluid convection and thermal radiation has been implemented through the thermal boundary conditions. Spatial distributions of indoor air temperature and velocity, as well as the heat transfer rates along the radiant floor and the outer wall, have been presented and analyzed covering the domains from complete natural convection to forced convection dominated flows. The numerical results demonstrate that the levels of average temperature in the room with lateral slot-ventilation are higher than those without slot-ventilation, but lower than those in the room with ceiling slot-ventilation. Overall, the slot-ventilation room with radiant floor heating unit could offer better indoor air quality through increasing the indoor air temperature and fresh air exchanging rate simultaneously. Concerning the airborne pollutant transports and moisture condensations, the performance of radiant floor heating unit will be further optimized in our future researches.
Radiant floor heating is a novel indoor heating technique that has received increasing attention in recent years. In the conventional heating methods, such as the air convection by radiators and the hot air supply by air conditioners, the hot air is always located in the upside or middle upside of the room instead of the occupied zone, leading to the obvious temperature differences between the upside and underside of the room. Under such condition, occupants usually feel uncomfortable. In the radiant floor heating, however, the effective temperature of the floor is higher than the temperature in the upside of the room, which can supply more heat to the underside of the room for warming the occupants’ feet instead of their heads that follows the rule of human’s physiologic adjustment. Therefore, the radiant floor heating improves the thermal comfort condition for the occupants as compared to the conventional heating methods. In addition, the radiant system has the advantages of energy saving, long life, wide selection of the heat sources, low cost, and environmental friendliness. The theoretical and experimental research [
Radiant heating system is such a complex system that involves the various heat transfer mechanisms, including the heat conduction in the floor, the radiative heat transfer between radiant surface and other surfaces, convective heat transfer between the radiant surface and its neighboring air, and the buoyancy’s effects. The numerical method provides a convenient way to solve such problem. Ghaly and Elbarbary [
This paper presents the numerical simulation of floor radiant heating system with three types of slot-ventilation, that is, lateral slot-ventilation (LSV), ceiling slot-ventilation (CSV) and no slot-ventilation (NSV). The indoor temperature, velocity, and heat flux distributions are calculated. This work is of great significance for the design and wider application of the floor radiant heating system.
The steady 2D model of the turbulent airflow and heat transfer in the room is developed in this study. The schematic of radiant heating system and coordinate system is shown in Figure
Schematic of radiant heating system and coordinate system.
Continuity equation:
The DO radiation model is employed to handle the radiative heat transfer, and the absorbing and scattering of air are omitted:
Based on the control volume and SIMPLEC method [
The calculation conditions are as follows: the constant wall temperature
Figure
The temperature and velocity distribution at
Figure
The temperature distributions at different
Figure
The velocity distributions at different
Figure
The velocity and temperature distributions for LSV at
Figure
The velocity and temperature distributions for CSV at
The different behaviors of the indoor air temperature under the different conditions are the combined results of the different heat transfer mechanisms. The heat fluxes along the floor and outside wall are studied and the Nusselt numbers for the convective heat transfer
Figures
The numerical stimulations of the airflow and heat transfer in the slot-vented room with radiant floor heating unit, including LSV, CSV, and NSV, are performed. The temperature, velocity, and the behaviors of the radiative and convective heat transfer are calculated. The results show that the air temperatures in the room are quite uniform under these three air-supply modes and the average temperature difference is less than 1°C. Under LSV, the forced ventilation has the same moving direction with the natural convection and thus increases the air velocity. Under CSV, the flow pattern is more complex as the combined result of the forced ventilation and natural convection. Radiation is main heat transfer mechanism at the floor and the outside wall under all the three conditions. Radiative heat flux accounts for 50–60% of the total heat flux, which is largest under CSV. LSV offers the strongest convection along the floor and outside wall, which increases the convective heat transfer, especially at cold outside wall. Therefore, the average temperature for LSV is lower than that for CSV.
Concerning the airborne pollutant transports and moisture condensations, the performance of radiant floor heating unit will be further optimized in our future researches.
The authors gratefully acknowledge the funding for this project provided by International Science and Technology Cooperative Project of China (2010DFB63830), Major Science and Technology Project of Hunan Province (2010FJ1013), and National Natural Science Foundation of China (51178477).