Thermal CFD Analysis of Tubular Light Guides

Abstract

Tubular light guides are applicable for daylighting of windowless areas in buildings. Despite their many positive indoor climate aspects they can also present some problems with heat losses and condensation. A computer CFD model focused on the evaluation of temperature distribution and air flow inside tubular light guides of different dimensions was studied. The physical model of the tested light guides of lengths more than 0.60 m proves shows that Rayleigh numbers are adequate for a turbulent air flow. The turbulent model was applied despite the small heat flux differences between the turbulent and laminar model. The CFD simulations resulted into conclusions that the growing ratio of length/diameter increases the heat transmission loss/linear transmittance as much as by 50 percent. Tubular light guides of smaller diameters have lower heat transmission losses compared to the wider ones of the same lengths with the same outdoor temperature being taken into account. The simulation results confirmed the thermal bridge effect of the tubular light guide tube inside the insulated flat roof details. The thermal transmittance of the studied light guides in the whole roof area was substituted with the point thermal bridges. This substitution gives possibility for simple thermal evaluation of the tubular light pipes in roof constructions.

Thermal and spectral impact of building integrated Mirrored Light Pipe to human circadian rhythms and thermal environment

“…The temperature measurement data show a significant increase in the temperature at the surface of the light pipe in response to the IR radiation. The author indicates that the light pipe could be supplemented with an additional vented pipe to prevent any overheating problems, which has been confirmed by other authors [14][15][16][17][18].…”

“…Several authors have been interested in studying the light pipe associated with a thermal draft [14][15][16][17][18].…”

“…Varga [14], Oakley [15], Šikula [16], Šikula [17], Ait-taleb [18] Interesting coupling of thermal draft + light contribution Double ducting limits the temperature rise of the reflective surface…”

Thermal testing of the light pipe prototype

“…Heat transfer and natural ventilation in light pipes were studied on models. Computer fluid dynamic simulations aimed at the light pipe thermal profiles were analyzed [27][28][29][30]. The simulations and experimental studies were carried out for integrated daylight-ventilation pipes [31][32][33].…”

“…Emissivity of mirrored surfaces of the light pipe prototype is 0.05 [43]. The thermal monitoring was compared to infrared thermography monitoring for heat transfer models [44] and the previous studies of computer simulations of light pipes thermal profiles [27,28].…”