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ABSTRACT
A neural network-based model for interior longwave radiative heat transfer has been developed and implemented into a new computer code, BERHT (Building Energy with Radiative Heat Transfer). The model accounts for the non-gray effect of absorbing species in a building environment and the geometric effect of a three-dimensional building structure. Numerical studies have been carried out on a rectangular single-story building. For nominal concentration of CO2, H2O, and small particulates, results show that the effect of radiative heat transfer is important. The surface emissivity of enclosure walls and optical properties of the absorbing/emitting medium are demonstrated to have significant effects on the distribution of heat transfer between convection and radiation, as well as the transient behavior of the indoor air temperature. Supplemental studies provide an insight that the one-zone, well-mixed model used in building energy simulation generates a “fictitious” non-local heat transfer behavior, leading to uncertainties in the understanding of the radiative heat transfer effect.
Nomenclature
| Symbols | = | |
| Ai (i = 1,6) | = | = bounding areas of building structure |
| cp | = | = specific heat of air or air mixture |
| hconv | = | = convective heat transfer coefficient |
| = | = mass flow rate due to infiltration of outside air | |
| Nload | = | = total number of internal convective loads |
| Nsurf | = | = total number of interior surfaces |
| = | = conduction heat flux | |
| = | = convective flux exchange | |
| = | = longwave radiative flux exchange | |
| = | = absorbed direct and diffuse solar radiation heat flux (shortwave) | |
| = | = sum of heat gains from lights, people, and equipment | |
| qo,i | = | = radiosity from surface Ai |
| qog,i | = | = radiosity from surface Ai due to mixture emission only |
| Qi | = | = total radiative heat transfer on surface Ai due to both surface and mixture emission |
| Qg | = | = total radiative heat transfer to medium due to both surface and mixture emission |
| Qw, i | = | = radiative heat transfer on surface Ai due to surface emission only |
| Qsys | = | = HVAC system output |
| Qload | = | = sum of internal convective loads |
| SiSj | = | = exchange factors |
| Tg | = | = temperature of medium |
| Tw | = | = temperature of interior surface |
| Tz | = | = temperature of zone air |
| σ | = | = Stefan–Boltzmann constant |
| ϵi | = | = emissivity of surface Ai |
| ρair | = | = density of air |
| ∀ z | = | = volume of zone air in the building structure |
| Subscripts | = | |
| ext | = | = exterior surfaces of the building structure |
| int | = | = interior surfaces of the building structure |
| Superscripts | = | |
| wall | = | = emission due to surface only |
| gas | = | = emission due to mixture only |
Nomenclature
| Symbols | = | |
| Ai (i = 1,6) | = | = bounding areas of building structure |
| cp | = | = specific heat of air or air mixture |
| hconv | = | = convective heat transfer coefficient |
| = | = mass flow rate due to infiltration of outside air | |
| Nload | = | = total number of internal convective loads |
| Nsurf | = | = total number of interior surfaces |
| = | = conduction heat flux | |
| = | = convective flux exchange | |
| = | = longwave radiative flux exchange | |
| = | = absorbed direct and diffuse solar radiation heat flux (shortwave) | |
| = | = sum of heat gains from lights, people, and equipment | |
| qo,i | = | = radiosity from surface Ai |
| qog,i | = | = radiosity from surface Ai due to mixture emission only |
| Qi | = | = total radiative heat transfer on surface Ai due to both surface and mixture emission |
| Qg | = | = total radiative heat transfer to medium due to both surface and mixture emission |
| Qw, i | = | = radiative heat transfer on surface Ai due to surface emission only |
| Qsys | = | = HVAC system output |
| Qload | = | = sum of internal convective loads |
| SiSj | = | = exchange factors |
| Tg | = | = temperature of medium |
| Tw | = | = temperature of interior surface |
| Tz | = | = temperature of zone air |
| σ | = | = Stefan–Boltzmann constant |
| ϵi | = | = emissivity of surface Ai |
| ρair | = | = density of air |
| ∀ z | = | = volume of zone air in the building structure |
| Subscripts | = | |
| ext | = | = exterior surfaces of the building structure |
| int | = | = interior surfaces of the building structure |
| Superscripts | = | |
| wall | = | = emission due to surface only |
| gas | = | = emission due to mixture only |