Evaluation of air impact on urban radiative transfer and building loads using discrete ordinate method

This paper presents a novel approach for evaluating the air impact on urban microclimate and building loads. Traditional software tools, such as TRNSYS and EnergyPlus, often employ the surface-to-surface method for radiation transfer calculations, which neglects the influence of air. To address this limitation, this work integrates the discrete ordinates method (DOM) with the spectral-line weighted-sum-of-gray-gases (SLW) air model to develop a microclimate energy approach. The SLW model uses outdoor temperature and humidity data to compute absorption coefficients, leveraging the air spectrum provided by the HITRAN database. The DOM is then employed to calculate both solar and infrared radiation transfers within the urban environment. A transient simulation is conducted over one year for an urban scene in Suzhou, China. The results indicate that the air impact on radiation transfer increases with rising outdoor temperature and humidity. Overall, the results demonstrate that air effects exert a non-negligible influence on building heating and cooling load calculations, with an impact magnitude comparable to the introduction of an auxiliary thermal source. This study highlights the significance of considering air properties in urban microclimate and building energy simulations for more accurate results.