A simplified analytical model to evaluate the impact of radiant heat on building cooling load

• Ignoring the inner radiation may cause significant uncertainty to cooling load.
• We develop a simple analytical model to evaluate the inner radiation effect.
• A simple method is proposed for improving the “air-to-air” conduction method.
• A quantitative analysis of the inner radiation effect is conducted.
• Radiative heat gains and building zoning configurations are two key factors.

In some building cooling load calculation methods, the conductive heat gain is calculated using the “air-to-air” conduction method in which the effect of radiative heat on the outer surface of external envelopes has been considered (e.g., using the sol-air temperature). However, the effect of the radiative heat on the inner surface is ignored, which results in uncertainty of conductive heat gain calculation and may bring significant errors in cooling load calculation under some particular conditions. This paper presents a simple method to consider the radiative heat on the inner surface of external envelopes for improving the accuracy of the “air-to-air” conduction method. A simplified analytical model is developed for evaluating the impact of inner radiant heat effect on cooling load. Five case studies are conducted in EnergyPlus to validate the model and to assess the radiative heat impact under different conditions. An illustrative example is presented to demonstrate the procedures of using the developed method to evaluate the inner radiation effect in a real building in Hong Kong. It is found that the most important factors determining the inner radiation effect are the radiative heat conditions and the building zoning configurations, and oversimplifying the zoning configuration might result in errors of up to 10% in cooling load calculations.