The Development of ARIMA Models for the Clear Sky Beam and Diffuse Optical Depths for HVAC Systems Design Using RTSM: A Case Study of the Umlazi Township Area, South Africa

Abstract

The increasing demand for energy in the building sector is mostly due to heat, ventilation and air conditioning (HVAC) systems. In the absence of the clear sky beam optical depth (CSBOD) and clear sky diffuse optical depth (CSDOD), there is a challenge to determine the solar heat gain for different orientations of the surface areas of buildings for HAVC design. The purpose of this research is to determine CSBOD and CSDOB from the available solar radiation data for the calculation of the cooling load in buildings. The numerical values of CSBOD and CSDOD are determined from simulations using three years of measured clear sky beam and diffuse irradiance data for the Umlazi area as a case study. From these results, the autoregressive integrated moving average (ARIMA) for both CSBOD and CSDOD was obtained, with ARIMA (2,1,1) (1,1,0) [12] and ARIMA (3,1,0) (1,1,0) [12] for CSBOD and CSDOD, respectively. The obtained values of 0.68073 and 2.64413 for CSBOD and CSDOD, respectively, were used to calculate the cooling load due to the solar irradiance heat gain for the hottest month of February in a newly built room in Mangosuthu University of Technology (MUT). The value of 1124 W was obtained using the radiant time series method (RTSM). A further study can be performed to use these models for the long-term forecasting of the solar radiation cooling load for optimal control of the HVAC systems.