Reduction of heat load in an air-conditioned bus employing phase change material integrated glass window and roof: A coupled numerical and analytical approach

Abstract

The study aims to analyze the heat load in an air-conditioned bus cabin by attaching a layer of phase change material to its roof and window glass. Enthalpy equation coupled with momentum and continuity equations has been solved in PCM layer, whereas only the diffusion equation is solved in roof and glass to obtain the spatiotemporal distribution of the temperature. A significant reduction in temperature on the inner and outer surfaces of the glass window and roof is noticed when PCM is attached. The inner surface of the glass shows a temperature reduction from 310 K to 301.5 K at 2.00 P.M, whereas the roof reveals a significant decrease of 14 K temperature when PCM is glued underneath. PCM helps keep the temperature at the inner surface under 302 K up to 12.00 pm However, the temperature rises to 308 K when PCM is not attached. The PCM thickness has a significant impact on temperature. An increase in thickness from 6 mm to 12 mm leads to a temperature reduction of 3 K to 4 K. Focusing on the performance of PCM, Na2SO4.10 H2O as a PCM is found to be beneficial since the phase change process (liquid fraction between 0 and 1) exists for a longer duration due to its high latent heat of fusion. The reduction in temperature using PCM is implicitly reflected in curtailing the total heat load in the cabin. Approximately 5 kW (45%) reduction in total heat load has been achieved using a 12 mm PCM layer on glass and roof during the peak time of solar radiation, substantially saving fuel and battery energy.