The Effect of Temperature and Moisture Variation on the Heat Transfer Through Building Envelope

This paper investigates the impact of the change of thermal conductivity of the insulation layer embedded in a typical residential building on the cooling effect. The simulation has been performed using the polystyrene (EPS), in extremely hot conditions of Al Ain (UAE) at different level of densities denoted as low density LD (12 kg/m3), high density HD (20 kg/m3), ultra-high density UHD (30 kg/m3) and super-high density SHD (35 kg/m3), and three moisture content levels (10%, 20%, and 30%) compared to dry insulation material for LD. The change of the thermal conductivity of the EPS material at different operating temperatures and moisture content has been investigated. The thermal wall resistance was evaluated by applying a conjugate heat transfer model based on enthalpy-based formulation. The thermal performance of the building incorporating polystyrene with variable thermal conductivity (λ -value) was compared to a constant thermal conductivity by quantifying the additional cooling demand and capacity due to the λ-relationship with time using the e-quest as a building energy analysis tool. The results show that, when the λ-value is modelled as a function of operating temperature, its effect on the temperature profile during daytime is significant compared with that obtained when a constant λ-value for the polystyrene (EPS) insulation is adopted, however, this trend is reversed at night time. A similar trend in the evolution of temperatures across the wall section was observed when EPS material was tested with different densities and moisture contents. The monthly energy consumption for cooling required by the building is found to be higher in case of variable thermal conductivity for LD sample. The yearly average change in space cooling demand and cooling capacity employing polystyrene with constant and variable thermal conductivity increases with the increase of the moisture content. Indeed, the highest change in cooling demand and capacity are 6.5% and 8.8% with 30% moisture content.