Building envelope such as external walls are still constructed from poor materials which results in higher heating and cooling loads thereby raising energy bills. Improving building energy efficiency with advanced technologies is being sought. In this context, a numerical study was conducted to solve the coupled heat transfers through a standard wall structure used in Libyan residential buildings. Different techniques were compared to reduce the thermal transmittance of the traditional wall structure for saving energy including the application of radiant shield, low-e coating, insulating filling and external insulation. The numerical results revealed that the thermal radiation inside the cavities of hollow block is important and accounts for 21% of total heat transfer, while conductive and convective heat transfer contributes by 65% and 14% from the total, respectively. The obtained thermal transmittance value of the common wall structure was considered as high as 2.33 W/m2·K due to lower resistance of wall elements. The adoption of 50 mm layer of expanded polystyrene insulation (EPS) to the exterior wall showed the best thermal performance with a reduction of thermal transmittance by 45%. On the other hand, filling the interior of cavities with EPS resulted in a 37% reduction of thermal transmittance compared to 20% of using 3 mm aluminum foil as a radiant barrier in the middle of the cavities. The last case was less effective with a reduction of almost 10% when a commercial coating of 0.4 surface emissivity was applied to the interior of cavities.
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