Effect of Thermal Bridges in Insulated Walls on Air-Conditioning Loads Using Whole Building Energy Analysis
Zedan, Mohamed F. . 2014
Thermal bridges in building walls are usually caused by mortar joints between insulated building blocks creating an easy path for heat transmission. The effects of these bridges on cooling and heating loads in a typical 2-storey villa in Riyadh were investigated by using a whole-building load calculation package. All loads found in such villa, which broadly include ventilation, transmission, solar and internal loads were considered with schedules based on local lifestyles. The thermal bridge effect was simulated by reducing wall thermal resistance by a percentage that corresponds to bridge to wall area ratio and nominal thermal insulation thickness. These percentage reductions were obtained from a correlation developed by the authors using rigorous 2-D analysis of heat transmission through walls. Results indicate that yearly cooling load increases almost linearly with thermal bridge to wall area ratio (Amj/Atot). The increase varies from about 3% for Amj/Atot = 0.02 to about 11% for Amj/Atot = 0.08. On a monthly basis, the variation of the cooling load with Amj/Atot is also approximately linear; however, the rate of increase is higher during summer months. In August, for example, the monthly cooling load increases by about 5% for Amj/Atot = 0.02 up to about 15% for Amj/Atot = 0.08. In winter, results show that heating loads are generally very small compared to cooling loads and that heating is required mainly in December, January, and February, starting from late night to late morning. Monthly heating loads increase with thermal bridge area ratio; however the variation is not as linear as observed in cooling loads. The present results highlight the importance of reducing or eliminating thermal bridging effects by maintaining the continuity of the insulation layer in walls in order to reduce energy consumption in air-conditioned buildings.
Thermal bridges in building walls are usually caused by mortar joints between insulated building blocks creating an easy path for heat transmission. The effects of these bridges on cooling and…