Effect of thermal mass on performance of insulated building walls and the concept of energy savings potential

摘要

Effects of varying amount and location of thermal mass on dynamic heat-transfer characteristics of insulated building walls with same nominal resistance (Revalue) are investigated numerically under steady periodic conditions using climatic data of Riyadh. Concepts of "thermal-mass energy-savings potential" (A) and "critical thermal-mass thickness" (L(mas,cr)) are developed and utilized in order to determine thermal mass thickness (L_(mas)) required for a selected desirable percentage of energy savings. Results show that daily transmission loads are not affected by L_(mas) for representative days of months in summer and winter. However, for moderate months, daily cooling and heating transmission loads decrease with increasing L_(mas) and either diminish to zero or be reduced asymptotically to constant values. For all months, peak transmission loads and decrement factor decrease, while time lag increases, with increasing L_(xas). For a given L_(mas), a wall with outside insulation gives better overall performance than a wall with inside insulation. While Rn-value is constant, wall dynamic resistance (Rd-value) changes and represents actual variations in transmission loads. For A in the range 70-99%, L_(mas,cr) ranges between 6 and 30 cm by using heavyweight concrete. It is found that maximum savings in yearly cooling and heating transmission loads are about 17% and 35%, respectively, as a result of optimizing L_(mas) for same R_n-value. It is recommended that building walls should contain L(mas,cr) that corresponds to high A (≈95%) and with insulation placed on outside for applications with continuously operating year-round AC.