Numerical analysis on the energy efficiency improvement of thermo-injection method of masonry walls drying by applying the variable temperature profiles of drying air

Abstract

The influence of the drying air temperature profile on the effectiveness of the thermo-injection masonry wall drying method was investigated by applying numerical modeling. The in-house non-equilibrium heat and moisture transfer model was used to perform simulations. A two weeks drying process was simulated. Four drying strategies characterized by constant, jump, stepwise, and periodic drying air temperature profiles were studied and compared. Three different heating intervals (i.e., 12, 24, and 48 h), which referred to drying air temperature profile changes, were examined. The drying air temperature varied between 20 and 60 °C. Moreover, the relative humidity of the drying air corresponded to the three seasons in Poland, i.e., winter, spring, and summer, and ranging between 70 and 90% at ambient conditions. It was found that drying strategies with the jump and stepwise temperature profiles may decrease the energy consumption required for masonry wall drying by up to 5.9% during the season with a low drying air relative humidity (i.e., during winter). However, energy savings were insufficient during the highly humid season (i.e., summer). The heating interval of 48 h was the best for the jump strategy and may be the best for the stepwise approach in a longer than two weeks drying process. The stepwise strategy removed significantly more water from the wall to reach the same level of moisture mass fraction in the drying zone as the constant and jump strategies. The slower wall heating process and the continuous action of capillary water uptake were responsible for this behavior. The same phenomena caused the periodic strategy to be ineffective.