Thermal performance evaluation of hempcrete masonry walls for energy storage in cold weather

Abstract

During winter, buildings tend to consume a lot of energy for heating due to insufficient insulation of their envelopes. To address this issue, this study explores the use of materials with low thermal conductivity and high specific heat capacity, such as hempcrete, to minimize energy losses through the building envelope. The study suggests optimizing hempcrete components to enhance their thermal properties and evaluates the stored and lost thermal energy to improve the overall thermal performance of building envelopes. Twenty-five hempcretes are experimentally produced and thermally characterized. The thermal assessment also includes some hemp concretes from the literature for comparison purposes. ANSYS Fluent software is used to model the hempcrete walls in a transient state in terms of thermal storage capacity and losses in cold weather (e.g., −20 °C). Results show that stored energy is mainly affected by the product of hempcrete ρ and Cp values, while lost energy depends on thermal conductivity and diffusivity. The highest stored energy over 24 h is observed at 1.91 and 5.54 MJ/m2 for HC3 (literature) and AAFA-NaOH (present study), respectively, with a difference of 190 %. Further, the lowest values for lost energy are 0.44 and 0.42 MJ/m2 for HC2 (literature) and S2-CA (present study), respectively. To combine both stored energy and lost energy together, HC2 shows the best performance for the literature walls with lost energy of 0.44 MJ/m2 and stored energy of 1.82 MJ/m2; however, the present S2-CA hempcrete has lower lost energy at 0.42 MJ/m2 and higher stored energy at 3.07 MJ/m2. Additionally, a present C + Li + 30 %SF hempcrete has a similar lost energy of 0.46 MJ/m2 but a higher stored energy of 3.36 MJ/m2. The increasing hemp content has been noticed to increase stored energy by up to 86 % and reduce lost energy by 14.8 %.