Purpose: This paper is to develop a simple and efficient conservative semi-Lagrangian scheme for solving advection equation in Fast Fluid Dynamics (FFD), so FFD can provide fast indoor airflow simulations while preserving conservation for energy and species transport. Design/methodology/approach: This study thus proposed a mass-fixing type conservative semi-Lagrangian scheme that redistributes global surplus/deficit on the advected field after performing the standard semi-Lagrangian advection.

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... he redistribution weights were designed to preserve the properties of conservatives and monotonicity. Findings: The effectiveness of the conservative semi-Lagrangian scheme was validated with several test cases, and the results show that the proposed scheme is indeed conservative with negligible impact on the accuracy of the standard solutions.Findings-Our numerical tests show that the proposed scheme was indeed conservative with negligible impact on the accuracy of the flow prediction. Originality/value: The FFD with conservative semi-Lagrangian scheme can effectively enforce the energy and species conservation for indoor airflow and predict airflow distributions with reasonable accuracy.