Driven by high carbon emissions and expensive fossil resources, energy efficiency is becoming an issue of global relevance. Industry, office and residential buildings generate enormous quantities of waste heat, especially in lower temperature ranges. To become thermally more efficient, waste heat recovery is an option. The most frequent heat sources, available in a temperature range below 240 °C, are also the most difficult to recover. Organic Rankine cyclic process (ORC) has proven to be a recovery method for waste heat in higher temperature ranges. Carbon Dioxide is suitable as ORC working fluid for low temperature waste heat recovery due its low critical temperature. In contrast to other ORC working fluids it is environmental friendly. However, sufficient efficiency and economic rentability sill have to be obtained. The objective of this PhD research project is to optimize the energy efficiency of low temperature waste heat recovery. A numerical investigation of ORC system based on transcritical carbon dioxide (CTRC) will be performed. The cyclic process will be implemented in MATLAB (mass and energy balance, heat transfer, pressure drop, mechanical losses, etc.). For a detailed study of the heat transfer characteristics of transcritical carbon dioxide, the system components will be modeled in ANSYS-FLUENT. A comparative study of the simulation of the system components will deliver the most effective system configuration. A Luxembourgish biogas plant using cogeneration will serve as a reference energy source for input data. While biogas is burned in a cogeneration plant to produce electricity, low temperature exhaust gas is emitted into the environment. Cogeneration plants are a technology that is used also frequently in buildings and industry, therefore the result will be applicable on a broad range.Results will be an optimized system to recover low temperature waste heat. Savings in money, fossil fuel and greenhouse gases are a benefit.