I am using flow simulation; HVAC module to analyze distribution of temperature, velocity, PMV and Co2 in a classroom of dimension 38m*28m*3m where the conditioned air is provided via 35 square diffuser. Various heat sources and humans generating C02 is modeled inside classroom. Auto mesh generation with level of initial mesh 5 and minimum gap size of 0.012m is done. There are 1.4 million fluid cells and 1.3 million of partial cells and after running simulation for 35 hour, the CPU time left is more than 100 hour with 0% progress. Is there a way to reduce computational time without compromising in accuracy ? I am interested in the distribution of thermal comfort parameters (PMV, temp, Vel, co2) in occupied region of height 1.1m. The global goals assumed are average mean radiant temperature, operative temperature, velocity and volume fraction of co2.