HVAC & Building Thermal Analysis — Energy & Comfort

What is the difference between a building energy model and a CFD analysis of a room?

Building energy models (EnergyPlus, OpenStudio) simulate multi-zone thermal balance over annual weather data to predict energy consumption — each room treated as well-mixed. CFD resolves 3D airflow, temperature gradients, and draft within a room, predicting local comfort metrics (PMV/PPD) at much higher cost, typically for a single design condition.

What is the PMV index and how does CFD contribute to predicting it?

PMV (Predicted Mean Vote) is a comfort index from -3 (cold) to +3 (hot) combining air temperature, radiant temperature, humidity, air velocity, activity level, and clothing insulation. CFD provides local air velocity and temperature at occupant locations as inputs to PMV. Areas with high draft or poor temperature distribution can be redesigned to improve comfort ratings.