A CFD Model for Air Flow vs. Pressure Loss Coefficient in HVAC Circular Ducts with a Motorized Damper
The pressure loss coefficient (k-factor) was determined for a circular duct with a damper using the CFD package Star-CD, and predicted the air flow and pressure distribution in the duct. The 3-D model simulated five different positions of the damper opening ranging from partially to completely opened position and for different Re number values. A k-ε turbulent model for high Reynolds number was used. The code generated the pressure drop across the damper, which was used to compute the pressure loss coefficient. This coefficient varied considerably with the damper angle opening with high values at low angles of opening indicating greater pressure losses. The Reynolds number had little impact on the k-factors. The predicted values were compared with previous experimental studies and found in good agreement. Knowledge of the pressure losses and k are suggested for the direct digital control of the motorized damper to obtain better flow control through that duct as a requirement for an optimum temperature control of the space the duct is serving. The control strategy, not discussed here, is done through a calibration of the flow required as a function of temperature difference between the set point temperature and the actual return temperature of space.