Analysis method for hydraulic condition of outdoor air system under thermal pressure

Thermal pressure results in the hydraulic imbalance of outdoor air systems supplying air through vertical risers and the unbalanced resistance of parallel pipes, so it is impossible to calculate the pipe network impedance and analyse hydraulic condition. For this problem, a hydraulic condition analysis method for outdoor air systems under thermal pressure is proposed. In this method, the whole pipe network is regarded as the virtual closed loop for each end ventilation branch pipe in parallel, the pressure-resistance balance equation system are solved, the characteristic curve equations for each closed loop and pipe network are fitted, and the impedance of virtual closed loop is determined. The description of fluid flow and flow distribution law of pipe network under thermal pressure is realized. The coupling relationship between the pipe network flow, friction resistance coefficient and local resistance coefficient is considered in the calculation. Taking the outdoor air system of an office building as an example, the loop impedance method is used to analyse the hydraulic condition of the pipe network under thermal pressure.The calculated results are consistent with the iterative calculation results of the equation system, which proves the accuracy of the proposed method.