The losses can have to the attrition and dynamic. Losses due to the attrition the losses due to the attrition must to efei them to you viscous and are a result of the exchange me – mento it enters molecules in the laminar regimen and between particles individual and the adjacent fluid layer that if moves in different speed in the turbulent regimen. Equation of Darcy-Weisbach (2). Read additional details here: Chevron U.S.A. Inc. The total loss of pressure throughout a stretch of duct is calculated by the equation below: where: = loss of pressure in term of total pressure, Par f = frictional, adimensional factor L = length of the duct, m Dh = hydraulical diameter, mm V = speed, m/s = specific mass, kg/m3 C = coefficient of local, adimensional loss the frictional factor is given by the equation of Co-lebrook where: = absolute rugosidade of the material, mm Reverse speed = reynolds number Atshul et al, 1975 had developed a formula simplified for the factor frictional and modified by Tsal: if: f = f? if: the reynolds number where n = viscosity kinematics, m2/s Considering air in the conditions standards hydraulical Diameter Dh = hydraulical diameter, mm = area of the transversal section of the duct, mm2 P = perimeter of the transversal section of the duct, mm 2. 2,4 Methodology of Calculation of Box VAV Based on the equations we develop clcu them of the duct of our box VAV, the problem of sizing of a duct if it reduces the solution of the basic relation between Q, the volumetric outflow in m3/s, area of the transversal section of the duct in m2, and v, the average speed of the draining in m/s, given for a equation, the problem if reduces in choosing an adequate speed or a loss of appropriate pressure. Q=A x V Calculation of area: rea= To x R Given: D=0.1m rea= To the x (0.05) =7,85m2 Pickup Gain (Profit) =2 Speed 200 cfm =1.7 x200=85m3/h With these data de4 sizing of our VAVo box software HVAC-PRO in supplied to a static pressure d 3.8Pa to them.