Proportional Balancing Ratio Method

Air systems are COUPLED: closing a damper at one outlet raises the pressure available to every other outlet on the branch, so an outlet set exactly to design will not be at design once the next one is adjusted. Balancing outlet by outlet chases that coupling around the branch, sometimes for hours, and often never converges. Proportional balancing exploits the coupling instead of fighting it. If every outlet sits at the same FRACTION of its design, then any change in branch flow scales them all by the same factor and the ratios are preserved. So the balancer equalizes ratios first, which is a stable target, and only then opens the branch damper to bring the whole set to 100 percent. One adjustment at the end sets everything. The reference outlet is the LOWEST ratio and it is left wide open, because it is the one with the least pressure available -- throttling everything to match a HIGH outlet would mean opening the low one beyond fully open, which is not available. That single rule is what makes the method converge, and it is the part that gets done backwards by someone balancing from the first outlet on the drawing. The targets reported here are where each outlet should read once equalized, and the branch adjustment factor is what the branch damper then has to deliver. Measured flows are ENTERED and should be corrected hood readings or traverse values rather than raw ones, because a systematic instrument error shifts every ratio together and moves the reference. This does not model the damper positions, the branch pressure, or the interaction between branches on a common trunk; a system with too little pressure at the reference outlet cannot be balanced by this or any other method, and that is a design or fan problem the method will reveal rather than solve. The AABC or NEBB procedure in force and the balancer's own judgment govern.

ratio = measured / design at every terminal; the LOWEST ratio is the reference and is left wide open; every other terminal is throttled to design x that reference ratio; the branch then reads design x the reference ratio, and the branch damper opens by the reciprocal of it.

The proportional balancing method as AABC and NEBB procedure states it. Measured flows are ENTERED and should be corrected readings, because a systematic instrument error shifts every ratio together and moves the reference. It does not model damper positions, branch pressure, or interaction between branches on a common trunk, and a branch with too little pressure at the reference outlet cannot be balanced by this or any other method.

A set of ratios and one multiplication each.

Estimate. AHJ and licensed professional govern.

Field names used by the API: design_1_cfm, measured_1_cfm, design_2_cfm, measured_2_cfm, design_3_cfm, measured_3_cfm, design_4_cfm, measured_4_cfm, design_5_cfm, measured_5_cfm, design_6_cfm, measured_6_cfm, reference_ratio, branch_design_cfm, branch_measured_cfm, branch_after_equalizing_cfm, branch_adjustment_factor

• Measured flows should be corrected a systematic instrument error moves the referenceflow-hood correction or a traverse
• One branch at a time interaction between branches on a common trunk is not modelledthe balancing procedure in force
• It cannot create pressure a branch short of pressure at the reference outlet is a design or fan problemthe mechanical engineer of record