Sizing cold water plumbing supply systems: comparative study using flow determination through the square root and binomial probabilistic methods

Abstract

ABSTRACT: To sizing cold water plumbing supply systems several methods of flow determination can be used. In Brazil, the standard NBR 5626 (ABNT, 2020) is responsible for establishing methodological criteria and recommendations regarding the design of these facilities components. The cited standard no longer recommends an empirical method for calculating the diameters of the water supply distribution pipes, as occurred in its previous version NBR 5626 (ABNT, 1998). In this way, the updated version of the standard makes it possible to use numerous different methods for sizing these systems. The binomial probabilistic model for determining the flow rates in water supply pipes is an alternative to the square root method, traditionally used by designers in Brazil. In water supply distribution pipes, positioned just below the reservoir, there are the highest concentrations of flows rates and, also, the lowest distribution pressures. Thus, this part of the water supply system is one of the most requested and must be sized so that all water use points have pressures and flows adequate to its final uses. Therefore, these pipeline section have the largest diameters, reinforced by the fact that the upstream pipe must always have a diameter greater or equal to the downstream pipe. Considering this situation, this paper presents a comparison between the flows rates and diameters of a water supply distribution pipelines of a single-family residence, when dimensioned using the procedure traditionally used in Brazil, called square root method, and a probabilistic method, which is based on the binomial model. The results show differences between the design flows rates determined by the different methods. This can result in better adjustments in the in the sizing and specifications of the plumbing components of the cold water supply distribution system.