Comparing the Hydraulic Performance of Cold-Water Premise Plumbing Systems Designed Based on Traditional and Modern Peak Demand Estimates

Abstract

Recent research has developed more accurate methods to estimate the peak demand for premise plumbing design in residential buildings. The improved accuracy produces lower design flow rates, leading to a reduction in pipe diameter, the size of pumps and control devices, and so on. Several industry case studies have presented the benefits of a reduced system size from cost, construction, embodied carbon, and energy consumption perspectives. However, little research has been done to (1) consider the wide array of demand scenarios (in addition to the peak demand) of premise plumbing systems (PPS), and (2) identify any potential risks aligned with improved peak demand estimation. To address the gap, the current study proposed a performance framework and used it to quantify and compare the performance (construction, hydraulics, energy consumption, and water quality) of PPS sized by a selected traditional and modern peak demand methods. Extended-period simulation (EPS) over a 24-h period at 1-s time steps is supported by a stochastic water demand model to enable the analysis of these PPS under a wide array of demand scenarios. For the PPS considered, the adoption of the modern peak demand design formula reduced copper pipe material by 69%; in the present study, total material weight was adopted to serve as a proxy for cost and embodied carbon because these metrics a susceptible to changes over time. Simulations demonstrated improved pump energy consumption between 28% and 46% depending on the system requirements and halved the relative water age in buildings. The traditional systems presented gross oversizing due to the predominant low-flow velocity values, which can negatively impact water quality and system performance. Conversely, the modern systems presented elevated flow velocity profiles and increased pipe frictional losses. Modern systems still performed within specified code performance requirements; however, simulations identified that designers will now need to be more conscious of velocity related phenomena (e.g., noise, erosion-corrosion, and water hammer) that were previously masked by oversized systems. The proposed performance framework serves as a foundational example of how EPS can be applied to quantify the performance of PPS.