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Estimating Peak Water Demand in Buildings with Efficient Fixtures: Methods, Merits, and Implications

Omaghomi, Toritseju O
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1562843108109428

Abstract Details

2019, PhD, University of Cincinnati, Engineering and Applied Science: Environmental Engineering.
In 1940, Roy Hunter developed the “fixture unit” method of estimating peak water demand in a building. Hunter’s iconic curve became the standard for plumbing codes across the globe. In recent decades, the growing need to conserve water and save energy has led to more efficient plumbing fixtures that consume less water per function. Accordingly, there have been empirical modifications to Hunter’s fixture unit method reflecting the general decreasing trend in water consumption, however, it continues to over-estimate peak indoor water demand. This results in over-sized premise plumbing systems (PPS) and a myriad of related issues. This dissertation develops a new method to estimate peak water demand in buildings with efficient fixtures. Like Hunter’s approach, the proposed method requires three key parameters: n – the number of fixtures, p – the probability that a fixture is being used, and q – the fixture flow rate. Parameters n and q are relatively straight forward to obtain; however, the parameter p is more elusive. In this study, the fixture probability of use for residential users were calculated from a high-resolution database of water consumption measured at over 1,000 US households. All parameters were incorporated in a three-tier model to estimate peak indoor water demand. Tier 1 involves exhaustive enumeration (EE), tier 2 involves the zero-truncated Poisson-binomial distribution (ZTPBD), and tier 3 involves the normal approximation of the Poisson-binomial distribution (NAPBD). The progression from tier 1 to 3 reflects the spatial scale transition from a single fixture in small buildings to many fixtures in large buildings. A water demand calculator (WDC) was developed to identify and execute the appropriate method to estimate peak indoor water demand. Results show that during the period of peak indoor water demand, the probability of fixture use ranges from a low of about 0.5% for dishwashers to a high of about 5.5% for a washing machine or a combined bathtub/shower. These relatively low probabilities values imply that stagnation is common, even during the peak hour of water use in single-family homes. Peak flow estimates from the WDC showed very good agreement with instantaneous peak flows measured at 11 multi-apartment buildings with efficient fixtures in Scottsdale, Arizona, and Denver, Colorado. The peak flow predictions from the WDC performed much better than the inflated peak flows generated from the conventional method based on Hunter’s curve. The reduced peak flow estimates from the WDC will lead to a smaller PPS. This means that pipes, meters, heaters, softeners and other components of the building water supply can be downsized with no appreciable loss in performance. The implications for water and energy savings, especially in future construction can be direct, immediate and profound. In addition, adopting the WDC with respect to hot water distribution reveal that with reduced pipe sizes, hot water arrives at fixtures faster and at higher temperatures and less energy is lost in the pipes. When a PPS is rightly sized with pipes complementing water conservation measures, there are savings in cost, water, and energy while reducing the risk of potential health issues.
Steven Buchberger, Ph.D. (Committee Chair)
Dominic Boccelli, Ph.D. (Committee Member)
Darren Lytle, Ph.D. (Committee Member)
Drew McAvoy, Ph.D. (Committee Member)
173 p.
Environmental Engineering
Peak Water Demand; Premise plumbing; Hunters demand curve; Water savings; Efficient fixtures

Recommended Citations

Citations

  • Omaghomi, T. O. (2019). Estimating Peak Water Demand in Buildings with Efficient Fixtures: Methods, Merits, and Implications [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1562843108109428

    APA Style (7th edition)

  • Omaghomi, Toritseju. Estimating Peak Water Demand in Buildings with Efficient Fixtures: Methods, Merits, and Implications. 2019. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1562843108109428.

    MLA Style (8th edition)

  • Omaghomi, Toritseju. "Estimating Peak Water Demand in Buildings with Efficient Fixtures: Methods, Merits, and Implications." Doctoral dissertation, University of Cincinnati, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1562843108109428

    Chicago Manual of Style (17th edition)

ucin1562843108109428
552
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This open access ETD is published by University of Cincinnati and OhioLINK.