Improved Assessment of Energy Recovery Potential in Water Supply Systems with High Demand Variation

Abstract

Enhancing energy efficiency of water supply systems by recovering part of the excessive pressure is currently an issue of growing interest for water companies. The installation of micro hydro plants for energy recovery can be profitable in sites with excessive pressure, though requiring proper technical and economical evaluation. This paper presents a methodology for assessing the energy recovery potential in water supply systems under high seasonal demand variation. The methodology is based on the calculation of head and flow rate conditions that maximize energy production for a specific energy recovery technology, given available head and flow rate ranges. The methodology is applied to the inlet of a storage tank of a water transmission system using hourly collected data over one year. Results show that, in systems of high variability of flow rate, the installation of turbomachines in parallel is necessary for maximizing energy recovery and that the developed methodology returns lower, but more realistic, energy production estimates than other approaches based on average head and flow rate data.

Microturbines at Drinking Water Tanks Fed by Gravity Pipelines: A Method and Excel Tool for Maximizing Annual Energy Generation Based on Historical Tank Outflow Data

“…For example, the flow rate ranges 25 to 30 m 3 /h and 30 to 35 m 3 /h have nearly the same frequency, but the latter range has a substantially greater expected annual energy generation. Some other authors have used long-term average values in their turbine design methods [15,25]. It is worth noting that average hourly or average daily flow data can be misleading, since the inflow rate might be much higher than the hourly average but occurring only periodically for only short periods of time (e.g., for 5 min at a time, with 15 min in between times of active flow).…”

“…The tool assumes the selection of a single turbine with a narrow acceptable operating range, and considers neither the possibility of turbines with wide operating ranges nor that of multiple turbines, the latter of which might lead to greater energy generation [25,27]. This was decided partly for simplicity's sake and partly out of the belief that a single turbine generally represents the most economically viable solution for class 1 sites, which is supported by one of the studies cited above [25].…”

“…The tool assumes the selection of a single turbine with a narrow acceptable operating range, and considers neither the possibility of turbines with wide operating ranges nor that of multiple turbines, the latter of which might lead to greater energy generation [25,27]. This was decided partly for simplicity's sake and partly out of the belief that a single turbine generally represents the most economically viable solution for class 1 sites, which is supported by one of the studies cited above [25]. Furthermore, as indicated in Section 1.2, these studies do take into account the fundamental advantage of class 1 sites, which is the ability to modify the inflow regime, instead using multiple turbines to adapt to the wide range of flow rates occurring based on the current site conditions.…”

“…Monteiro et al [25] introduce a method for assessing energy generation and determining the optimal number and parameters of turbines at class 1 sites, which they apply to one of three identified sites in Portugal. However, they seem to effectively treat class 1 sites as if they were class 2 sites, assuming that the inflow regime remains unchanged and attempting to design turbines to fit the inflow regime, rather than adjusting the inflow regime to allow the choice of a single, optimized turbine.…”

Optimization Design of a Rain-Power Utilization System Based on a Siphon and Its Application in a High-Rise Building

“…Scholars have contributed to studies of RRHS from different perspectives. Monteiro, based on an estimation of the turbine performance, maximized the energy production by giving the available head and flow rate values over one year for a specific energy recovery technology [17]. Alnaimi demonstrated that the stability of RRHS can be guaranteed by force analysis to help select durable material under pressure.…”