Energy Assessment of Pressurized Water Systems

Abstract

This paper presents three new indicators for assessing the energy efficiency of a pressurized water system and the potential energy savings relative to the available technology and economic framework. The first two indicators are the ideal and real efficiencies of the system and reflect the values of the minimum energy required by users-the minimum amount of energy to be supplied to the system (because of its ideal behavior) and the actual energy consumed. The third indicator is the energy performance target, and it is estimated by setting an ambitious but achievable level of energy loss attributable to inefficiencies in the system (e.g., pumping stations, leakage, friction loss). The information provided by these three key performance indicators can make a significant contribution towards increasing system efficiency. The real efficiency indicator shows the actual performance of the system; the energy performance target provides a realistic goal on how the system should be performing; and finally, the ideal efficiency provides the maximum and unachievable level of efficiency (limited by the topographic energy linked to the network topography). The applicability and usefulness of these metrics will be demonstrated with an application in a real case study.

Labeling Water Transport Efficiencies

“…Further details are provided in a previous study [16]. Figure 1 shows the profile of one pipe of the network that includes intermediate water consumption points.…”

“…In a previous paper [16], this concept was generalized for water networks. Although from a conceptual point of view, the single pipeline network approach is identical, there are three differences to underline.…”

Discussion of “Energy Metrics for Water Distribution System Assessment: Case Study of the Toronto Network” by Rebecca Dziedzic and Bryan W. Karney

“…In summary, identical concepts that have been structured differently to reach the same conclusions. The only issue missed by the authors is the important concept of topographic energy (Cabrera et al 2014), which is absent from Equation 8 because the energy balance has been applied to a single pipe with no user demand nodes (leaks are not such nodes). The excess of energy delivered to the users at these nodes with respect to the required energy (= po/γ + znode) is the topographic energy.…”

“…Are the benefits worth such effort? The answer to this question lies in performing a diagnosis (Cabrera et al, 2014). If the result of this diagnosis shows that the energy efficiency is poor and a much better value can be achieved, the results justify the effort of a deeper analysis regardless of the time period used.…”

On the weaknesses and limitations of EPANET as regards energy

“…By comparing these values, the system's margin of energy efficiency improvement can be estimated. Furthermore, assessing the relevance of topographical energy permits us to identify the pipes in which this energy can be recovered by installing Pumps as Turbines (PATs) or, if that is not an option, dissipating it by pressure reducing valves (Cabrera et al 2014).…”