PAT Design Strategy for Energy Recovery in Water Distribution Networks by Electrical Regulation

TLDR

Water distribution networks can achieve significant energy savings by exploiting head drop, yet ensuring the required head drop under variable operating conditions remains a design challenge, and efficient, economically viable solutions are still needed. The authors extend the Variable Operating Strategy (VOS) design procedure to both hydraulic regulation (HR) via a series‑parallel hydraulic circuit and electrical regulation (ER) via an inverter, applying it to a pump‑as‑turbine (PAT) system to evaluate efficiency. The study finds that HR is both more flexible and more efficient than ER, and that HR offers a shorter payback period in a preliminary economic assessment.

Abstract

In the management of water distribution networks, large energy savings can be yielded by exploiting the head drop due to the network pressure control strategy, i.e., for leak reductions. Hydropower in small streams is already exploited, but technical solutions combining efficiency and economic convenience are still required. In water distribution networks, an additional design problem comes out from the necessity of ensuring a required head drop under variable operating conditions, i.e., head and discharge variations. Both a hydraulic regulation (HR)—via a series-parallel hydraulic circuit- and an electrical regulation (ER)—via inverter- are feasible solutions. A design procedure for the selection of a production device in a series-parallel hydraulic circuit has been recently proposed. The procedure, named VOS (Variable Operating Strategy), is based on the overall plant efficiency criteria and is applied to a water distribution network where a PAT (pump as a turbine) is used in order to produce energy. In the present paper the VOS design procedure has been extended to the electrical regulation and a comparison between HR and ER efficiency and flexibility within a water distribution network is shown: HR was found more flexible than ER and more efficient. Finally a preliminary economic study has been carried out in order to show the viability of both systems, and a shorter payback period of the electromechanical equipment was found for HR mode.