Energy equations to analyze pressurized water transport systems

Abstract

[EN] Pressurized water systems are high energy demanders. They must deliver the demanded volume of water at the minimum service pressure. There is currently a marked change in production and energy tariffs, which is causing prices for water services to rise. In addition to the economic aspect, the energy demand of water systems has an environmental implication linked to gas emissions. With increasing demands, the climate change situation and the shift in energy tariffs, it is necessary to improve the efficiency of pressurized water transport systems. The lower the kWh required to supply, the more energy efficient they will be. The energy analysis of the systems will allow us to know the current situation of the systems, and to know if it is necessary to undertake improvement measures. There are different processes to know the energy status of the networks. The simplest one is to carry out a diagnosis, with little data, which will give an initial idea of the energy status of the networks. This diagnosis can be carry through by applying Bernoulli's equation. Applied from the supply points to the most unfavorable point of the system. If it is desired to know more precisely the energetic status of the networks, the use of the integral energy equation seems more reasonable. This equation makes it possible to audit the system and to know in detail the energy use for a given control volume. It allows the energy supplied to be broken down into: useful energy, structural energy losses (linked to topography) and operational energy losses (friction losses, pumping losses, leakage losses and excess energy). In order to be able to apply this method, it is mandatory to have the mathematical model of the system. This paper discusses the advantages and disadvantages of carrying out the energy analysis of a system using the Bernoulli equation (diagnosis) or the energy integral equation (audit), and when it is convenient to apply one or the other. On one hand, the Bernoulli equation makes it possible to estimate the energy level of the network with very little data, without knowing exactly in which processes the energy introduced into the system is invested. The audit based on the integral energy equation, on the other hand, requires precise data collection and mathematical modelling, but it will provide a detailed understanding of the energy breakdown of the network. Depending on the objective of the energy analysis, it seems reasonable to apply one process or another. For a first estimation and as a start of the energy analysis, it will be sufficient to carry out a diagnosis as quickly as possible, which will allow to know if it is necessary to continue with a more in-depth research of the system status such as an energy audit.