Development of a Model Predictive Controller for Tankless Water Heaters

Abstract

This paper describes the development of a novel approach to temperature control of tankless water heaters (TWHs). Conventional methods of controlling TWHs typically allow a high degree of error in the outlet water temperature when subjected to disturbances in flow rate or inlet water temperature. Poor control affects comfort, safety, and energy consumption associated with TWHs. The novel control approach presented here uses model predictive control (MPC) to minimize the outlet temperature error. A dynamic heat transfer model of an electric TWH is developed and validated and used within a MPC-based controller. The controller is interfaced to a physical prototype TWH and tested using an experimental test bed developed for this project. An integral performance criterion is used to compare performance and to tune the MPC in a standardized series of tests, also developed for this project. MPC is shown to provide excellent control of the prototype TWH.