The development of a dynamic model to simulate boiler controls

Abstract

There has long been the need to improve the guidance for the control of multiple boiler installations. The literature shows that there is no generic guidance on how boiler plant — as opposed to the heating system — should be best controlled, despite their widespread use and many years of experience with these systems. This paper presents a simulation model that enables detailed investigation of multiple boiler operation under different control regimes. Five different conditions are presented in this paper. The first three show that individual boiler firing patterns behave as would be expected under ideal conditions. The loads for these simulations were chosen specifically to test this, and to provide some verification of the model. Two further tests were conducted to show firing patterns that may occur under typical control regimes. The resulting firing patterns showed unnecessary cycling of both boilers, a cause of premature failure and reduced efficiency. Practical applications: This paper presents the first stages of an investigation into the setting up and operation of multiple boiler control systems. A review of academic and industrial literature shows there to be very little guidance on how such control systems should be configured, and how different configurations will affect the system performance. This work is developing validated boiler models that can be used to investigate how sensor positioning and switching differentials can affect firing rates and interactions between boiler modules. In this way control settings can be more appropriately specified and commissioned. Excessive boiler cycling can lead to early failure of boilers and increased energy use. The results presented in this paper show that interaction between boilers due to poor sequence control settings will lead to additional and unnecessary cycling of boilers under part load conditions. The guidance arising from this work will help to extend boiler life and reduce fuel waste.