Coupling of Modelica Domestic Hot Water Simulation Model with Controller

Abstract

The energy needed for Domestic Hot Water (DHW) represents an important share in the total energy use of well-insulated and airtight buildings. One of the main reasons for this high energy demand is that DHW is produced at temperatures above 60°C to mitigate the risk of contaminating the hot water system with Legionella pneumophila. However, this elevated temperature is not necessary for most DHW applications, and has a negative effect on the efficiency of hot water production units. A Modelica simulation model has been developed that proposes an alternative to this constant 60°C by predicting the L. pneumophila concentration dynamically throughout the DHW system. Based on this knowledge, the topic of this paper is coupling the simulation model with a virtual DHW controller prototype. The DHW controller sets a comfortable DHW set point temperature in combination with heat shocks. The simulation model algorithm predicts the concentration of L. pneumophila present in the system, as this concentration cannot be measured in real time. When this predicted concentration passes a predefined threshold level, the controller will increase the set point temperature of the boiler (heat shock) in order to lower the concentration of L. pneumophila present until the predicted concentration is below a predefined boundary level. The energy savings by implementing the heat shock regime instead of the constant 60°C regime can be predicted with the simulation model. This new DHW controller is expected to become an important alternative for the current, energy intensive, constant high temperature tap water heating systems.