Simulation of Legionella concentration in domestic hot water: comparison of pipe and boiler models

The energy needed for the production of domestic hot water (DHW) represents an important share in the total energy demand of well-insulated and airtight buildings. DHW is produced, stored and distributed above 60 degrees C to kill Legionella pneumophila. This elevated temperature is not necessary for DHW applications and has a negative effect on the efficiency of hot water production units. In this paper, system component models are developed/updated with L. pneumophila growth equations. For that purpose, different existing Modelica pipe and boiler models are investigated to select useful models that could be extended with equations for simulation of bacterial growth. In future research, HVAC designers will be able to investigate the contamination risk for L. pneumophila in the design phase of a hot water system, by implementing the customized pipe and boiler model in a hot water system model. Additionally it will be possible, with simulations, to optimize temperature regimes and estimate the energy saving potential without increasing contamination risk.