Energy-efficient Legionella control that mimics nature and an open-sourcecomputational model to aid system design

The Duck Foot Heat Exchange Model (DFHXM) was developed to aid design of energy efficient thermal pasteurization systems for water but applies to all fluids. Here, the freely available Microsoft Excel model and potential applications are described. The principle imitates countercurrent heat exchange in the feet of ducks which reduces environmental heat losses in cold climates. The designed system pasteurizes the chosen fluid by maintaining a required disinfection temperature for a given time. A heat exchanger preheats incoming fluid before reaching a heating reservoir (electric, solar, gas, etc.). Upon exiting the heater, fluid reenters the same heat exchanger to cool down, simultaneously preheating new incoming fluid. Thus, the design only requires a heater to add the necessary heat not gained in the heat exchanger and to cover environmental heat losses. The DFHXM allows users to input parameters to simulate their specific duck foot (DF) systems and obtain transient and steady-state fluid temperatures within the heat exchanger and heating reservoir. The model has the flexibility to simulate a wide variety of designs, and potential applications to Legionella control and solar-thermal water disinfection are discussed. Reported simulations agreed well with experimental results for transient and steady-state temperatures, the largest discrepancy in steady-state temperatures being 4.6 %.