Energy Efficiency Improvement in a Water Heater with a Run-Around Heat Exchanger System

A significant portion of the energy consumed by home appliances that uses hot water is used for heating cold supply water. Such home appliances generally use supply water at a temperature lower than the ambient temperature. Thus, the water is normally heated from below the ambient temperature to its designed maximum temperature by the appliance, often using natural gas or an electrical heater. During the period when the heater is energized, electrical energy is used to increase a water temperature to the designed maximum temperature. It may be possible to save energy by preheating the supply water before this period. In order to save the energy, a run-around heat exchanger system is used to transfer heat from the ambient to the water before the electrical heater is energized. A simple model to predict the dynamic performance of this system is developed and validated using experimental data. Despite the additional power consumption by the fan and pump, the experimental data and analysis show that overall energy efficiency can be improved.